CYP19A1 and neoplasm: All three concentrations of calcitriol tested exerted significant tumor inhibitory effects, and maximal inhibition was seen with the highest dose used (0.1 μg/mouse). Of note, the combined treatments caused higher inhibition of estrogen synthesis in the tumor microenvironment as reflected by estrogen levels measured in the tumors and surrounding mammary fat.Calcitriol decreased aromatase expression in various tissues.