Safety and efficacy analysis of modified TOPAZ-1: A biweekly regimen of gemcitabine and cisplatin plus monthly durvalumab in advanced biliary tract cancer.

e16265 Background: The pivotal TOPAZ-1 trial established durvalumab plus gemcitabine and cisplatin (GC) as a new first-line standard of care for advanced biliary tract cancer (ABTC). However, weekly administration of GC can lead to significant toxicity limiting its tolerability in clinical practice. Based on previous studies, we implemented biweekly regimen of GC on days 1 and 15 together with durvalumab on day 1 of each 28-day cycle to optimize the treatment delivery and improve tolerability. Here, we report the Mayo Clinic experience with biweekly GC with monthly durvalumab in patients with ABTC. Methods: At our three-site institution, we retrospectively identified patients with ABTC between January 2021 and August 2024, who received biweekly GC with monthly durvalumab. Patient demographics, tumor characteristics, treatment details - treatment related adverse events (trAEs) graded according to the NCTCAE V5.0 were collected. Outcomes included median progression-free survival (mPFS), median overall survival (mOS) and clinically assessed overall response rate (ORR) and disease control rate (DCR). Results: 57 patients were included in our analysis, median age was 68 years (range 35-90), and 57.9% were females. 91.2% of patients had ECOG performance status of 0-1. 71.9% had intrahepatic cholangiocarcinoma, 19.3% extrahepatic cholangiocarcinoma and 8.7% gallbladder carcinoma. 70.2% had metastatic disease, 21 % locally advanced unresectable disease and 8.7% recurrent metastatic disease. Patients were followed for a median of 9.1 months (2.3-28.5). 91.2% of the patients received biweekly GC plus monthly durvalumab while 8.8% switched from weekly to biweekly GC plus monthly durvalumab due to treatment toxicities. Median number of treatment cycles was 5. Maintenance regimens included durvalumab (19.3%), gemcitabine/durvalumab (8.8%) and GC/durvalumab (8.8%). Median duration of follow up was 9.1 months (range 2.3 – 28.5). ORR was 36.9% and DCR was 72% (complete response 5.3%, partial response 31.6% and stable disease 35.1%). mPFS was 7.2 months, while mOS was 16 months. Grade(G) 3 or 4 trAEs included abnormal liver function tests (15.7%), infections (11.5%), anemia (8.7%), thrombocytopenia (5.2%), peripheral neuropathy (1.7%), acute kidney injury (1.7%). Immune-related AEs were noted in 6 patients (10.5%) including colitis, gastritis, hepatitis, myocarditis and hypothyroidism. There was no patient with severe neutropenia or febrile neutropenia. Only 5 patients (8.8%) stopped treatment due to trAEs. Conclusions: Biweekly GC on days 1 and 15 plus durvalumab on day 1 of each 28-day cycle is associated with a more favorable toxicity profile while maintaining efficacy similar to that observed in the TOPAZ-1 trial indicating that a de-escalation strategy is feasible with improvement in patient centered outcomes.