Dihydropyrimidine dehydrogenase (DPD) is a metabolic enzyme that is crucial in 5-fluorouracil (5-FU) degradation. A deficiency in it is associated with the occurrence of adverse events following fluoropyrimidine-based therapies. We describe a case of toxicity grade 5 after the administration of capecitabine and oxaliplatin in a patient with stage III colorectal cancer and DPD congenital deficiency, which was identified later. Several polymorphisms have been associated with the global toxicity of 5-FU; however, genetic tests are low in sensitivity and therefore they cannot as yet be used as prescreening techniques in clinical practice.

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