Background: Improved therapy is needed for patients (pts) with early-stage non-small cell lung cancer (NSCLC), as the majority relapse after curative resection. Our group reported the first trial of neoadjuvant PD-1 blockade in resectable NSCLC, finding therapy to be safe and feasible. Here we report extended clinical follow-up and long-term molecular response data from this trial. Methods: IV nivolumab 3 mg/kg was given every 2 weeks for 2 doses prior to surgery in 20 pts with resectable NSCLC at Johns Hopkins and MSKCC. Blood for correlative studies was taken prior to each dose of nivolumab, prior to surgery, 2-4 weeks post-surgery, and during long-term follow up. In a subgroup of pts, longitudinal molecular data was assessed in peripheral blood for circulating tumor DNA (ctDNA) and dynamics of tumor-infiltrating T-cell clonotypes. Results: At median follow up of 30 months (m), 15 of 20 pts are disease-free and alive. Two pts have died (one from relapsed disease). Median recurrence free survival (RFS) has not been reached. The 24m RFS rate is 69% (95% CI: 51-93). Thus far, presence of ctDNA at diagnosis and major pathologic response (MPR - ≤10% viable tumor in resected specimen) do not associate with RFS. One long-term immune-related adverse event has occurred (skin, G3). All pts who on pathologic review had ≥30% reduction in viable tumor in response to nivolumab demonstrated clearance of detectable ctDNA from blood prior to surgery. Pts with MPR experienced expansion of neoantigen-specific T-cells in peripheral blood. In one patient with ongoing disease free status, expansion of tumor-associated T-cells has persisted in peripheral blood beyond 15m from surgery. By contrast, in a patient who had detectable peri-operative ctDNA and 75% residual disease at surgery, minimal T-cell expansion was observed in peripheral blood, with a decreasing frequency of expanded T-cell clones over time that correlated with eventual cancer relapse. Conclusions: Long-term follow up reinforces the safety of neoadjuvant nivolumab in resectable NSCLC. Analysis of ctDNA and peripheral T-cell expansion in responders compared with non-responders suggests potential biomarkers for response and surveillance. While RFS data is encouraging, phase 3 trials are ongoing to evaluate efficacy of PD-(L)1 blockade in early-stage NSCLC. Clinical trial information: NCT02259621