Pembrolizumab significantly improved progression-free survival (PFS) and safety over standard care chemotherapy in patients with microsatellite instability–high/mismatch repair–deficient (MSI-H/dMMR) metastatic colorectal cancer (mCRC), according to data presented at the virtual 2020 ASCO Annual Meeting.

“KEYNOTE-177 is a phase 3, randomized open-label study evaluating the efficacy and safety of pembrolizumab versus standard of care chemotherapy ± bevacizumab or cetuximab as first-line therapy for patients with MSI-H/dMMR mCRC,” wrote Thierry Andre, MD, Sorbonne University and Saint-Antoine Hospital, Paris, France, and co-investigators on background of the study findings being presented.

A total of 307 patients were randomly assigned in a 1:1 ratio to receive pembrolizumab 200 mg every 3 weeks for up to 2 years (n = 143) or standard care chemotherapy of mFOLFOX6 or FOLFIRI every 2 weeks with or without bevacizumab or cetuximab (n = 154).

The primary end points were PFS and overall survival (OS), and secondary endpoints included overall response rate and safety.

The data cutoff for this analysis was February 19, 2020. Median study follow-up 28.4 months in the pembrolizumab arm versus 27.2 months in the standard arm.

The median PFS was doubled in the pembrolizumab arm, at 16.5 months, compared to 8.2 months in the standard therapy arm. The PFS rates at 12- and 24- months were 55.3% and 48.3%, respectively, for patients in the pembrolizumab arm versus 37.3% and 18.6%, respectively, for patients in the standard arm.

The researchers found that the confirmed overall response rate was 43.8% with pembrolizumab versus 33.1% in the standard arm.

Additionally, treatment with pembrolizumab improved safety of standard care. Significantly less grade 3-5 treatment related adverse events were experienced in the pembrolizumab arm (22%) versus the standard care arm (66%).

“Pembrolizumab…. should be the new standard of care for these patients”, concluded Dr Andre and co-investigators.

The study is ongoing to evaluate overall survival.—Kaitlyn Manasterski

Andre T, Shiu K, Kim TW, et al. Pembrolizumab versus chemotherapy for microsatellite instability-high/mismatch repair deficient metastatic colorectal cancer: The phase 3 KEYNOTE-177 study. Presented at: the 2020 ASCO Annual Meeting; May 29-31, 2020. Abstract LBA4.