Genetic Analysis-Guided Irinotecan Hydrochloride Dosing of mFOLFIRINOX in Treating Patients With Locally Advanced Gastroesophageal or Stomach Cancer

PRIMARY OBJECTIVES: I. To determine the residual tumor (R) 0 resection rate. II. To determine the pathologic complete response (pCR) rate of up to 36 patients treated with 4 cycles of neoadjuvant mFOLFIRINOX (UGTA1A1 genotype-dosed irinotecan \[irinotecan hydrochloride\]) regimen. SECONDARY OBJECTIVES: I. Response rate (radiographic \[computed tomography (CT)\], and metabolic (positron emission tomography \[PET\] maximum standardized uptake value \[SUVmax\]) to chemotherapy. II. Chemotherapy-related toxicity. III. Surgical morbidity. IV. Overall survival (OS) measured from the time of histologic diagnosis. V. Disease-free survival measured from the time of histologic diagnosis. VI. Pattern of recurrence (distant, locoregional, both). VII. Human epidermal growth factor receptor 2 positive (HER2+) vs HER2 negative (-) difference in clinical outcomes. OUTLINE: PREOPERATIVE THERAPY: Patients receive oxaliplatin intravenously (IV) over 2 hours, leucovorin calcium IV over 2 hours, irinotecan hydrochloride IV over 90 minutes, and fluorouracil IV over 46 hours continuously on day 1. Courses repeat every 2 weeks for 4 courses in the absence of disease progression or unacceptable toxicity. SURGERY: Patients undergo surgery. POST-OPERATIVE THERAPY: Beginning 5-10 weeks after surgery, patients receive oxaliplatin IV over 2 hours, leucovorin calcium IV over 2 hours, irinotecan hydrochloride IV over 90 minutes, and fluorouracil IV over 46 hours continuously on day 1. Courses repeat every 2 weeks for 4 more courses in the absence of disease progression or unacceptable toxicity. After completion of study treatment, patients are followed up every 3 months for 2 years and then every 6 months for 3 years.