A Study of Different Dosing Schedules of Selumetinib With Cisplatin/Gemcitabine (CIS/GEM) Versus CIS/GEM Alone in Biliary Cancer

Inclusion Criteria: * Unresectable, recurrent or metastatic, measurable biliary tract cancer or gall bladder cancer * No prior systemic therapy * Performance status 0, 1, or 2 * Age 18 years or older * Estimated life expectancy \> 3 months * Adequate hematological, liver, renal function * No evidence of active uncontrolled infection * Capable of giving written consent * Acceptable recovery of previous side effects Exclusion Criteria: * Progressing within 3 or 6 months of receiving certain treatments * Prior chemotherapy for non-resectable or metastatic disease or a MEK inhibitor * Progressing within 6 months of adjuvant treatment. * May not have received prior chemotherapy for non-resectable/metastatic disease. * Prior MEK, RAS, or RAF inhibitors or history of hypersensitivity to study drugs. * Ampullary carcinoma * Incomplete recovery from previous surgery * Undergoing treatment with curative intent * Prior malignancy that could interfere with the response evaluation * Severe or uncontrolled systemic diseases or lab finding that makes it undesirable for patient to participate * Any psychiatric or other disorder likely to impact consent * Pregnant or breastfeeding * Patients with significant cardiac-related issues * History of eye-related issues. * Systemic disease, active infection, bleeding diatheses or renal transplant, including hep B, hep C or HIV * Receiving potent inhibitors or inducers of CYP3A4/5, CYP2C19 and CYP1A2 can continue with caution