Population Attributable Risk of Modifiable and Nonmodifiable Breast Cancer Risk Factors in Postmenopausal Breast Cancer

Abstract

We examined the proportions of multiple types of breast cancers in the population that were attributable to established risk factors, focusing on behaviors that are modifiable at menopause. We estimated the full and partial population attributable risk percentages (PAR%) by combining the relative risks and the observed prevalence rates of the risk factors of interest. A total of 8,421 cases of invasive breast cancer developed in postmenopausal women (n = 121,700) in the Nurses' Health Study from 1980-2010. We included the following modifiable risk factors in our analyses: weight change since age 18 years, alcohol consumption, physical activity level, breastfeeding, and menopausal hormone therapy use. Additionally, the following nonmodifiable factors were included: age, age at menarche, height, a combination of parity and age at first birth, body mass index at age 18 years, family history of breast cancer, and prior benign breast disease. When we considered all risk factors (and controlled for age), the PAR% for invasive breast cancers was 70.0% (95% confidence interval: 55.0, 80.7). When considering only modifiable factors, we found that changing the risk factor profile to the lowest weight gain, no alcohol consumption, high physical activity level, breastfeeding, and no menopausal hormone therapy use was associated with a PAR% of 34.6% (95% confidence interval: 22.7, 45.4). The PAR% for modifiable factors was higher for estrogen receptorpositive breast cancers (PAR% = 39.7%) than for estrogen receptor-negative breast cancers (PAR% = 27.9%). Risk factors that are modifiable at menopause account for more than one-third of postmenopausal breast cancers; therefore, a substantial proportion of breast cancer in the United States is preventable. modifiable factors; PAR%; postmenopausal breast cancer Abbreviations: BMI, body mass index; CI, confidence interval; ER, estrogen receptor; ER−, estrogen receptor-negative; ER+, estrogen receptor-positive; MHT, menopausal hormone therapy; PAR%, population attributable risk percentage; RR, relative risk.Breast cancer is the most common cancer among women in the United States, and it is a major cause of morbidity and mortality globally. It has been estimated that 232,340 cases of invasive breast cancer and 39,620 breast cancer deaths occur annually in the United States (1). A nearly 5-fold difference in breast cancer incidence rates exists among countries globally (2). This geographic variability in incidence rates for breast cancer suggests that differences in the prevalence rates of risk factors among countries are associated with variation in breast cancer rates. Additionally, in migration studies, incidence rates of breast cancer among the descendants of women who moved from low-incidence countries to high-incidence countries converged to those of the high-incidence countries (3-7), which suggests that modifiable lifestyle factors account for much of the global difference in incidence rates. Thus, identification of modifiable risk factors for breast cancer has important impl...

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