TKTL1 and breast cancer: Thus, in this study, we sought to analyze by immunohistochemistry the expression of TKT, a key enzyme in the non-oxidative part of the PPP, and TKTL1, a TKT isoform frequently reported in human tumor related pathways, in a retrospective patient cohort with invasive canine mammary tumor as well as in normal and hyperplastic mammary glands.