Dihydropyrimidine dehydrogenase (DPD) is an enzyme that breaks down 5-FU. Some people have a deficiency of this enzyme. They're more likely to have severe or life threatening side effects from 5-FU.
Before starting FLOT, your treatment team will test your DPD levels. If you have low levels of DPD, a reduced dose of 5-FU may be used, or another type of treatment may be recommended.