Pembrolizumab for previously treated advanced anal squamous cell carcinoma

Outcomes in advanced anal squamous cell carcinoma are poor, with few treatment options. Cohort A of the multinational phase 2 KEYNOTE-158 study evaluated pembrolizumab monotherapy for previously treated advanced or metastatic anal squamous cell carcinoma. Objective response was seen in 11 of 75 patients with PD-L1 positive tumors (ORR 15%; 95% CI 8-25) and one of 30 patients with PD-L1 negative tumors (3%; 0-17). Grade 3 or 4 treatment-related adverse events occurred in 20 patients (18%). The authors conclude that pembrolizumab is a possible treatment option with a favourable benefit/risk-ratio for patients with previously treated advanced anal squamous cell carcinoma who have no alternative satisfactory treatment options.