Highlight on DPYD gene polymorphisms and treatment by capecitabine (.).

BACKGROUND: Sequencing of DPYD exome was conducted in a prospective cohort of advanced breast cancer patients receiving capecitabine.

METHODS: A total of 243 patients were analyzed. Digestive, neurologic and hematotoxicity over cycles 1-2 showed 10.3% G3 and 2.1% G4, including one toxic death. DPYD exome, flanking intronic regions (20 bp), 3'UTR and part of 5'UTR (500 bp) were sequenced on MiSeq Illumina (Integragen, 97% coverage, HWE checked).

RESULTS: In total, 48 SNPs were identified: three in 3'UTR, 19 in coding regions (four synonymous including E412E; 15 missenses including D949V, V732I, R592W, I560S, I543V, S534N, S492L, M406I, D342G, M166V, T65M, C29R), 19 in flanking intronic regions (including *2A) and seven in 5'UTR. In total, 11 SNPs have not been previously described, including three missense variations each heterozygous in three separate patients: R696H, F100L and A26T. The patient with a toxic death carried one D949V allele. The three consensual variants *2A, D949V and I560S were carried by seven patients (heterozygous). Analysis of consensual variants showed that they were associated with G3-4 toxicity (OR = 21.0, sensitivity 16.7%) but not with G4 toxicity. Adding the variants previously associated with DPD deficiency in vitro, i.e. R592W, S492L and D342N/G, increased sensitivity on G3-4 (23.3%, OR = 21.1) and was predictive of G4 toxicity (sensitivity 40%, OR = 19.0). Of note, adding the new F100L variant further improved predictivity of genotyping on G4 toxicity (sensitivity 60%, OR = 42.8).

CONCLUSIONS: Present data establish the impact of consensual variants on capecitabine toxicity and reveal the existence of a novel DPYD variant, F100L, associated with G4 toxicity.