Genetic polymorphisms of the adenosine triphosphate-binding cassette transporters (ABCC2, ABCG2) and irinotecan toxicity in cancer patients

13096 Background: Irinotecan is subject to substantial interindividual variability in pharmacokinetic and the occurrence of unpredictably severe toxicities of leukopenia or diarrhea. These toxicities have been reported to be associated with increased levels of SN-38, the active metabolite of irinotecan. ABCC2 and ABCG2, members of adenosine triphosphate-binding cassette transporters, are involved in mediating the elimination of anionic antitumor drugs, such as SN-38 and SN-38G. Recently, Innocenti et al. reported SN-38G AUC and SN-38G/SN-38 AUC ratios were correlated with ABCC2 3972T>C. The variant ABCG2 421C>A was associated with low ABCG2 expression levels and altered sensitivity to several drugs, including SN-38, in vitro as compared with the reference-type protein. Methods: We assessed whether the variants ABCC2 3972T>C and ABCG2 421C>A would be associated with severe toxicity (leucopenia of grade 4 and/or diarrhea of grade 3 or worse) in 120 Japanese cancer patients in which 27 patients experienced severe toxicity. Results: 74 patients (62%) were homozygotes for the reference allele of ABCC2 3972T>C, 39 heterozygous (33%), and 7 homozygous (6%) for the variant, whereas 62 patients (52%) were homozygous for the reference allele of ABCG2 421C>A, 48 heterozygous (40%) and 10 homozygous (8%) for the variant. Logistic regression analysis did not show any significant associations between the occurrence of severe toxicity and carrying these variants (see Table ). Conclusions: It suggests that genotyping of ABCC2 3972T>C and ABCG2 421C>A would not be useful for predicting severe toxicity caused by irinotecan. [Table: see text] No significant financial relationships to disclose.