ZACKS·2025-07-11 15:46Core Insights - Merus N.V. (MRUS) shares have increased by 29.9% over the past three months, driven by positive interim results from a phase II study of its bispecific antibody, petosemtamab (MCLA-158), in combination with Merck's Keytruda for treating PD-L1-positive recurrent or metastatic head and neck squamous cell carcinoma (HNSCC) [1][4] Study Results - As of February 27, 2025, 45 patients were treated, with 43 deemed efficacy-evaluable, resulting in a confirmed overall response rate (ORR) of 63%, which included six complete responses and 21 partial responses [2] - The ORR varied with PD-L1 expression levels, showing a 73% ORR in patients with a combined positive score (CPS) greater than 20 and 47% in those with CPS 1–19 [2] - Median progression-free survival was reported at nine months, with an overall survival rate of 79% at 12 months [3] Safety Profile - The safety profile of the combination therapy was manageable, with no significant overlapping toxicities reported with Keytruda; treatment-related adverse events occurred in all patients, with infusion-related reactions observed in 38% [5][6] Future Prospects - The promising data suggests that the petosemtamab combination therapy could become a new standard of care for HNSCC, a cancer type with poor prognosis [6] - Merus is also conducting a registrational phase III study (LiGeR-HN1) for the combination therapy and another study (LiGeR-HN2) for petosemtamab monotherapy [7][8] Market Context - Merck's Keytruda, a leading anti-PD-1 therapy, generated $7.21 billion in sales in Q1 2025, reflecting a 6% year-over-year increase, and continues to expand into new indications and markets [8][10]