Final answer:
DYPD testing is not routinely performed in patients taking 5-FU. It is only done in specific cases where a patient is at a higher risk of toxicity. DYPD is an enzyme responsible for the metabolism of 5-FU.
Step-by-step explanation:
Prospective DYPD testing is not routinely performed in patients taking 5-FU. DYPD is an enzyme that is responsible for the metabolism of 5-FU in the body. Some patients may have a deficiency in this enzyme, which can increase their risk of experiencing severe side effects from 5-FU treatment. However, DYPD testing is not widely available and is typically only performed in specific cases where a patient is at a higher risk of toxicity.