Oral contraceptives and breast cancer: the current controversy.

Abstract

This article reviews current knowledge of breast cancer etiology and attempts to evaluate conflicting research findings on the effects of oral contraceptives (OCs) on breast cancer risk. Breast cancer is associated with age at menarche and menopause, suggesting a link with hormones of the pituitary-gonadal axis. In addition, there is a strong relationship between weight and postmenopausal breast cancer risk. The risk decreases with increased parity. The apparent protective effect of parity may be due to the relationship between parity and age at 1st fullterm pregnancy. The initial harmful effect of the 1st fullterm pregnancy may be caused by the tremendous growth of breast epithelium during pregnancy. Finally, progesterone may be positively associated with breast cancer risk. Mitotic activity is considered the explanation for the protective effect of OCs against endometrial but not breast cancer. It can be predicted that combination OCs with high estrogen and progestogen content will produce the greatest mitotic activity and thus are most likely to increase the risk of breast cancer. The increased risk is likely to be caused by such OC use either at perimenopausal ages or at very young ages when long and frequent anovular cycles are common. Further research on breast mitotic activity in women on different OCs is needed to construct a rational classification scheme for OCs. A policy of prescribing OCs with a low dose of both estrogen and progestogen appears to be warranted.