M7824 Monotherapy in Locally Advanced or Metastatic Second Line (2L) Biliary Tract Cancer (Cholangiocarcinoma and Gallbladder Cancer)

Inclusion Criteria * Are participants with histologically or cytologically confirmed locally advanced or metastatic BTC. * Availability of tumor (primary or metastatic) archival material or fresh biopsies is mandatory * Participants with BTC must have failed or be intolerant to 1L systemic platinum-based chemotherapy administered for locally advanced or metastatic disease. Only one prior treatment line is allowed * Disease must be measurable with at least 1 unidimensionally measurable lesion by RECIST 1.1 * Eastern Cooperative Oncology Group (ECOG) Performance Status (PS) of 0 to 1 * Life expectancy \>= 12 weeks as judged by the Investigator * Adequate hematological function defined by white blood cell (WBC) count \>= 3 \* 10\^9/Litre with absolute neutrophil count (ANC) \>= 1.5 \* 109/Litre, lymphocyte count \>= 0.5 \* 10\^9/Litre, platelet count \>=75 \* 10\^9/Litre, and hemoglobin (Hgb) \>= 9 grams/decilitre * Adequate hepatic function defined by a total bilirubin level =\< 1.5 \* upper limit of normal (ULN), an aspartate aminotransferase (AST) level =\< 2.5 \* ULN, and an alanine aminotransferase (ALT) level =\<2.5 \* ULN. For participants with liver involvement in their tumor, AST =\< 5.0 \* ULN and ALT =\< 5.0 \* ULN is acceptable * Adequate coagulation function defined as prothrombin time (PT) or international normalized ratio (INR) =\< 1.5 \* ULN unless the participant is receiving anticoagulant therapy * Albumin \>= 3.0 grams/decilitre * Hepatitis B virus (HBV) deox…