Merus’ Petosemtamab with Pembrolizumab Interim Data Demonstrates Robust Efficacy and Durability in 1L PD-L1+ r/m HNSCC

-  63% response rate observed among 43 evaluable patients

-  79% overall survival rate at 12-months; 9 months median progression-free survival

-  Conference Call on Thursday, May 22 at 5:30 p.m. ET

UTRECHT, The Netherlands and CAMBRIDGE, Mass., May 22, 2025 (GLOBE NEWSWIRE) -- 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), today announced 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. 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) Annual Meeting on Monday, June 2 at 9 a.m. - 12:00 p.m. CT.

“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