1. Organization and Basis of Presentation Tocagen Inc. (Tocagen or the Company) is a clinical-stage, cancer-selective gene therapy company focused on developing first-in-class, broadly-applicable product candidates designed to activate a patients immune system against their own cancer. The Companys cancer-selective gene therapy platform is built on retroviral replicating vectors which are designed to selectively deliver therapeutic genes into the DNA of cancer cells. Tocagens gene therapy approach is designed to fight cancer through immunotherapeutic mechanisms of action without the autoimmune toxicities commonly experienced with other immunotherapies. The Company views its operations and manages its business in one operating segment. From inception through December 31, 2018, the Company has devoted substantially all of its efforts to developing its gene therapy platform and its lead product candidate, Toca 511 &amp; Toca FC, as well as raising capital and building its infrastructure. The Company has not generated revenues from its principal operations. Initial Public Offering On April 19, 2017, the Company completed its initial public offering (IPO), whereby the Company sold an aggregate of 9,775,000 shares of its common stock, at $10.00 per share, resulting in net proceeds of $86.9 million after underwriting discounts, commissions and offering costs of $10.8 million. In addition, in connection with the IPO, all of the Companys outstanding shares of convertible preferred stock were converted into an aggregate of 6,690,066 shares of the Companys common stock, warrants to purchase up to 68,572 shares of the Companys Series H convertible preferred stock were converted into warrants to purchase up to 9,936 shares of the Companys common stock, each at an exercise price of $36.23 per share, and $11.1 million of aggregate principal and accrued interest underlying convertible promissory notes were automatically converted into an aggregate of 1,109,176 shares of the Companys common stock at the IPO price of $10.00 per share. ATM Facility In November 2018, the Company entered into an Equity Distribution Agreement with Citigroup Global Markets Inc. (Citigroup), pursuant to which the Company may sell and issue shares of its common stock having an aggregate offering price of up to $30,000,000 from time to time through Citigroup, as its sales agent (the ATM facility). As of December 31, 2018, the Company has not sold any shares of its common stock under the ATM facility. Public Offering In December 2018, the Company completed a public offering in which it sold an aggregate of 3,000,000 shares of common stock at a price of $10.00 per share. Net proceeds from the public offering, after deducting underwriting discounts, commissions and offering expenses, were approximately $28.0 million. Liquidity The Company has a limited operating history and the sales and income potential of the Companys business and patient markets are unproven. The Company has experienced net losses and negative cash flows from operating activities since its inception. As of December 31, 2018, the Company had an accumulated deficit of $215.9 million and working capital of $81.2 million available to fund future operations. As the Company continues to incur net losses, its transition to profitability is dependent upon the successful development, approval, and commercialization of its product candidates and achieving a level of revenues adequate to support the Companys cost structure. The Company may never achieve profitability, and unless and until it does, the Company will continue to need to raise additional capital. The Company plans to continue to fund its losses from operations and capital funding needs through debt and equity financing, or through collaborations or partnerships with other entities. Debt or equity financing, or collaborations and partnerships with other entities may not be available on a timely basis on terms acceptable to the Company, or at all. As of December 31, 2018, the Company had cash, cash equivalents and marketable securities of $96.1 million. The Company has evaluated and concluded that there are no conditions or events, considered individually or in the aggregate, that raises substantial doubt about its ability to continue as a going concern for a period of one year following the date that these financial statements are issued. Use of Estimates The Companys financial statements are prepared in accordance with accounting principles generally accepted in the United States, which requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenue and expenses and the disclosure of contingent assets and liabilities in the financial statements accompanying notes. Significant estimates in the Companys financial statements relate to clinical trial accruals, the valuation of equity awards, and the development period used for license revenue recognition. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results may differ from these estimates under different assumptions or conditions.