Mersana Therapeutics reports additional interim Phase 1 data for Emi-Le

Mersana Therapeutics (MRSN) announced additional interim Phase 1 clinical data for emiltatug ledadotin, the company’s B7-H4-directed Dolasynthen ADC. These data are being presented in an oral session today at the American Society of Clinical Oncology 2025 Annual Meeting in Chicago, Illinois. The presentation will focus on Emi-Le’s Phase 1 dose escalation and backfill cohorts as of a March 8, 2025 data cut-off in patients with triple-negative breast cancer; hormone-receptor-positive, human epidermal growth factor receptor 2-negative breast cancer; ovarian cancer; endometrial cancer and adenoid cystic carcinoma type 1. Safety and tolerability as of the March 8, 2025 data cut-off were consistent with initial data previously reported in January 2025, and no new safety signals were observed. Additionally, the following clinical activity data are being presented from evaluable patients: 31% confirmed objective response rate across all enrolled tumor types with B7-H4 high tumor expression receiving intermediate Emi-Le doses. 44% confirmed ORR in the subset of patients with less than or equal to4 prior lines of therapy. 56% ORR in ACC-1 regardless of dose and B7-H4 expression. Among all ACC-1 patients who were enrolled in the Phase 1 clinical trial, the median progression free survival had not yet been reached as of the March 8, 2025 data cut-off. ACC-1 is a rare and aggressive cancer that most frequently originates in the salivary glands. With no approved therapies, median PFS and median overall survival for patients with ACC-1 are reported to be 2-3 months and 2-3 years, respectively.