The relationship between idiopathic atrial fibrillation and cancer

Atrial fibrillation (AF) is the most common sustained arrhythmia worldwide, and its intersection with cancer has emerged as a significant clinical concern. Recent large-scale cohort studies reveal a bidirectional association, with new-onset - particularly idiopathic - AF linked to an elevated risk of subsequent cancer diagnosis. This risk peaks within the first 3 months after AF onset, most notably for thoracic, abdominal, and hematologic malignancies, and diminishes thereafter. Proposed mechanisms include shared risk factors, systemic inflammation, prothrombotic states, oxidative stress, paraneoplastic phenomena, and detection bias from increased medical surveillance. While patients with secondary AF and multiple comorbidities bear the highest cancer risk, those with idiopathic AF also demonstrate a nonnegligible risk, albeit lower in magnitude. Cancer diagnosed shortly after AF onset is associated with poorer prognosis, heightened cardiovascular complications, and increased bleeding risk. Current guidelines do not recommend routine cancer screening for idiopathic AF but advocate individualized evaluation when clinical suspicion exists. Significant research gaps remain, particularly in differentiating idiopathic from secondary AF, elucidating biological pathways, and defining evidence-based screening strategies. Addressing these gaps will require coordinated, multidisciplinary research to clarify causality, refine risk stratification, and guide early detection approaches.