Estrogen alpha and progesterone receptor expression in the normal mammary epithelium in relation to breast cancer risk

Estrogens play a central role in the etiology of breast cancer, and results from observational studies and randomized trials have also implicated progestins. The effects of these hormones in the mammary tissue are exerted through binding with specific receptor proteins in the cell nucleus. It has been proposed that higher estrogen receptor alpha expression in the normal breast epithelium may increase breast cancer risk. In a study in Greece, we determined estrogen alpha and progesterone receptor expression in normal mammary tissue adjacent to the pathological tissue from 267 women with breast cancer and 299 women with benign breast disease. Mouse monoclonal antibodies specific for estrogen receptor alpha and progesterone receptor were applied. The H-index, which incorporates frequency and intensity of staining of the cells, and can range from 0 to 300, was deemed positive when it exceeded 9. Among premenopausal women, there was no evidence for an association with breast cancer risk for expression of either type of receptors. Among postmenopausal women, breast cancer risk was inversely associated with expression of both estrogen alpha (odds ratio (OR)=0.39; p=0.015) and progesterone (OR=0.40; p=0.008) receptors. The hypothesis that overexpression of estrogen receptors alpha or progesterone receptors in normal breast epithelium may increase the risk of breast cancer was not supported by our data. Instead, we found evidence that overexpression of these receptors may be associated with reduced risk for breast cancer in line with the well-known association of expression of these receptors in the malignant tissue and better breast cancer prognosis.