Risk of cumulative toxicity after complete melanoma response with pembrolizumab.

Pembrolizumab is an approved first-line systemic therapy for unresectable metastatic melanoma. Despite the achievement of complete and durable responses in a small subgroup of patients, it is standard practice that pembrolizumab therapy continues beyond complete response. Nevertheless, the incidence of immune-related toxicities gradually increases with continuing pembrolizumab therapy. We report a case highlighting the occurrence of serious induced immune-related adverse events, which were attributed to pembrolizumab in a patient with metastatic melanoma who obtained a complete response (CR) after receiving pembrolizumab for a total of 6.5 months. Although mild pembrolizumab-related toxicity persists, the patient remains disease-free 5.5 months after discontinuation of pembrolizumab. Accordingly, we believe that cessation of pembrolizumab should be considered in patients who achieve a CR because of the ongoing risk of toxicity with extended pembrolizumab administration.