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# FDA Clinical Hold on Mersana Tumor Drug
- URL: https://www.fdaweb.com/fda-clinical-hold-on-mersana-tumor-drug/
- Published: 2023-03-13T12:00:00.000Z
- Updated: 2026-09-14T18:19:14.000Z
- Author: David McFarland
- Tags: Drugs, #legacy-id-D5153959

FDA has placed a clinical hold on Mersana Therapeutics’ Phase 1 trial of XMT-2056 after the company suspended it due to a recent Grade 5 (fatal) serious adverse event (SAE) that was deemed to be related to the study drug. The company says the SAE and its cause remain under investigation.

XMT-2056 is described by Mersana as an immmunosynthen STING-agonist antibody-drug conjugate. The adverse event occurred in the second patient who had been enrolled at the initial dose level in the dose escalation portion of the Phase 1 trial in previously treated patients with HER2+ recurrent or metastatic solid tumors.