In the seminal study that assessed the potential association of UMPS polymorphisms with FP-toxicity, Ichikawa et al. (2006) reported a significant association between UMPS 638G>A variant (rs1801019) and 5-FU induced grade 3–4 toxicity in a cohort consisting of 69 5-FU treated colon or rectum cancer patients. This evidence concerns the gene UMPS and rectal cancer.