Background: D (anti-PDL1) plus T (anti-CTLA-4) combination immunotherapy showed encouraging results in hepato-biliary cancers. Its efficacy in non-Asian Pts with pretreated BTC is unknown. Methods: IMMUNOBIL GERCOR-D18-1 PRODIGE-57 was initially a 2-arm, open-label, randomized non-comparative phase II study. Pts with recurrent/advanced pathologically proven BTC (intrahepatic cholangiocarcinoma [iCCA]/extrahepatic CCA [eCCA]/gallbladder cancer [GC]), ECOG PS 0-1, pre-treated with platinum-based CTx were randomized (1:1) to D (1500 mg Q4W) plus T (75 mg Q4W x 4 cycles [T75]) (Arm A) or D plus T in combination with weekly paclitaxel (Arm B). Arm B was closed prematurely for toxicity after inclusion of 10 Pts. The study continued with Arm A only. It was further amended to modify the T schedule (300 mg at cycle 1 [T300], amended Arm A) due to higher efficacy reported in other tumors as compared to T75 mg x 4. The new primary endpoint was the overall survival (OS) rate at 6 months (M6) in amended Arm A (D + T300) with a Fleming two-stage design (H0: 50%, H1: 65%, one-sided alpha: 5%, power: 90%). A total of 100 evaluable Pts were required (efficacy threshold: 59%). We present here the efficacy data of Arm A (D + T75). Results: From 12/2018 to 12/2020, 106 Pts were included in Arm A; 103 were evaluable for OS at M6. Median age was 66 years, 47% were male, 46% had ECOG PS 0, 69%/18%/13% had iCCA/eCCA/GC, 76% had metastatic disease, and 28% had prior tumor resection. First-line CTx was GEMCIS/GEMOX/5-FU-based/other in 63%/22%/4%/11%. The M6-OS rate was 59.2%. With a median follow-up of 12 months (95% Cl 11.4-14.9), the median OS was 8.0 months (95% Cl 5.7-11.7) and median PFS was 2.5 months (95% Cl 2.0-3.2). Complete response (CR) was observed in 2 (1.9%) Pts, partial response (PR) in 8 (7.8%), and stable disease (SD) in 32 (31.1%), resulting in an objective response rate of 9.7% and a disease control rate of 40.8%. Absence of progression (PD, iRECIST) after 2 cycles (M6-OS rate: 84% vs 41%, median OS: 17.9 months vs 4.4 months) and CR/PR as a best overall response (M6-OS rate: 100% vs 84% and 39% for SD and PD, respectively) were associated with markedly prolonged OS. 65 (63.1%) Pts had ≥1 grade 3-4 (G3-4) adverse event (AE) and 22 (21.4%) had ≥1 G3-4 treatment-related AE (TRAE). The most commonly reported G3-4 AEs were fatigue (12.6%), abdominal pain (5.8%), and aspartate aminotransferase increase (5.8%) and G3-4 TRAEs were fatigue (4.9%) and diarrhea (2.9%). One death was possibly related to treatment. Conclusions: Although no statistical conclusions can be drawn from this exploratory analysis of Arm A, D+T75 reached the pre-defined threshold for efficacy, with no unexpected toxicity. Results from amended Arm A (D+T300, N = 106 additional Pts), quality of life, and ancillary studies are pending. Clinical trial information: NCT03704480.