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) deoxyribonucleic acid (DNA) positive participants must be treated and on a stable dose of antivirals
* Adequate renal function defined by either creatinine =\< 1.5 \* ULN or an estimated creatinine clearance (CCr) \> 40 milliliter (mL) per minute (min) according to the Cockcroft-Gault formula or by measure of CCr from 24-hour urine collection
* Other protocol defined inclusion criteria could apply

Exclusion Criteria:

* Ampullary cancer was excluded
* Significant acute or chronic infections
* Active autoimmune disease that might deteriorate when receiving an immunostimulatory agent
* Interstitial lung disease or its history
* Participants who were not eligible for or have not been treated with 1L systemic chemotherapy
* Anticancer treatment within 21 days before the start of study intervention
* Concurrent treatment with nonpermitted drugs
* Prior participation in a M7824 clinical trial
* Prior therapy with other immunotherapy or checkpoint inhibitors, such as anti-PD 1, anti PD L1, anti- cytotoxic T-cell lymphocyte-4 (CTLA-4) antibodies.
* Pregnancy or breast feeding
* Systemic anticancer treatment after failing 1L platinum-based chemotherapy
* Other protocol defined exclusion criteria could apply