The impact of cancer on clinical outcomes in patients with atrial fibrillation (AF) is unclear. The aim of this study was to assess how cancer influences the prediction and risk of embolic and hemorrhagic events in patients with AF.

The study population comprised 16 056 patients from a Spanish health area diagnosed with AF between 2014 and 2018. Of these, 1137 (7.1%) had a history of cancer. During a median follow-up of 4.9 years, we assessed the relationship between cancer and bleeding and embolic events by competing risk analysis, considering death as a competing risk.

No association was detected between an increased risk of embolic events and cancer overall (sHR, 0.73; 95%CI, 0.41-1.26), active cancer, or any subgroup of cancer. However, cancer was associated with an increased risk of bleeding, although only in patients with active cancer (sHR, 1.42; 95%CI, 1.20-1.67) or prior radiotherapy (sHR, 1.40; 95%CI, 1.19-1.65). Both the CHA2DS2-VASc and HAS-BLED scores showed suboptimal performance to predict embolic and bleeding risk (c-statistic <0.50), respectively, in nonanticoagulated patients with active cancer. The ratio between the increase in bleeding and the decrease in embolisms with anticoagulation was similar in patients with and without cancer (5.6 vs 7.8; P <.001).

Cancer was not associated with an increased risk of embolic events in AF patients, only with an increased risk of bleeding. However, active cancer worsened the ability of the CHA2DS2-VASc and HAS-BLED scores to predict embolic and bleeding events, respectively, in nonanticoagulated patients.