Testing for dihydropyrimidine dehydrogenase deficiency in New Zealand to improve the safe use of 5-fluorouracil and capecitabine in cancer patients

Dihydropyrimidine dehydrogenase deficiency is a rare inherited disorder. Approximately 3% of people of European ancestry are likely to have a partial deficiency in this enzyme. These individuals are typically asymptomatic until exposed to 5-fluorouracil (5-FU) or capecitabine (which forms 5-FU) for treatment of gastrointestinal or breast cancer. These individuals are then at considerably increased risk of severe to life-threatening adverse events. There are four well established risk variants within the DPYD gene that encodes dihydropyrimidine dehydrogenase. Although consensus guidelines for genotype-guided dosing of 5-FU and capecitabine have existed for a number of years, the implementation of this type of personalised medicine has not been widely adopted. This viewpoint covers the current state of knowledge about both genotype and phenotype testing, as well as the reported cost-savings and clinical effectiveness of pre-screening patients followed by dose-adjustment. Recent recommendations by agencies and professional societies, both in Europe and the USA, highlight the need for New Zealand oncologists to begin an informed discussion about whether it is now an appropriate time to advocate for routine access to testing for this enzyme deficiency in New Zealand cancer patients.