Primary Objective: To determine the feasibility of patients completing stereotactic body radiation therapy and at least one (1) cycle of Pembrolizumab.~Secondary Objectives:~Evaluate the radiographic response after decompressive stereotactic body radiation therapy and Pembrolizumab by calculating the improvement in thecal sac patency (see 5.2.1).~Evaluate accrual rate,~Evaluate pain relief.~Evaluate quality of life.~Evaluate cumulative incidence of adverse events.~Evaluate potential correlative blood biomarkers.
The purpose of this research study is to find out what effects (good and bad) Pembrolizumab and radiosurgery have on participants with high-grade epidural disease of the spine.