Aetiology of breast cancer: a brief review.

Cancer of the human breast is probably a group of diseases which have different causes. Changes in hormonal status that increase breast cancer risk probably do so by 'promoting' tumour development rather than by 'initiating' it. Exogenous oestrogens seem to act as tumour promoters in this context, but there is to date no evidence that oral contraceptives, some of which contain oestrogens in low dosage, increase breast cancer risk. On the contrary, they appear to reduce the incidence of benign breast tumours. Prolactin-release is associated with increased mammary tumour incidence in rats but not in humans. There is no evidence that viruses or exposure to hair-dyes increase breast cancer risk. The fact that slight dietary restriction can dramatically reduce mammary tumour incidence in rats, suggests that dietary factors should be looked at more closely in the search for aetiological factors in man.