Treating patients with dihydropyrimidine dehydrogenase (DPD) deficiency with fluoropyrimidine chemotherapy since the onset of routine prospective testing—The experience of a large oncology center in the United Kingdom

Background

Fluoropyrimidine chemotherapy is used across many tumor types and settings. The incidence of severe adverse events (SAEs) is around 20%. Mortality is 0.5%-1%. Dihydropyrimidine dehydrogenase (DPD) plays a key role in fluoropyrimidine inactivation. Key DPYD mutations are linked to a high risk of SAEs. Pretreatment DPD screening was mandated by EMA guidelines in April 2020 and widely adopted thereafter. Uncertainty remains regarding optimal dosing practice.

Methods

We retrospectively examined records of all 23 patients with DPYD mutation who started chemotherapy between April and November 2020. Our center tests for the mutations considered clinically actionable by Clinical Pharmacogenetics Implementation Consortium and uses the Gene Activity Score (GAS) to guide dose reduction.

Results

Most patients started on a 50% dose. One started on 100% and experienced mild diarrhea after cycle 2; DPD was tested belatedly, subsequent cycles were reduced to 50% and he remained well. Three patients receiving chemo-radiotherapy started on 76% dose; 50% was felt to be subtherapeutic. One of them had no toxicities; another had grade 2 nausea and a hospital attendance with non-neutropenic fever; the third was admitted for 6 weeks with pancolitis. Seven patients did not have toxicities above grade 1 and no hospital attendances. Five patients had further dose reductions. None had dose escalation.

Conclusion

As our experience shows, patients with DPD deficiency are heterogeneous. Worryingly, SAEs occur despite dose reduction according to GAS. Others had minimal toxicity and may be under-dosed by GAS. There are clearly many factors at play other than the 4 DPYD variants. The DPD result must be available and inform first cycle dosing. Dose should be cautiously titrated up if tolerated; this was not done at our center due to clinician caution. Further research is needed to guide this. Patients should be reviewed frequently, counselled regarding their DPD status, and empowered to seek advice promptly when they feel unwell.