RecruitingPhase 2Drug trialGemcitabine, Cisplatin, Nab-paclitaxel (GAP) and Cemiplimab for Locally Advanced Biliary Tract Cancer (BTC)This study is being conducted to find out if treatment with gemcitabine, cisplatin, nab-paclitaxel, and cemiplimab can shrink previously inoperable tumors enough for surgery.