UDP-glucuronosyltransferase 1A1 (UGT1A1) is an enzyme that catalyzes glucuronidation of substances, including bilirubin and other drug metabo lites. Certain UGT1A1 polymorphisms reduce UGT1A1 activity, notably UGT1A1*28 contains thymine-adenine repeats in the TATA box of the promo tor region. Irinotecan, a chemotherapy agent for solid cancers, is converted in the body to an active metabolite, SN-28, and then excreted, after
being conjugated with glucuronide by UGT1A1. If UGT1A1 activity decreases (e.g. UGT1A1*28), the risk of irinotecan toxicity increases, which can
develop into severe neutropenia and diarrhea. UGT1A1*37, a rare allele that has never been found in Asians, was previously reported to be asso ciated with severe neutropenia by reducing UGT1A1 activity further than UGT1A1*28. In this study, we first detected UGT1A1*37 in a 69-year-old
Korean woman diagnosed with pancreatic cancer and excluded irinotecan from her chemotherapy regimen, in consideration of the increased risk
of toxicity, based on pre-treatment UGT1A1 genotyping.