Clinical response to capecitabine in a DPYD*2A homozygous patient: Case report and therapeutic guidance.

Complete DPD deficiency (DPYD*2A/*2A) → standard fluoropyrimidine contraindication; ultra-low-dose capecitabine use (0.5-0.76% of standard dose) with PK monitoring

A 36-year-old male with metastatic rectal adenocarcinoma and complete DPD deficiency (DPYD*2A homozygous) received ultra-low-dose capecitabine (150 mg on days 1, 6, and 16 of a 21-day cycle, i.e., 0.76% of BSA-based standard dose) combined with oxaliplatin and cetuximab. Grade 3 mucositis led to a further dose reduction (150 mg on days 1 and 8, 0.50% of standard). Pharmacokinetic analysis confirms prolonged 5-FU exposure due to DPD deficiency even at ultra-low dose.

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Complete DPD deficiency is a formal contraindication to fluoropyrimidines, but this case shows that ultra-low-dose use with strict pharmacokinetic monitoring may be considered in patients with no therapeutic alternative. This therapeutic guidance data is valuable for oncologists and pharmacologists facing this rare but potentially lethal situation.

Clinical impact: 3/3 · Evidence strength: 1/3 · Novelty: 2/2 · Sample size: 0/1 · Publication status: 1/1 → Total: 7/10