will ever generate significant revenues or achieve profitability. We expect to use cash, cash equivalents and investment proceeds to fund our clinical and operating activities. Our future liquidity and capital requirements will depend on numerous factors, including the initiation and progress of clinical trials and research and product development programs; obtaining approvals and complying with regulations; the timing and effectiveness of product commercialization activities, including marketing arrangements; the timing and costs involved in preparing, filing, prosecuting, defending and enforcing intellectual property rights; and the effect of competing technological and market developments.
At September 30, 2019, we had cash, cash equivalents and restricted cash totaling $15.5 million, as compared to cash, cash equivalents and restricted cash totaling $3.6 million at December 31, 2018 and $10.0 million at September 30, 2018. During the nine months ended September 30, 2019 and 2018, we used $18.3 million and $12.9 million respectively, of cash in our operating activities.
Our condensed consolidated financial statements as of September 30, 2019 have been prepared under the assumption that we will continue as a going concern for the next twelve months. We expect to incur significant expenses and operating losses for the foreseeable future. These factors raise substantial doubt about our ability to continue as a going concern. Because our business does not generate positive cash flow from operating activities, we will need to obtain substantial additional capital in order to fund clinical trial research and support development efforts relating to ocular melanoma liver metastases, ICC, HCC or other indications, and to fully commercialize the product. We believe we will be able to raise additional capital in the event it is in our best interest to do so. We anticipate raising such additional capital by either borrowing money, selling shares of our capital stock, or entering into strategic alliances with appropriate partners. To the extent additional capital is not available when needed or on acceptable terms, we may be forced to abandon some or all of our development and commercialization efforts, which would have a material adverse effect on the prospects of our business. Further, our assumptions relating to our cash requirements may differ materially from our actual requirements because of a number of factors, including significant unforeseen delays in the regulatory approval process, changes in the timing, scope, focus and direction of clinical trials and costs related to commercializing the product.
We have funded our operations through a combination of private placements and public offerings of its securities in each of 2000, 2003, 2009, 2010, 2011, 2012, 2013, 2015, 2016, 2018 and 2019, including registered direct offerings in 2007, 2009 and 2013, “at the market” equity offering programs in 2012 and 2013, and by the private placement of convertible notes in 2016 and 2018, and, most recently, in July and August 2019, we raised $29.5 million in the closing of two private placements of convertible preferred stock and warrants to purchase common stock. For a detailed discussion of our various sales of debt and equity securities see Notes 8, 9, and 14 to our condensed consolidated financial statements as well as Notes 10 and 11 to our audited consolidated financial statements.
In October 2018, we filed a registration statement on FormS-3 with the SEC, which was declared effective on December 21, 2018 and allowed us to offer and sell, from time to time in one or more offerings, up to $100.0 million of common stock, preferred stock, warrants, debt securities and stock purchase contracts as it deems prudent or necessary to raise capital at a later date. We lost our FormS-3 eligibility due to the late filing of our Annual Report for the year ended December 31, 2018.
Results of Operations for the Year Ended December 31, 2018; Comparisons of Results of the Years Ended December 31, 2018 and 2017
Revenue
We recorded approximately $3.4 million in product revenue during the year ended December 31, 2018. During the same period in 2017, We recorded $2.7 million in total revenue related to product sales. The year over year increase is a result of greater product sales in 2018 as we continued to see increased market acceptance of its product in the EU, particularly in Germany where the establishment of the ZE code has contributed to increased treatments.
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