The Food and Drug Administration (FDA) has approved Keytruda (pembrolizumab; Merck) for the treatment of patients with recurrent or metastatic cutaneous squamous cell carcinoma (cSCC) that is not curable by surgery or radiation. 

The approval was based on data from the multicenter, nonrandomized, open-label phase 2 KEYNOTE-629 trial that evaluated the efficacy and safety of pembrolizumab in 105 adults with recurrent or metastatic cSCC; 87% of patients had received 1 or more prior lines of therapy and 74% had received prior radiation therapy. Patients were administered pembrolizumab 200mg intravenously every 3 weeks until disease progression, unacceptable toxicity, or a maximum of 24 months. 

The major efficacy outcome measures were objective response rate (ORR) and duration of response (DoR) as assessed by blinded independent central review (BICR) according to Response Evaluation Criteria in Solid Tumors (RECIST) v1.1, modified to follow a maximum of 10 target lesions and a maximum of 5 target lesions per organ.

Results showed an ORR of 34% (95% CI, 25-44), with 4% of patients achieving a complete response and 31% achieving a partial response. After a median follow-up of 9.5 months, median DoR had not been reached (range: 2.7 to 13.1+ months). Among the 36 responders, 69% had responses of ≥6 months.

The safety profile of pembrolizumab in patients with cSCC was observed to be similar to that seen in previous studies. The most common adverse reactions were fatigue, musculoskeletal pain, decreased appetite, pruritus, diarrhea, nausea, rash, pyrexia, cough, dyspnea, constipation, pain, and abdominal pain. 

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The recommended Keytruda dosages for cSCC are 200mg every 3 weeks or 400mg every 6 weeks.

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