On June 2, 2025 Mersana Therapeutics, Inc. (NASDAQ: MRSN), a clinical-stage biopharmaceutical company focused on the development of antibody-drug conjugates (ADCs) targeting cancers in areas of high unmet medical need, reported additional interim Phase 1 clinical data for emiltatug ledadotin (Emi-Le; XMT-1660), the company’s B7-H4-directed Dolasynthen ADC (Press release, Mersana Therapeutics, JUN 2, 2025, View Source [SID1234653615]). These data are being presented in an oral session today at the American Society of Clinical Oncology (ASCO) (Free ASCO Whitepaper) 2025 Annual Meeting in Chicago, Illinois.
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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 (TNBC); hormone-receptor-positive, human epidermal growth factor receptor 2-negative breast cancer; ovarian cancer; endometrial cancer and adenoid cystic carcinoma type 1 (ACC-1).
"We are excited to share additional interim data in an oral presentation at ASCO (Free ASCO Whitepaper)," said Martin Huber, M.D., President and Chief Executive Officer of Mersana Therapeutics. "The results from our dose escalation and backfill cohorts led us to focus our initial expansion work on patients with TNBC who have previously been treated with a topoisomerase-1 inhibitor ADC, a population with high unmet need that we believe Emi-Le may be uniquely suited to address within the B7-H4 ADC field. We also continue to be encouraged by the activity observed in other B7-H4-expressing tumor types, demonstrating Emi-Le’s broader development potential. On behalf of the Mersana team, we would like to express our gratitude to the patients and investigators who have participated in this clinical trial."
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 (those with measurable disease at baseline and at least one post-baseline scan):
· 31% confirmed objective response rate (ORR) (8/26) across all enrolled tumor types with B7-H4 high tumor expression (defined as a tumor proportion score of 70% or higher) receiving intermediate Emi-Le doses (38.1 milligrams per meter squared (mg/m2) to 67.4 mg/m2 per cycle).
o 44% confirmed ORR (7/16) in the subset of patients with ≤4 prior lines of therapy.
· 56% ORR (5/9, including one unconfirmed response as of the March 8, 2025 data cut-off that was subsequently confirmed) 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 (PFS) 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.
"The clinical activity observed for emiltatug ledadotin across all enrolled tumor types is encouraging, and its safety and tolerability profile appears differentiated from many other ADCs," said Antonio Giordano, MD, Ph.D., Assistant Professor of Medicine, Harvard Medical School, Dana-Farber Cancer Institute. "The objective responses were particularly notable in patients with late-stage triple-negative breast cancer who were previously treated with topoisomerase-1 inhibitors and in patients with ACC-1, both of which are aggressive and difficult-to-treat cancers with high unmet need."
The 2025 ASCO (Free ASCO Whitepaper) Annual Meeting data presentation can be accessed on the Publications section of the Mersana website at www.mersana.com.
About Emi-Le
Emi-Le is a B7-H4-directed Dolasynthen ADC with a precise, target-optimized drug-to-antibody ratio (DAR 6) and a proprietary auristatin payload with controlled bystander effect. This candidate is being investigated in Mersana’s ongoing Phase 1 clinical trial. The dose expansion portion of the Phase 1 clinical trial is enrolling patients with triple-negative breast cancer (TNBC) who have received one to four prior treatment lines, including at least one topoisomerase-1 inhibitor (topo-1) ADC.
The U.S. Food and Drug Administration has granted two Fast Track designations to Emi-Le for the treatment of 1) adult patients with advanced or metastatic triple-negative breast cancer, and 2) advanced or metastatic HER2 low / HER2 negative breast cancer post-topo-1 ADC (including TNBC and certain HR+ breast cancers). For more information about Mersana’s ongoing Phase 1 trial of Emi-Le, please visit clinicaltrials.gov (NCT05377996).