RecruitingPhase 2Drug trialAdjuvant Pembrolizumab vs Observation Following Curative Resection for Stage I Non-small Cell Lung Cancer (NSCLC) With Primary Tumors Between 1-4 cmA randomized trial of adjuvant Pembrolizumab following surgical resection versus observation following surgical resection in patients with stage I non-small cell lung cancer (NSCLC) with primary tumors between 1-4 cm. Patients will be randomized (1:1) 4-12 weeks following surgery to either: * Arm A: Pembrolizumab 400 mg every 6 weeks × 9 cycles * Arm B: Observation Stratification factors will include: PD-L1 TPS (\<50% vs. ≥50%), and tumor size (1-2 cm vs. \>2-4 cm)