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Mersana Therapeutics Halts Phase I HER2-Targeted Antibody-Drug Conjugate Trial After Patient Death

NEW YORK – Mersana Therapeutics said on Monday that the US Food and Drug Administration has placed a hold on the firm's Phase I clinical trial of the HER2-targeting antibody-drug conjugate XMT-2056.

The hold comes in the wake of a patient death on the trial, which is still under investigation but believed to be related to XMT-2056.

The patient who died was the second patient enrolled in the Phase I trial's initial dose level in the dose-escalation portion of the trial, in which Mersana is evaluating XMT-2056 among patients with advanced HER2-positive solid tumors, including gastric, colorectal, and non-small cell lung cancers, as well as both HER2-positive and HER2-low breast cancers, among other tumor types.

In August 2022, GlaxoSmithKline paid Mersana $100 million upfront in exchange for the global license option to develop and commercialize XMT-2056. Mersana designed the agent to target a novel epitope of HER2, which activates the innate immune system through STING signaling.

For the duration of the clinical hold, Cambridge, Massachusetts-based Mersana will stop enrolling or dosing patients in the trial.

"With the clinical hold in place, our efforts for XMT-2056 are now focused on undertaking the work required to fully analyze this serious adverse event and consider potential next steps for development," Mersana CEO and President Anna Protopapas said in a statement, adding that the firm's other clinical trials remain unaffected.