Pharmacogenomics — SCE Medical Oncology MCQ
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Correct answer: B — Offer pretreatment DPYD testing irrespective of the patient’s ethnicity
UK fluoropyrimidine safety practice offers pretreatment DPYD testing irrespective of self-reported ancestry. Offer pretreatment UGT1A1 testing across all ancestry groups: UGT1A1 predicts irinotecan toxicity rather than capecitabine toxicity. Offer pretreatment TPMT testing across all ancestry groups: TPMT testing applies to thiopurines rather than fluoropyrimidines. Offer pretreatment CYP2C8 testing across all ancestry groups: CYP2C8 is not the mandated capecitabine pharmacogenomic screen. Offer DPYD phenotyping after completing the first treatment cycle: risk assessment must precede fluoropyrimidine exposure.
Reference: MHRA fluoropyrimidines: test all patients for DPD deficiency before treatment (Published October 2020; current MHRA safety advice): https://www.gov.uk/drug-safety-update/5-fluorouracil-intravenous-capecitabine-and-tegafur-containing-products-test-all-patients-for-dpd-deficiency-before-initiation-to-identify-those-at-increased-risk-of-severe-and-fatal-toxicity; Capecitabine 500 mg UK summary of product characteristics (Current UK SmPC, accessed July 2026): https://www.medicines.org.uk/emc/product/14545/smpc