In a phase 2 clinical trial of the immunotherapy drug pembrolizumab as a first-line systemic therapy for advanced Merkel cell carcinoma, or MCC – a rare, aggressive type of skin cancer – the clinical response rate was similar to that typically seen with standard chemotherapy, but the duration of the response appeared to be markedly longer. There are currently no therapies that have been approved by the U.S. Food and Drug Administration for this cancer.
Multispectral immunofluorescence shows the interface between Merkel cell tumor cells (orange) and host immune cells (yellow marks CD8+ lymphocytes, red marks CD68+ macrophages). Cell-surface PD-L1 expression (green) is observed on macrophages, lymphocytes and tumor cells, adjacent to PD-1 expression (white) on lymphocytes.
Credit: Courtesy of Janis Taube, Johns Hopkins.