[Two cases of advanced colorectal cancer with UGT1A1*28 homozygosity treated by FOLFIRI].

Severe neutropenia attributable to irinotecan hydrochloride (CPT-11) is reportedly associated with gene polymorphism of UGT1A1 related to its metabolism. Case 1 is a 70-year-old male patient with rectal cancer that had spread to the liver. Although he received six courses of mFOLFOX6, his hepatic metastasis recurred. Therefore, the regimen was switched to FOLFIRI. The CPT-11 dosage was 150 mg/m(2). Twelve days after the first course was attempted, neutropenia at grade 4 and a fever of 39 degrees C were found. Case 2 is a 65-year-old male whose sigmoid colon cancer had spread to the liver. We started FOLFIRI with a CPT-11 dosage of 120 mg/m(2). Nine days following administration of the first course, we found neutropenia of grade 3 and a fever of 38 degrees C. Analysis of the UGT1A1 gene polymorphism after symptom improvement revealed UGT1A1()28 homozygosity in both cases, which suggests that when FOLFIRI is conducted on a patient with homozygous UGT1A1()28, it is necessary to pay attention to neutropenia even with a CPT-11 dosage of 120 mg/m(2).