Genmab shares jump 13% on colorectal cancer drug trial results

Genmab shares jumped as much as 13% on Monday after the Danish biotech said its experimental drug petosemtamab, combined with chemotherapy, shrank tumours in 75% of previously untreated patients with advanced colorectal cancer in a mid-stage trial.

The 75% figure combines confirmed and unconfirmed responses among first-line patients who could be evaluated, after a median follow-up of 5.9 months. In second-line patients, treated after one earlier chemotherapy regimen, the rate was 67% after a median follow-up of 7.1 months. 

With longer follow-up, most responses that were unconfirmed earlier were later confirmed, Genmab said.

The response rate was 81% among first-line patients with left-sided tumours. For patients whose cancer had spread to the liver, which Genmab called a poor prognostic factor, rates were 76% in the first-line group and 67% in the second-line group. The disease control rate was 95% in first-line and 93% in second-line patients.

The data cover 79 patients treated as of May 15, 2026: 45 in the first-line setting and 34 in the second-line setting. 

At the data cutoff, 76% of first-line and 74% of second-line patients remained on treatment. Patients received petosemtamab plus chemotherapy regimens FOLFOX or FOLFIRI in an open-label, single-arm study.

Petosemtamab-related side effects led to discontinuation of the drug in 2 of 42 patients, or 5%, who received it with FOLFOX and in 1 of 37, or 3%, who received it with FOLFIRI.

Genmab reported no side effects leading to death. Infusion-related reactions occurred in 48% of patients on the FOLFOX combination and 43% on FOLFIRI. Grade 3 reactions occurred in 3 of 42 patients, or 7%, and 1 of 37, or 3%, respectively.

Tahamtan Ahmadi, Genmab’s chief medical officer, said the results provide "a compelling rationale" for the company’s ongoing Phase 3 trials. Genmab has Phase 3 trials under way in first- and second-line RAS/BRAF wild-type colorectal cancer.

The results were presented at the European Society for Medical Oncology Congress in Madrid.  

On Oct. 24, Genmab and biopharmaceutical company Incyte announced a clinical trial collaboration to test petosemtamab with Incyte’s experimental KRAS G12D inhibitor, INCB161734, and standard chemotherapy in first-line patients whose metastatic colorectal cancer carries a KRAS G12D mutation. 

Genmab will run the Phase 1/2 study, and Incyte will co-fund it and supply INCB161734. KRAS mutations occur in about 40% of colorectal cancers, with G12D the most common.