HapB3 and the deep intronic variant c.1129-5923 C>G of the dihydropyrimidine dehydrogenase gene (DPYD) to predict toxicity in stage III colon cancer (CC) patients (pts) (NCCTG Alliance N0147).

Abstract

508 Background: Severe adverse events (AEs) to 5-fluorouracil (5-FU) constitute a major dilemma in CC treatment. We recently demonstrated that specific deleterious DPYD variants in the coding region were highly predictive of grade >3 (G3+) AEs in stage III CC pts receiving adjuvant 5-FU based combination chemotherapy [Lee et al. JNCI. In press]. Other studies have suggested potential associations between AEs and non-coding DPYD variants: a novel haplotype (HapB3) containing three intronic variants (c.483+18 G>A, c.680+139 G>A, and c.959-51 T>C), one synonymous variant (c.1236 G>A, E412E), and a deep intronic variant (c.1129-5923 C>G) that affects pre-mRNA splicing. However, these studies included a diversity of cancer types, stages and treatments. The findings require further evaluation in a refined population. Methods: A total of 2,134 Caucasian stage III CC pts without DPYD*2A, D949V, and I560S variants from NCCTG N0147 trial who received adjuvant FOLFOX or FOLFIRI +/- cetuximab were genotyped by multiplexed single-base extension assays on the Sequenom MassARRAY. G3+ AEs were recorded (CTCAE v3) and classified as common to 5-FU treatment (5FU-AEs). Logistic regressions were used to assess the univariate and multivariate associations. Results: Analyzed pts displayed the following characteristics: 54.3% male, median age 59 [19-85], proficient MMR 87.5%, PS-0 76.5%, + irinotecan 8.5%, and + cetuximab 46.5%. Pts carrying c.1129-5923 C>G were significantly associated with higher risk of G3+ 5FU-AEs (Odds Ratio [OR]=1.539, 95% confidence interval [CI]=1.001 – 2.367, p=0.049). Only marginal association was observed for one of the HapB3 variants, c.1236 G>A (p=0.058). A linearly increasing risk of G3+ 5FU-AEs was identified for HapB3, comparing pts with no, one or >1 variant present (unadjusted OR=1.539, 95% CI=1.001 – 2.367, p=0.041; adjusted OR=1.198, 95% CI=0.998-1.437, p=0.052). Conclusions: In the largest study to date, c.1129-5923 C>G and HapB3 were predictive of 5FU-AE risk in stage III CC patients without DPYD*2A, D949V, and I560S variants receiving 5-FU-based combination chemotherapy.