Capecitabine-induced severe adverse events-therapeutic drug monitoring and DPYD -gene analysis are recommended.

In this report, two cases of patients with severe adverse events after an adjuvant treatment with capecitabine are described in detail. The first patient suffered from a severe ileocolitis, where ultimately intensive care treatment, total colectomy and ileum resection was necessary. The second patient experienced a toxic enteritis, which could be managed conservatively. Post-therapeutic DPYD genotyping was negative in the former and positive in the latter case. Patients can be categorised in normal, moderate and poor DPYD metabolisers to predict the risk of adverse events of capecitabine treatment. Guidelines in various European countries recommend pretherapeutic DPYD genotyping, whereas it is not recommended by the National Comprehensive Cancer Network in the USA. Irrespective of DPYD genotyping, strict therapeutic drug monitoring is highly recommended to reduce the incidence and severity of adverse events.