Genmab Reports 75% Response Rate for Experimental Drug in First-Line Colorectal Cancer
Key Facts
Genmab said on October 25, 2026, that its experimental drug petosemtamab, in combination with chemotherapy, posted an objective response rate of 75% among patients with first-line metastatic colorectal cancer and 67% in the second-line setting. The rates included confirmed and unconfirmed responses, after median follow-up of 5.9 months in the first line and 7.1 months in the second line. As of May 15, 2026, 79 patients had received the combination, including 45 in the first line and 34 in the second line. The company presented the follow-up analysis at the 2026 European Society for Medical Oncology congress in Madrid. The results provide early indicators of treatment activity in an open-label, single-arm study, while ongoing Phase 3 trials compare the drug with another treatment.
In subgroup analyses, the response rate was 81% among first-line patients with left-sided tumors, and 76% among first-line patients with liver metastases, compared with 67% among their second-line counterparts. The left-sided tumor result is directly relevant to the design of LiGeR-CRC1, the Phase 3 first-line study targeting this group. The disease control rate was 95% in the first line and 93% in the second line. At the data cutoff, 76% of first-line patients and 74% of second-line patients were still receiving treatment. These figures present response, disease control and continued treatment as separate measures in a follow-up period that remains limited.
On safety, adverse events related to petosemtamab led to its discontinuation in 2 of 42 patients who received the combination with mFOLFOX6, or 5%, and in 1 of 37 patients who received the combination with FOLFIRI, or 3%. The study recorded no treatment-emergent adverse events leading to death. Infusion-related reactions occurred in 48% of patients receiving petosemtamab with FOLFOX, compared with 43% with FOLFIRI. Grade 3 infusion reactions occurred in 3 of 42 patients in the FOLFOX group, or 7%, and 1 of 37 patients in the FOLFIRI group, or 3%. The company’s data distinguish the discontinuation group with mFOLFOX6 from the infusion-reaction group with FOLFOX.
The study is multicenter, ongoing, open-label and single-arm, and includes patients with metastatic colorectal cancer that is wild-type for RAS and BRAF and who have not previously received anti-EGFR therapy. Participants receive 1500 mg of petosemtamab every two weeks with FOLFOX or FOLFIRI. The experimental drug is a bispecific antibody targeting EGFR and LGR5. Co-investigator Ruth Vera said the response rates in both treatment lines “may point to a potential new treatment approach,” citing limited options for some patients with metastatic disease after chemotherapy and targeted therapy. Because the study is single-arm and open-label, its design does not include a randomized comparison between the combination and an alternative treatment.
Genmab’s plan includes four Phase 3 trials of petosemtamab, two in head and neck cancer and two in colorectal cancer. LiGeR-CRC1 is studying the drug against cetuximab with chemotherapy in both arms, among first-line patients with unresectable or metastatic left-sided tumors and no KRAS, NRAS or BRAF mutations. LiGeR-CRC2 targets the second-line setting. The company scheduled an investor update for October 28, 2026, at 12:00 p.m. Eastern Time to review the latest data. The results come two days after Genmab announced that the Phase 3 RAINFOL-02 trial of Rina-S met its progression-free survival and overall survival goals in patients with platinum-resistant ovarian cancer.
Genmab shares closed at $40 on October 22, then at $43.79 on October 23, before the company announced the petosemtamab results on October 25. A report published by Investing.com on October 26 said the shares rose 13.2% to 2,992 Danish kroner after the Phase 2 results were announced. That move reflects trading after the announcement, unlike the two earlier closes, which do not capture the impact of the colorectal cancer results. The company had announced separate results on October 23 from the Phase 3 RAINFOL-02 trial in ovarian cancer. The investor update scheduled for October 28 is the next date Genmab announced for reviewing petosemtamab data.