IntroductionEvidence supports the addition of immunotherapy to definitive chemoradiation for unresectable stage IIIA NSCLC. Adding pembrolizumab to neoadjuvant chemoradiation in patients with resectable stage IIIA NSCLC requires study for safety and feasibility. MethodsPatients with resectable stage IIIA NSCLC received neoadjuvant cisplatin, etoposide, and pembrolizumab concurrently with thoracic radiotherapy of 45 Gy in 25 fractions. Patients without progression underwent resection followed by 6 months of consolidation pembrolizumab. Safety and feasibility were defined as less than or equal to 30% grade 3 or higher pulmonary toxicity or any grade 4 or 5 nonhematologic toxicity. A total of 10 patients were to be enrolled initially. If less than or equal to two patients had events, another 10 were to be enrolled. ResultsThe study closed after enrolling nine patients. The median age was 66 (range: 49-76) years. A total of 67% were female. Median follow-up was 38.3 months. Serious adverse events occurred in seven patients, including two grade 5 events: one sudden cardiac arrest in the neoadjuvant phase and one fatal pneumocystis pneumonia after resection. Eight patients were assessable for response. The overall response rate was 67%. Six underwent complete resection. Four achieved pathologic complete response, whereas one additional patient had complete nodal clearance. Median progression-free survival has not been reached. The 3-year overall survival was 64%. ConclusionsAdding pembrolizumab to neoadjuvant concurrent cisplatin, etoposide, and radiotherapy in resectable stage IIIA NSCLC resulted in an encouraging pathologic complete response rate. Higher-than-expected toxicities necessitated trial closure after meeting the rule for infeasibility. The relationship of grade 5 events to the addition of pembrolizumab is unclear.