Fatal outcome after immunotherapy in metastatic Merkel cell carcinoma of unknown primary cause.

Merkel cell carcinoma (MCC) is a rare form of skin cancer characterised by a high mortality rate. Despite limited evidence regarding the treatment of metastatic MCC, anti-programmed cell death protein 1 immunotherapy has emerged as a primary strategy for managing advanced stages of the disease. This report presents the case of a woman in her early 80s with stage IV MCC after consultation for declining general health, with the primary lesion remaining unidentified. Pembrolizumab therapy was initiated, which led to acute renal failure after the first infusion. The case highlights the high pathogenicity of MCC and the risk of renal complication associated with pembrolizumab, underscoring the need for vigilance in anticipating and preventing such adverse effects. The discussion examines recent recommendations on the best treatment options for metastatic MCC, which currently includes immunotherapy.