Results of a comprehensive pharmacogenetic analysis of dihydropyrimidine dehydrogenase in patients treated with fluoropyrimidines and patterns of polymorphisms partially related to treatment tolerability.

Abstract

e13057 Background: Metabolic clearance of fluoropyrimidines is highly dependent on the rate-limiting enzyme dihydropyrimidine dehydrogenase (DPD). Deficiency of DPD is associated with drug accumulation and severe toxicities. The DPD gene (DPYD) is highly polymorphic; however, except the G>A mutation in the splicing consensus sequence of intron 14 (IVS14+1G>A), which is responsible of severe enzyme impairment, the association of other variants with adverse reactions is unclear. Therefore, this study was aimed at examining the prevalence of DPYD variants in patients with toxicities and in subjects with good tolerability to fluoropyrimidine-based regimens. Methods: Patients affected by colorectal, breast and head/neck cancers requiring standard treatment with 5-FU or capecitabine in combination with other cytotoxic agents (irinotecan, oxaliplatin, cyclophosphamide or methotrexate) and/or antibodies (cetuximab or bevacizumab) were enrolled: 224 suffered from grade ≥2 non-hematological and ≥3 hematological toxicities (CTCAE v. 4) and 61 control patients developed adverse events to an extent not requiring dose-delay or reduction (i.e., <2 non-hematological and <3 hematological toxicities). DNA was extracted from blood and used to screen patients for known DPD variants (IVS14+1G>A, 496A>G, 1601G>A, 1627A>G, 1896T>C, 2194G>A and 2846T>C) by automatic sequencing. The study was approved by local Ethics Committee. Results: A complex pattern of DPYD variants was identified in both cohorts; the following genotypes were detected in patients with severe toxicities vs controls: 496AG+GG: 24.1 vs 21.3%; 1601GA: 12.5 vs 1.6%; 1627AG+GG: 37.1 vs 32.8%; 1896TC+TT: 6.25 vs 8.2%; IVS14+1GA: 4.9 vs 0%; 2194GA: 25.9 vs 9.8; 2846AT: 1.3 vs 0%. Conclusions: Although there was a higher prevalence of DPYD variants in patients with severe toxicities, their presence also in subjects with good tolerability suggest that their role needs to be re-evaluated, with the exception of IVS14+1GA and 2846AT which were found only in patients with poor tolerability. This study was supported in part by a grant from AIRC to R. Danesi.