Hyperbilirubinemia in Lapatinib Treated Patients Is Associated with Gilbert's Syndrome UGT1A1 Polymorphism.

Background: Lapatinib, an oral EGFR/HER2 tyrosine kinase inhibitor, is approved in combination with capecitabine for the treatment of patients with advanced or metastatic HER2-positive breast cancer who have been treated previously with an anthracycline, taxane and trastuzumab. Treatment associated elevations in transaminases and bilirubin have been observed in lapatinib clinical trials. A common TA repeat polymorphism in the promoter region of uridine diphosphoglucuronyl transferase ( UGT1A1 *28, TA7 allele) reduces UGT1A1 enzyme levels and has been associated with hyperbilirubinemia for a range of drugs. We sought to determine the effect of the UGT1A1 *28 variant on bilirubin elevation in lapatinib treated patients. Patients and Methods: Association between the UGT1A1 TA repeat polymorphism and total bilirubin levels (TBL) was examined in lapatinib treated patients using data pooled from 12 trials in advanced and metastatic breast cancer. A total of 899 lapatinib treated (as monotherapy or combined with chemotherapy) patients provided a germline DNA sample and were available for this analysis. UGT1A1 TA repeat genotype was determined by PCR amplification and sequencing. For case-control analysis, patients were defined as having normal TBL at baseline, with on-treatment TBL ≥1.5 and ≤1 times upper limit of normal for cases and controls, respectively, and at least 13 weeks of treatment for controls. Results: The UGT1A1 TA repeat polymorphism strongly correlated with lapatinib associated hyperbilirubinemia. A significant association (P=1.03x10 -5 , 60 cases and 396 controls) was observed. For hyperbilirubinemia cases, 21/60 (35%) were carriers of two TA7 alleles and 28/60 (47%) were carriers of one TA7 allele. Overall, when compared with other genotypes, the odds ratio (95% confidence interval) of the TA7/TA7 genotype for developing hyperbilirubinemia was 10.7 (5.3-21.6). Conclusion: These data suggest that UGT1A1 *28 accounts for the major proportion of total bilirubin elevation observed during lapatinib treatment. This is consistent with an underlying predisposition to Gilbert9s syndrome. Given the life-threatening nature of advanced and metastatic breast cancer and the benign clinical course of Gilbert9s syndrome, these data support treatment continuation with lapatinib for patients with mild to moderate, isolated, indirect bilirubin elevation, when accompanied by appropriate ongoing safety evaluation (eg, bilirubin fractionation, ALT evaluation) to exclude liver injury risk in these patients. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 1112.