DPYD (Dihydropyrimidine Dehydrogenase): DPYD is an enzyme that breaks down fluoropyrimidine drugs such as 5-fluorouracil (5-FU) and capecitabine, which are commonly used in cancer treatment. Genetic variations in DPYD can reduce the enzyme's activity, increasing the risk of severe toxicity, including bone marrow suppression and gastrointestinal side effects. Testing for DPYD helps identify individuals who may need dose adjustments or alternative treatments to enhance safety and effectiveness.