Merus' Petosemtamab Demonstrates Antitumor Activity and Manageable Safety Profile

Merus N.V. has announced initial interim clinical data from its ongoing phase 2 trial of petosemtamab in combination with FOLFOX/FOLFIRI for 1st and 2nd line metastatic colorectal cancer (mCRC), and as monotherapy for 3rd line+ mCRC. The data shows antitumor activity and a manageable safety profile. Updated data will be presented at the AACR-NCI-EORTC International Conference.

Merus N.V. has released initial interim clinical data from its ongoing phase 2 trial of petosemtamab, a bispecific antibody, in combination with FOLFOX/FOLFIRI for 1st and 2nd line metastatic colorectal cancer (mCRC), and as monotherapy for 3rd line+ mCRC. The data, presented by Dr. Moh’d Khushman M.D. at the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics, demonstrated antitumor activity and a manageable safety profile.

The trial evaluated petosemtamab at a dose of 1500 mg every two weeks, either in combination with standard of care FOLFOX/FOLFIRI or as monotherapy. As of an April 28, 2025 data cutoff, the study included 36 patients with left- and/or right-sided, KRAS, NRAS, and BRAF wildtype microsatellite stable mCRC.

In the 1st line setting, seven patients were treated with petosemtamab plus FOLFOX/FOLFIRI, with six ongoing. Among the three efficacy evaluable patients, there was one unconfirmed complete response and two partial responses. In the 2nd line setting, ten patients were treated with petosemtamab plus FOLFOX/FOLFIRI, with eight ongoing. Four partial responses, three stable diseases, and one clinical deterioration were observed. For 3rd line+ patients treated with petosemtamab monotherapy, 19 patients were enrolled, with 12 ongoing. One unconfirmed partial response, six stable diseases, six progressive diseases, and one death unrelated to treatment were reported.

No fatal treatment-related adverse events were observed in any cohort. Common adverse events included dermatitis acneiform, constipation, fatigue, peripheral neuropathy, diarrhea, mucosal inflammation, rash, and nausea, with most events being grade 1 or 2.

Merus N.V. President and CEO Bill Lundberg stated, "We are encouraged by these early data indicating the promise of petosemtamab to combine safely with chemotherapy, and its potential to benefit a wide range of cancer patients that have metastatic colorectal cancer." Updated data will be presented at the conference on October 24, 2025.