Fluoropyrimidines are frequently used as anti-cancer treatment for gastro-intestinal malignancies, breast, head and neck cancer and others. The enzyme dihydropyrimidine dehydrogenase (DPD) is crucial in the first and rate limiting enzyme step of 5-fluorouracil (5-FU) catabolism. Reduced or complete deficiency leads to severe and even fatal toxicity. The Belgian Group of Digestive Oncology (BGDO) has agreed upon a recommendation on screening for DPD deficiency before starting treatment, which was endorsed by the Belgian Society of Medical Oncology (BSMO), the College of Genetics (CG), and the Toxicological Society of Belgium and Luxembourg (BLT). This article focuses on the clinical flows and practical recommendations. Both targeted germline genotype testing and phenotyping are supported. It was suggested to use a stepwise approach, with a phenotype testing upfront because of higher sensitivity and lower societal cost. In patients with uracil levels above 14 ng/ mL, targeted germline genotype screening should follow. Fluoropyrimidines are contra-indicated in patients with complete DPD deficiency and starting dose recommendations have been validated for patients with partial deficiency.
(BELG J MED ONCOL 2022;16(3):119–24)