Simple SummaryIn Asian patients with breast cancer, venous thromboembolism (VTE) has been an under-recognized condition. We demonstrated close association between VTE and breast cancer in a Korean cohort. The incidence of VTE was not low, as previously described. The risk factors for VTE included old age, male breast cancer, chronic kidney disease, breast reconstruction, and advanced stage. VTE was associated with poor disease-free and overall survival. Most of the patients with VTE were manageable with anticoagulation, although mortality occurred in some patients. Our findings provide valuable information on comprehensive care for Asian patients with breast cancer.AbstractThe relationship between cancer and venous thromboembolism (VTE) has long been described. The risk of VTE in Asian patients with breast cancer remains largely unknown. This study described the incidence and risk factors of VTE in Korean patients with breast cancer. Data were collected from a retrospective database of patients who underwent breast cancer surgery between 2011 and 2020 at a single institution. The Cox proportional-hazards model was used to identify factors associated with VTE occurrences. Among the 2246 patients with breast cancer, 48 (2.1%) developed VTE during a median follow-up period of 53 months. The average incidence of VTE was 459 per 100,000 person-years. Age ≥ 60 years, male sex, chronic kidney disease, reconstructive procedures, and stage II or higher were independent predictive factors for VTE. VTE was associated with poor disease-free survival (hazard ratio (HR), 6.140; 95% confidence interval (CI), 3.480–10.835), and overall survival (HR, 8.842; 95% CI 4.386–17.824). Most VTE events were manageable with anticoagulation; three (6.3%) patients died of VTE, despite intensive care. The incidence of VTE was significantly elevated in Korean patients with breast cancer. Since VTE has a negative effect on oncologic outcomes of breast cancer, clinicians should manage its risk throughout their lifetime.