Genomic and non-genomic actions of progestogens in the breast

• We summarize the available data on genomic and non-genomic effects of progestins in the breast.
• The structure and functionality of nuclear progesterone receptors is described.
• We highlight the action of progestogens in the normal human breast and in human breast cancer cells.
• We focus on the proliferative effect of progestogens on breast cancer cells via progesterone receptor component 1 in vitro.

Evidence is growing that progestogens may enhance breast cancer risk under hormone therapy in the postmenopause or hormonal contraception. However, differences may exist within the progestogen class and certain progestogens may have a higher potency in terms of breast cancer risk. The mechanism(s) by which these progestogens might influence breast cancer risk appear to be mediated via genomic and/or non-genomic effects triggered by activated progestogen receptors. In general, regulation of gene expression by progestogen receptors seems to be a multifactorial process involving both actions which often converge. In the present review, we describe the known genomic and non-genomic effects in the breast, especially focusing on the progestins.This article is part of a Special Issue entitled ‘Menopause’.