67% response rate observed among 24 evaluable patients

Conference Call on Tuesday, May 28th at 8 a.m. ET

UTRECHT, The Netherlands and CAMBRIDGE, MA, USA I May 28, 2024 I Merus N.V. (Nasdaq: MRUS) (Merus, the Company, we, or our), a clinical-stage oncology company developing innovative, full-length multispecific antibodies (Biclonics® and Triclonics®), today announced interim clinical data as of a March 6, 2024 data cutoff from the ongoing phase 1/2 trial of the bispecific antibody petosemtamab in combination with pembrolizumab. These data will be presented by Dr. Jerome Fayette M.D. Ph.D., Centre Léon Bérard, Lyon, France at the 2024 American Society of Clinical Oncology® (ASCO®) Annual Meeting on Monday, June 3 at 8 a.m. CT.

“In this interim dataset, petosemtamab in combination with pembrolizumab has demonstrated clinically meaningful activity in first line head and neck cancer, with a 67% response rate overall, observed across tumor PD-L1 expression levels and HPV status and with encouraging safety,” said Bill Lundberg, M.D., President, Chief Executive Officer of Merus. “I’m excited to announce plans to initiate a phase 3 registration trial of petosemtamab in combination with pembrolizumab, regardless of HPV status, in first line, PD-L1 expressing, head and neck cancer, which we expect will start by year end 2024.”

“Despite recent advancements, head and neck squamous cell carcinoma remains a deadly disease with limited treatment options,” added Dr. Fayette. “Based on these data, I’m optimistic petosemtamab, in combination with pembrolizumab, has the potential to become a new standard of care for patients with previously untreated head and neck cancer.”

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

Rapid oral presentation title: Petosemtamab (MCLA-158) with pembrolizumab as first-line (1L) treatment of recurrent/metastatic (r/m) head and neck squamous cell carcinoma (HNSCC): Phase 2 study
Observations in the presentation include:  

  • As of a March 6, 2024 data cutoff date, 45 patients (pts) were treated
    • 26 patients were enrolled as of the abstract cutoff date
      • The efficacy population consisted of 24 patients who had the opportunity for 4 or more months follow up, with ≥2 treatment cycles and ≥1 post-baseline tumor assessment; or who discontinued early due to disease progression or death
      • Two patients were not included: One patient withdrew consent prior to first tumor assessment and the other patient discontinued due to toxicity with less than 2 cycles of treatment   
    • Response rates overall (N=24): 67%, including 1 confirmed complete response, 12 confirmed partial responses (PRs) and 3 unconfirmed PRs (all of whom confirmed after the data cutoff) by Response Evaluation Criteria in Solid Tumors (RECIST) v1.1. per investigator assessment, including
      • 3 of 4 patients with HPV associated cancer responded
      • Responses observed across PD-L1 levels (CPS 1-19: 60% [6/10]; CPS ≥ 20: 71% [10/14])
    • At the time of data cutoff, 32 patients of the 45 enrolled, remained on treatment, including 14 of 16 responders and 18 of the initial 26 patients enrolled
    • Median follow up of 3.6 months for the 45 patients
  • In 45 patients the combination was well tolerated and no significant overlapping toxicities with pembrolizumab were observed
  • Treatment-emergent adverse events (AEs) were reported in 45 pts
    • Most were Grade (G) 1 or 2 in severity (no G4–5 were observed)
    • Infusion-related reactions (composite term) were reported in 38% (all Gs) and 7% (G3) of pts, most occurred during the first infusion and resolved

Presentation Details:
Abstract #: 6014 
Session Title: Head and Neck Cancer
Session Date and Time: June 3, 2024, 8:00-9:30 a.m. CT

As full presentations become available at the 2024 ASCO® Annual Meeting, they will contemporaneously be available on the Merus website.

About Merus N.V.  
Merus is a clinical-stage 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, https://www.merus.nl and https://twitter.com/MerusNV.