Association of genetic variation with irinotecan infusion reactions and severe toxicity

Irinotecan treatment is often complicated by gastrointestinal, hematological, and infusion-related toxicities, the latter of which typically presents as acute cholinergic syndrome (ACS). While genetic variation in UGT1A1 increases toxicity risk, fewer studies have investigated variation in other genes. This study aimed to assess the impact of variation in other genes involved in irinotecan pharmacokinetics with irinotecan-related toxicity. This was a retrospective study of patients receiving standard irinotecan doses (180 mg/m2) with available genetic and clinical data. The primary analysis was to investigate the impact of carboxylesterase (CES) genetic variation on irinotecan infusion-related ACS. Exploratory secondary analyses evaluated variation in CES1, CES2, UGT1A7, UGT1A9, ABCB1, ABCG2, ABCC2, and SLCO1B1 with severe toxicity, treatment modification, diarrhea, and neutropenia. Univariate associations with P less than 0.05 were adjusted for UGT1A1*28 and UGT1A1*6 genotype. A total of 93 patients were included in this analysis. CES1 variants were not associated with infusion-related ACS. In the exploratory analysis, CES1 rs3785161 AA was associated with an increased likelihood of severe irinotecan toxicity (37 vs. 16%; P = 0.034), and ABCG2 rs2231142 AA/AC was associated with an increased likelihood of severe neutropenia (33 vs. 8%; P = 0.017). CES1 and ABCG2 variants may increase the risk of irinotecan toxicity. Further studies are needed to validate these associations to justify prospective studies investigating the clinical benefits of genetics-guided irinotecan dosing.