Genotype-guided Dosing of mFOLFIRINOX Chemotherapy in Patients With Previously Untreated Advanced Gastrointestinal Malignancies

PRIMARY OBJECTIVES: I. To determine the dose-limiting toxicity (DLT) rate in cycle #1 in each of two UGT1A1 genotype groups (\*1\*1, \*1\*28) using genotype-guided dosing of irinotecan as part of the modified (m) FOLFIRINOX regimen. SECONDARY OBJECTIVES: I. To determine the cumulative dose intensity of irinotecan achieved in each genotype group. II. To determine the response rates by Response Evaluation Criteria in Solid Tumors (RECIST) (version 1.1) for each different disease (pancreatic cancer, biliary cancers, gastric cancer, colorectal cancer, adenocarcinoma of unknown primary) treated in the study. OUTLINE: Patients receive oxaliplatin intravenously (IV) over 2 hours, irinotecan hydrochloride IV over 1.5 hours, leucovorin calcium IV over 2 hours, and fluorouracil IV continuously over 46 hours on days 1 and 15. Treatment repeats every 4 weeks for up to 6 courses in the absence of disease progression or unacceptable toxicity.