Catalase (p < 0.001) and not GSH (p = 0.173) showed a statistically significant association with Vitamin D categorization, while the mean value of catalase in vitamin D-deficient cancer patients (173.85 U/mg Hb) was significantly lower than the respective values in cancer patients with insufficiency (196.29 U/mg Hb p = 0.019) and vitamin D sufficiency (211.69 U/mg Hb, p = 0.001). This evidence concerns the gene CAT and cancer.