Application of dihydropyrimidine dehydrogenase deficiency testing for the prevention of fluoropyrimidine toxicity: a real-world experience in a Southern Italy cancer center

Fluoropyrimidines (FPs) are antineoplastic agents used for the treatment of various solid tumors, especially gastrointestinal cancers. Patients with variations in dihydropyrimidine dehydrogenase gene (<i>DPYD</i>), which can determine the partial or complete deficiency of the dihydropyrimidine dehydrogenase enzyme (DPD), are at an increased risk of developing severe and potentially life-threatening toxicity. Worldwide the introduction of pharmacogenetic testing into clinical practice has been a slow process and in our center the analysis of the <i>DPYD</i> gene has been adopted since April 2020. We evaluated the clinical application of routine DPYD screening and its ability to prevent early-onset of fluoropyrimidine-related toxicity in patients treated at the Oncology Reference Center of Basilicata (IRCCS-CROB), a recognized cancer centre in Southern Italy. From April 2020 to November 2022, 300 patients (male 137; female 163) diagnosed with various types of cancer were subjected to <i>DPYD</i> genotyping, before starting treatment with FPs. In accordance with the current European Medicines Agency (EMA) and the Italian Association of Medical Oncology (AIOM) guidelines patients were tested for four <i>DPYD</i> variants that are associated with reduced DPD activity. FPs dose adjustments in <i>DPYD</i> variant carriers were made following the previously mentioned guidelines. Three hundred patients underwent <i>DPYD</i> testing and thirteen (4.3%) patients were found to be heterozygous variant carriers; ten out of thirteen patients received FP dose reduction as indicated by the guidelines, one out of thirteen patients received alternative treatment, two of the thirteen patients received no treatment at all. The main toxicities observed in patients who received a <i>DPYD</i> genotype-based dose reduction were anemia, neutropenia, nausea and mucositis but events were primarily grade 1 or 2. Our experience confirms the technical feasibility and the usefulness of <i>DPYD</i> genotyping to reduce the risk of severe FPs toxicities.