The Food and Drug Administration (FDA) has granted accelerated approval to Keytruda (pembrolizumab; Merck) for patients with unresectable or metastatic, microsatellite instability-high (MSI-H) or mismatch repair deficient (dMMR) solid tumors that have progressed following prior treatment and who have no satisfactory alternative treatment options or for patients with MSI-H or dMMR colorectal cancer that has progressed following treatment with a fluoropyrimidine, oxaliplatin, and irinotecan. 

The approval, which marks the FDA’s first tissue/site-agnostic approval, was based on data from 149 patients enrolled across five uncontrolled, multi-cohort, multicenter, single-arm clinical studies. Patients were given Keytruda 200mg every 3 weeks or Keytruda 10mg/kg every 2 weeks until unacceptable toxicity or disease progression that was either symptomatic, rapidly progressive, required urgent intervention, or was associated with a decline in performance status. 

The major efficacy endpoint was objective response rate (ORR) and response duration. The data showed ORR was 39.6% (95% CI: 31.7, 47.9). Patients’ responses lasted ≥6 months for 78% of pembrolizumab responders. ORR was similar regardless of having a colorectal cancer (36%) or different type of cancer (46% across 14 other types).   

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As this indication was granted accelerated approval based on tumor response and durability of response, continued approval may be contingent upon verification and description of clinical benefit in the confirmatory trials. The safety and efficacy of Keytruda have not been established in pediatric patients with MSI-H central nervous system cancers. 

The most common adverse reactions were fatigue, pruritus, diarrhea, decreased appetite, rash, pyrexia, cough, dyspnea, musculoskeletal pain, constipation, and nausea.

Keytruda, a programmed death receptor-1 (PD-1)-blocking antibody, recently gained approval for urothelial carcinoma and metastatic non-small cell lung cancer (NSCLC)

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