Women of all ethnicities face the same increased risk for breast cancer related to postmenopausal hormone therapy, a study suggests.
The study also found that leaner women taking hormone therapy (HT) had a relatively greater increase in breast cancer risk than did heavier women.
The study, led by Sulggi Lee, M.D., of the Keck School of Medicine at the University of Southern California, Los Angeles, provides some of the first data comparing breast cancer risk among different ethnic groups in relation to HT use.
The cohort study was conducted among 55,371 African-American, Native Hawaiian, Japanese-American, Hispanic, and white postmenopausal women, aged 45–75 years, in the Hawaii-Los Angeles Multiethnic Cohort study.
A total of 1,615 incident invasive breast cancer cases were identified over an average of 7.3 years (Int. J. Cancer [Epub ahead of print] 2005;doi: 10.1002/ijc.21481 www.interscience.wiley.com
Current estrogen-progestin therapy (EPT) use was associated with a 29% increased risk of breast cancer after 5 years of use. Current use of unopposed estrogen therapy (ET) was associated with a 10% increase in risk after 5 years. These results assume that women using hormones at baseline continued to do so.
The increase in risk with EPT use was clearly seen in all ethnic groups, whereas the increase with ET use was seen in all groups except African Americans.
Relative risks for current EPT and ET use were greater for women with a body mass index of less than 25 kg/m
“Data on this aspect of the relationship between EPT use and risk are scarce, and it is too early to draw a firm conclusion,” the authors wrote.
Current EPT use was significantly associated only with estrogen receptor-positive (ER+)/ progesterone receptor-positive (PR+) tumors (relative risk 1.34), but risk also was increased for both ER+/progesterone receptor-negative (PR−) tumors (RR 1.15) and estrogen receptor-negative (ER−)/PR+ tumors (RR 1.18).
Estrogen therapy was associated with both ER+/PR+ and ER+/PR− tumors. These findings are generally consistent with earlier studies.
There was little difference in risk by stage of disease or histological subtype.
The authors noted the possibility that their results may have been influenced by the fact that HT users are more likely to be screened for breast cancer.