patients with DPD mutation and 41.9% without DPD mutation presented AE. The most common AE in this population were gastrointestinal such as nausea (25.7%), constipation (14.3%), diarrhoea (11.4%) and vomiting (11.4%). No withdrawal treatments were registered. Conclusion and relevancePatients with DPD polymorphisms in our population completed treatment with 50% of the dose. AE were more prevalent in DPD mutation group. Determination of variants of DPD can help avoid serious or fatal EA.