Based on this study and reported data we concluded that the potentiation of antitumor activity observed in the combined treatment of MCF-7 tumor-bearing mice is accomplished in two ways: reducing the activity of aromatase by both anastrozole (enzyme inhibition) and vitamin D compounds (switched off/decreased aromatase gene expression, decreased expression of other genes related to estrogen signaling) and by regulation of the expression of the estrogen receptor ERα and VDR. This evidence concerns the gene CYP19A1 and neoplasm.