Pembrolizumab and Stereotactic Radiosurgery for Melanoma or Non-Small Cell Lung Cancer Brain Metastases

Inclusion Criteria: * Be willing and able to provide written informed consent/assent for the trial * Eastern Cooperative Oncology Group (ECOG) performance scale (PS) of 0-1; Karnofsky performance status ≥ 70% * Patients must have histological diagnosis of melanoma or non-small cell lung cancer (biopsy will be done per standard of care, if needed to prove metastatic melanoma and/or NSCLC as well as for clinically relevant mutation analysis); additional biopsy will be per standard of care * Patients can be treated either in first line or in the refractory setting; programmed death-ligand 1 (PD-L1) positivity is not required for enrollment * All melanoma patients may be tested for proto-oncogene B-Raf (BRAF) as part of routine standard of care, but is not a requirement for the trial; all NSCLC patients may be tested for with epidermal growth factor receptor (EGFR) and anaplastic lymphoma kinase (ALK) as part of standard of care, but is not a requirement of the trial * Having gotten prior programmed cell death protein 1 (PD1) therapy is allowed for, especially if they have previously progressed on it; progression may include extra-cranial as well as intra-cranial progression; after progressing on PD1 therapy, intervening chemotherapy and/or targeted therapy (BRAF inhibitors \[BRAFi\], etc) is allowed; if they are on intervening chemotherapy and/or targeted therapy (BRAFi, etc), they have to have progression intra-cranially and/or extra-cranially and must be off intervening thera…