Complete Response of Merkel Cell Carcinoma to Immunotherapy and Single-Fraction Radiotherapy Following Severe COVID-19 Infection: A Case Report and Review of Immune Mechanism.

Merkel cell carcinoma (MCC) is a rare, aggressive neuroendocrine form of skin cancer. This case report describes a 70-year-old Hispanic male with stage IIA MCC of the upper back which rapidly progressed during hospitalization for severe COVID-19 infection requiring ventilatory support. After resolution of his severe acute illness, he received one dose of anti-PD-1 therapy and single-fraction radiotherapy to his primary lesion for local control. His tumor then underwent a rapid regression and he completed 17 cycles of immunotherapy with a complete clinical and radiologic response sustained more than 4 years. This case illustrates a possible synergistic effect of radiation therapy and immune checkpoint inhibition after rebounding immune-system hyperactivation from infection with COVID-19.