Perioperative Gemcitabine, Cisplatin, and Pembrolizumab in Potentially Resectable Biliary Tract Cancers

Inclusion Criteria: Must have a newly diagnosed, biopsy-proven biliary tract cancer (BTC) including gallbladder, intrahepatic, extrahepatic, and hilar cholangiocarcinoma. Resectable BTC (biliary tract cancer) Measurable disease per RECIST 1.1 as determined by the investigator. Age ≥18 years. ECOG (Eastern Cooperative Oncology Group) performance status ≤1 or Karnofsky ≥80 Patients must have adequate organ and marrow function defined by study-specified laboratory tests. Patients must have adequate liver function defined by study-specified laboratory tests. Patients with chronic or acute HBV or HCV infection must have disease controlled prior to enrollment. Women of childbearing potential (WOCBP) must have a negative urine or serum pregnancy test. For both Women and Men, must use acceptable form of birth control while on study. Ability to understand and willingness to sign a written informed consent document. Exclusion Criteria: Receiving, or previously received, any systemic chemotherapy, or investigational agent for BTC. Has received prior radiotherapy within 2 weeks of start of study intervention. Patients with a history of prior treatment with anti-PD-1 and anti-PD-L1. Have been diagnosed with another cancer or myeloproliferative disorder whose natural history or treatment has the potential to interfere with safety or efficacy assessment of this study's investigational drugs. Has a known history of Human Immunodeficiency Virus (HIV)/AIDS Has active co-infection with HBV and HDV. Has a diagnosis of immunodeficiency. Has active autoimmune disease that has required systemic treatment in the past 2 years. Systemic or topical corticosteroids at immunosuppressive doses. Prior allogeneic stem cell transplantation or organ transplantation. Prior tissue or organ allograft or allogeneic bone marrow transplantation, including corneal transplants. Uncontrolled intercurrent active medical and/or psychiatric illness/social psychosocial problems that that would limit compliance with study requirements. Uncontrolled intercurrent illness including, but not limited to, uncontrolled infection, symptomatic congestive heart failure, unstable angina, cardiac arrhythmia, metastatic cancer, or psychiatric illness/social situations that would limit compliance with study requirements. Evidence of clinical ascites. Has a history of (non-infectious) pneumonitis/interstitial lung disease that required steroids or has current pneumonitis/interstitial lung disease. Previously identified allergy or hypersensitivity to monoclonal antibodies or any component of the study treatment formulations. Pregnant or breastfeeding. WOCBP and men with female partners (WOCBP) who are not willing to use contraception. Subjects unable to undergo venipuncture and/or tolerate venous access. Patient is at the time of signing informed consent a regular user (including "recreational use") of any illicit drugs or had a recent history (within the last year) of substance abuse (including alcohol).