Capecitabine

Capecitabine, sold under the brand name Xeloda among others, is a chemotherapy medication used to treat breast cancer, gastric cancer and colorectal cancer. For breast cancer it is often used together with docetaxel.Wikipedia

Capecitabine is a prodrug that is selectively tumour-activated to its cytotoxic moiety, fluorouracil, by thymidine phosphorylase, an enzyme found in higher concentrations in many tumors compared to normal tissues or plasma.Drugbank

Most fluorouracil is metabolized by dihydropyrimidine dehydrogenase (DPD), encoded by the DPYD gene. A small proportion of patients develop extreme toxicity after administration of a fluoropyrimidine due to partial or complete DPD deficiency and hence a strongly reduced capacity to degrade 5-FU (also known as Folfox). 5-fluorouracil treatment may even result in a lethal outcome in patients with complete DPD deficiency. Mutations in the TPMT gene also increase risk for 5-FU toxicity.

PGx Table for Capecitabine (Xeloda)

Genotype/Genoset	Diplotype	Gene	Drug Use/Category/Class	Medical Field	Summary	Descriptive Sentence
gs313	Normal metabolizer	DPYD	Chemotherapeutic	Oncology	Normal Response Expected	You do not appear to carry any DPYD mutations linked to adverse side effects from capecitabine use.
gs312	Intermediate Metabolizer	DPYD	Chemotherapeutic	Oncology	Consider Half-Dose and/or Pharmacokinetic Studies	You carry a nonfunctional DPYD allele that increases your risk for a toxicity upon capecitabine administration; consider starting at half-dose and/or doing pharmacokinetic studies.
gs306	Poor Metabolizer	DPYD	Chemotherapeutic	Oncology	Avoid 5-FU; use an alternative drug	You may be at very high risk for severe toxicity from capecitabine administration; all major drug regulatory agencies recommend you select a non-fluoropyrimidine alternative chemotherapeutic.