To the Editor We read with interest the article by Conen et al1 published in the April issue of JAMA Cardiology. In an analysis of the Women鈥檚 Health Study, the authors found an association between incident atrial fibrillation (AF) and cancer. While the study cohort was large, the incidences of AF and cancer were low, placing the findings at risk of a type II error. In addition, this association was not generalizable to men. Therefore, we sought to validate these findings in a larger real-world cohort among both sexes.