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. Immune checkpoint inhibitors have activity in metastatic PD-L1 positive EAC. Preclinical studies have shown radiation +/- chemotherapy upregulates PD-1/PD-L1 pathway. Methods: We conducted a phase II trial evaluating safety and efficacy of PD-L1 inhibitor durvalumab(durva) in pts with LA-EAC and GEJ adenocarcinoma who had residual disease in surgical specimen after neoadjuvant CRT and R0 resection. Pts received durva 1500mg IV every 4 weeks for up to 1yr. Results: Initially 24 pts were enrolled, study was expanded to enroll additional 13 pts. Median age: 61yrs (range, 43-73). 31 received carbo/paclitaxel and 6 received cis/5-FU concurrently with RT. 24(64.9%) pts had positive lymph nodes(LN) at the time of surgery following CRT: N3(n = 3,8.1%), N2(n = 10, 27%), N1(n = 11,29.7%).17 pts relapsed: 11 on tx, 6 had late relapses. 3/5 late relapses were locoregional and were re-treated with chemo-RT. Remaining relapses were systemic with lung and LN being the most common sites. 2 of 3 pts who developed grade 3 irAEs are alive and disease free at 17 and 23 mo. RFS/OS:1 yr- 79.2%/95.5%, 2yr-55.5%/67.4%. 20/37 pts have HER-2 status available: 5/6 HER2 positive pts had disease relapse, 1 is undergoing tx. Molecular profiling is available on 8 relapsed pts: all were microsatellite stable with low TMB and PD-L1 < 10% CPS. Mutations in DNA repair genes (ARID1A, ATM, ATR, CHEK2), and PIK3CA E542K were more prevalent among late relapsing pts. Circulating tumor cells (CTCs) analysis is available for 10/37 pts. 4/5 pts where CTCs increased from C1 to C4 had disease relapse. Molecular profiling of the remaining pts and correlation of PD-L1 expression, TMB, specific genes mutations, CTCs, and Immunoscore with outcomes with durva is being evaluated will be presented at the meeting. Conclusions: Adjuvant durva following trimodality therapy for LA-EAC and GEJ adenocarcinoma improved 1-yr RFS to 79.2% compared to historical rate of 50%.2-yr RFS and OS data are encouraging in this high risk pt population. HER-2 positivity may be associated with lack of benefit from durva. Mutations in DNA repair genes are prevalent in pts with delayed relapse. Rise in CTCs during durva tx may be an early marker of disease relapse. Clinical trial information: NCT02639065.