D’Souza M, et al. - Using nationwide registries, researchers determined the long-term incidence of atrial fibrillation (AF) in patients with breast cancer vs those in the background population. Female patients who received a diagnosis of breast cancer from 1998 to 2015 were included, and 74,155 patients were matched (1:3) by age and sex with 222,465 patients from the background population. Using cumulative incidence curves and multivariable Cox regression models, they calculated the long-term incidence of AF. Findings revealed an increased long-term incidence of AF in patients with breast cancer. An association of breast cancer with incident AF was evident, and this link varied between age groups and follow-up time periods. During the first 6 months—and from 6 months to 3 years—the investigators observed an increased incidence of AF in relation to breast cancer among patients younger than 60 years of age. No association of breast cancer with increased incidence of AF during the first 6 months was noted in patients older than 60 years of age, although these patients had increased incidence of AF from 6 months to 3 years noted in relation to breast cancer.