Exhibit 99.1 Mersana Therapeutics Provides Business Update and Announces Fourth Quarter and Full Year 2023 Financial Results CAMBRIDGE, Mass., February 28, 2024 – Mersana Therapeutics, Inc. (NASDAQ: MRSN), a clinical-stage biopharmaceutical company focused on discovering and developing a pipeline of antibody-drug conjugates (ADCs) targeting cancers in areas of high unmet medical need, today provided a business update and reported financial results for the fourth quarter and full year ended December 31, 2023 ...