1. Organization and Principal Activities

Description of Business

Sutro Biopharma, Inc. (the “Company”), is a clinical-stage oncology company developing site-specific and novel-format antibody drug conjugates, or ADCs. The Company was incorporated on April 21, 2003 and is headquartered in South San Francisco, California.

The Company operates in one business segment, the development of biopharmaceutical products.

At-The-Market Sales

During the three months ended March 31, 2023, the Company sold an aggregate of 1,641,374 shares of its common stock through its At-the-Market Facility (“ATM Facility”) pursuant to its Open Market Sales AgreementSM dated April 2, 2021 with Jefferies LLC (“Jefferies”), as sales agent (the “Sales Agreement”).

During the three months ended March 31, 2023, the gross proceeds from these sales were approximately $11.2 million, before deducting fees of approximately $0.3 million, resulting in net proceeds of approximately $10.9 million, to the Company.

Liquidity

The Company has incurred significant losses and has negative cash flows from operations. As of March 31, 2023, the Company had an accumulated deficit of $502.7 million. Management expects to continue to incur additional substantial losses in the foreseeable future as a result of the Company’s research and development and other operational activities.

As of March 31, 2023, the Company had unrestricted cash, cash equivalents and marketable securities of $251.5 million and equity securities of $25.0 million, consisting solely of common stock of Vaxcyte, which are available to fund future operations. The Company will need to raise additional capital to support the completion of its research and development activities and to support its operations.

The Company believes that its unrestricted cash, cash equivalents, marketable securities and equity securities as of March 31, 2023 will enable the Company to maintain its operations for a period of at least 12 months following the filing date of its condensed financial statements.