The use of combination therapy with estrogen plus progestin, previously shown to be associated with an increased incidence of estrogen receptor–positive breast cancer in postmenopausal women in studies based largely on white women, has been shown to increase this type of breast cancer among postmenopausal African American women. “Our results provide strong evidence that combination use is an important risk factor for estrogen receptor–positive cancer in African American women,” Lynn Rosenberg, ScD, of Boston University, and co-investigators stated in the Journal of the National Cancer Institute. “As in white women, a reduction in combination use by African American women would be expected to reduce the number of estrogen receptor–positive cancers.”
Pooled Data From Four Studies
To assess the use of estrogen alone and of combination therapy in relation to estrogen receptor–positive and estrogen receptor–negative breast cancer risk in postmenopausal African American women, the researchers used data, collected from 1993 to 2013, from the African American Breast Cancer Epidemiology and Risk (AMBER) Consortium. The AMBER Consortium pools data from four studies of breast cancer subtypes among African American women: the Black Women’s Health Study, the Carolina Breast Cancer Study, the Multiethnic Cohort Study, and the Women’s Circle of Health, comprising women from New York and New Jersey.
The study included 1,132 estrogen receptor–positive patients, 512 estrogen receptor–negative patients, and 6,693 control patients. Among the controls, 47% had used estrogen alone, combination therapy, or both.
Risk Greatest Among Leaner Women
“The odds ratio [OR] for estrogen receptor–positive breast cancer associated with combination use, relative to never use of either estrogen alone or combination therapy, was 1.50 (95% confidence interval [CI] = 1.25–1.79),” the researchers reported. The risk was greater for those who had used combination therapy within the past 5 years (OR = 1.55, 95% CI = 1.21–1.99) and among those who had used it for 10 or more years (OR = 1.75, 95% CI = 1.13–2.73). “Breast cancer risk was increased regardless of the interval between onset of menopause and initiation of combination use,” the investigators noted.
The odds ratio associated with combination therapy was higher among leaner women (OR = 1.91 for women with body mass index [BMI] < 25 kg/m2) than for overweight women (OR = 1.69 for women with BMI = 25–29 kg/m2) “and closest to the null among obese women” (OR = 1.24 for women with BMI ≥ 30 kg/m2).
“Combination use was not associated with risk of estrogen receptor–negative breast cancer,” the authors added, “and use of estrogen alone was not associated with risk of either estrogen receptor–positive or estrogen receptor–negative breast cancer.”
The study was funded by the National Institutes of Health, the Breast Cancer Research Foundation, and the University Cancer Research Fund of North Carolina.
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