Use of estrogen replacement therapy, particularly when it includes the hormone progestin, significantly increases the risk that a woman will develop breast cancer by age 70, according to researchers at Harvard University, Boston, Massachusetts.
　　Earlier studies of the effects of postmenopausal hormone use on breast cancer risk have been limited by the inability to completely account for other risk factors, particularly age at menopause, Drs. Graham A. Colditz and Bernard Rosner explain in the November issue of the American Journal of Epidemiology.

In order to get around this issue, the investigators developed a model that calculates the cumulative risk of breast cancer resulting from several risk factors, and applied it to data collected on over 58,000 women followed for over 14 years.

The researchers report that in women who used unopposed postmenopausal estrogen from ages 50 to 60, the risk over time increased by 23% compared with women who had never used hormones. The risk was increased by 67% in those who used estrogen plus progestin.

Colditz and Rosner also found that a woman's cumulative risk of breast cancer to age 70 was increased by 57% if she had a history of benign breast disease, such as cysts.

Among other risk factors, the authors report that alcohol use increased the cumulative by 7% in women who reported one alcoholic drink per day from age 18 years, compared with nondrinkers. Family history of breast cancer, age at menopause, age that menstruation started, height and parity also affected the cumulative risk of breast cancer, according to the report.

In general, the findings are "consistent with a broad range of epidemiologic studies," Colditz and Rosner report. However, "the observation regarding risk in women with benign breast disease was unexpected." The researchers believe further studies are needed to identify the genetic and environmental factors that account for this association.

(From Reuters Health)