Mersana Therapeutics, Inc. provided a business update for the first quarter ended March 31, 2025, alongside updated clinical data for emiltatug ledadotin (Emi-Le; XMT-1660). Updated clinical data, as of a March 8, 2025 data cutoff, from Emi-Le’s Phase 1 dose escalation and backfill cohorts were presented in a mini oral session at the European Society for Medical Oncology Breast Cancer 2025 Annual Congress.
For evaluable B7-H4 high patients across all tumor types who received intermediate Emi-Le doses (38.1 mg/m² to 67.4 mg/m²), the confirmed objective response rate (ORR) increased to 31% (8 of 26 patients), up from 23% previously reported. Specifically for evaluable triple-negative breast cancer (TNBC) patients at intermediate doses, the ORR was 29% (5 of 17 patients), with preliminary progression-free survival (PFS) of 16 weeks and preliminary overall survival (OS) of 5.7 months.
Mersana continues to advance the dose expansion portion of its Phase 1 clinical trial of Emi-Le in TNBC patients previously treated with topo-1 ADCs, with significant progress in enrollment for the 'Dose A' cohort (67.4 mg/m² Q4W). Enrollment in the 'Dose B' cohort (44.5 mg/m² on days 1 and 8, followed by 80 mg/m² Q4W) was recently initiated, with initial clinical data from the expansion portion expected in the second half of 2025. The dose escalation for XMT-2056 is ongoing, and initial clinical pharmacodynamic STING activation data is anticipated in 2025.
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