Considering his extreme toxicity despite a 50% dose reduction of capecitabine and a complete DPD deficiency according the second phenotyping test, DPYD full sequencing was carried out (using SOPHiA DDM® for Pharmacogenomics on a MiSeq Illumina Inc., United States) confirming the additional heterozygous presence of a NM_000110.4:c.2872A>G (p.K958E, rs141044036) variant, known to be associated with a total loss of DPD activity (Offer et al., 2014). Here, DPYD is linked to dihydropyrimidine dehydrogenase deficiency.