OUTLINE: Patients are genotyped for UGT1A1 enzyme and classified as "Gilbert's" (7/7), "heterozygotes" (6/7), and "homozygotes for allele 6" (6/6). The DNA is analyzed for the UGT1A1 coding region mutation (Gly71Arg) and CYP3A4 promoter polymorphism. Patients are also examined for glucuronidator ratio of SN-38, the active metabolite of irinotecan, and classified as "low/slow" (very low or zero SN-38G/SN-38 ratio), "intermediate" (less than 50% normal ratio), or "normal".