Severe toxicities after irinotecan-based chemotherapy in a patient with lung cancer: A homozygote for the SLCO1B1*15 allele

Irinotecan is used widely in the treatment of several malignancies, but unpredictable severe toxicites such as myelosuppression and delayed-type diarrhea are sometimes experienced. Polymorphisrh of the UGT1A1 gene is one of the likely reasons for interindividual differences in irinotecan pharmacokinetics and severe toxicity. Also, polymorphic organic anion-transporting polypeptide 1131 (OATP1B1, SLCO1B1) is reported to be involved in the hepatocellular uptake of SN-38. A 61-year-old man with lung cancer developed severe toxicities, including grade 3 diarrhea, grade 4 leukopenia, and grade 4 neutropenia, after the first cycle of irinotecan (60 mg/m(2)) plus cisplatin chemotherapy. The irinotecan and SN-38 areas under the concentration-time curve from time zero to infinity in this patient were 43% and 87% higher than the corresponding mean values for 10 other patients with lung cancer treated with irinotecan (60-100 mg/m(2)) normalized for the dose of irinotecan. Analysis of genetic variants in genes encoding the drug-metabolizing enzyme (UGT1A1) and transporter (SLCO1B1) involving irinotecan disposition revealed, that this patient was homozygous for the SLCO1B1 *15 allele, which may result in severe toxicities attributable to the extensive accumulation of SN-38 Screening of SLCO1B1 *15 is suggested to be useful in irinotecan chemotherapy to avoid unpredicted severe toxicity, although the homozygous genotype is rare among the Japanese.