14. Income Taxes

There is no provision for income taxes because the Company has incurred operating losses since inception. As of December 31, 2016, the Company had federal and state net operating loss carryforwards of approximately $332.1 million which may be used to offset future taxable income. The Company also had federal research and development tax credit carryforwards and other federal tax credit carryforwards which aggregate to $3.5 million at December 31, 2016. These carryforwards expire at various times through 2036 and may be limited in their annual usage by Section 382 of the Internal Revenue Code, as amended, relating to ownership changes.

The following table sets forth the tax effects of temporary differences that give rise to significant portions of the Company’s net deferred tax assets (in thousands).

	December 31,
	2016			2015			2014
Deferred tax assets:
Net operating loss carryforwards	$	133,514		$	123,647		$	115,870
Research and other credits		3,482			5,610			6,047
Other temporary differences		2,319			4,804			(2,478	)
Deferred tax assets - before valuation allowance		139,315			134,061			119,439
Valuation allowance		(139,315	)		(134,061	)		(119,439	)
Net deferred tax assets - after valuation allowance	$	-		$	-		$	-

The Company’s deferred tax assets represent an unrecognized future tax benefit. The Company recognizes uncertain tax positions net, against any operating losses or applicable research credits as they arise. Currently, there are no uncertain tax positions recognized at December 31, 2016. The Company has provided a full valuation allowance on its deferred tax assets at December 31, 2016 and 2015, as management believes it is more likely than not that the related deferred tax asset will not be realized. The reported amount of income tax expense differs from the amount that would result from applying domestic federal statutory tax rates to pretax losses, primarily because of changes in the valuation allowance.

The following table sets forth reconciling items from income tax computed at the statutory federal rate.

	Year Ended December 31,
	2016			2015			2014
Federal income tax at statutory rate		35.0	%		35.0	%		35.0	%
State income taxes, net of federal benefits		2.9	%		5.4	%		4.5	%
Research and other credits		-5.8	%		-1.2	%		-1.3	%
Permanent deductions		-18.0	%		-4.0	%		-2.2	%
Valuation allowance		-14.1	%		-35.2	%		-36.0	%

Effective tax rate		0.0	%		0.0	%		0.0	%

Accounting literature regarding liabilities for unrecognized tax benefits provides guidance for the recognition and measurement in financial statements of uncertain tax positions taken or expected to be taken in a tax return. The Company’s evaluation was performed for the tax periods from inception to December 31, 2016, which remain subject to examination by major tax jurisdictions as of December 31, 2016.

The Company may from time to time be assessed interest or penalties by major tax jurisdictions, although there have been no such assessments historically, with any material impact to its financial results. The Company would recognize interest and penalties related to unrecognized tax benefits within the income tax expense line in the accompanying consolidated statements of operations. Accrued interest and penalties would be included within the related tax liability line in the consolidated balance sheets.