Genetic Trial to Study Diarrhea in Patients With Stage III Colon Cancer Who Are Receiving Chemotherapy

OBJECTIVES: * Determine whether the presence of a 7 allele at the UGT1A1 locus is associated with either grade 3-4 diarrhea or grade 4 neutropenia in patients with stage III colon cancer after treatment with irinotecan, fluorouracil, and leucovorin calcium. * Determine whether polymorphisms in the TS enhancer and/or MTHFR gene are associated with grade 3-4 diarrhea in these patients after treatment with fluorouracil and leucovorin calcium. * Determine whether polymorphisms in UGT1A1, TS, MTHFR, CYP3A4, or CYP3A5 are associated with either grade 3-4 diarrhea or grade 4 neutropenia in these patients after treatment with irinotecan, fluorouracil, and leucovorin calcium. OUTLINE: Patients are stratified according to prior therapy (irinotecan, fluorouracil, and leucovorin calcium vs fluorouracil and leucovorin calcium) and prior toxic effects (grade 3-4 diarrhea vs grade 4 neutropenia vs grade 1 or lower diarrhea AND grade 2 or lower neutropenia). Patients undergo collection of blood specimens for polymerase chain reaction and restriction fragment length polymorphism analysis. Genotyping assays are performed to determine UGT1A1 promoter genotyping, UGT1A1 coding polymorphisms, TS promoter polymorphisms, and MTHFR polymorphisms.