Background: Concurrent chemoradiation(CRT) followed by esophagectomy is a standard of care for locally advanced esophageal(LA-EAC) and GEJ adenocarcinoma. Approximately 50% of patients(pts) experience disease relapse within the 1^st yr after treatment(tx) completion. No adjuvant tx has been shown to improve survival in these pts. Immune checkpoint inhibitors have activity in metastatic PD-L1 positive EAC. Preclinical studies have shown radiation +/- chemotherapy upregulate PD-1/PD-L1 pathway. Methods: We conducted a phase II trial evaluating safety and efficacy of durvalumab(durva) in pts with LA-EAC and GEJ adenocarcinoma who have residual disease in surgical specimen after neoadjuvant CRT and R0 resection. Pts received durva 1500mg IV every 4 weeks for up to 1yr. Results: 24 pts were enrolled from 4/2016-1/2018(median age: 60yrs (range, 43-70). 18 received carbo/paclitaxel and 6 received cis/5-FU concurrently with radiation. Staging at diagnosis: T2N0(n = 3, 12.5%), T2N2(n = 3, 12.5%),T3N0(n = 6, 25%), T3N1(n = 6, 25%), T3N2(n = 4, 17%), T3N3(n = 1, 4%), T3Nx(n = 1, 4%).19 pts(79%) had positive lymph nodes(LNs) at the time of surgery following CRT. 12 pts completed 1yr of tx, 12 came off tx because of relapse(6), AEs(5), and consent withdrawal(1). Most common AEs were fatigue(n = 8, 33.3%) and nausea(n = 6, 25%). 3pts (12.5%) developed grade 3 irAEs: pneumonitis(1), hepatitis(1), colitis(1). At median follow up of 21.9mo(range, 1.7-23.9mo), 11 pts have relapsed: 9 distant and 2 locoregional. Two of 3 pts with grade 3 irAEs are alive and disease free at 17 and 23 mo respectively. 1-yr RFS and OS were 79.2% and 95.5%, respectively. RFS at 26 mo was 20.6%. Overall mOS and mOS after relapse were 28.1mo(range, 22.9-28.1) and 11.1 mo(range, 0.1-11.3mo) respectively. The study was expanded to enroll 14 additional pts who are currently undergoing tx. Conclusions: Adjuvant durvalumab following trimodality therapy for LA-EAC and GEJ adenocarcinoma is safe with improvement in 1-yr RFS to 79.2% compared to historical rate of 50%. RFS was 20.6% at 26 months. Evaluation of predictive biomarkers of RFS with durva is underway. Clinical trial information: NCT02639065