Pembrolizumab After Lung SBRT for Medically Inoperable Early Stage Non-small Cell Lung Cancer

The primary objective of this pilot safety study is to determine the tolerability and feasibility of administering pembrolizumab in the adjuvant setting following completion of definitive SBRT to the lung for patients with medically inoperable early stage NSCLC with tumors greater than 3 cm in diameter Secondary Objectives 1. Distant metastases free survival (DMFS) 2. Disease Free Survival (DFS) 3. Overall survival (OS) Study design including dose escalation / cohorts This is an open-label, single arm feasibility study of lung SBRT followed 2 to 4 weeks after completion by the addition of pembrolizumab. Eligible patients will have biopsy-confirmed T1b-T3N0M0 (stage IA-IIB) non-small cell lung cancer (adenocarcinoma, squamous cell carcinoma, or large cell/NSCLC NOS), performance status 0-2, deemed medically inoperable by a thoracic surgeon or pulmonologist, and no contraindications to pembrolizumab. The primary endpoint for this study is safety and feasibility. For the first stage of this study, 8 patients will be enrolled. If \>7 of the initial 8 patients complete the therapy without experiencing a Grade \>3 pulmonary toxicity or any Grade \>4 toxicity, an additional 7 patients will be enrolled for a total of 15 patients. If \>2 of the original 8 patients (\>25%) experience a Grade \>3 pulmonary toxicity or any Grade \>4 toxicity the trial will be closed and the study therapy will be considered too toxic. If \>4 of 15 patients (\>26.7%) experience a Grade \>3 pulmonary toxicity or any Grade \>4 toxicity, the study drug regimen will be deemed too toxic and unsafe. If \>12 out of 15 patients complete the study without experiencing a Grade \>3 pulmonary toxicity or any Grade \>4 toxicity, the study drug regimen will be considered safe and feasible for further study.