Inclusion Criteria:

          -  Histologically or cytologically confirmed locally advanced or metastatic pancreatic
             adenocarcinoma, colorectal adenocarcinoma, gastric adenocarcinoma, cholangiocarcinoma,
             gall bladder adenocarcinoma, ampullary carcinoma, adenocarcinoma of unclear primary
             (with a gastrointestinal primary suspected), or other primary gastrointestinal
             malignancy for which the treating physician feels that mFOLFIRINOX is a reasonable
             therapeutic option.

          -  Amendment (January 2014): only subjects with the following histologies will be
             eligible

        Cohort # 1 (pancreatic cohort): locally advanced or metastatic pancreatic adenocarcinoma
        (19 subjects evaluable for the primary endpoint after the amendment)

        Cohort #2 (biliary tract cohort): locally advanced or metastatic cholangiocarcinoma, gall
        bladder adenocarcinoma, or ampullary carcinoma (19 subjects evaluable for the primary
        endpoint after the amendment). Patients with adenocarcinoma of unclear primary that are
        most likely of biliary tract origin (in the opinion of the treating physician) will also be
        allowed on this cohort.

          -  Patients with a history of obstructive jaundice due to the primary tumor must have a
             metal biliary stent in place,

          -  Eastern Cooperative Oncology Group (ECOG) performance status =< 1,

          -  Life expectancy > 3 months,

          -  Absolute neutrophil count (ANC) >= l500/ul,

          -  Hemoglobin >= 9g/dL,

          -  Platelets >= 100,000/ ul,

          -  Total bilirubin < 1.5 x upper limit of normal,

          -  Serum glutamic oxaloacetic transaminase (SGOT) and serum glutamic pyruvate
             transaminase (SGPT) < 2.5 x upper limit of normal for patients without liver
             metastases OR SGOT and SGPT < 5 x upper limit of normal for patients with liver
             metastases,

          -  Creatinine =< 1.5 x upper limit of normal,

          -  Measurable or non-measurable disease will be allowed,

          -  Women of child-bearing potential and men must agree to use adequate contraception
             (hormonal or barrier method of birth control; abstinence) prior to study entry and for
             the duration of study participation, up until 30 days after final study treatment;
             should a woman become pregnant or suspect that she is pregnant while participating in
             this study, she should inform her treating physician immediately,

          -  Patients taking substrates, inhibitors, or inducers of Cytochrome P450 3A4 (CYP3A4)
             should be encouraged to switch to alternative drugs whenever possible, given the
             potential for drug-drug interactions with irinotecan

          -  Signed informed consent.

        Exclusion Criteria:

          -  Prior chemotherapy or radiation therapy for any cancer,

          -  Inflammatory bowel disease (Crohn's disease, ulcerative colitis),

          -  Diarrhea, grade 1 or greater by the National Cancer Institute Common Terminology
             Criteria for Adverse Events (NCI-CTCAE, v. 4.0); pancreatic cancer patients with
             clinical evidence of pancreatic insufficiency must be taking pancreatic enzyme
             replacement,

          -  Neuropathy, grade 2 or greater by NCI-CTCAE, v. 4.0,

          -  Documented brain metastases,

          -  Serious underlying medical or psychiatric illnesses that would, in the opinion of the
             treating physician, substantially increase the risk for complications related to
             treatment,

          -  Active uncontrolled bleeding,

          -  Pregnancy or breastfeeding,

          -  Major surgery within 4 weeks,

          -  Previous or concurrent malignancy, except for adequately treated basal cell or
             squamous cell skin cancer, in situ cervical cancer, or any other cancer for which the
             patient has been previously treated and the lifetime recurrence risk is less than 30%,

          -  Patients with any polymorphism in UGT1A1 other than *1 or *28.