To the Editor I read the article published by Fujii et al. with great interest. The development of de novo cancer is related to increased bleeding events but not thrombotic events in patients with previous myocardial infarction with ST segment elevation (STEMI) (1).Atrial fibrillation (AF) is common in patients with acute coronary syndrome and its incidence after STEMI has been reported to be 10.4-12% after STEMI (2). Cancer and cancer treatment are well-defined risk factors for the development of AF. Recent evidence shows a 47% higher risk of AF in cancer patients, especially in the first 3 months after their diagnosis. There is also an inverse association, with a 24% increased risk of developing cancer in patients with AF (3). Numerous anticancer drugs, including anthracyclines, antimetabolites, alkylating agents, tyrosine kinase inhibitors, proteasome inhibitors, and immune checkpoint inhibitors, have been proven to be associated with AF (4). Since patients with cancer are more closely monitored, AF may have been detected more frequently and oral anticoagulation may have been initiated more frequently than in their counterparts without cancer. This may have caused thromboembolic events to be lower than expected and bleeding events to be higher than expected in cancer patients.The laboratory parameters presented as baseline characteristics represent values at the time of STEMI. However, bleeding and thrombotic events occurred during follow-up.