Endocrinology of breast cancer

Oestrogen predominance over progesterone may cause hyperproliferation of mammary epithelium and thus promote breast carcinogenesis. In patients with a hormone-dependent tumour, oestrogens may also accelerate cancer growth. Conversely, they may inhibit tumour growth in patients with an oestrogen receptor-negative carcinoma which has grown in an oestrogen-poor environment. Progesterone opposes oestrogen-induced epithelial proliferation and causes cellular differentiation with decreased mitosis, thus reducing the risk of breast cancer. Prolactin brings about mammary epithelial differentiation for secretory function; in the lactation state, epithelial proliferation is minimal. The role of androgens, melatonin, thymosin, metabolic hormones (growth hormone, thyroid hormone(s), insulin, glucocorticosteroids) and prostaglandins in the pathobiology of breast cancer is poorly understood. A breast cancer population consists of individuals in whom more than 20 different tumour subsets may be present, i.e. patients with different individual tumour pathobiology and endocrinology patterns and therefore different prognoses. Progress in the endocrinology of breast cancer seems possible through prospective studies in which hormones are determined in normal breast tissue (ductal fluid, cyst fluid) and then related to the corresponding concentrations in the plasma and urine of patients who develop breast cancer and those who do not. In addition, genetic and nonhormonal risk factors for breast cancer must be taken into consideration to define the endocrinological aspects involved.