On May 15, 2025 Mersana Therapeutics, Inc. (NASDAQ: MRSN), a clinical-stage biopharmaceutical company focused on developing a pipeline of antibody-drug conjugates (ADCs) targeting cancers in areas of high unmet medical need, reported a business update and announced financial results for the first quarter ended March 31, 2025 (Press release, Mersana Therapeutics, MAY 15, 2025, View Source [SID1234653175]).

Schedule your 30 min Free 1stOncology Demo!
Discover why more than 1,500 members use 1stOncology™ to excel in:

Early/Late Stage Pipeline Development - Target Scouting - Clinical Biomarkers - Indication Selection & Expansion - BD&L Contacts - Conference Reports - Combinatorial Drug Settings - Companion Diagnostics - Drug Repositioning - First-in-class Analysis - Competitive Analysis - Deals & Licensing

                  Schedule Your 30 min Free Demo!

"Given recent positive front-line data reported from topo-1 ADC registrational trials, we believe the post-topo-1 breast cancer patient population is poised to expand significantly. Our initial aim is to develop Emi-Le to serve this high unmet need population," said Martin Huber, M.D., President and Chief Executive Officer of Mersana Therapeutics. "To that end, we were pleased to present encouraging preliminary progression free survival and overall survival data for Emi-Le among patients with post-topo-1 TNBC today at ESMO (Free ESMO Whitepaper) Breast Cancer 2025. Additionally, our team has made considerable progress enrolling these patients in our dose expansion cohorts thus far in 2025, putting us on track for an initial expansion data readout later this year."

Emiltatug Ledadotin (Emi-Le; XMT-1660)

Mersana has continued to advance the development of Emi-Le, the company’s B7-H4-directed Dolasynthen ADC.

Updated Clinical Data Presented at ESMO (Free ESMO Whitepaper) Breast Cancer 2025 Today: Earlier this morning at the European Society for Medical Oncology Breast Cancer 2025 Annual Congress (ESMO Breast Cancer 2025) in Munich, Germany, 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.

The presentation included clinical activity data among evaluable patients (those with measurable disease at baseline and at least one post-baseline scan) across all tumor types (TNBC, hormone-receptor-positive, human epidermal growth factor receptor 2 (HER2) negative breast cancer; ovarian cancer; endometrial cancer and adenoid cystic carcinoma type 1) with B7-H4 high tumor expression (defined as a tumor proportion score of 70% or higher) who received intermediate Emi-Le doses of 38.1 milligrams per meter squared (mg/m2) to 67.4 mg/m2 per cycle. For these patients, the confirmed objective response rate (ORR) was 31% (8 of 26 patients). This is an increase from the 23% ORR (6 of 26 patients) previously reported based upon a December 13, 2024 data cutoff.

The primary focus of the presentation was on TNBC patients enrolled in dose escalation and backfill cohorts. Safety and tolerability data from these patients were consistent with previously reported data with no new safety signals. Among evaluable patients with TNBC who received intermediate Emi-Le doses, ORR, preliminary progression free survival (PFS) and preliminary overall survival (OS) data include the following:

Patients with B7-H4 high
TNBC receiving ≤4 prior
treatment lines in advanced/
metastatic setting (n=7)* Patients with B7-H4 low
TNBC receiving ≤4 prior
treatment lines in advanced/
metastatic setting (n=11)
Received ≥1 Prior Topo-1 ADC 100% (7/7) 73% (8/11)
ORR 29% (2/7) 0% (0/11)
Median PFS 16.0 weeks 6.4 weeks
Median OS Not reached 5.7 months
* Mersana’s ongoing expansion cohorts are enrolling TNBC patients who have received 1 to 4 prior lines of treatment, including at least one topo-1 ADC, with a primary focus on patients with B7-H4 high tumor expression

In the ASCENT Phase 3 clinical trial of sacituzumab govitecan, a topo-1 ADC, the ORR, median PFS and median OS for the standard-of-care single-agent chemotherapy control arm in topo-naïve relapsed/refractory TNBC were approximately 5%, 7 weeks and 7 months, respectively.

"The performance of today’s standard of care for patients with TNBC who have previously been treated with a topo-1 ADC is poor," said Erika Hamilton, M.D., Director Breast Cancer Research, Sarah Cannon Research Institute in Nashville, Tennessee, who presented these data at ESMO (Free ESMO Whitepaper) Breast Cancer 2025. "In light of this significant unmet medical need and research indicating that B7-H4 tumor expression is a negative prognostic factor, the data presented today are promising. I am looking forward to Emi-Le’s continued development."

The ESMO (Free ESMO Whitepaper) Breast Cancer 2025 presentation can be accessed on the Publications section of the Mersana website at www.mersana.com.

Expansion Update: Mersana continues to advance the dose expansion portion of its Phase 1 clinical trial of Emi-Le in patients with TNBC who have received one to four prior lines of therapy, including at least one topo-1 ADC. In recent months, the company has made significant progress in the enrollment of patients in its "Dose A" cohort, in which patients are receiving 67.4 mg/m2 of Emi-Le every four weeks (Q4W).

Mersana also recently initiated enrollment in its "Dose B" cohort. These patients are receiving a starting dose of 44.5 mg/m2 of Emi-Le on days 1 and 8 of the first four-week cycle followed by 80 mg/m2 of Emi-Le Q4W.

The company plans to report initial clinical data from the expansion portion of its Phase 1 clinical trial in the second half of 2025.

Upcoming ASCO (Free ASCO Whitepaper) Presentation: There will be two presentations regarding Emi-Le at the American Society of Clinical Oncology (ASCO) (Free ASCO Whitepaper) 2025 Annual Meeting taking place May 30-June 3, 2025 at McCormick Place, Chicago, IL. The first is an oral presentation that includes clinical data from the company’s Phase 1 dose escalation and backfill cohorts across all enrolled tumor types based upon a March 8, 2025 data cutoff. The second is a trial-in-progress poster presentation discussing the ongoing expansion portion of Mersana’s Phase 1 clinical trial of Emi-Le.

XMT-2056
The dose escalation portion of Mersana’s Phase 1 clinical trial of XMT-2056, the company’s lead Immunosynthen ADC candidate targeting a novel HER2 epitope, is ongoing. GSK plc has an exclusive global license option to co-develop and commercialize XMT-2056. Mersana plans to continue enrolling patients in dose escalation and expects to present initial clinical pharmacodynamic STING activation data for XMT-2056 in 2025.

Collaborations
Mersana continues to support its collaborations with both Johnson & Johnson (Dolasynthen research collaboration) and Merck KGaA, Darmstadt, Germany (Immunosynthen research collaboration).

First Quarter 2025 Financial Results

Cash and cash equivalents as of March 31, 2025 were $102.3 million. Due in part to the strategic restructuring and reprioritization plan that was announced on May 6, 2025, Mersana expects that its capital resources will be sufficient to support its current operating plan commitments into mid-2026.
Net cash used in operating activities for the first quarter of 2025 was $29.3 million.
Collaboration revenue for the first quarter of 2025 was $2.8 million, compared to $9.2 million for the same period in 2024. The year-over-year change was primarily related to reduced revenue recognized under the company’s collaboration and license agreements with Johnson & Johnson and Merck KGaA, Darmstadt, Germany, partially offset by increased revenue recognized under its agreement with GSK.
Research and development (R&D) expense for the first quarter of 2025 was $18.3 million, compared to $18.7 million for the same period in 2024. Included in the first quarter of 2025 R&D expense was $1.4 million in non-cash stock-based compensation expense. The year-over-year change in R&D expense was primarily related to lower headcount and related employee compensation costs, partially offset by an increase in costs related to clinical development activities for Emi-Le.
General and administrative (G&A) expense for the first quarter of 2025 was $8.9 million, compared to $11.6 million during the same period in 2024. Included in the first quarter of 2025 G&A expense was $1.3 million in non-cash stock-based compensation expenses. The year-over-year change in G&A expense was primarily related to a reduction in consulting and professional services fees as well as the company’s lower headcount and related employee compensation costs.
Net loss for the first quarter of 2025 was $24.1 million, or $0.19 per share, compared to a net loss of $19.3 million, or $0.16 per share, for the same period in 2024.
Conference Call Reminder
Mersana will host a conference call today at 8:00 a.m. ET to discuss business updates and its financial results for the first quarter of 2025. To access the call, please dial 833-255-2826 (domestic) or 412-317-0689 (international). A live webcast of the presentation will be available on the Investors & Media section of the Mersana website at www.mersana.com, and a replay of the webcast will be available in the same location following the conference call for approximately 90 days.