Mersana reports promising Phase 1 ADC trial results

CAMBRIDGE, Mass. - Mersana Therapeutics, Inc. (NASDAQ: MRSN), a biopharmaceutical company specializing in antibody-drug conjugates (ADCs) for cancer treatment, today announced new interim Phase 1 clinical trial results for its drug candidate emiltatug ledadotin (Emi-Le; XMT-1660). The data presented at the American Society of Clinical Oncology (ASCO) Annual Meeting in Chicago showed a 31% objective response rate (ORR) in patients with B7-H4 high tumors at intermediate doses of Emi-Le. According to InvestingPro data, while the company maintains a healthy cash position relative to its debt, it faces challenges with cash burn and profit margins, reflecting the typical profile of an early-stage biotech company.

The study focused on a variety of cancer types, including triple-negative breast cancer (TNBC), hormone-receptor-positive breast cancer, ovarian, endometrial, and adenoid cystic carcinoma type 1 (ACC-1). Notably, a subset of patients with four or fewer prior lines of therapy experienced a 44% ORR. In ACC-1 patients, the ORR was 56%, and the median progression-free survival had not been reached by the March 8, 2025 data cut-off, suggesting a potential advance for a cancer with limited treatment options and historically short median survival times.

Martin Huber, M.D., President and CEO of Mersana, expressed optimism about Emi-Le’s potential, particularly for TNBC patients previously treated with a topoisomerase-1 inhibitor ADC. The safety and tolerability reported were consistent with previous data, with no new safety concerns noted.

Antonio Giordano, MD, Ph.D., from Harvard Medical School and Dana-Farber Cancer Institute, highlighted the encouraging clinical activity of Emi-Le across various tumors and its differentiated safety profile from other ADCs. The responses in late-stage TNBC and ACC-1 were especially notable given the high unmet need in these aggressive cancers.

Emi-Le has received two Fast Track designations from the U.S. Food and Drug Administration for the treatment of advanced or metastatic TNBC and HER2 low/negative breast cancer post-topoisomerase-1 inhibitor ADC therapy.

Mersana’s ongoing Phase 1 trial of Emi-Le is enrolling TNBC patients who have undergone one to four prior treatments, including at least one topoisomerase-1 inhibitor ADC. The company continues to develop a pipeline of wholly-owned and partnered ADC candidates aimed at addressing high unmet medical needs in cancer treatment.

The information in this article is based on a press release statement from Mersana Therapeutics.

In other recent news, Mersana Therapeutics reported a net loss of $24.1 million for the first quarter of 2025, aligning with analyst expectations of an EPS of -0.19. However, the company’s revenue of $2.75 million fell short of the $6.05 million forecast. Despite the revenue miss, Mersana’s strategic focus on its breast cancer treatment pipeline and recent operational restructuring have drawn attention. The restructuring includes a 55% reduction in headcount, which is expected to extend the company’s cash runway into mid-2026 and reduce general and administrative expenses by 25% year-over-year in 2025. Truist Securities has responded positively to these developments, raising the price target for Mersana’s stock to $10 while maintaining a Buy rating. The firm’s optimism is also fueled by promising clinical developments in Mersana’s investigational therapy, Emi-Le, which has shown a notable objective response rate in ongoing studies. As Mersana plans a Phase 3 trial, analysts anticipate that the significant effect size observed might allow for a smaller sample size. The company is set to present further data at the American Society of Clinical Oncology meeting, with dose-expansion results expected in the second half of 2025.

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