Calcitriol supplementation effects on Ki67 expression and transcriptional profile of breast cancer specimens from...

High concentration of 1,25(OH)2D3 (50-100 nM), which cause hypercalcemia in vivo, induce the hormone transcriptional targets and exert antiproliferative effects in cultured breast cancer lineages, however, no studies investigated whether these effects might be reproduced in tumor specimens in vivo. Our aim was to evaluate the effects of calcitriol supplementation on the proliferative index (Ki67 expression) and gene expression profile of post-menopausal breast cancer samples.

Tumor samples were collected from 33 patients, most of whom (87.5%) presenting 25(OH)D3 insufficiency, before and after a short term calcitriol supplementation (0.50 μg/day PO, for 30 days). Tumor dimension remained stable in ultrasound evaluations. A slight reduction in Ki67 immunoexpression was detected, however in only 10/32 post-calcitriol samples an expressively low proliferative index [Ln (%Ki67+) < 1] was achieved. Gene expression from 15 matched pre/post-supplementation samples was analyzed by microarray (U133 Plus 2.0 GeneChip, Affymetrix) and 15 genes were over-expressed in post-supplementation tumors, including FOS and EGR1, which were previously shown to be regulated by vitamin D. However, these results were not confirmed in another four breast cancer samples.

Calcitriol supplementation is neither sufficient to expressively elicit an antiproliferative response nor to induce the hormone transcriptional signaling pathway in breast cancer specimens.