Dear Editor:Fluoropyrimidines are widely used in oncology. 5-Fluorouracil (5-FU) is the reference drug in the treatment of more than 50 % of the gastrointestinal, gynecological, and upper aerodigestive tract cancers. As most of anti-cancer drugs, it has a narrow therapeutic index leading to organ toxicities that could be lethal in 0.5 % of cases. Toxicity is linked to some specific parameters to patients (age, comorbidities, treatment duration) and genetic polymorphisms that can affect dihydropyrimidine dehydrogenase (DPD) key enzyme of fluoropyrimidine catabolism. Some mutations significantly modify DPD activity with more or less clinical impact. We report the clinical course and outcome of a 63-year-old woman exhibiting a complete DPD deficiency, leading to death after administration of only one standard dose of 5-FU infusion.Case reportA 63-year-old patient with no medical history underwent a sigmoidectomy because of a moderately differentiated Lieberkühnien adenocarcinoma (pT3pN1M0 ...