Validation of DPYD variants DPYD*2A, I560S, and D949V as predictors of 5-fluorouracil (5-FU)-related toxicity in stage III colon cancer (CC) patients from adjuvant trial NCCTG N0147.

Abstract

3510 Background: Prediction of 5-FU-related adverse events (5FU-AEs) continues to be problematic. Pharmacogenetic studies on the rate-limiting enzyme in 5-FU metabolism, dihydropyrimidine dehydrogenase (DPD), suggest a link between three variants and both decreased enzyme activity and increased toxicity: c.1905+1 G>A (DPYD*2A; rs3918290), c.1679 T>G (I560S; DPYD*13; rs55886062), and c.2846A>T (D949V; rs67376798). Since the adverse impact of DPYD variants on 5-FU toxicity remains controversial, we determined associations between the three known DPYD variants and 5FU-AEs in stage III CC patients receiving FOLFOX or FOLFIRI (+ cetuximab) after curative resection. Methods: 2886 patients were genotyped by multiplexed single-base extension assays using the IPLEX Gold Kit and analyzed on the Sequenom MassARRAY system. Grade 3+ AEs were recorded per CTCAE v3. Fisher’s exact test, unequal variance two-sample t-test, and Wilcoxon rank sum test were used to compare categorical variables, continuous variables, and counts between patients with wild-type and mutant status. Logistic regressions were used to assess univariate and multivariate associations. Results: Patients displayed the following characteristics: male gender 53.2%, median age 58 [19-86], proficient DNA mismatch repair status 88.6%, PS-0 76.6%, + irinotecan 8.1%, and + cetuximab 45.9%. A total of 27 (0.9%), 4 (0.1%), and 32 (1.1%) patients carried the DPYD*2A, I560S, and D949V variants, respectively. Analysis identified significant associations between DPYD*2A and D949V variants and toxicity, with grade 3+ 5FU-AEs identified in 22 DPYD*2A carriers (OR=11.9, 95% CI 4.0-32.7, p<0.0001) and 22 D949V carriers (OR=5.5, 95% CI 2.5-12.1, p< 0.0001). No interaction effect was found between DPYD*2Aand D949V on grade 3+ 5FU-AEs (p = 0.98), nor on overall grade 3+ AEs (p = 0.97). No significant association was identified between I560S and grade 3+ 5FU-AEs. Conclusions: In the largest study to date, statistically significant associations were found between DPYD*2A and D949V variants and increased incidence of grade 3+ 5FU-AEs, suggesting utility in 5-FU toxicity prediction.