Merus to present interim data on petosemtamab at AACR-NCI-EORTC conference

Merus (MRUS) announced interim clinical data as of a July 29, 2025 data cutoff from the ongoing phase 2 trial of the bispecific antibody petosemtamab in combination with standard of care FOLFOX/FOLFIRI in 1L and 2L metastatic colorectal cancer, and petosemtamab monotherapy in 3L+ mCRC. These data will be presented in a plenary session oral presentation by Dr. Moh’d Khushman M.D., Washington University School of Medicine, St. Louis, MO, at the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics on Friday, October 24 at 10:20 a.m. ET. Petosemtamab: Presentation title: Petosemtamab monotherapy or with chemotherapy in metastatic colorectal cancer: Preliminary antitumor activity and safety data from a phase 2 trial. Observations in the presentation include: As of a July 29, 2025 data cutoff date: 54 patients with left- and/or right-sided, KRAS, NRAS, and BRAF wildtype microsatellite stable mCRC received petosemtamab 1500 mg every two weeks, in combination with FOLFOX/FOLFIRI or as monotherapy; Pts treated in 1L or 2L had no prior anti-EGFR therapy;Pts treated in 2L received 1 prior chemotherapy regimen in the metastatic setting; Pts treated in 3L+ received at least 2 prior regimens in the metastatic setting, including a prior anti-EGFR therapy; Efficacy evaluable population consisted of patients with greater than or equal to1 dose of petosemtamab who had opportunity for greater than or equal to8 weeks follow up and greater than or equal to1 post baseline tumor assessment or discontinued petosemtamab early due to disease progression, symptomatic deterioration and/or death; 1L petosemtamab with FOLFOX/FOLFIRI; 14 pts were treated in 1L; 10 pts were efficacy evaluable, 8 left-sided; 10 remained on treatment; 80% response rate: 1 confirmed complete response, 7 partial responses; 2 stable diseases; 88% response rate in left-sided: 1 confirmed complete response, 6 PRs; 1 SD; One SD observed to be an unconfirmed PR post data cutoff leading to 100% response rate left-sided and 90% response rate overall in 1L; All unconfirmed PRs remained on treatment without disease progression; 2L petosemtamab with FOLFOX/FOLFIRI; 14 pts were treated in 2L; 13 were efficacy evaluable; 10 remained on treatment; 62% response rate: 8 PRs; 4 SDs and 1 clinical deterioration prior to first scan; All unconfirmed PRs and SDs remained on treatment without disease progression; 3L+ petosemtamab monotherapy: 26 pts were treated; 20 were efficacy evaluable, 6 remained on treatment; 10% confirmed response rate: 2 PRs; 9 SDs; Safety: Petosemtamab safety profile in mCRC observed thus far, appears consistent with its established safety profile in recurrent/metastatic head and neck squamous cell carcinoma; No significant overlapping toxicities identified in combination with FOLFOX/FOLFIRI’ No new safety signals identified; Infusion related reactions were managed with premedication and prolonged infusion on cycle 1 day 1; no discontinuations due to IRRs