Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2018

Summary of Significant Accounting Policies

Summary of Significant Accounting Policies

B.       Summary of Significant Accounting Policies

Principles of Consolidation

The consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries, ImmunoGen Securities Corp., ImmunoGen Europe Limited, ImmunoGen (Bermuda) Ltd., ImmunoGen BioPharma (Ireland) Limited, and Hurricane, LLC. All intercompany transactions and balances have been eliminated.

Use of Estimates

The preparation of financial statements in conformity with accounting principles generally accepted in the United States (U.S.) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.

Subsequent Events

The Company has evaluated all events or transactions that occurred after December 31, 2018 up through the date the Company issued these financial statements. In January 2019, the Company sold its residual rights to receive royalty payments on commercial sales of Kadcyla to OMERS, the defined benefit pension plan for municipal employees in the Province of Ontario, Canada, for $65.2 million, net of fees.

On March 1, 2019, the Company announced that FORWARD I did not meet its PFS primary endpoint in either the entire study population or in the pre-specified subset of patients with high-FRα expression. The Company plans to conduct a full review of the FORWARD I data to determine potential next steps with mirvetuximab as a single agent, and assess its ongoing FORWARD II combination studies as a separate path forward to support a registration in ovarian cancer.

 The Company did not have any other material recognizable or unrecognizable subsequent events.

Adoption of ASC Topic 606, Revenue from Contracts with Customers

The Company adopted Accounting Standards Codification Topic or ASC, 606 – Revenue from Contracts with Customers, (ASC 606) on January 1, 2018, using the modified retrospective method for all contracts not completed as of the date of adoption. The reported results for 2018 reflect the application of ASC 606 guidance, while the reported results prior to 2018 were prepared under the guidance of ASC 605, Revenue Recognition (ASC 605), which is also referred to herein as "legacy GAAP" or the "previous guidance." 

Financial Statement Impact of Adopting ASC 606

The cumulative effect of applying the new guidance to all contracts with customers that were not completed as of December 31, 2017, was recorded as an adjustment to accumulated deficit as of the adoption date. As a result of applying the modified retrospective method to adopt the new revenue guidance, the following adjustments were made to accounts on the condensed consolidated balance sheet as of January 1, 2018:

IMMUNOGEN, INC.

ADJUSTED CONSOLIDATED BALANCE SHEET

In thousands, except per share amounts

			Adjustments		Balance at
	December 31,		Due to		January 1,
	2017		ASC 606		2018
ASSETS
Cash and cash equivalents	$	267,107	$	—	$	267,107
Accounts receivable		2,649		—		2,649
Unbilled revenue		2,580		—		2,580
Non-cash royalty receivable		—		8,900		8,900
Inventory		1,038		—		1,038
Prepaid and other current assets		2,967		—		2,967
Total current assets		276,341		8,900		285,241
Property and equipment, net of accumulated depreciation		14,538		—		14,538
Other assets		3,797		—		3,797
Total assets	$	294,676	$	8,900	$	303,576
LIABILITIES AND SHAREHOLDERS’ DEFICIT
Accounts payable	$	8,562	$	—	$	8,562
Accrued compensation		11,473		—		11,473
Other accrued liabilities		15,767		—		15,767
Current portion of deferred lease incentive		784		—		784
Current portion of liability related to the sale of future royalties, net		17,779		—		17,779
Current portion of deferred revenue		1,405		41		1,446
Total current liabilities		55,770		41		55,811
Deferred lease incentive, net of current portion		5,129		—		5,129
Deferred revenue, net of current portion		93,752		(5,231)		88,521
Convertible 4.5% senior notes, net		2,050		—		2,050
Liability related to the sale of future royalties, net		151,634		—		151,634
Other long-term liabilities		4,236		—		4,236
Total liabilities		312,571		(5,190)		307,381
Shareholders’ deficit:
Preferred stock		—		—		—
Common stock		1,325		—		1,325
Additional paid-in capital		1,009,362		—		1,009,362
Accumulated deficit		(1,028,582)		14,090		(1,014,492)
Total shareholders’ deficit		(17,895)		14,090		(3,805)
Total liabilities and shareholders’ deficit	$	294,676	$	8,900	$	303,576

Under the previous guidance, the Company deferred revenue pertaining to the transfer of certain exclusive commercialization and development licenses, and to account for these agreements under the legacy GAAP, the Company identified the deliverables included within the agreements and evaluated which deliverables represented separate units of accounting based on whether certain criteria were met, including whether the delivered element had stand-alone value to the collaborator.  The consideration received was allocated among the separate units of accounting, and the applicable revenue recognition criteria were applied to each of the separate units.  Under ASC 606, the Company recognizes revenues from non-refundable, up-front fees allocated to the license when the license is distinct from other performance obligations, is transferred to the customer and the customer is able to use and benefit from the license. 

Under the previous guidance, milestones that were considered substantive because the Company contributed significant effort to the achievement of such milestones were recognized as revenue upon achievement of the milestone. Under ASC 606, if the achievement of a milestone is considered a direct result of the Company’s efforts to satisfy a performance obligation or transfer a distinct good or service, the associated milestone value is allocated to that distinct good or service. If a milestone is not specifically related to the Company’s effort to satisfy a performance obligation or transfer a distinct good or service, the amount is allocated to all performance obligations using the relative standalone selling price method.

Under ASC 606, the Company also evaluates the milestone to determine whether the milestone is probable of being achieved and estimates the amount to be included in the transaction price. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price to be allocated, otherwise, such amounts are constrained and excluded from the transaction price until the probable threshold is met. The Company determined it was probable that a future $5.0 million milestone for Takeda enrolling a patient in a Phase I trial as of the date of adoption would occur and, accordingly, recorded a reduction to accumulated deficit of $4.6 million related to this previously delivered license as approximately $400,000 was allocated to undelivered rights to future technological improvements. The $5.0 million contract asset recorded for the probable milestone was netted against contract liabilities related to the specific contract.

Prior to the adoption of ASC 606, the Company recognized royalty revenue when it could reliably estimate such amounts and collectability was reasonably assured. As such, the Company generally recognized revenue for sales royalties in the quarter the amounts were reported to the Company by its licensees, or one quarter following the quarter in which sales by the Company’s licensees occurred. Under ASC 606, if the license is deemed to be the predominant item to which the royalties relate, the Company will recognize revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). As a result of recognizing royalties for sales in the fourth quarter of fiscal year 2017, the Company recognized a reduction to accumulated deficit of $8.9 million.

The net impact of these changes resulted in a $14.1 million reduction to accumulated deficit, a $5.2 million reduction to deferred revenue and an $8.9 million increase in non-cash royalty receivable.

The adoption of ASC 606 resulted in the acceleration of revenue through December 31, 2017, which in turn reduced the related net deferred tax asset by $3.9 million. As the Company fully reserves its net deferred tax assets, the impact was offset by the valuation allowance. 

Impact of ASC 606 Revenue Guidance on Financial Statement Line Items

The following tables compare the reported condensed consolidated balance sheet and statement of operations, as of and for the year ended December 31, 2018, to the pro-forma amounts had the previous guidance been in effect:

IMMUNOGEN, INC.

PRO FORMA CONSOLIDATED BALANCE SHEET

In thousands, except per share amounts

	As of December 31, 2018
			Pro forma as if the
			previous accounting
	As reported		was in effect
ASSETS
Cash and cash equivalents	$	262,252	$	262,252
Accounts receivable		1,701		1,701
Unbilled revenue		617		617
Contract asset		500		—
Non-cash royalty receivable		9,249		—
Inventory		—		—
Prepaid and other current assets		4,462		4,462
Total current assets		278,781		269,032
Property and equipment, net of accumulated depreciation		12,891		12,891
Other assets		3,709		3,709
Total assets	$	295,381	$	285,632
LIABILITIES AND SHAREHOLDERS’ EQUITY (DEFICIT)
Accounts payable	$	11,365	$	11,365
Accrued compensation		11,796		11,796
Other accrued liabilities		20,465		20,465
Current portion of deferred lease incentive		837		837
Current portion of liability related to the sale of future royalties, net		25,880		25,880
Current portion of deferred revenue		317		297
Total current liabilities		70,660		70,640
Deferred lease incentive, net of current portion		4,675		4,675
Deferred revenue, net of current portion		80,485		83,710
Convertible 4.5% senior notes, net		2,064		2,064
Liability related to the sale of future royalties, net		122,345		122,345
Other long-term liabilities		4,180		4,180
Total liabilities		284,409		287,614
Shareholders’ equity (deficit):
Preferred stock		—		—
Common stock		1,494		1,494
Additional paid-in capital		1,192,813		1,192,813
Accumulated deficit		(1,183,335)		(1,196,289)
Total shareholders’ equity (deficit)		10,972		(1,982)
Total liabilities and shareholders’ equity (deficit)	$	295,381	$	285,632

As a result of adoption of ASC 606, a receivable is recorded for royalties earned during the current quarter rather than one quarter in arrears under the previous guidance. Deferred revenue increased under ASC 606 due to a greater amount of the transaction prices being allocated to the future technological improvement rights under ASC 606.

IMMUNOGEN, INC.

PRO FORMA CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS

In thousands, except per share amounts

	Year ended
	December 31, 2018
			Pro forma as if the
			previous accounting
	As reported		was in effect
Revenues:
License and milestone fees	$	15,280	$	16,765
Non-cash royalty revenue related to the sale of future royalties		32,154		31,805
Research and development support		1,377		1,377
Clinical materials revenue		4,635		4,635
Total revenues		53,446		54,582
Operating Expenses:
Research and development		174,456		174,456
General and administrative		36,746		36,746
Restructuring charge		3,693		3,693
Total operating expenses		214,895		214,895
Loss from operations		(161,449)		(160,313)
Investment income, net		4,227		4,227
Non-cash interest expense on liability related to the sale of future royalties and convertible senior notes		(10,631)		(10,631)
Interest expense on convertible senior notes		(95)		(95)
Other (expense) income, net		(895)		(895)
Net loss	$	(168,843)	$	(167,707)
Basic and diluted net loss per common share	$	(1.21)	$	(1.20)

Under the previous guidance, non-cash royalty revenue would have been lower than the amount recorded for the year ended December 31, 2018, due to higher Kadcyla sales in the fourth quarter of 2018 versus 2017 (because under the previous guidance, the Company recorded the royalties one quarter in arrears as previously described). License and milestone fee revenue for the year ended December 31, 2018 would have been higher due to a $5.0 million milestone that would have been included as license and milestone fee revenue in 2018 under the legacy accounting, however, due to its probability of occurring at the time of transition to ASC 606, it was recognized as part of the transition adjustment. Partially offsetting this change, less license and milestone fee revenue would have been recognized under the previous guidance related to a partner foregoing its remaining rights under a right-to-test agreement upon expiration in March 2018, as well as partners terminating their rights under certain development and commercialization licenses during the year. A greater amount of the transaction price was allocated to the expired and terminated material rights under ASC 606 than under the previous guidance. 

The adoption of ASC 606 had no aggregate impact on the Company’s cash flows from operations. The aforementioned impact resulted in offsetting shifts in cash flows through net losses and working capital accounts.

Revenue Recognition

The Company enters into licensing and development agreements with collaborators for the development of

ADCs. The terms of these agreements contain multiple deliverables/performance obligations which may include (i) licenses, or options to obtain licenses, to the Company’s ADC technology, (ii) rights to future technological improvements, (iii) research activities to be performed on behalf of the collaborative partner, (iv) delivery of cytotoxic agents, and (v) prior to the decommission of the Company’s Norwood facility in 2018, the manufacture of preclinical or clinical materials for the collaborative partner. Payments to the Company under these agreements may include upfront fees, option fees, exercise fees, payments for research activities, payments for the manufacture of preclinical or clinical materials, payments based upon the achievement of certain milestones, and royalties on product sales.

Prior to 2018, the Company identified the deliverables included within the agreement and evaluated which deliverables represented separate units of accounting based on whether certain criteria are met, including whether the delivered element had stand‑alone value to the collaborator in accordance with ASC 605. The consideration received was allocated among the separate units of accounting, and the applicable revenue recognition criteria were applied to each of the separate units.

In 2018, revenue is recognized when a customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services in accordance with ASC 606. In determining the appropriate amount of revenue to be recognized as it fulfills its obligations under the agreements, the Company performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when or as the Company satisfies each performance obligation.  

The Company only applies the five-step model to contracts when it is probable that the Company will collect the consideration to which it is entitled in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations, and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when or as the performance obligation is satisfied.

As part of the accounting for the arrangement, the Company must develop assumptions that require judgment to determine the selling price for each deliverable under ASC 605 and performance obligation under ASC 606 that were identified in the contract, which is discussed in further detail below.

At December 31, 2018, the Company had the following material types of agreements with the parties identified below:

· Development and commercialization licenses, which provide the party with the right to use the Company’s ADC technology and/or certain other intellectual property to develop and commercialize anticancer compounds to a specified antigen target:

Bayer (one exclusive single-target license)

Biotest (one exclusive single-target license)

CytomX (one exclusive single-target license)

Debiopharm (one exclusive single-compound license)

Fusion Pharmaceuticals (one exclusive single-target license)

Novartis (five exclusive single-target licenses)

Oxford BioTherapeutics/Menarini (one exclusive single target license sublicensed from Amgen)

Roche, through its Genentech unit (five exclusive single-target licenses)

Sanofi (five fully-paid, exclusive single-target licenses)

Takeda, through its wholly owned subsidiary, Millennium Pharmaceuticals, Inc. (one exclusive single-target license)

· Collaboration and option agreement for a defined period of time to secure development and commercialization licenses to develop and commercialize specified anticancer compounds on established terms:

Jazz Pharmaceuticals

· Collaboration and license agreement to co-develop and co-commercialize a specified anticancer compound on established terms:

MacroGenics

There are no performance, cancellation, termination, or refund provisions in any of the arrangements that contain material financial consequences to the Company.

Development and Commercialization Licenses

The obligations under a development and commercialization license agreement generally include the license to the Company’s ADC technology with respect to a specified antigen target, and may also include obligations related to rights to future technological improvements, research activities to be performed on behalf of the collaborative partner and the manufacture of preclinical or clinical materials for the collaborative partner.

Generally, development and commercialization licenses contain non‑refundable terms for payments and, depending on the terms of the agreement, provide that the Company will (i) at the collaborator’s request, provide research services at negotiated prices which are generally consistent with what other third parties would charge, (ii) prior to the decommissioning of the Company’s Norwood facility in 2018, at the collaborator’s request, manufacture and provide preclinical and clinical materials or deliver cytotoxic agents at negotiated prices which are generally consistent with what other third parties would charge, (iii) earn payments upon the achievement of certain milestones, and (iv) earn royalty payments, generally until the later of the last applicable patent expiration or 10 to 12 years after product launch. Royalty rates may vary over the royalty term depending on the Company’s intellectual property rights and/or the presence of comparable competing products. In the case of Sanofi, its licenses are fully-paid and no further milestones or royalties will be received. In the case of Debiopharm, no royalties will be received. The Company may provide technical assistance and share any technology improvements with its collaborators during the term of the collaboration agreements. The Company does not directly control when or whether any collaborator will request research or, achieve milestones or become liable for royalty payments.

In determining the units of accounting under ASC 605, management evaluated whether the license had stand‑alone value from the undelivered elements to the collaborative partner based on the consideration of the relevant facts and circumstances for each arrangement. Factors considered in this determination include the research capabilities of the partner and the availability of ADC technology research expertise in the general marketplace.  If the Company concluded that the license had stand‑alone value and therefore accounted for as a separate unit of accounting, the Company then determined the estimated selling prices of the license and all other units of accounting.

In determining the performance obligations under ASC 606, management evaluates whether the license is distinct, and has significant standalone functionality, from the undelivered elements to the collaborative partner based on the consideration of the relevant facts and circumstances for each arrangement. Factors considered in this determination include the research capabilities of the partner and the availability of ADC technology research expertise in the general marketplace and whether technological improvements are required for the continued functionality of the license. If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenues from non-refundable, up-front fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license.

The Company determined that the estimated selling price under ASC 605 and the stand-alone selling price under ASC 606 to be consistent. The estimates the selling prices of the license and all other deliverables under ASC 605 and performance obligations under ASC 606 are based on market conditions, similar arrangements entered into by third parties, and entity‑specific factors such as the terms of the Company’s previous collaborative agreements, recent preclinical and clinical testing results of therapeutic products that use the Company’s ADC technology, the Company’s pricing practices and pricing objectives, the likelihood that technological improvements will be made, and, if made, will be used by the Company’s collaborators and the nature of the research services to be performed on behalf of its collaborators and market rates for similar services.

The Company recognizes revenue related to research services under ASC 605 and ASC 606 as the services are performed. The Company performs research activities, including developing antibody specific conjugation processes, on behalf of its collaborators and potential collaborators during the early evaluation and preclinical testing stages of drug development. The Company also develops conjugation processes for materials for later stage testing and commercialization for certain collaborators. The Company is compensated at negotiated rates that are consistent with what other third parties would charge and may receive milestone payments for developing these processes which are also recorded as a component of research and development support revenue. The Company may also produce research material for potential collaborators under material transfer agreements. The Company records amounts received for research materials produced or services performed as a component of research and development support revenue.

The Company may also provide cytotoxic agents to its collaborators and previously produced preclinical and clinical materials (drug substance) at negotiated prices generally consistent with what other third parties would charge. The Company recognizes revenue on cytotoxic agents and, previously, on preclinical and clinical materials when the materials have passed all quality testing required for collaborator acceptance and control has transferred under ASC 606 to the collaborator, while ASC 605 required title and risk of loss to transfer. The majority of the Company’s costs to produce these preclinical and clinical materials were fixed and then allocated to each batch based on the number of batches produced during the period. Therefore, the Company’s costs to produce these materials were significantly affected by the number of batches produced during the period. The volume of preclinical and clinical materials the Company produced was directly related to the scale and scope of preclinical activities and the number of clinical trials the Company and its collaborators were preparing for or currently had underway, the speed of enrollment in those trials, the dosage schedule of each clinical trial and the time period such trials last. Accordingly, the volume of preclinical and clinical materials produced, and therefore the Company’s per‑batch costs to manufacture these preclinical and clinical materials, varied significantly from period to period, which affected the margins recognized on such product sales. 

The Company recognizes revenue related to the rights to future technological improvements under ASC 605 and ASC 606 over the estimated term of the applicable license.

The Company’s development and commercialization license agreements have milestone payments which for reporting purposes are aggregated into three categories: (i) development milestones, (ii) regulatory milestones, and (iii) sales milestones. Development milestones are typically payable when a product candidate initiates or advances into different clinical trial phases. Regulatory milestones are typically payable upon submission for marketing approval with the U.S. Food and Drug Administration, or FDA, or other countries’ regulatory authorities or on receipt of actual marketing approvals for the compound or for additional indications. Sales milestones are typically payable when annual sales reach certain levels.

Under ASC 605, at the inception of each agreement that includes milestone payments, the Company evaluated whether each milestone was substantive and at risk to both parties on the basis of the contingent nature of the milestone. This evaluation included an assessment of whether (a) the consideration was commensurate with either (1) the entity’s performance to achieve the milestone, or (2) the enhancement of the value of the delivered item(s) as a result of a specific outcome resulting from the entity’s performance to achieve the milestone, (b) the consideration related solely to past performance and (c) the consideration was reasonable relative to all of the deliverables and payment terms within the arrangement. The Company evaluated factors such as the scientific, regulatory, commercial and other risks that must be overcome to achieve the respective milestone, the level of effort and investment required to achieve the respective milestone and whether the milestone consideration was reasonable relative to all deliverables and payment terms in the arrangement in making this assessment.   Non‑refundable development and regulatory milestones that were expected to be achieved as a result of the Company’s efforts during the period of substantial involvement were considered substantive and were recognized as revenue upon the achievement of the milestone, assuming all other revenue recognition criteria under ASC 605 were met. Milestones that were not considered substantive because the Company did not contribute effort to the achievement of such milestones were generally achieved after the period of substantial involvement and were recognized as revenue upon achievement of the milestone, as there were no undelivered elements remaining and no continuing performance obligations, assuming all other revenue recognition criteria under ASC 605 were met.

Under ASC 606, at the inception of each arrangement that includes developmental and regulatory milestone payments, the Company evaluates whether the achievement of each milestone specifically relates to the Company’s efforts to satisfy a performance obligation or transfer a distinct good or service within a performance obligation. If the achievement of a milestone is considered a direct result of the Company’s efforts to satisfy a performance obligation or transfer a distinct good or service and the receipt of the payment is based upon the achievement of the milestone, the associated milestone value is allocated to that distinct good or service. If the milestone payment is not specifically related to the Company’s effort to satisfy a performance obligation or transfer a distinct good or service, the amount is allocated to all performance obligations using the relative standalone selling price method. In addition, the Company evaluates the milestone to determine whether the milestone is considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price to be allocated; otherwise, such amounts are considered constrained and excluded from the transaction price. At the end of each subsequent reporting period, the Company re-evaluates the probability of achievement of such development or regulatory milestones and any related constraint, and if necessary, adjusts its estimate of the transaction price. Any such adjustments to the transaction price are allocated to the performance obligations on the same basis as at contract inception. Amounts allocated to a satisfied performance obligation shall be recognized as revenue, or as a reduction of revenue, in the period in which the transaction price changes.

For development and commercialization license agreements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue under ASC 606 at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied) in accordance with the royalty recognition constraint. Under the Company’s development and commercialization license agreements, except for the Sanofi and Debiopharm licenses, the Company receives royalty payments based upon its licensees’ net sales of covered products. Generally, under the development and commercialization agreements, the Company receives royalty reports and payments from its licensees approximately one quarter in arrears.  The Company estimates the amount of royalty revenue to be recognized based on historical and forecasted sales and/or sales information from its licensees if available. Under ASC 605, royalty revenue was recognized when it could reliably estimate such amounts and collectability was reasonably assured. As such, the Company generally recognized revenue for sales royalties in the quarter the amounts were reported to the Company by its licensees, or one quarter following the quarter in which sales by the Company’s licensees occurred.

Collaboration and Option Agreements/Right-to-Test Agreements

The Company’s right-to-test agreements provide collaborators the right to test the Company’s ADC technology for a defined period of time through a research, or right‑to‑test, license. Under both right-to-test agreements and collaboration and option agreements, collaborators may (a) take options, for a defined period of time, to specified targets and (b) upon exercise of those options, secure or “take” licenses to develop and commercialize products for the specified targets on established terms. Under these agreements, fees may be due to the Company (i) at the inception of the arrangement (referred to as “upfront” fees or payments), (ii) upon the opt-in to acquire a development and commercialization license(s) (referred to as exercise fees or payments earned, if any, when the development and commercialization license is “taken”), (iii) at the collaborator’s request, after providing research services at negotiated prices which are generally consistent with what other third parties would charge, or (iv) some combination of all of these fees.

The accounting for collaboration and option agreements and right-to-test agreements under ASC 605 and ASC 606 is dependent on the nature of the options granted to the collaborative partner.

Under ASC 605, options are considered substantive if, at the inception of the agreement, the Company is at risk as to whether the collaborative partner will choose to exercise the options to secure development and commercialization licenses. Factors that are considered in evaluating whether options are substantive include the overall objective of the arrangement, the benefit the collaborator might obtain from the agreement without exercising the options, the cost to exercise the options relative to the total upfront consideration, and the additional financial commitments or economic penalties imposed on the collaborator as a result of exercising the options.  The exercise price for non-substantive options are included in the initial consideration.  In determining the units of accounting for substantive options, management evaluates whether the options have stand‑alone value from the undelivered elements to the collaborative partner based on the consideration of the relevant facts and circumstances. If the Company concludes that an option has stand‑alone value and therefore will be accounted for as a separate unit of accounting, it then determines the estimated selling prices of the option and all other units of accounting based on an option pricing model using the following inputs; a) estimated fair value of each program, b) the amount the partner would pay to exercise the option to obtain the license, c) volatility during the expected term of the option and d) risk free interest rate. A risk adjusted discounted cash flow model is then used to estimate the fair value of the option with volatility determined using the stock prices of comparable companies. The cash flow is discounted at a rate representing the Company’s estimate of its cost of capital at the time.

Under ASC 606, options are considered distinct performance obligations if they provide a collaborator with a material right. Factors that are considered in evaluating whether options convey a material right include the overall objective of the arrangement, the benefit the collaborator might obtain from the agreement without exercising the options, the cost to exercise the options relative to the fair value of the licenses, and the additional financial commitments or economic penalties imposed on the collaborator as a result of exercising the options. As of December 31, 2018, all right-to-test agreements have expired. 

If the Company concludes that an option provides the customer a material right, and therefore is a separate performance obligation, the Company then determines the estimated selling prices of the option and all other units of accounting using the following inputs: a) estimated fair value of each program, b) the amount the partner would pay to exercise the option to obtain the license and c) probability of exercise.

The Company does not control when or if any collaborator will exercise its options for development and commercialization licenses. As a result, the Company cannot predict when or if it will recognize revenues in connection with any of the foregoing.

Upfront payments on development and commercialization licenses may be recognized upon delivery of the license if facts and circumstances dictate that the license has stand-alone functionality and is distinct from the undelivered elements.

In determining whether a collaboration and option agreement is within the scope of ASC 808, Collaborative Arrangements, management evaluates the level of involvement of both companies in the development and commercialization of the products to determine if both parties are active participants and if both parties are exposed to risks and rewards dependent on the commercial success of the licensed products. If the agreement is determined to be within the scope of ASC 808, the Company will segregate the research and development activities and the related cost sharing arrangement. Payments made by the Company for such activities will be recorded as research and development expense and reimbursements received from its partner will be recognized as an offset to research and development expense.

Transaction Price Allocated to Future Performance Obligations

Remaining performance obligations under ASC 606 represent the transaction price of contracts for which work has not been performed (or has been partially performed) and includes unexercised contract options that are considered material rights. As of December 31, 2018, the aggregate amount of the transaction price allocated to remaining performance obligations comprising deferred revenue was $80.8 million. The Company expects to recognize revenue on approximately .4%,  1.6%, and 98% of the remaining performance obligations over the next 12 months, 13 to 60 months, and 61 to 120 months, respectively, however it does not control when or if any collaborator will exercise its options for, or terminate existing development and commercialization licenses.

Contract Balances from Contracts with Customers

The following table presents changes in the Company’s contract assets and contract liabilities during the year ended December 31, 2018 (in thousands):

	Balance at								Balance at
	January 1, 2018								End
	(ASC 606 adoption)		Additions		Deductions		Impact of Netting		of Period
Contract asset	$	—	$	500	$	(5,000)	$	5,000	$	500
Contract liabilities	$	89,967	$	730	$	(14,895)	$	5,000	$	80,802

During the year ended December 31, 2018, the Company recognized the following revenues as a result of changes in contract asset and contract liability balances in the respective periods (in thousands):

		Year Ended
		December 31, 2018
Revenue recognized in the period from:
Amounts included in contract liabilities at the beginning of the period	$	14,139
Performance obligations satisfied in previous periods	$	1,476

As a result of adoption of ASC 606, a contract asset of $5 million was recorded for a probable milestone which was subsequently earned and paid during the year ended December 31, 2018. During 2018, a milestone from Fusion was deemed probable, and accordingly, a contract asset was created in the amount of $500,000. In December 2018, the Company recorded a  $1 million development milestone earned under a sublicense agreement with Oxford BioTherapeutics Ltd. as revenue, which is included in accounts receivable as of December 31, 2018. Also, as a result of Takeda not executing a second license it had available, or extending or expanding its right-to-test agreement, the Company recognized $10.9 million of revenue previously deferred, with a net reduction in deferred revenue of $5.9 million due to contract asset and contract liability netting. In addition, $750,000 of the deferred revenue balance at December 31, 2017 was recognized as revenue during the year ended December 31, 2018 upon completion of the Debiopharm and another collaborator’s performance obligations, $2.1 million of amortization of deferred revenue was recorded related to numerous collaborators’ rights to technological improvements and $335,000 of deferred revenue was recognized upon shipment of clinical materials to a partner and is included in clinical material revenue.

The timing of revenue recognition, billings, and cash collections results in billed receivables, contract assets, and contract liabilities on the consolidated balance sheets. When consideration is received, or such consideration is unconditionally due, from a customer prior to transferring goods or services to the customer under the terms of a contract, a contract liability is recorded. Contract liabilities are recognized as revenue after control of the products or services is transferred to the customer and all revenue recognition criteria have been met.

Financial Instruments and Concentration of Credit Risk

Cash and cash equivalents are primarily maintained with three financial institutions in the U.S. Deposits with banks may exceed the amount of insurance provided on such deposits. Generally, these deposits may be redeemed upon demand and, therefore, bear minimal risk. The Company’s cash equivalents consist of money market funds with underlying investments primarily being U.S. Government‑issued securities and high quality, short‑term commercial paper. Financial instruments that potentially subject the Company to concentrations of credit risk consist principally of cash, cash equivalents, and marketable securities. The Company held no marketable securities as of December 31, 2018 or 2017. The Company’s investment policy, approved by the Board of Directors, limits the amount it may invest in any one type of investment, thereby reducing credit risk concentrations.

Cash and Cash Equivalents

All highly liquid financial instruments with maturities of three months or less when purchased are considered cash equivalents. As of December 31, 2018 and 2017, the Company held $262.3 million and $267.1 million, respectively, in cash and money market funds consisting principally of U.S. Government-issued securities and high quality, short-term commercial paper which were classified as cash and cash equivalents.

Non-cash Investing Activities

The Company had $715,000 and $482,000 of accrued capital expenditures as of December 31, 2018 and 2017 which have been treated as a non-cash investing activity and, accordingly, are not reflected in the consolidated statement of cash flows.

Fair Value of Financial Instruments

ASC Topic 820 defines fair value, establishes a framework for measuring fair value in accordance with accounting principles generally accepted in the U.S., and expands disclosures about fair value measurements. Fair value is defined under ASC Topic 820 as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. The standard describes a hierarchy to measure fair value which is based on three levels of inputs, of which the first two are considered observable and the last unobservable, as follows:

· Level 1—Quoted prices in active markets for identical assets or liabilities.

· Level 2—Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

· Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.

As of December 31, 2018, the Company held certain assets that are required to be measured at fair value on a recurring basis. The following table represents the fair value hierarchy for the Company’s financial assets measured at fair value on a recurring basis as of December 31, 2018 (in thousands):

	Fair Value Measurements at December 31, 2018 Using
			Quoted Prices in				Significant
			Active Markets for		Significant Other		Unobservable
			Identical Assets		Observable Inputs		Inputs
	Total		(Level 1)		(Level 2)		(Level 3)
Cash equivalents	$	242,604	$	242,604	$	—	$	—

As of December 31, 2017, the Company held certain assets that are required to be measured at fair value on a recurring basis. The following table represents the fair value hierarchy for the Company’s financial assets measured at fair value on a recurring basis as of December 31, 2017 (in thousands):

	Fair Value Measurements at December 31, 2017 Using
			Quoted Prices in				Significant
			Active Markets for		Significant Other		Unobservable
			Identical Assets		Observable Inputs		Inputs
	Total		(Level 1)		(Level 2)		(Level 3)
Cash equivalents	$	240,013	$	240,013	$	—	$	—

The fair value of the Company’s cash equivalents is based primarily on quoted prices from active markets.

The carrying amounts reflected in the consolidated balance sheets for accounts receivable, unbilled revenue, prepaid and other current assets, accounts payable, accrued compensation, and other accrued liabilities approximate fair value due to their short‑term nature. The gross carrying amount and estimated fair value of the convertible 4.5% senior notes was $2.1 million and $2.8 million, respectively, as of December 31, 2018 compared to $2.1 million and $3.8 million, respectively, as of December 31, 2017. In the second half of 2017, $97.9 million of convertible debt outstanding was converted to 26,160,187 shares of the Company’s common stock causing the decrease in the gross carrying amount. The estimated fair value per $1,000 note on the debt remaining as of December 31, 2018 decreased compared to December 31, 2017 due primarily to a decrease in the Company’s stock price. The fair value of the Convertible Notes is influenced by interest rates, the Company’s stock price and stock price volatility and is determined by prices for the Convertible Notes observed in a market which is a Level 2 input for fair value purposes due to the low frequency of trades.

Inventory

Inventory costs relate to clinical trial materials being manufactured for sale to the Company’s collaborators. Inventory is stated at the lower of cost or net realizable value as determined on a first‑in, first‑out (FIFO) basis.

Inventory at December 31, 2018 and 2017 is summarized below (in thousands):

	December 31,		December 31,
	2018		2017
Raw materials	$	—	$	40
Work in process		—		998
Total	$	—	$	1,038

In February 2018, the Company made the decision to implement a new operating model that will rely on external manufacturing and quality testing for drug substance and drug product for its internal development programs, and would discontinue providing such services to its collaborators. The implementation of this new operating model led to the ramp-down and ultimate discontinuation of manufacturing and quality activities at the Company’s Norwood, Massachusetts facility during 2018, and accordingly, there was no inventory on-hand as of December 31, 2018. Raw materials inventory historically consisted entirely of proprietary cell‑killing agents the Company developed as part of its ADC technology.

Work in process inventory at December 31, 2017 consisted of drug substance manufactured for sale to the Company’s collaborators to be used in preclinical and clinical studies. All conjugate was made to order at the request of the collaborators and subject to the terms and conditions of respective supply agreements. Based on historical reprocessing or reimbursement required for drug substance that did not meet specification and the status of conjugate on hand or conjugate shipped to collaborators but not yet released per the terms of the respective supply agreements, no reserve for work in process inventory was determined to be required at December 31, 2017. The Company’s costs to manufacture conjugate on behalf of its partners are greater than the supply prices charged to partners, and therefore costs are capitalized into inventory at the supply prices which represent net realizable value.

Raw materials inventory cost is stated net of a $1.1 million write-down as of December 31, 2017. The write‑down represents the cost of raw materials that the Company considers to be in excess of a twelve‑month supply based on firm, fixed orders and projections from its collaborators as of the respective balance sheet date.

The Company produced preclinical and clinical materials for its collaborators either in anticipation of or in support of preclinical studies and clinical trials, or for process development and analytical purposes. Under the terms of supply agreements with its collaborators, the Company generally received rolling six‑month firm, fixed orders for conjugate that the Company was required to manufacture, and rolling twelve‑month manufacturing projections for the quantity of conjugate the collaborator expected to need in any given twelve‑month period. The amount of clinical material produced was directly related to the number of collaborator anticipated or on‑going clinical trials for which the Company was producing clinical material, the speed of enrollment in those trials, the dosage schedule of each clinical trial and the time period, if any, during which patients in the trial receive clinical benefit from the clinical materials. Because these elements are difficult to estimate over the course of a trial, substantial differences between collaborators’ actual manufacturing orders and their projections could result in the Company’s usage of raw materials varying significantly from estimated usage at an earlier reporting period. To the extent that a collaborator had provided the Company with a firm, fixed order, the collaborator was required by contract to reimburse the Company the full negotiated price of the conjugate, even if the collaborator subsequently canceled the manufacturing run.

The Company capitalized raw material as inventory upon receipt and accounted for the raw material inventory as follows:

a) to the extent that the Company had up to twelve months of firm, fixed orders and/or projections from its collaborators, the Company capitalized the value of raw materials that will be used in the production of conjugate subject to these firm, fixed orders and/or projections;

b) the Company considered more than a twelve month supply of raw materials that was not supported by firm, fixed orders and/or projections from its collaborators to be excess and established a reserve to reduce to zero the value of any such excess raw material inventory with a corresponding charge to research and development expense; and

c) the Company also considered any other external factors and information of which it became aware and assessed the impact of such factors or information on the net realizable value of the raw material inventory at each reporting period.

During the year ended December 31, 2017, the six month transition period ended December 31, 2016 and fiscal year 2016, the Company obtained additional amounts of its cell-killing agents DMx from its supplier which yielded more material than would be required by the Company’s collaborators over the next twelve months, and as a result, the Company recorded $403,000,  $150,000, and $1.1 million, respectively, of charges to research and development expense related to raw material inventory identified as excess. There were no such excess charges during 2018.

Unbilled Revenue

Unbilled revenue substantially represents research funding earned based on actual resources utilized under the Company’s various collaborator agreements.

Clinical Trial Accruals

Clinical trial expenses are a significant component of research and development expenses, and the Company outsources a significant portion of these costs to third parties. Third party clinical trial expenses include investigator fees, site costs (patient cost), clinical research organization costs, and costs for central laboratory testing and data management. The accrual for site and patient costs includes inputs such as estimates of patient enrollment, patient cycles incurred, clinical site activations, and other pass-through cost.  These inputs are required to be estimated due to a lag in receiving the actual clinical information from third parties. Payments for these activities are based on the terms of the individual arrangements, which may differ from the pattern of costs incurred, and are reflected on the consolidated balance sheets as prepaid asset or accrued clinical trial cost.  These third party agreements are generally cancelable, and related costs are recorded as research and development expenses as incurred. Non-refundable advance clinical payments for goods or services that will be used or rendered for future R&D activities recorded as a prepaid asset and recognized as expense as the related goods are delivered or the related services are performed. The Company also records accruals for estimated ongoing clinical research and development costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates may be made in determining the accrued balances at the end of any reporting period. Actual results could differ from the estimates made by the Company. The historical clinical accrual estimates made by the Company have not been materially different from the actual costs. 

Other Accrued Liabilities

Other accrued liabilities consisted of the following at December 31, 2018 and 2017 (in thousands):

	December 31,		December 31,
	2018		2017
Accrued contract payments	$	6,389	$	4,901
Accrued clinical trial costs		11,087		8,400
Accrued professional services		1,171		723
Accrued employee benefits		651		574
Accrued public reporting charges		164		156
Other current accrued liabilities		1,003		1,013
Total	$	20,465	$	15,767

Deferred Revenue

Deferred revenue represents amounts related to partner agreements that have yet to be recognized as revenue. Included in the total of deferred revenue is $5.9 million related to the rights to future technological improvements for our partners at December 31, 2018 and $6.8 million at December 31, 2017.  The balance of deferred revenue substantially relates to revenue to be recognized upon the granting of a license to partners.

Research and Development Expenses

The Company’s research and development expenses are charged to expense as incurred and relate to (i) research to evaluate new targets and to develop and evaluate new antibodies, linkers, and cytotoxic agents, (ii) preclinical testing of its own and, in certain instances, its collaborators’ product candidates, and the cost of its own clinical trials, (iii) development related to clinical and commercial manufacturing processes, and (iv) manufacturing operations which also include raw materials. Payments made by the Company in advance for research and development services not yet provided and/or materials not yet delivered and accepted are recorded as prepaid expenses and are included in the accompanying Consolidated Balance Sheets as prepaid and other current assets.

Income Taxes

The Company uses the liability method to account for income taxes. Deferred tax assets and liabilities are determined based on differences between the financial reporting and income tax basis of assets and liabilities, as well as net operating loss carry forwards and tax credits and are measured using the enacted tax rates and laws that will be in effect when the differences reverse. A valuation allowance against net deferred tax assets is recorded if, based on the available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized.

Property and Equipment

Property and equipment are stated at cost. The Company provides for depreciation based upon expected useful lives using the straight‑line method over the following estimated useful lives:

Machinery and equipment	5 years
Computer hardware and software	3 years
Furniture and fixtures	5 years
Leasehold improvements	Shorter of remaining lease term or 7 years

Equipment under capital leases is amortized over the lives of the respective leases or the estimated useful lives of the assets, whichever is shorter, and included in depreciation expense.

Maintenance and repairs are charged to expense as incurred. Upon retirement or sale, the cost of disposed assets and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is included in the statement of operations. The Company recorded $(115,000),  $(239,000),  $(1.1 million), and $21,000 of (losses) gains on the sale/disposal of certain furniture and equipment during the years ended December 31, 2018 and 2017, the six months ended December 31, 2016, and the year ended June 30, 2016, respectively.

Impairment of Long‑Lived Assets

In accordance with ASC Topic 360, “Property, Plant, and Equipment,” the Company continually evaluates whether events or circumstances have occurred that indicate that the estimated remaining useful life of its long‑lived assets may warrant revision or that the carrying value of these assets may be impaired if impairment indicators are present. The Company evaluates the realizability of its long‑lived assets based on cash flow expectations for the related asset. Any write‑downs to fair value are treated as permanent reductions in the carrying amount of the assets. The year ended December 31, 2017 and the six months ended December 31, 2016 include $180,000 and $970,000, respectively, of leasehold impairment charges resulting from the restructuring, the details of which are further discussed in Note I. Based on this evaluation, the Company believes that, as of each of the balance sheet dates presented, none of the Company’s remaining long‑lived assets were impaired.

Computation of Net Loss per Common Share

Basic and diluted net loss per share is calculated based upon the weighted average number of common shares outstanding during the period. During periods of income, participating securities are allocated a proportional share of income determined by dividing total weighted average participating securities by the sum of the total weighted average common shares and participating securities (the “two‑class method”). Shares of the Company’s restricted stock participate in any dividends that may be declared by the Company and are therefore considered to be participating securities. Participating securities have the effect of diluting both basic and diluted earnings per share during periods of income. During periods of loss, no loss is allocated to participating securities since they have no contractual obligation to share in the losses of the Company. Diluted (loss) income per share is computed after giving consideration to the dilutive effect of stock options, convertible notes and restricted stock that are outstanding during the period, except where such non-participating securities would be anti-dilutive.

The Company’s common stock equivalents, as calculated in accordance with the treasury‑stock method for the options and unvested restricted stock and the if-converted method for the convertible notes, are shown in the following table (in thousands):

			Six Months
			Ended	Year Ended
	Years Ended December 31,		December 31,	June 30,
	2018	2017	2016	2016
Options outstanding to purchase common stock, shares issuable under the employee stock purchase plan, and unvested restricted stock at end of period	17,380	14,290	13,878	11,919
Common stock equivalents under treasury stock method for options, shares issuable under the employee stock purchase plan, and unvested restricted stock	3,001	1,579	1	735
Shares issuable upon conversion of convertible notes at end of period	501	501	23,878	23,878
Common stock equivalents under if-converted method for convertible notes	501	501	23,878	718

The Company’s common stock equivalents have not been included in the net loss per share calculation because their effect is anti‑dilutive due to the Company’s net loss position.

Stock‑based Compensation

As of December 31, 2018, the Company is authorized to grant future awards under one employee share‑based compensation plan, which is the ImmunoGen, Inc. 2018 Employee, Director and Consultant Equity Incentive Plan, or the 2018 Plan. At the annual meeting of shareholders on June 20, 2018, the 2018 Plan was approved and provides for the issuance of Stock Grants, the grant of Options and the grant of Stock‑Based Awards for up to 7,500,000 shares of the Company’s common stock, as well as up to 19,500,000 shares of common stock which represent awards granted under the previous stock option plans, the ImmunoGen, Inc. 2016 and 2006 Employee, Director and Consultant Equity Incentive Plans, or the 2016 and 2006 Plans, that forfeit, expire, or cancel without delivery of shares of common stock or which resulted in the forfeiture of shares of common stock back to the Company subsequent to June 19, 2018. Option awards are granted with an exercise price equal to the market price of the Company’s stock at the date of grant. Options vest at various periods of up to four years and may be exercised within ten years of the date of grant.

The stock‑based awards are accounted for under ASC Topic 718, “Compensation—Stock Compensation.” Pursuant to Topic 718, the estimated grant date fair value of awards is charged to the statement of operations over the requisite service period, which is the vesting period. Such amounts have been reduced by an estimate of forfeitures of all unvested awards. The fair value of each stock option is estimated on the date of grant using the Black‑ Scholes option‑pricing model with the weighted average assumptions noted in the following table. As the Company has not paid dividends since inception, nor does it expect to pay any dividends for the foreseeable future, the expected dividend yield assumption is zero. Expected volatility is based exclusively on historical volatility of the Company’s stock. The expected term of stock options granted is based exclusively on historical data and represents the period of time that stock options granted are expected to be outstanding. The expected term is calculated for and applied to one group of stock options as the Company does not expect substantially different exercise or post‑vesting termination behavior amongst its employee population. The risk‑free rate of the stock options is based on the U.S. Treasury rate in effect at the time of grant for the expected term of the stock options.

					Six Months
	Years Ended				Ended		Year Ended
	December 31,				December 31,		June 30,
	2018		2017		2016		2016
Dividend	None		None		None		None
Volatility	71.02	%	67.34	%	65.63	%	66.34	%
Risk-free interest rate	2.73	%	2.00	%	1.29	%	1.80	%
Expected life (years)	6.0		6.0		6.3		6.3

Using the Black‑Scholes option‑pricing model, the weighted average grant date fair values of options granted during the years ended December 31, 2018 and 2017, the six months ended December 31, 2016, and fiscal year 2016 were $6.70,  $1.98,  $1.76,  and $8.91 per share, respectively.

A summary of option activity under the option plans as of December 31, 2018, 2017 and 2016, and changes during the years ended December 31, 2018 and 2017, six-month period ended December 31, 2016, and the fiscal year ended June 30, 2016 is presented below (in thousands, except weighted‑average data):

		Weighted-		Weighted-
	Number	Average		Average	Aggregate
	of Stock	Exercise		Remaining	Intrinsic
	Options	Price		Life in Yrs.	Value
Outstanding at June 30, 2015	9,689	$	12.49	6.76	$	—
Granted	3,340	$	14.34
Exercised	(555)		9.30
Forfeited/Canceled	(661)		14.84
Outstanding at June 30, 2016	11,813		13.03	6.82	$	—
Outstanding at June 30, 2016—vested or unvested and expected to vest	11,475		13.05	6.76	$	—
Exercisable at June 30, 2016	6,453	$	12.63	5.30		—
Outstanding at June 30, 2016	11,813	$	13.03
Granted	3,536		2.90
Exercised	—		—
Forfeited/Canceled	(1,670)		10.64
Outstanding at December 31, 2016	13,679		10.70	6.55	$	23
Outstanding at December 31, 2016—vested or unvested and expected to vest	13,516		10.76	6.52	$	22
Exercisable at December 31, 2016	7,898	$	13.15	4.70		—
Outstanding at December 31, 2016	13,679	$	10.70
Granted	1,589		3.21
Exercised	(191)		3.42
Forfeited/Canceled	(3,106)		10.33
Outstanding at December 31, 2017	11,971		9.92	6.17	$	13,513
Outstanding at December 31, 2017—vested or unvested and expected to vest	11,881	$	9.96	6.15	$	13,283
Exercisable at December 31, 2017	7,996	$	12.16	4.97	$	3,733
Outstanding at December 31, 2017	11,971	$	9.92
Granted	5,513		10.36
Exercised	(742)		4.67
Forfeited/Canceled	(1,178)		11.49
Outstanding at December 31, 2018	15,564	$	10.20	6.46	$	5,818
Outstanding at December 31, 2018—vested or unvested and expected to vest	15,386	$	10.21	6.43	$	5,781
Exercisable at December 31, 2018	8,405	$	11.47	4.45	$	3,122

In September 2018, the Company granted 295,200 performance stock options to certain employees that will vest in two equal installments upon the achievement of specified performance goals within the next five years. These options are included in the table above. None of the awards subject to performance conditions have been expensed to date. The fair value of the performance based options that could be expensed in future periods is $1.8 million.

 A summary of restricted stock activity under the option plans as of December 31, 2018, 2017, and 2016, and changes during the year ended December 31, 2018 and 2017, and the six-month period ended December 31, 2016, and the fiscal year ended June 30, 2016 is presented below (in thousands, except weighted‑average data):

	Number of	Weighted-
	Restricted	Average Grant
	Stock Shares	Date Fair Value
Unvested at June 30, 2015	50	$	9.23
Awarded	75		5.65
Vested	(19)		10.13
Unvested at June 30, 2016	106	$	6.54
Awarded	118		3.15
Vested	—		—
Forfeited	(25)		7.52
Unvested at December 31, 2016	199	$	4.41
Awarded	2,253		2.71
Vested	(25)		5.87
Forfeited	(108)		2.68
Unvested at December 31, 2017	2,319	$	2.82
Vested	(503)		2.64
Unvested at December 31, 2018	1,816	$	2.87

In August 2016, February 2017, and June 2017, the Company granted 117,800,  529,830, and 239,000 shares of restricted common stock with grant date fair values of $3.15,  $2.47, and $4.71, respectively, to certain officers of the Company, however, 71,380 of these shares have subsequently been forfeited. These restrictions will lapse in three equal installments upon the achievement of specified performance goals within the next five years. None of the awards subject to performance conditions have been expensed to date. The fair value of the performance based shares that could be expensed in future periods is $2.6 million.

In June 2018, the Company's Board of Directors, with shareholder approval, adopted the Employee Stock Purchase Plan, or ESPP. An aggregate of 1,000,000 shares of common stock have been reserved for issuance under the ESPP. The ESPP is generally available to all employees who have been continuously employed for three months per year, have customary employment of more than five months in a calendar year, and more than 20 hours per week. Under the ESPP, eligible participants purchase shares of the Company's common stock at a price equal to 85% of the lesser of the closing price of the Company's common stock on the first business day and the final business day of the applicable plan purchase period. Plan purchase periods are six months and begin on January 1 and July 1 of each year, with purchase dates occurring on the final business day of the given purchase period. To pay for the shares, each participant authorizes periodic payroll deductions of up to 15% of his or her eligible cash compensation. All payroll deductions collected from the participant during a purchase period are automatically applied to the purchase of common stock on that period's purchase date provided the participant remains an eligible employee and has not withdrawn from the ESPP prior to that date and are subject to certain limitations imposed by the ESPP and the Internal Revenue Code. On December 31, 2018, 205,000 shares were issued to participating employees at a fair value of approximately $3.55 per share. The fair value of each ESPP award is estimated on the first day of the offering period using the Black-Scholes option-pricing model. The expected volatility used in the fair value calculation was 70.1%, the expected life was .5 years, the expected dividend yield was zero, and the risk-free rate was 2.14%. The Company recognizes share-based compensation expense equal to the fair value of the ESPP awards on a straight-line basis over the offering period.

Stock compensation expense related to stock options and restricted stock awards granted under the option plans was $16.4,  $11.1, $8.1,  and $21.9 million during the years ended December 31, 2018 and 2017, the six months ended December 31, 2016, and the fiscal year ended June 30, 2016, respectively. During the years ended December 31, 2018 and 2017, the Company recorded approximately $116,000 and $742,000 of stock compensation cost related to the modification of certain outstanding common stock options with former officers of the Company. During fiscal year 2016, the Company recorded $3.1 million of stock compensation cost related to the modification of certain outstanding common stock options with the former Chief Executive Officer. No similar charges were recorded in the six-month transition period ended December 31, 2016. As of December 31, 2018, the estimated fair value of unvested employee awards was $28.0 million, net of estimated forfeitures. The weighted‑average remaining vesting period for these awards is approximately two years. Included in stock compensation expense for the years ended December 31, 2018 and 2017, the six months ended December 31, 2016, and the fiscal year ended June 30, 2016 are 361,000,  206,000,  $215,000,  and $380,000, respectively, of expense recorded for directors’ deferred share units, the details of which are discussed in Note H of the Company’s consolidated financial statements.  

A summary of option activity for options vested during the years ended December 31, 2018 and 2017 and the six months ended December 31, 2016, and the fiscal year ended June 30, 2016 is presented below (in thousands):

	Years Ended December 31,				Six Months Ended December 31,		Year Ended June 30,
	2018		2017		2016		2016
Total fair value of options vested	$	7,496	$	10,964	$	17,121	$	15,298
Total intrinsic value of options exercised		3,787		598		—		3,142
Cash received for exercise of stock options		4,301		650		—		5,161

Comprehensive Loss

The Company presents comprehensive loss in accordance with ASC Topic 220, Comprehensive Income. Comprehensive loss is comprised of the Company’s net loss for all periods presented.

Segment Information

During all periods presented, the Company continued to operate in one reportable business segment under the management approach of ASC Topic 280, Segment Reporting, which is the business of the discovery and development of ADCs for the treatment of cancer.

The percentages of revenues recognized from significant customers of the Company in the years ended December 31, 2018, and 2017, the six months ended December 31, 2016, and the year ended June 30, 2016 are included in the following table:

	Years Ended December 31,				Six Months Ended December 31,		Year Ended June 30,
Collaborative Partner:	2018		2017		2016		2016
Bayer	—	%	—	%	—	%	17	%
CytomX	8	%	13	%	—	%	—	%
Debiopharm	2	%	26	%	—	%	—	%
Lilly	2	%	1	%	4	%	11	%
Novartis	2	%	—	%	24	%	1	%
Roche	60	%	24	%	60	%	43	%
Sanofi	—	%	31	%	—	%	—	%
Takeda	23	%	4	%	8	%	16	%

There were no other customers of the Company with significant revenues in the periods presented.

Other Recently Adopted Accounting Pronouncements

In January 2016, the FASB issued ASU 2016-1, Recognition and Measurement of Financial Assets and Financial Liabilities (Topic 825). The amendments in this ASU supersede the guidance to classify equity securities with readily determinable fair values into different categories (that is, trading or available-for-sale) and require equity securities (including other ownership interests, such as partnerships, unincorporated joint ventures, and limited liability companies) to be measured at fair value with changes in the fair value recognized through net income. The amendments allow equity investments that do not have readily determinable fair values to be remeasured at fair value either upon the occurrence of an observable price change or upon identification of an impairment. The amendments also require enhanced disclosures about those investments. The amendments improve financial reporting by providing relevant information about an entity’s equity investments and reducing the number of items that are recognized in other comprehensive income. This guidance is effective for annual reporting beginning after December 15, 2017, including interim periods within the year of adoption, and calls for prospective application, with early application permitted. Accordingly, the standard is effective for the Company on January 1, 2018. The adoption of this guidance did not have a material impact on the Company’s consolidated financial statements.

In May 2017, the FASB issued ASU 2017-09, Stock Compensation – Scope of Modification Accounting (Topic 718) regarding changes to terms and conditions of share-based payment awards. The ASU provides guidance about which changes to terms or conditions of a share-based payment award require an entity to apply modification accounting. The guidance is effective for annual periods beginning after December 15, 2017, including interim periods within that year. The adoption of this guidance did not have a material impact on the Company’s consolidated financial statements.

Recently issued accounting pronouncements, not yet adopted

In February 2016, the FASB issued ASU 2016-2, Leases (Topic 842). The purpose of this update is to increase the transparency and comparability among organizations by recognizing lease assets and liabilities on the balance sheet, including those previously classified as operating leases under current U.S. GAAP, and disclosing key information about leasing arrangements. Topic 842 as amended is effective for annual periods beginning after December 15, 2018, including interim periods within those annual periods. The Company currently plans to adopt the standard using the transition method provided by ASC Update No. 2018-11, Leases(Topic 842): Targeted Improvements. Under this method, the Company will initially apply the new leasing rules on January 1, 2019, rather than at the earliest comparative period presented in the financial statements. Prior periods presented will be in accordance with the existing lease guidance.

Upon transition, the Company plans to apply the package of practical expedients permitted under Topic 842 transition guidance to its entire lease portfolio at January 1, 2019. As a result, the Company is not required to reassess (i) whether any expired or existing contracts are or contain leases, (ii) the classification of any expired or existing leases, and (iii) initial direct costs for any existing leases. Furthermore, the Company will be electing not to separate lease and non-lease components for our leases. Instead, for these applicable classes of underlying assets, the Company will account for each separate lease component and the non-lease components associated with that lease component, as a single lease component. Lastly, the Company will be electing not to apply the recognition requirements of ASC 842 to short-term leases and instead to recognize the lease payments as lease cost on a straight-line basis over the lease term.

Although the Company has not finalized its process of evaluating the impact of adoption of the ASU on its consolidated financial statements, the Company expects to record an increase in the recorded amounts of assets and liabilities related to the recognition of new right-of-use assets and lease liabilities on the Company’s balance sheet for leases currently classified as operating leases for an amount that is expected to range between $16 million to $19 million. The Company does not expect the adoption to have an impact to the statement of operations.

In June 2018, the FASB issued ASU No. 2018-07, Compensation — Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting, which expands the scope of Topic 718 to include all share-based payment transactions for acquiring goods and services from non-employees. ASU 2018-07 specifies that Topic 718 applies to all share-based payment transactions in which the grantor acquires goods and services to be used or consumed in its own operations by issuing share-based payment awards. ASU 2018-07 also clarifies that Topic 718 does not apply to share-based payments used to effectively provide (1) financing to the issuer or (2) awards granted in conjunction with selling goods or services to customers as part of a contract accounted for under ASC 606. ASU 2018-07 is effective for annual periods beginning after December 15, 2018, with early adoption permitted. This ASU is not expected to have a material effect on the Company’s consolidated financial statements.

In November 2018, the FASB issued ASU 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606, which clarifies that certain transactions between participants in a collaborative arrangement should be accounted for under ASC 606 when the counterparty is a customer. In addition, ASU 2018-18 adds unit-of-account guidance to ASC Topic 808, Collaborative Arrangements, in order to align this guidance with ASC 606 and also precludes an entity from presenting consideration from a transaction in a collaborative arrangement as revenue from contracts with customers if the counterparty is not a customer for that transaction. This guidance will be effective for annual reporting periods beginning after December 15, 2019, including interim periods within those annual reporting periods, and early adoption is permitted. The Company is currently evaluating the potential impact that ASU 2018-18 may have on the consolidated financial statements.

No other recently issued or effective ASUs had, or are expected to have, a material effect on the Company's results of operations, financial condition, or liquidity.