Mid- and Long-Term Risk of Venous Thromboembolism Among Female Breast Cancer Survivors: A Nationwide Cohort Study.

Venous thromboembolism (VTE) is a serious complication for breast cancer (BC) survivors. We identified records of female BC survivors from the Korean Health Insurance Service database between January 1, 2010, and December 31, 2016. After applying exclusion criteria (age < 18 years, prior cancers or VTE, absence of BC surgery, or missing data), 112,522 BC survivors were included; for the comparison group, BC survivors were matched (1:3) to women without cancer history. VTE risk was evaluated with a Fine and Gray model, accounting for death as a competing risk; multiple time periods were analyzed. Associations between VTE risk and treatment modalities also were estimated. Over a mean analysis period of 7.4 years, BC survivors had 3621 VTE events; their subdistribution hazard ratio (sHR) for VTE was greater than that of the comparison group (sHR 1.68, 95% CI 1.61-1.75). The risk was prominent within the first year post-diagnosis (sHR 7.78, 95% CI 6.88-8.80) and attenuated in analyses restricted to VTE events occurring beyond 1 year after diagnosis (sHR 1.34, 95% CI 1.28-1.40), but remained significantly elevated in landmark (delayed-entry) analyses starting at later time points. Anthracycline (sHR 1.11, 95% CI 1.00-1.23) and taxane (sHR 1.73, 95% CI 1.57-1.91) therapies were associated with an increased risk of VTE in 1-year landmark analysis. Female BC survivors are at increased risk of VTE, especially during the first year post-diagnosis, which underscores the importance of VTE risk assessment for BC survivors.