LAUSR

The correlation between DPYD*9A (c.85T>C) genotype and dihydropyrimidine dehydrogenase (DPD) deficiency phenotype is controversial. In a cohort of 28 patients, DPYD*9A was the most commonly diagnosed variant (46%) and there was a noticeable genotype-phenotype correlation. Here we genotyped a larger cohort of a mixed racial background to explore the incidence of DPYD*9A variant and to further study the genotype-phenotype correlation. Genotyping for high-risk DPYD variants (DPYD*2A, DPYD*13, and DPYD*9B) and the DPYD*9A variant was performed on 113 patients with gastrointestinal malignancies (GI) treated with fluoropyrimidines, using TaqMan chemistry. The prevalence of different DPYD variants was further analyzed in 1,283 retrospective data from ARUP laboratories. Fluoropyrimidines-associated toxicity was graded according to the National Cancer Institute Common Terminology Criteria for Adverse Events (v 5.0). Fisher’s exact test was used for statistical analysis. In total, 1,283 were retrospectively reviewed for DPYD variants. Four patients (0.31%) carried DPYD c.-1590T>C, 10 patients (0.55%) carried DPYD c.1679T>G (*13), 36 patients (2.8%) carried DPYD c.2846A>T, and 527 patients (41.1%) carried DPYD c.85T>C (*9A). In the GI cancer cohort, DPYD variants were identified in 61 patients (54%), showing similar prevalence as the retrospective analysis. Caucasians represented 54% and African Americans represented 43%. Twenty-eight patients (46%) were females. Heterozygous DPYD*9A was identified in 46 patients (41%) and homozygous DPYD*9A was identified in 11 patients (10%). DPYD*2A was identified in 3 patients and DPYD*9B was identified in 2 patients (one patient had double heterozygous *9A and *9B). Grade 3 to 4 toxicities were experienced in 26 patients with mutant DPYD*9A (3 patients had homozygous DPYD*9A) and in 20 patients with no identified DPYD mutation (P = .7035). In patients who received full-dose fluoropyrimidines (N = 85), grade 3 to 4 toxicities were experienced in 22 patients with mutant DPYD*9A (2 patients had homozygous DPYD*9A) and in 17 patients with no identified DPYD mutation (P = .8275). In the GI cancer population, the DPYD*9A variant was identified in 54% of patients. The correlation between DPYD*9A variant and DPD clinical phenotype was not significant. The noticeable correlation that was previously reported is likely due to small sample size and selection bias.