Genmab Shares Surge 13% on Positive Colorectal Cancer Drug Trial Results

Shares of Danish biotechnology firm Genmab (GMAB) surged as much as 13% on Monday following the release of promising mid-stage trial data for its experimental cancer drug, petosemtamab. The company announced the drug, when combined with chemotherapy, shrank tumors in 75% of previously untreated patients with advanced colorectal cancer.

Key Efficacy Data

The results, presented at the European Society for Medical Oncology Congress, are from a mid-stage, single-arm study involving 79 patients as of a May 15, 2026 data cutoff. The data showed a high overall response rate (ORR) and disease control rate (DCR) in patients receiving their first or second line of treatment.

Key findings include:

• First-line patients: A 75% ORR (confirmed and unconfirmed) after a median follow-up of 5.9 months, with a 95% DCR.
• Second-line patients: A 67% ORR after a median follow-up of 7.1 months, with a 93% DCR.
• High-risk patients: The drug also showed strong efficacy in patients with liver metastases, a poor prognostic factor, with response rates of 76% in the first-line group and 67% in the second-line group.

Genmab noted that with longer follow-up, most of the initially unconfirmed responses were later confirmed. At the time of the data cutoff, approximately 75% of patients in both groups remained on treatment.

Safety Profile and Path Forward

Ad

The treatment combination was generally manageable. Petosemtamab-related side effects led to discontinuation of the drug in 3% to 5% of patients, depending on the chemotherapy regimen used. Genmab reported that no side effects led to death. Infusion-related reactions, a common side effect for this class of drugs, occurred in 43-48% of patients, with most being low-grade.

Tahamtan Ahmadi, Genmab’s chief medical officer, stated the results provide "a compelling rationale" for the company’s ongoing Phase 3 trials. The company already has late-stage studies underway for petosemtamab in both first- and second-line colorectal cancer, signaling a clear path toward potential regulatory submission.

Strategic Collaboration

Further boosting investor confidence, Genmab and Incyte announced a clinical trial collaboration on October 24. The partnership will evaluate petosemtamab in combination with Incyte's experimental drug and standard chemotherapy for first-line patients whose colorectal cancer carries a KRAS G12D mutation.

This collaboration is significant as KRAS mutations occur in about 40% of colorectal cancers, with G12D being the most common type. Success in this area could significantly expand the potential market for petosemtamab.