FDA lifts clinical hold from Mersana’s breast cancer trial

The FDA has lifted the partial clinical hold it placed on a phase 1 trial of Mersana Therapeutics’ HER2-targeted antibody-drug conjugate (ADC). Regulatory officials put enrollment in the XMT-1522 breast cancer trial on hold in July after learning of the death of a participant.

Mersana got out from under the partial hold by agreeing to increase monitoring and exclude patients with advanced hepatic impairment from the trial. The Massachusetts-based biotech is making similar changes to a clinical trial of anti-NaPi2b ADC XMT-1536, which was not subject to a clinical hold.

XMT-1522 and XMT-1536 are both based on Mersana’s Dolaflexin ADC platform, and the company is treating the trials as a pair in some regards.

Having assessed a monthly dosing regimen in the trial of XMT-1536, Mersana is now set to explore the same schedule in the study of XMT-1522. Mersana said it tested the monthly XMT-1536 regimen "at previously explored dose levels in order to enable a comparison of relevant doses and their impact on the safety, efficacy and [pharmacokinetic] profile of the drug candidate." The company is considering assessing other regimens, too.

The speed with which Mersana reached an agreement about the changes with the FDA means the clinical hold has had little near-term effect on the progress of XMT-1522. But there is still a risk that the safety red flag that triggered the hold will become an impediment to the progress of XMT-1522 as it makes its way through the 120-person phase 1 breast cancer trial and onto bigger evaluations of its safety and efficacy.

Shares in Mersana rose 8% in premarket trading. The uptick moves Mersana’s stock back up toward the level it was at before news of the clinical hold took a chunk out of its market capitalization.

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