Among responding patients, 69% had ongoing responses of 6 months or longer. After a median follow-up time of 9.5 months, the median duration of response (DOR) had not been reached (range 2.7-13.1+ months). The efficacy of pembrolizumab was investigated in patients with recurrent or metastatic cSCC enrolled in KEYNOTE-629 (NCT03284424), a multicenter, multicohort, nonrandomized, open-label trial. The trial excluded patients with autoimmune disease or a medical condition that required immunosuppression. The major efficacy outcome measures were ORR and DOR, assessed by blinded independent central review according to Response Evaluation Criteria in Solid Tumors v1.1, modified to follow a maximum of 10 target lesions and five target lesions per organ.
Among the 105 patients treated, 87% received one or more prior lines of therapy and 74% received prior radiation therapy. Forty-five percent of patients had locally recurrent–only cSCC, 24% had metastatic only cSCC, and 31% had both locally recurrent and metastatic cSCC. The study population characteristics were median age of 72 years (range 29-95 years), 71% aged 65 or older, 76% male, 71% white, 25% race unknown, 34% Eastern Cooperative Oncology Group (ECOG) Performance Status (PS) of 0 and 66% ECOG PS of 1. Pembrolizumab demonstrated an ORR of 34% (95% CI, 25-44), with a complete response rate of 4% and a partial response rate of 31%. Among the 36 responding patients, 69% had ongoing responses of 6 months or longer. After a median follow-up time of 9.5 months, the median DOR had not been reached (range 2.7-13.1+ months).
Patients received pembrolizumab 200 mg IV every 3 weeks until documented disease progression, unacceptable toxicity, or a maximum of 24 months. Patients with initial radiographic disease progression could receive additional doses of pembrolizumab during confirmation of progression, unless disease progression was symptomatic, was quickly progressive, needed urgent intervention, or occurred with a deterioration in performance status. Evaluation of tumor status was performed every 6 weeks during the first year and every 9 weeks during the second year. Among the 105 patients with cSCC enrolled in KEYNOTE-629, the median duration of exposure to pembrolizumab was 5.8 months (range 1 day-16.1 months).
Adverse reactions occurring in patients with cSCC were similar to those occurring in 2,799 patients with melanoma or non-small cell lung cancer treated with pembrolizumab as a single agent. Laboratory abnormalities (Grades 3-4) that occurred at a higher incidence included lymphopenia (11%).