ABSTRACT
The controversy surrounding oral contraceptive use and breast cancer risk arose from epidemiologic studies, yet the direct effect of such use on breast tissue remained undefined. Breast epithelial proliferation was assessed by [3H]thymidine labelling of normal lobular units dissected from benign biopsies of 347 females aged 14-48 years. Factors shown to influence this response included cycle phase, time since menarche (breast age), and parity status. Multivariate analysis allowing for these influences was used to compare activity of natural cycles and those artificially regulated by oral contraceptives. The increased activity in nulliparous oral contraceptive users was highly significant (p 0.005). Comparing the effect of differences in oral contraceptive type, whether combined, triphasic, progestin only, or according to oestrogen or progestin content, showed a heterogeneity in response that was significant (p 0.01). Examined specifically, the formulation of oral contraceptive according to progestin content did not have a significant influence although progestin-only oral contraceptives were most active, while the influence of increasing oestrogen content was significant (p 0.05). However, emphasis was placed on acknowledging the multiple factors and interactive processes responsible for breast epithelial stimulation when considering strategies or intervention.
