CAMBRIDGE, MA, USA I October 31, 2023 I 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 announced that the U.S. Food and Drug Administration (FDA) has lifted the clinical hold on the company’s Phase 1 clinical trial of XMT-2056. XMT-2056 is a systemically administered Immunosynthen STING-agonist ADC that is designed to target a novel human epidermal growth factor receptor 2 (HER2) epitope and locally activate STING signaling in both tumor-resident immune cells and in tumor cells, providing the potential to treat patients with HER2-high or -low tumors as monotherapy and in combination with standard-of-care agents.

“An in-depth analysis of cytokine, pharmacokinetic and other clinical data from patients enrolled in our Phase 1 trial indicated that XMT-2056 is a highly potent innate immune agonist,” said Martin Huber, M.D., President and Chief Executive Officer of Mersana Therapeutics. “Based on these data and with patient safety at the forefront of our efforts, we have lowered the starting dose in our Phase 1 dose escalation design. We are pleased to have aligned with FDA on the path forward and are excited to have the opportunity to continue to investigate the potential of XMT-2056 and our Immunosynthen ADC platform in the clinic.”

The multicenter Phase 1 open-label trial is investigating XMT-2056 in previously treated patients with advanced/recurrent solid tumors expressing HER2, including breast, gastric, colorectal and non-small-cell lung cancers. The dose escalation and dose expansion portions of the trial will evaluate and characterize the relationship of safety, tolerability and exposure of XMT-2056 and this candidate’s preliminary anti-tumor activity, as measured by overall response rate, duration of response and disease control rate.

The FDA has granted orphan drug designation to XMT-2056 for the treatment of gastric cancer. In August 2022, Mersana entered into a global collaboration providing GSK plc with an exclusive option to co-develop and commercialize XMT-2056. GSK has not exercised this option to date.

About Mersana Therapeutics
Mersana Therapeutics is a clinical-stage biopharmaceutical company focused on the development of novel antibody-drug conjugates (ADCs) and driven by the knowledge that patients are waiting for new treatment options. The company has developed proprietary cytotoxic (Dolasynthen) and immunostimulatory (Immunosynthen) ADC platforms that are generating a pipeline of wholly-owned and partnered product candidates with the potential to treat a range of cancers. Its pipeline includes XMT-1660, a Dolasynthen ADC targeting B7-H4, and XMT-2056, an Immunosynthen ADC targeting a novel epitope of human epidermal growth factor receptor 2 (HER2). Mersana routinely posts information that may be useful to investors on the “Investors & Media” section of its website at

SOURCE: Mersana Therapeutics