A Study of Pembrolizumab in People With Ultra-Rare Sarcomas

The purpose of the study is to find out if pembrolizumab is a useful treatment that causes few or mild side effects in people with ultra-rare sarcoma. The researchers will also study how the immune system responds to the study treatment.

Pembrolizumab is a type of drug called a PD-1 inhibitor. It is designed to block a protein called programmed cell death protein 1 (PD-1) that usually acts as a "brake" on the immune system. Blocking this protein is like releasing the brakes, so that the immune system can target cancer cells and destroy them.