DPYD (Dihydropyrimidine Dehydrogenase): DPYD is an enzyme responsible for breaking down fluoropyrimidine drugs, such as 5-fluorouracil (5-FU) and capecitabine, commonly used in cancer treatment. Genetic variations in DPYD can lead to reduced enzyme activity, increasing the risk of severe toxicity, including bone marrow suppression and gastrointestinal side effects. Testing DPYD helps identify individuals who require dose adjustments or alternative treatments to improve safety and effectiveness.