Mersana Therapeutics Reports Additional Positive Interim Phase 1 Clinical Data for Emi-Le in Oral Presentation at 2025 ASCO Annual Meeting

Core Viewpoint - Mersana Therapeutics announced additional interim Phase 1 clinical data for emiltatug ledadotin (Emi-Le), a B7-H4-directed Dolasynthen ADC, at the ASCO 2025 Annual Meeting, highlighting its potential in treating cancers with high unmet medical need [1][3][4] Group 1: Clinical Data and Results - The presentation focused on Emi-Le's Phase 1 dose escalation and backfill cohorts for patients with triple-negative breast cancer (TNBC), hormone-receptor-positive, HER2-negative breast cancer, ovarian cancer, endometrial cancer, and adenoid cystic carcinoma type 1 (ACC-1) [2] - The confirmed objective response rate (ORR) was 31% (8 responses in 26 evaluable patients) across all enrolled tumor types with high B7-H4 expression [6][7] - In patients with ≤4 prior lines of therapy, the confirmed ORR was 44% (7 responses in 16 evaluable patients) [6][7] - For ACC-1 patients, the ORR was 56% (5 responses in 9 patients), with median progression-free survival (PFS) not yet reached [7] Group 2: Safety and Tolerability - Safety and tolerability data as of March 8, 2025, were consistent with earlier reports, showing no new safety signals [3][4] - The safety profile of Emi-Le appears differentiated from many other ADCs, particularly in late-stage TNBC and ACC-1 patients [4] Group 3: Regulatory Designations and Development Potential - The U.S. FDA granted two Fast Track designations to Emi-Le for treating advanced or metastatic TNBC and advanced or metastatic HER2 low/HER2 negative breast cancer post-topo-1 ADC [8] - The company is focusing initial expansion work on TNBC patients previously treated with topoisomerase-1 inhibitor ADCs, indicating a strategic direction in addressing high unmet needs [3][5] Group 4: Company Overview - Mersana Therapeutics is a clinical-stage biopharmaceutical company developing novel ADCs, with a pipeline that includes Emi-Le and XMT-2056, targeting various cancers [9] - The company emphasizes the urgency for new treatment options for patients, driven by its proprietary ADC platforms [9]