June 10, 1999 CHICAGO --- Using hormone replacement therapy during menopause increases a woman's risk for developing some types of breast cancer that occur rarely, but not the more commonly occurring ductal carcinoma that remains confined to the site of origin or invasive ductal or lobular cancer.
These are the findings of a study by researchers from Northwestern University Medical School and the Mayo Clinic that appears in the June 9 issue of The Journal of the American Medical Association.
Susan M. Gapstur, assistant professor of preventive medicine, and Monica Morrow, M.D., professor of surgery, of Northwestern, and Thomas A. Sellers, of the Mayo Clinic, studied over 37,100 postmenopausal women in the Iowa Women's Health Study to determine if use of hormone replacement therapy was associated with subsequent risk for specific types of breast cancer.
"We observed a positive, dose-response relationship between duration of postmenopausal hormone use and incidence of breast cancer with a favorable prognosis; this relationship appeared to be stronger for current users compared with past users," the researchers said.
Conversely, among the women studied, the incidence of ductal carcinoma in situ and invasive ductal or lobular carcinoma was not related to ever having used hormones. However, the data suggest a modest increased risk for invasive ductal or lobular carcinoma among women who, at the beginning of the study, reported current hormone replacement therapy use for five or fewer years.
The authors reported that the risk for favorable breast cancers for women who ever used hormone replacement therapy for five or fewer years was 1.8 times greater than for women who never used hormone replacement therapy. Women who used hormone replacement therapy for more than five years had 2.6 times the risk.
The association of hormone replacement therapy with breast cancer is controversial. According to the researchers, despite the positive effect of hormone replacement therapy on reducing menopausal symptoms, lowering risk for osteoporosis and a potentially beneficial effect on primary prevention of coronary heart disease, concerns about breast cancer cause many women not to take estrogens. A considerable amount of epidemiologic data supports a modest increase in risk for breast cancer with long-term hormone use.
The researchers said that although there may be several possible reasons for a specific risk association of hormone replacement therapy with favorable breast cancers, increased medical surveillance cannot explain this observation since these tumors are not precursor lesions for other types of invasive breast cancers.
The authors agreed that further study is needed and that this research should explore more fully differences in the association between types of postmenopausal hormone use and breast cancer risk across tumor types.
They also noted that if hormone replacement therapy increases the risk for less commonly occurring tumors with a good prognosis, then the overall risks and benefits of hormone use in the population should be reexamined.
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