Pembrolizumab Alone or Sequentially Following Single Fraction Non-ablative Radiation to One of the Target Lesions, in Previously Treated Patients With Stage IV NSCLC

The goal of this clinical trial is to determine if low single palliative dose radiation to the lung cancer will improve your immune response against the tumor and if sequential treatment with pembrolizumab (the study drug) would offer superior results compared to pembrolizumab alone in participants with non-small cell lung cancer. The purpose of this research is also to study whether there are any changes present in the DNA, RNA, and proteins of a participant's tumor or the blood cells that may contribute to a response to the study treatment or progression of cancer. This research may help researchers in the future to learn more about the causes, risks, treatments, or prevention of cancers or other health problems. Participants will consent to a screening period, a core or treatment phase, and a post-study observation phase. During the screening phase, participants will undergo a series of tests to determine if they are eligible for the study. The core study period, or treatment period, will start with a single dose of radiation and then continue for the first eight treatments of pembrolizumab, approximately 24-28 weeks. Participants will have a new biopsy taken after two treatments of the study drug. Following the 24-28 week treatment cycle, if the cancer is responding to treatment, the participant's physician will continue to treat with pembrolizumab as a standard treatment. Following treatment, the post-study observation phase will monitor participant response to drugs and outcomes.