Summary of Significant Accounting Policies

Liquidity Matters

The Company has incurred net losses since its inception and anticipates net losses and negative operating cash flows for the near future. For the year ended December 31, 2019, the Company had a net loss of $124.8 million, which increased the accumulated deficit to $699.2 million from $574.5 million at December 31, 2018 following the modified retrospective adoption of ASU 2018-07, which required a cumulative-effect adjustment to accumulated deficit as of the earliest period presented in the consolidated financial statements. At December 31, 2019, the Company had $62.0 million in cash, cash equivalents and restricted cash, $379.1 million in marketable securities, $50.1 million of outstanding balance of the Credit Line (as defined in Note 10) including accrued interest, and $73.7 million of net carrying amount of the 2017 Term Loan (as defined in Note 10). While the Company has introduced multiple products that are generating revenues, these revenues have not been sufficient to fund all operations. Accordingly, the Company has funded the portion of operating costs that exceeds revenues through a combination of equity issuances, debt issuances, and other financing.

The Company continues to develop and commercialize future products and, consequently, it will need to generate additional revenues to achieve future profitability and may need to raise additional equity or debt financing. If the Company raises additional funds by issuing equity securities, its stockholders would experience dilution. Additional debt financing, if available, may involve covenants restricting its operations or its ability to incur additional debt. Any additional debt financing or additional equity that the Company raises may contain terms that are not favorable to it or its stockholders and require significant debt service payments, which diverts resources from other activities. Additional financing may not be available at all, or in amounts or on terms acceptable to the Company. If the Company is unable to obtain additional financing, it may be required to delay the development, commercialization and marking of its products and significantly scale back its business and operations.

On April 23, 2019, the Company completed an underwritten equity offering to sell 5,263,158 shares of its common stock at a price to the public of $19 per share. On April 26, 2019, the Company sold an additional 789,473 shares of its common stock to the underwriters at the same price upon their exercise of the option to purchase those shares. Before offering expenses of $0.6 million, the Company received proceeds of $108.1 million net of the underwriting discount.

On October 17, 2019, the Company completed an underwritten equity offering to sell 5,714,286 shares of its common stock at a price to the public of $35 per share. The same day, the Company sold an additional 857,142 shares of its common stock to the underwriters at the same price upon their exercise of the option to purchase those shares. Before offering expenses of $0.4 million, the Company received proceeds of $216.2 million net of the underwriting discount.

Based on the Company’s current business plan, the Company believes that its existing cash and marketable securities will be sufficient to meet its anticipated cash requirements for at least 12 months after February 28, 2020.

Use of Estimates

The preparation of financial statements in accordance with U.S. GAAP requires management to make estimates and assumptions about future events that affect the amounts of assets and liabilities reported, disclosures about contingent assets and liabilities, and reported amounts of revenues and expenses. Significant items subject to such estimates include the allowance for doubtful accounts, deferred revenues associated with unsatisfied performance obligations, accrued liability for potential refund requests, stock-based compensation, the fair value of common stock and warrants, income tax uncertainties, and the expected consideration to be received from contracts with customers. These estimates and assumptions are based on management's best estimates and judgment. Management regularly evaluates its estimates and assumptions using historical experience and other factors, including contractual terms and statutory limits; however, actual results could differ from these estimates and could have an adverse effect on the Company's financial statements.

Cash and Cash Equivalents

Cash and cash equivalents consist of cash and money market deposits with financial institutions.

Investments

Investments consist primarily of debt securities such as U.S. Treasuries, U.S. agency and municipal bonds. Management determines the appropriate classification of securities at the time of purchase and reevaluates such determination at each balance sheet date. The Company generally classifies its entire investment portfolio as available-for-sale. The Company views its available-for-sale portfolio as available for use in current operations. Accordingly, the Company classifies all investments as short-term, even though the stated maturity may be more than one year from the current balance sheet date. Available-for-sale securities are carried at fair value, with unrealized gains and losses reported in accumulated other comprehensive income (loss), which is a separate component of stockholders’ equity.

Allowance for Doubtful Accounts

Trade accounts receivable are recorded at the amount billed to the laboratory partners and clinics, insurance payers, oncologists, pharmaceutical companies, and patients. Reducing this amount is an allowance for doubtful accounts for estimated losses resulting from the inability of its customers to make the contracted payments. Management analyzes accounts receivable and historical bad debt experience, customer creditworthiness, current economic trends, and changes in customer payment history when evaluating the adequacy of the allowance for doubtful accounts. Accounts receivable are written off against the allowance when there is substantive evidence that the account will not be paid.

Cost of Product Revenues

The components of cost of product revenues are material and service costs, impairment charges associated with testing equipment, personnel costs, including stock-based compensation expense, equipment and infrastructure expenses associated with testing samples, electronic medical record, order and delivery systems, shipping charges to transport samples, third-party test processing fees and allocated overhead including rent, information technology costs, equipment depreciation and utilities. Costs associated with the performance of diagnostic services are recorded as tests are accessioned.

Research and Development

The Company records research and development costs in the period incurred. Research and development costs consist of personnel costs, contract services, cost of materials utilized in performing tests, costs of clinical trials and allocated facilities and related overhead expenses.

Product Shipment Costs

The Company expenses product shipment costs in cost of product revenues in the accompanying statements of operations. Shipping and handling costs for the years ended December 31, 2019, 2018 and 2017 were $13.3 million, $12.4 million and $9.5 million, respectively.

Stock-Based Compensation

Stock-based compensation related to stock options and restricted stock units (“RSUs”) granted to the Company’s employees is measured at the grant date based on the fair value of the award. The fair value is recognized as expense over the requisite service period, which is generally the vesting period of the respective awards. No compensation cost is recognized when the requisite service has not been met and the awards are therefore forfeited.

For stock options with market conditions, the Company derives the requisite service period using the Monte Carlo simulation model. For stock options and RSUs that vest upon meeting performance conditions or market conditions in combination with performance conditions, the Company derives the requisite service period from the grant date to the date it is probable that the vesting conditions will be met.

The Company also recognizes stock-based compensation from option awards and RSUs granted to non-employees. Prior to January 1, 2019, the fair value of non-employee awards was subject to remeasurement at the end of each reporting period until the vesting date of such awards, and the resulting change in fair value was recognized in the Company's statements of operations and comprehensive loss during the period that the related services were rendered.

On January 1, 2019, the Company adopted ASU 2018-07, which allows the accounting for nonemployee awards to be treated the same as for employee awards. The fair value of non-employee awards is now determined based on a one-time measurement at the grant date, and it is no longer subject to periodic remeasurement. The Company continues to recognize stock-based compensation expense as services are rendered by the non-employees over the vesting period, which is accounted for on a straight-line basis. See further discussion under the Recently Adopted Accounting Pronouncements section within this footnote, as well as the election of certain accounting policy as a result of the adoption.

The Company uses the Black‑Scholes option‑pricing model and the Monte Carlo simulation model to estimate the fair value of stock options issued to employees and non-employees. The model requires the input of the Company's expected stock price volatility, the expected term of the awards, and a risk-free interest rate. Determining these assumptions requires significant judgment. See further discussion on the valuation assumptions used under Note 9.

Capitalized Software Held for Internal Use

The Company capitalizes salaries and related costs of employees and consultants who devote time to the development of internal-use software development projects. Capitalization begins during the application development stage, once the preliminary project stage has been completed, which includes successful validation and approval from management. If a project constitutes an enhancement to previously developed software, the Company assesses whether the enhancement is significant and creates additional functionality to the software, thus qualifying the work incurred for capitalization. Once the project is available for general release, capitalization ceases and the Company estimates the useful life of the asset and begins amortization. The Company periodically assesses whether triggering events are present to review internal-use software for impairment. Changes in estimates related to internal-use software would increase or decrease operating expenses or amortization recorded during the reporting period. Refer to Property and Equipment, net under Note 6 for more detail regarding an impairment charge recorded to write off certain project development costs during the first quarter of 2018.

The Company amortizes its internal-use software over the estimated useful lives of three years. The net book value of capitalized software held for internal use was $1.2 million and $1.7 million as of December 31, 2019 and 2018, respectively. Amortized expense for amounts previously capitalized for the years ended December 31, 2019, 2018 and 2017 was $1.2 million, $1.3 million and $1.0 million, respectively. In addition, the Company recorded $0.1 million of impairment expense in relation to the disposal of business in the year ended December 31, 2019.

Property and Equipment

Property and equipment, including purchased and internally developed software, are stated at cost. Depreciation is calculated using the straight-line method over the estimated useful lives of the assets, which are generally three to five years. Leasehold improvements are amortized using the straight-line method over the estimated useful lives of the assets or the remaining term of the lease, whichever is shorter. The Company periodically reviews the depreciable lives assigned to property and equipment placed in service and change the estimates of useful lives to reflect the results of such reviews.

Inventory

Inventory is valued at the lower of the standard cost, which approximates actual cost, or market. Cost is determined using the first-in, first-out ("FIFO") method. Inventory consists entirely of supplies, which are consumed when providing its test reports, and therefore does not maintain any finished goods inventory. The Company enters into inventory purchases and commitments so that it can meet future delivery schedules based on forecasted demand for its tests.

The Company recorded inventory obsolescence charges totaling $0.3 million, $0.3 million, and $0.5 million in the years ended December 31, 2019, 2018, and 2017, respectively.