Estrogen effects assessed.

Estrogen effects assessed

A large study of the relationship between estrogen supplements and breast cancer in postmenopausal women adds lots of new numbers to the existing mountain of conflicting data. The study of 23,244 Swedish women suggests estrogen pills may increase a woman's risk of breast cancer significantly-or not at all-depending on the number of years she takes them, the type of estrogen used and whether the estrogen is taken with another hormone, progestin.

Estrogen therapy cuts the risk of cardiovascular disease in postmenopausal women and helps prevent osteoporosis. But after more than a dozen studies, its effects on the incidence of breast cancer remain uncertain. In the new report, researchers led by Leif Bergkvist at the University Hospital in Uppsala, Sweden, calculate a 10 percent added risk of breast cancer overall among postmenopausal women who take estrogen for an average of 5.7 years. The added risk exceeds 70 percent after nine years of use.

In contrast to previous U.S. studies, however, the Swedish numbers show no clear evidence of increased breast cancer risk among women who use conjugated estrogen - the kind most commonly prescribed in the United States. The Swedish researchers say they don't know if they would have recognized a small risk increase among these women, because only 20 percent of their group took conjugated estrogen and the doses were lower than those taken by most U.S. women. Estradio, another estrogen form, carried the highest risk, they say in the Aug. 3 NEW ENGLAND JOURNAL OF MEDICINE.

Progestin, increasingly prescribed with estrogen because of its ability to counter estrogen's links with endomentrial cancer, did nothing to lessen the women's risk of breast cancer and may even have increased it slightly. The researchers say their report highlights the need for further studies to solve estrogen's complex risk-benefit equation.