Clinical Stage III Merkel Cell Carcinoma AJCC v8

This phase I/II trial tests the safety and tolerability of an experimental personalized vaccine when given by itself and with pembrolizumab in treating patients with solid tumor cancers that have spread to other places in the body (advanced). The experimental vaccine is designed target certain proteins (neoantigens) on individuals' tumor cells. Immunotherapy with monoclonal antibodies, such as pembrolizumab, may help the body's immune system attack the cancer, and may interfere with the ability of tumor cells to grow and spread. Giving the personalized neoantigen peptide-based vaccine with pembrolizumab may be safe and effective in treating patients with advanced solid tumors.