ABO blood group and bleeding or thromboembolic risk in patients with cancer and atrial fibrillation: a competing-risk analysis

Background Patients with cancer and atrial fibrillation (AF) are at increased risk for both bleeding and thromboembolic events. ABO blood groups have been linked to hemostatic and thrombotic variability in the general population, largely mediated by differences in von Willebrand factor and factor VIII levels. However, evidence regarding their impact on bleeding and thromboembolic outcomes in patients with cancer and AF remains limited. Purpose To evaluate the association between ABO blood group and the cumulative incidence of bleeding and composite thromboembolic major adverse cardiovascular events (MACE) in patients with cancer and AF using competing-risk methodology. Methods This retrospective cohort study included patients with cancer and AF followed between January 2018 and June 2024. Analyses were restricted to blood groups O, A, and B; blood group AB was excluded due to small sample size. Two competing-risk analyses were conducted for bleeding and composite MACE (including venous thromboembolism, ischemic stroke, and acute coronary syndrome), with death treated as a competing event. Cumulative incidence functions were estimated using the Aalen–Johansen method, and between-group differences were assessed using a Gray-type k-sample test. Results A total of 213 patients were included (blood group O: n=65; A: n=105; B: n=43). Mean age was 70.8 ± 9.0 years, and 56.3% were female. The most common malignancies were breast (32.3%), gastrointestinal (21.1%), and lung cancer (18.3%). Valvular AF was present in 10.3% of patients. Median cancer stage was IV (I–IV), median CHA2DS2-VA score was 3 (0–6), and median HAS-BLED score was 2 (0–5). The cumulative incidence of bleeding increased over time in all blood groups, with numerically higher estimates in blood group B; however, no significant differences were observed (Gray-type test p = 0.915) (Figure 1). Similarly, cumulative incidence of composite MACE did not differ significantly among blood groups O, A, and B when accounting for death as a competing event (Gray-type test p = 0.825) (Figure 2). Conclusions In patients with cancer and AF, ABO blood group was not associated with the cumulative incidence of bleeding or composite thromboembolic MACE when death was appropriately considered as a competing event. These findings suggest that ABO blood group alone is unlikely to be a major determinant of hemorrhagic or thromboembolic risk in this population. Larger studies incorporating multivariable competing-risk models are needed to confirm these results.