Predictive testing for DPD deficiency in a patient with familial history of fluoropyrimidine-associated toxicity

Reduced activity of DPD leads to severe toxicity in cancer patients receiving standard doses of fluoropyrimidines, particularly in the case of combination regimens. We describe a 38-year-old man with a resectable metastasis from hereditary nonpolyposis colorectal cancer, with indication of neoadjuvant chemotherapy and a family history of fluoropyrimidine-associated toxicity. We tested our patient for functional DPYD variants, before any choice of the neoadjuvant regimen, including for the c.496A>G, already described in his mother, and a deep intronic variant c.1129-5923C>G recently reported associated to severe toxicity. Our patient was found to be heterozygous for both c.469A>G and c.1129-5923C>G DPYD variants. We thus offered the most active perioperative regimen, capecitabine, oxaliplatin, irinotecan plus bevacizumab by which we reduced the dosing of capecitabine to 50%. Treatment was well tolerated, with grade 2 diarrhea as the most significant adverse event, and led to a complete pathological response after liver resection. We provide a rationale approach to improve the safety of fluoropirimidine-based therapy in a patient with family history of fluoropyrimidine-associated toxicity.