The US FDA is urging oncologists to test patients for variants of the DPYD gene before starting treatment with capecitabine (Xeloda) and other widely used chemotherapies. Deficiency of the enzyme dihydropyrimidine dehydrogenase (DPD), which is encoded by this gene, can lead to severe toxicity when treated with these drugs. Oncologists have a duty to inform patients about the risks associated with DPD deficiency before starting treatment. Testing for DPYD variants is important for patient safety and prevention of serious adverse events. The FDA issued these recommendations based on observations of serious toxic reactions in patients with DPD deficiency. The goal is to improve the safety of treatment and reduce the risk of complications when using these chemotherapy drugs.