Estrogens and breast cancer: present position.

Oestrogen is probably involved in breast cancer in two main ways: (1) in the aetiology of the disease as a promoting substance rather than as a carcinogen; (2) in stimulating the growth of at least some established breast cancers, acting through the oestrogen receptor. Successful modes of endocrine therapy would then be interpreted as interfering with (a) the supply of oestrogen to the tumour (b) the nuclear events in oestrogen action or (c) receptor replenishment.