Progesterone-induced secretion of growth hormone, insulin-like growth factor I and prolactin by human breast cancer explants.

The aim of the study was to evaluate the potential of human breast cancer tissue to secrete growth hormone (GH), insulin-like growth factor I (IGF-I) and prolactin in response to 10(-7) M progesterone stimulation. Explants were divided according to estrogen receptor (ER)/progesterone receptor (PR) phenotype (ER(-)PR(-); ER(+)PR(-); ER(+)PR(+); ER(-)PR(+)). Our results show distinct differences in cultured breast cancer tissue responses to progesterone stimulation with regard to secretion of proliferative agents such as GH, IGF-I and prolactin. All but ER(-)PR(-) breast cancer cell types responded in vitro to progesterone stimulation with an increase in local GH secretion, while in non-malignant tissue progesterone induced local GH secretion only in PR(+) cells. Moreover, only in PR(+) cells did progesterone stimulate local IGF-I and prolactin secretion, in both malignant and non-malignant tissue. This study provides evidence for the first time that in PR(+) breast cancer tissue, progesterone may increase GH, prolactin and IGF-I secretion in both malignant and surrounding non-malignant tissue. These hormones may act as local growth factors that stimulate the proliferation of mammary tumors.