An easy-to-handle DPD deficiency test in saliva to identify patients at high-risk for life-threatening toxicity due to fluoropyrimidine therapy.

Abstract

e14019 Background: Severe dihydropyrimidine dehydrogenase (DPD) deficiency can be lethal in 0.5-3.0% of patients receiving fluoropyrimidines. Unfortunately, there is no routine test in medical practice to identify high-risk patients. Here, we evaluated the use of plasma and saliva uracil (U) to dihydrouracil (UH2) metabolic ratio and DPYD genotyping, as a means to identify patients with DPD deficiency and fluoropyrimidine toxicity. In addition, we report on a functional test using UH2/U metabolic ratio in dried saliva spots (DSS). Methods: Prior to fluoropyrimidine therapy, plasma and saliva samples were obtained from 60 patients with GI cancer. U and UH2 levels were measured by LC-MS/MS in plasma and saliva. Patients were also genotyped for DPYD (*7/*2A/*13/Y186C). WHO grading were used to report treatment toxicity. Results: In 21 patients (35%) toxicity was documented. For those, no variant allele carrier for DPYD was identified. The UH2/U metabolic ratios were 0.1-26.7 in plasma and 0.1-24.0 in saliva, with a higher correlation with toxicity grade in saliva as compared to plasma (rs 0.52 vs 0.28). Median metabolic ratios were lower in patients with severe toxicity as compared to those with no toxicity (0.59 vs 2.83 saliva; 1.62 vs 6.75 plasma, P < 0.01). A cut-off of 1.16 for the salivary UH2/U ratio was set (AUC 0.84) with 86% sensitivity and 77% specificity for the identification of grade 3-4 toxicity. A plasma cut-off of 4.0 (AUC 0.75) revealed a 71% sensitivity and 76% specificity. Moreover, saliva of 21 patients were applied to filter paper to obtain DSS and sent to the laboratory by regular mail. U and UH2 were stable in DSS stored at 45°C up to 7 days. In this set of patients, grade 3-4 toxicity was documented in 3/21 cases (14%), all three cases had metabolic ratios below 1.16 in DSS, confirming our prior results. Conclusions: DPYD genotyping failed to identify severe DPD deficiency, but the UH2/U metabolic ratios in saliva showed enough sensitivity and specificity to deserve further evaluation. DSS samples allowed medical oncologists working at distant sites to send us samples by post, with results available within a week. This test is being validated in a larger sample population.