Petosemtamab

–  63% response rate observed among 43 evaluable patients –  79% overall survival rate at 12-months; 9 months median progression-free survival UTRECHT, The Netherlands and CAMBRIDGE, MA, USA I May 22, 2025 I 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: 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 ® 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. About Merus N.V. Merus is an oncology company developing innovative full-length human bispecific and trispecific antibody therapeutics, referred to as Multiclonics ® . Multiclonics ® are manufactured using industry standard processes and have been observed in preclinical and clinical studies to have several of the same features of conventional human monoclonal antibodies, such as long half-life and low immunogenicity. For additional information, please visit Merus’ website , LinkedIn and Bluesky . SOURCE: Merus