Michael YL, Wu C, Pan K, et al. - To know how breast cancer influences change in physical function (PF), researchers compared PF changes over time between women with and without breast cancer, by invasive status, stage, and age, using difference-in-differences method in a longitudinal cohort study. For inclusion, eligible people were participants from the Women's Health Initiative, aged 50 to 79 years at baseline, with four completed functional status evaluations (mean age = 62.1 ± 6.9 years). A comparison was performed between women who received a diagnosis of breast cancer between the 3rd and 11th enrollment year (n = 1,636) vs those without breast cancer (n = 35,660). Greater influence of breast cancer on PF was seen in women in older age groups, as revealed in stratified analyses. A significant decline in PF, which was beyond what is observed in typical aging, was experienced by women diagnosed with breast cancer in this cohort.