Pembrolizumab and GM-CSF in Biliary Cancer

Inclusion Criteria: * Be willing and able to provide written informed consent for the trial. * Have a performance status of 0 or 1 on the Eastern Cooperative Oncology Group (ECOG) Performance Scale. * Demonstrate adequate organ function * Absolute neutrophil count (ANC) \>= 1,000/microliter (mcL)(performed within 28 days of treatment initiation) * Platelets \>= 60,000/mcL (\>= 75,000/mcL in expansion cohort) (performed within 28 days of treatment initiation) * Hemoglobin \>= 9 g/dL or \>= 5.6 mmol/L without transfusion or erythropoietin (EPO) dependency (within 7 days of assessment) (performed within 28 days of treatment initiation) * Serum creatinine =\< 1.5 X upper limit of normal (ULN) OR measured or calculated creatinine clearance (glomerular filtration rate (GFR) can also be used in place of creatinine or creatinine clearance (CrCl)) \>= 60 mL/min for subject with creatinine levels \> 1.5 X institutional ULN (performed within 28 days of treatment initiation) * Serum total bilirubin =\< 1.5 X ULN OR direct bilirubin =\< ULN for subjects with total bilirubin levels \> 1.5 ULN (performed within 28 days of treatment initiation) * Aspartate aminotransferase (AST) (serum glutamic-oxaloacetic transaminase (SGOT)) and alanine aminotransferase (ALT) (serum glutamate pyruvate transaminase (SGPT)) =\< 5 X ULN (performed within 28 days of treatment initiation) * Albumin \>= 2.5 mg/dL (performed within 28 days of treatment initiation) * International normalized ratio (INR) or prothrombin time (PT) =\< 1.5 X ULN unless subject is receiving anticoagulant therapy as long as prothrombin time (PT) or partial thromboplastin time (PTT) is within therapeutic range of intended use of anticoagulants (performed within 28 days of treatment initiation) * Activated partial thromboplastin time (aPTT) =\< 1.5 X ULN unless subject is receiving anticoagulant therapy as long as PT or PTT is within therapeutic range of intended use of anticoagulants (performed within 28 days of treatment initiation) * Patients with known hepatitis B (HBV) or hepatitis C virus (HCV) infection are eligible provided liver function parameters meet laboratory eligibility criteria * Female subjects of childbearing potential should be willing to use 2 methods of birth control or be surgically sterile, or abstain from heterosexual activity for the course of the study through 120 days after the last dose of study medication * Male subjects should agree to use an adequate method of contraception starting with the first dose of study therapy through 120 days after the last dose of study therapy. ADDITIONAL EXPANSION COHORT SUBJECT INCLUSION CRITERIA * Tumor measurable by RECIST 1.1 including \>= 1 target lesion not planned for biopsy * Presence of \>= 1 tumor lesion not included as a RECIST 1.1 target lesion which is assessed by investigator and/or radiologist as likely to be amenable to percutaneous biopsy by punch, computed tomography (CT)-, or ultrasound-guided core needle biopsy for serial sampling on treatment * Platelet count \>= 75,000/mcL * No contraindication to tumor biopsy at time of study enrollment * Consent for on-treatment paired biopsies Exclusion Criteria: * Is currently participating and receiving study therapy or has participated and received study therapy in a study of an investigational agent, or used an investigational device within 4 weeks of the first dose of treatment. * Has a diagnosis of immunodeficiency or is receiving systemic steroid therapy for purposes of immunosuppression or any other form of immunosuppressive therapy within 7 days prior to the first dose of trial treatment. * Has a known history of active Bacillus Tuberculosis (TB). * Has a known history of Human Immunodeficiency Virus (HIV) (HIV 1/2 antibodies). * Has untreated active Hepatitis B (e.g., HBsAg reactive). * Has an active infection requiring systemic antibiotic therapy at time of enrollment. • Treatment with antibiotic prophylaxis for indwelling biliary stent(s) or peri-procedural antibiotics for uncomplicated biliary stent exchanges is allowed and not an exclusion * Hypersensitivity to pembrolizumab or any of its excipients. * Has received treatment with an anti-cancer monoclonal antibody (mAb) within 4 weeks prior to study Day 1 or who has not recovered (i.e., ≤ Grade 1 or at baseline) from adverse events due to agents administered more than 4 weeks earlier. * Has received treatment with chemotherapy, targeted small molecule therapy, or radiation therapy to non-liver sites within 2 weeks prior to study Day 1 or who has not recovered (i.e., ≤ Grade 1 or at baseline) from adverse events due to a previously administered agent administered more than 2 weeks earlier. * Has had prior chemoembolization, bland embolization, radioembolization, local ablative therapies, radiation to liver tumors, or major surgery such as liver resection within 4 weeks prior to study enrollment or who has not recovered (i.e., ≤ Grade 1 or at baseline) from adverse events due to intervention more than 4 weeks earlier. * Has a known additional malignancy that is progressing or requires active treatment. Exceptions include basal cell carcinoma of the skin or squamous cell carcinoma of the skin that has undergone potentially curative therapy or in situ cervical cancer. * Has known active central nervous system (CNS) metastases and/or carcinomatous meningitis. Subjects with previously treated brain metastases may participate provided they are stable (without evidence of progression by imaging for at least four weeks prior to the first dose of trial treatment and any neurologic symptoms have returned to baseline), have no evidence of new or enlarging brain metastases, and are not using steroids for at least 7 days prior to trial treatment. * Has active autoimmune disease that has required systemic treatment in the past 2 years (i.e. with use of disease modifying agents, corticosteroids or immunosuppressive drugs). Replacement therapy (e.g., thyroxine, insulin, or physiologic corticosteroid replacement therapy for adrenal or pituitary insufficiency, etc.) is not considered a form of systemic treatment. * Has known history of or any evidence of active, non-infectious pneumonitis. * Has had prior liver or other organ transplantation. * Has a history or current evidence of any condition, therapy, or laboratory abnormality that might confound the results of the trial, interfere with the subject's participation for the full duration of the trial, or is not in the best interest of the subject to participate, in the opinion of the treating investigator. * Has known psychiatric or substance abuse disorders that would interfere with cooperation with the requirements of the trial. * Is pregnant or breastfeeding, or expecting to conceive or father children within the projected duration of the trial, starting with the pre-screening or screening visit through 120 days after the last dose of trial treatment. * Has received prior therapy with an anti-PD-1, anti-PD-L1, or anti-PD-L2 agent. * Has received a live vaccine within 30 days of planned start of study therapy.