Women with higher levels of physical activity may have a reduced risk of breast cancer after menopause, according to a report in the December 11/25 issue of Archives of Internal Medicine, one of the JAMA/Archives journals. The association appears to be stronger for estrogen receptor positive/progesterone receptor negative tumors (which are typically more aggressive) than for other types of breast cancer tumors.
Breast cancer appears to be biologically heterogeneous, meaning that not all cases have the same causes or disease processes, according to background information in the article. One way cancers differ is by hormone receptor status. Tumors are classified as estrogen- and progesterone-receptor (ER/PR) positive or negative based on whether these hormones bind to the surface of the tumor. "Recent studies have found that various well-established risk factors for breast cancer vary by the ER/PR profile of the tumor, including age, menopausal status, parity, age at menarche, age at first pregnancy, hormonal use, family history, body mass index (BMI), waist-hip ratio, alcohol consumption, dietary fat intake and folate level," the authors write.
Aditya Bardia, M.D., M.P.H., of the Mayo Clinic College of Medicine, Rochester, Minn., and colleagues reported findings from the Iowa Womens Health Study, which includes 41,836 postmenopausal women who were age 55 to 69 in 1986. The women filled out a 16-page questionnaire at the beginning of the study that included information about how often and with what intensity they participated in physical activity during "free time." High physical activity (9,111 women) was defined as vigorous activity (such as jogging, swimming or racket sports) two or more times per week or moderate activity (such as bowling, golf, gardening or walking) more than four times per week; medium physical activity (10,030 women) was defined as participation in vigorous activity once per week or moderate activity one to four times
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