The four 1,25D genes commonly upregulated in breast cancer cell lines, as well as KLK6 (kallikrein‐related peptidase 6)—a gene that was highly induced in both tumor explants and MCF7 cells—were confirmed as 1,25D regulated in breast cancer cell lines and in a subset of human clinical samples from normal tissue and breast cancer. Here, KLK6 is linked to breast carcinoma.