Merus Stock Soars 15.38% on Positive Cancer Trial Data

Merus' stock surged 15.38% in pre-market trading on May 23, 2025, driven by positive interim clinical data from its ongoing phase 2 trial of the bispecific antibody petosemtamab in combination with pembrolizumab.

Merus announced that the interim data showed a 63% overall response rate among 43 evaluable patients, with a 79% overall survival rate at 12 months and a median progression-free survival of 9 months. These results were presented at the 2025 American Society of Clinical Oncology Annual Meeting, highlighting the potential of petosemtamab as a new standard of care for head and neck cancer.

The company's CEO, Bill Lundberg, emphasized the significance of these interim data, stating that they were significantly better than pembrolizumab monotherapy. The data also underscored the rapid site initiation and execution of the trial, with the potential for top-line interim readout of one or both of the phase 3 trials in 2026.

Dr. Carla M. L. van Herpen, who presented the data, noted the poor prognosis and high mortality rate associated with head and neck squamous cell carcinoma, emphasizing the need for new treatment options. She highlighted the profound tumor shrinkage observed with petosemtamab administration and the durability of the responses, which could significantly impact the future of head and neck cancer treatment.