Conjugated estrogens and fibrocystic breast disease.

The association between replacement estrogen use and subsequent development of fibrocystic breast disease was studied at Group Health Cooperative of Puget Sound. Included were 142 women aged 50-64 years diagnosed by biopsy as having fibrocystic breast disease during the years 1978 through 1983. The relative incidence of hospitalization for estrogen users compared with non-users was 1.9 (95% confidence interval 1.3-2.7). The association became stronger with increasing duration of estrogen use.