On May 22, 2025 Merus N.V. (Nasdaq: MRUS) (Merus, the Company, we, or our), an oncology company developing innovative, full-length multispecific antibodies and antibody drug conjugates (Biclonics, Triclonics and ADClonics), reported interim clinical data as of a February 27, 2025 data cutoff from the ongoing phase 2 trial of the bispecific antibody petosemtamab in combination with pembrolizumab (Press release, Merus, MAY 22, 2025, View Source [SID1234653321]). These data will be presented by Dr. Carla M. L. van Herpen M.D. Ph.D., Radboud University Medical Center, Nijmegen, Netherlands at the 2025 American Society of Clinical Oncology (ASCO) (Free ASCO Whitepaper) Annual Meeting on Monday, June 2 at 9 a.m. – 12:00 p.m. CT.

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"By essentially every metric, we believe these interim data are significantly better than pembrolizumab monotherapy, the control arm of our ongoing phase 3 trial, and underscores the opportunity petosemtamab holds to become a new standard of care, if approved, in head and neck cancer," said Bill Lundberg, M.D., President, Chief Executive Officer of Merus. "Additionally, we believe our execution is outstanding with rapid site initiation. We are looking forward to potentially sharing top line interim readout of one or both of our phase 3 trials in 2026."

"Head and neck squamous cell carcinoma is associated with a poor prognosis and high mortality rate, and there remains a need for new treatment options for patients," added Dr. van Herpen. "In my clinic, I have witnessed firsthand profound tumor shrinkage with petosemtamab administration, and the efficacy results petosemtamab has shown thus far in combination with the current standard of care, pembrolizumab. I’m excited by the impressive ORR and durability of those responses, and what these results, if replicated more broadly could mean for the future of our practice in head and neck cancer."

Petosemtamab (MCLA-158: EGFR x LGR5 Biclonics): Solid Tumors

Presentation title: Petosemtamab (MCLA-158) with pembrolizumab as first-line (1L) treatment of PD-L1+ recurrent/metastatic (r/m) head and neck squamous cell carcinoma (HNSCC): Phase 2 trial

Observations in the presentation include as of a February 27, 2025 data cutoff date:

45 patients (pts) were treated
The efficacy evaluable population consisted of 43 patients who were treated (with one or more doses) as of the data cutoff date and either ≥1 post-baseline tumor assessment, or discontinued early due to disease progression or death
Median follow up of 14.3 months for the 45 patients
In 43 evaluable patients:
Confirmed overall response rate: 63% (27/43, 95% CI: 49-75), including 6 complete responses, 21 partial responses by Response Evaluation Criteria in Solid Tumors v1.1. per investigator assessment, including:
4 of 8 patients with HPV associated cancer responded
Responses observed across PD-L1 levels (CPS 1-19: 47% [8/17]; CPS > 20: 73% [19/26])
Median progression-free survival was 9 months (95% CI: 5.2-12.9)
Median duration of response and median overall survival (OS) were not reached
79% overall survival rate at 12-months (30/43 censored)
At the time of data cutoff, 14 patients, each of whom are responders, remained on treatment
In 45 patients the combination was generally well tolerated and no significant overlapping toxicities with pembrolizumab were observed
Treatment-emergent adverse events (TEAEs) were reported in 45 pts
G≥3 TEAEs occurred in 27 (60%) patients, including 20 (44%) patients who experienced treatment-related TEAEs
Infusion-related reactions (composite term) were reported in 38% of patients (all Gs) and 7% (G3), no G4 or 5, mainly occurred during the first infusion and were resolved
Abstract #: 6024
Poster Board: 432
Session Title: Head and Neck Cancer
Session Date and Time: June 2, 2025, 9:00-12:00 CT

As full presentations become available at the 2025 ASCO (Free ASCO Whitepaper) Annual Meeting, they will contemporaneously be available on the Merus website.

An analysis of the confirmed responses observed from administration of petosemtamab across the first line combination (as of the February 27, 2025 data cutoff date) and second-line plus monotherapy phase 2 cohorts (as of the July 5, 2024 data cutoff date), demonstrated that two-thirds of these responses with petosemtamab in HPV-associated p16+ oropharyngeal cancer occurred in never-smokers.

Company Conference Call and Webcast Information
Merus will hold a conference call and webcast for investors on Thursday, May 22, 2025 at 5:30 p.m. ET. A replay will be available after the completion of the call in the Investors and Media section of our website for a limited time.
Date & Time: May 22, 2025 at 5:30 p.m. ET
Webcast link: Available on our website
Dial-in: Toll Free: (800) 715-9871 / International: (646) 307-1963
Conference ID: 7517301 or Merus NV call