Estrogen replacement therapy and benign breast disease.

The relationship between estrogen replacement therapy (ERT) and the risk of benign breast disease (BBD) was examined among 929 postmenopausal cases and 846 postmenopausal controls identified through a large breast cancer screening program. Prior use of ERT among postmenopausal women was associated with an increased risk of both fibrocystic breast disease [odds ratio (OR) = 1.4; 95% confidence interval (Cl) = 1.1-1.8] and fibroadenoma (OR = 1.6; Cl = 0.8-3.5). The risk of all BBD rose with increasing years of use (OR = 1.9 for greater than or equal to 15 yr of total use) and with years since initial use (OR = 1.6 for greater than or equal to 15 yr since first use). Among users of the conjugated estrogen Premarin, increased risks were found at all but the lowest dose. Finally, risks associated with ERT were higher in women with a bilateral oophorectomy than in other postmenopausal women. These results suggested, overall, an increased risk of BBD associated with ERT.