Direct comparison of the effect of 1,25D on six putative VDR target genes (CYP24A1, ITGβ3, SLC1A1, KDR, BIRC3, and GLUL)(37) in various breast cell lines indicated that, with the exception of CYP24A1, which was induced in all cell lines, breast cancer cell lines were less responsive to 1,25D than were immortalized cells with respect to induction or repression of the selected genes, despite reasonably comparable VDR expression. This evidence concerns the gene CYP24A1 and breast cancer.