Pretherapeutic uracil and dihydrouracil levels in saliva of colorectal cancer patients are associated with toxicity during adjuvant 5-fluorouracil-based chemotherapy

5-fluorouracil (5-FU) competes with uracil (Ura) as a substrate for dihydropyrimidine dehydrogenase (DPD). Low DPD activity impairs breakdown of Ura to dihydrouracil (UH2) and is associated with toxicity during 5-FU-based chemotherapy. Calculation of the 5-FU dose is based on body surface area, and new tools are needed to individualize treatment. The aim of study was to measure Ura and UH2 in saliva of patients with colorectal cancer and relate levels to treatment-induced toxicity. Saliva was collected from 73 patients with stage III colorectal cancer prior to adjuvant 5-FU-based treatment. Ura and UH2 were analyzed by a column-switching HPLC method. Toxicity was evaluated before each treatment cycle and the highest grade was noted at end of treatment. Toxicity was more common and severe among women compared with men. The Ura and UH2 concentrations in saliva were 5.0 ± 6.8 and 5.0 ± 4.0 nmol/ml, respectively. The UH2/Ura ratio was lower in women compared with men (1.2 ± 1.0 and 2.2 ± 2.5, respectively, p = 0.0026). Patients who needed to reduce the drug dose during treatment (or terminate treatment) due to toxicity had a lower ratio (1.3 ± 0.85) compared to patients who completed treatment without dose reduction (4.1 ± 4.3, p