periods in 2020 were primarily due to increased G&A staffing and spending on professional services and facility costs.
Total other income, net, for the third quarter ended September 30, 2021 was $1.1 million, compared to $4.2 million in the same period in 2020. Other income for the nine months ended September 30, 2021 was $57.5 million, compared to $7.5 million in the same period in 2020. Other income for the first nine months of 2021 includes realized gains on the sale of an investment equity security and an increase in unrealized gains on the Company’s marketable equity investments.
Non-cash, stock-based compensation expense for the nine months ended September 30, 2021 was $26.6 million, compared to $23.1 million for the same period in 2020.
Net loss for the third quarter ended September 30, 2021 was $40.2 million, or $(0.69) on a fully diluted per share basis, compared to net loss of $12.6 million, or $(0.22) on a fully diluted per share basis, for the same period in 2020. The increased net loss reported for the third quarter, compared to the same period of 2020, was primarily due to lower milestone revenue and higher operating expenses in 2021. For the nine months ended September 30, 2021, net income was $9.6 million, or $0.16 on a fully diluted per share basis, compared to net loss of $55.6 million, or $(0.97) on a fully diluted per share basis, for the same period in 2020. Net income reported for the first nine months of 2021, compared to the net loss reported for the same period in 2020, was primarily due to higher collaboration revenues and realized and unrealized gains from equity investment securities in 2021 compared to 2020.
The total shares outstanding were 58,454,811 as of September 30, 2021, compared to 57,374,937 as of September 30, 2020.
Financial Guidance
Based on current operating plans, Xencor expects to have cash to fund research and development programs and operations into 2025. Xencor expects to end 2021 with between $575 million and $625 million in cash, cash equivalents, receivables and marketable debt securities.
Conference Call and Webcast
Xencor will host a conference call today at 4:30 p.m. ET (1:30 p.m. PT) to discuss these third quarter 2021 financial results and provide a corporate update.
The live call may be accessed by dialing (877) 359-9508 for domestic callers or +1 (224) 357-2393 for international callers and referencing conference ID number 5536153. A live webcast of the conference call will be available online from the Investors section of Xencor's website at www.xencor.com. The webcast will be archived on Xencor's website for 30 days.
About Xencor, Inc.
Xencor is a clinical-stage biopharmaceutical company developing engineered monoclonal antibodies and cytokines for the treatment of cancer and autoimmune diseases. Currently, 22 candidates engineered with Xencor's XmAb® technology are in clinical development internally and with partners. Xencor's XmAb antibody engineering technology enables small changes to the structure of proteins resulting in new mechanisms of therapeutic action. For more information, please visit www.xencor.com.