Genmab: Phase 2 petosemtamab shows high response rates in metastatic colorectal cancer
- 79 patients treated overall: 45 first‑line (1L) and 34 second‑line (2L).
- Confirmed and unconfirmed ORRs were 75% in 1L and 67% in 2L, with 81% ORR in 1L left‑sided tumors.
- Median follow‑up was 5.9 months (1L) and 7.1 months (2L), with 76% and 74% of patients remaining on treatment at cutoff.
- Infusion‑related reactions occurred in 48% (FOLFOX) and 43% (FOLFIRI); grade 3 IRRs were 7% and 3%, and discontinuations due to TEAEs were 5% and 3% respectively.
Study population and design
The Phase 2, single‑arm trial evaluated petosemtamab—an investigational EGFR/LGR5 IgG1 bispecific—given at 1,500 mg every two weeks with mFOLFOX6 or FOLFIRI in RAS/BRAF wild‑type, anti‑EGFR naïve metastatic colorectal cancer patients treated in either first‑line (1L) or second‑line (2L) settings. As of the May 15, 2026 cutoff, 79 patients were treated (45 1L; 34 2L).
Efficacy
At median follow‑up of 5.9 months (1L) and 7.1 months (2L), confirmed and unconfirmed objective response rates (ORRs) were 75% in 1L and 67% in 2L; 1L patients with left‑sided tumors had an ORR of 81%. Disease control rates were 95% (1L) and 93% (2L). Most previously unconfirmed responses became confirmed with longer follow‑up.
Safety
No treatment‑emergent adverse events leading to death were reported. Infusion‑related reactions occurred in 48% of patients receiving petosemtamab plus FOLFOX and 43% with FOLFIRI; grade 3 IRRs occurred in 3/42 (7%) and 1/37 (3%) patients, respectively. Petosemtamab‑related TEAEs led to discontinuation in 2/42 (5%) with mFOLFOX6 and 1/37 (3%) with FOLFIRI.
Next steps
Results presented at ESMO 2026 support the ongoing global Phase 3 LiGeR program testing petosemtamab in 1L and 2L metastatic CRC; patient enrollment in those trials is active. An investor update was scheduled for October 28, 2026.
Source: Genmab