Which enzyme deficiency puts patients at high risk for severe, life-threatening toxicity when treated with 5-Fluorouracil (5-FU) or Capecitabine?
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Correct answer: Dihydropyrimidine dehydrogenase (DPD)
DPD is the rate-limiting enzyme in the catabolism of fluoropyrimidines. Patients with DPYD genetic variants (DPD deficiency) cannot clear 5-FU effectively, leading to profound hematologic and gastrointestinal toxicity.
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