Pfeiffer RM, et al. - Researchers assessed the impact of long term changes in risk factor distributions (from 1980-2008) on breast cancer incidence in the US. They used data for US women from large nationally representative surveys and data from the National Cancer Institute's Surveillance, Epidemiology and End Results registries from 1980-2011. Analyses were stratified by age and race. Findings revealed a significant impact of changes in body mass index (BMI) and number of births, as observed since 1980, on US breast cancer incidence. Fewer births has been linked with a 22.2% increase in breast cancer incidence in women aged 40-44, and a and 3.99% increase in those aged 55-59 years. A 7.6% reduced incidence in women aged 40-44 and 2.6% increased incidence for women aged 55-59 was linked to increased BMI. Understanding the impact of risk factor trends on incidence is important so clinicians can assess future breast cancer burden and update prevention efforts.