Risk factors for breast cancer in elderly women.Am J Epidemiol 2004; 160(9):868-75AJ
As the population ages, an increasing fraction of women diagnosed with breast cancer will be elderly. Heterogeneity of breast cancer risk factors between pre- and postmenopausal women is recognized, but few studies have examined elderly women specifically. The authors describe the age-specific influence of risk factors for postmenopausal breast cancer, with emphasis on women aged 75 or more years. Among 36,658 members of the Iowa Women's Health Study (1986-2001), a population-based cohort study, 428 incident breast cancers were diagnosed in women aged 55-64 years, 1,297 in women aged 65-74 years, and 561 in women aged 75-84 years. Women with a body mass index (weight (kg)/height (m)(2)) in the highest versus the lowest quartile were at increased risk of breast cancer at age 75 or more years (adjusted hazard ratio = 1.44, 95% confidence interval (CI): 1.12, 1.84). Family history of breast cancer (hazard ratio = 1.54, 95% CI: 1.24, 1.93 for a first-degree family history vs. none) and an older age at menopause (p(trend) = 0.07) conferred increased risk for women aged 75 or more years, and a high number of livebirths was protective (hazard ratio = 0.67, 95% CI: 0.51, 0.88 for five or more births compared with one or two). Obesity, a modifiable risk factor, remained positively associated with breast cancer for all age groups of postmenopausal women.