Oral contraceptives and risk of benign proliferative epithelial disorders of the breast

In a case‐control study conducted in Adelaide, South Australia, we investigated the hypothesis that use of oral contraceptives is associated with increased risk of benign proliferative epithelial disorders (BPED) of the breast, conditions strongly associated with increased risk of breast cancer and thought to have pre‐malignant potential. The study was restricted to women with no prior history of breast biopsy, and involved 383 cases of biopsy‐confirmed BPED, 192 controls whose biopsy did not show epithelial proliferation, and 383 unbiopsied community controls individually matched to cases by age and socio‐economic grading of area of residence. When cases were compared with community controls, the adjusted odds ratio (OR) for the association between ever‐use of oral contraceptives and risk of BPED was 1.1 (95% CI 0.7 to 1.7), while when cases were compared with biopsy controls, the adjusted OR was 0.9 (95% CI 0.5 to 1.5). There was little variation in risk of BPED with total duration of use of oral contraceptives, and with duration of use before first pregnancy, while current users had a statistically significant 60% reduction in risk, irrespective of the control group used for comparative purposes. Also, there was little variation in risk with years since first and last use of oral contraceptives, and there was no trend in the association between ever‐use of oral contraceptives and risk of BPED by degree of cytological atypia.