Chemotherapy-related hyperbilirubinemia in pediatric acute lymphoblastic leukemia: a genome-wide association study from the AIEOP-BFM ALL Study Group

Abstract Background : Hyperbilirubinemia is a well-recognized but poorly understood adverse effect of chemotherapy for acute lymphoblastic leukemia (ALL). To analyze its impact on treatment outcome and to identify inherited genetic risk factors we evaluated hyperbilirubinemia in 1547 pediatric ALL patients and conducted a genome-wide association study (GWAS). Patients and Methods : Patients were treated in multicenter trial AIEOP-BFM ALL 2000 for pediatric ALL. Bilirubin toxicity was graded 0 to 4 according to the Common Toxicity Criteria (CTC) of the National Cancer Institute. In the GWAS discovery cohort, including 650 of the 1547 individuals, genotype frequencies of 745,895 single nucleotide variants were compared between 435 patients with hyperbilirubinemia (CTC grades 1-4) during induction/consolidation treatment and 215 patients without it (grade 0). Replication analyses included 224 patients from the same trial. Results : Compared to patients with moderate or no hyperbilirubinemia, patients with CTC grades 3-4 experienced more therapy delays, requiring 91 days to complete induction/consolidation versus 88 days for grades 1-2 and 89 days for grade 0 ( P =0.002). They also had a poorer 5-year event free survival with 76.6±3% versus 87.7±1% for grades 1-2 ( P =0.003) and 85.2±2% for grade 0 ( P <0.001), respectively, and a higher cumulative incidence of relapse with 15.6±3% compared to 9.0±1% (grades 1-2, P =0.08) and 11.1±1% (grade 0, P =0.007), respectively. In the GWAS, the rs6744284 variant T-allele in the UGT1A gene cluster, showed the strongest association with hyperbilirubinemia (allelic odds ratio (OR)=2.1, P =7x10 -8 ). TT-homozygotes had a 6.5-fold increased risk of hyperbilirubinemia (grades 1-4; 95% confidence interval (CI)=2.9-14.6, P =7x10 -6 ) and an impressive high risk of grade 3-4 hyperbilirubinemia (OR=16.4, 95% CI 6.1-43.8, P =2x10 -8 ). Replication (OR=2.3, 95% CI=1.5-3.7, P =2.4x10 -4 ) and joint analyses of both datasets (OR=2.1, 95% CI 1.7-2.7, P =6x10 -11 ) supported initial results. UGT1A is crucial for bilirubin conjugation and forms the mechanistic basis of Gilbert’s syndrome (GS). rs6744284 genotypes were strongly linked to the GS-associated UGT1A1 *28/*37 allele (r²=0.699), providing functional support for our findings. Of clinical importance, homozygosity for the rs6744284 T-allele counterbalanced the adverse prognostic impact of high hyperbilirubinemia on therapy outcome. Conclusions : Chemotherapy-related hyperbilirubinemia is a prognostic factor for treatment outcome in pediatric ALL and genetic variation in UGT1A aids in predicting the clinical impact of hyperbilirubinemia.