The FDA approved pembrolizumab on June 29, 2020, for the treatment of patients with unresectable or metastatic microsatellite instability-high (MSI-H) colorectal cancer with no prior systemic treatment for advanced disease. The approval was based on data from Study Keynote-177, which randomly allocated patients to receive either pembrolizumab or standard of care (SOC) with chemotherapy. Overall survival (OS) and independently assessed progression-free survival (PFS) were the primary endpoints. At the time of the final PFS analysis and second prespecified interim OS analysis, the estimated median PFS was 16.5 months (95% CI: 5.4-32.4) versus 8.2 months (95% CI: 6.1-10.2) in the pembrolizumab and SOC arms, respectively [HR: 0.60 (95% CI: 0.45-0.80); two-sided P = 0.0004]. FDA assessed unblinded OS data during the review of the application and identified no safety concerns that would preclude approval of this supplement. Adverse reactions occurring in >30% of patients receiving pembrolizumab were diarrhea, fatigue/asthenia, and nausea. Adverse reactions occurring in >30% of patients receiving SOC were diarrhea, nausea, fatigue/asthenia, neutropenia, decreased appetite, peripheral neuropathy (high-level term), vomiting, abdominal pain, constipation, and stomatitis. Duration of treatment in the pembrolizumab arm was almost double (median 11.1 months, range 0-30.6 months) than the duration of treatment in patients receiving SOC (median, 5.7 months). Approval of pembrolizumab is likely to change the treatment paradigm for first-line treatment with MSI-H advanced colorectal cancer given the study results and different safety profile.
