Venous thromboembolism in women with hormone-dependent breast cancer. To continue or discontinue hormonal treatment? Insights from the RIETE registry.

ABSTRACT

INTRODUCTION: Hormone therapy (HT) for breast cancer is associated with an increased risk of venous thromboembolism (VTE). This study examines the effects of continuing versus discontinuing HT on VTE recurrence, major bleeding, and mortality, after an acute VTE event. METHODS: Using data in the RIETE-registry from March 2001 through September 2021, we calculated incidence rates and rate-ratios (RR) for VTE events in patients on- and off HT. Cox regression models assessed the impact of HT continuation. RESULTS: Among 479 women with breast cancer on HT who developed VTE (pulmonary embolism 279, isolated deep vein thrombosis 200), 350 (73 %) continued HT. These women were slightly older (70 ± 13 vs. 67 ± 16 years) than those discontinuing HT, with no significant differences in other baseline characteristics. Over a median follow-up of 294 days, 25 (5.2 %) developed VTE recurrences, 18 (3.7 %) had major bleeding, and 73 (15.2 %) died. Rates of VTE recurrence did not differ significantly between groups (RR 1.28, 95 % CI 0.44-3.75), except in the first three months post-VTE, where a higher rate was observed in those continuing HT (6.02/100 patients-year vs. no events). On multivariable analysis, HT continuation showed no association with VTE recurrences after adjusting for other thromboembolic risk factors (adjusted hazard ratio [aHR] 1.49, 95 % CI 0.5-4.45). CONCLUSION: Continuing HT after a VTE event in women with breast cancer does not generally affect the long-term risk of VTE recurrences but is associated with a higher risk in the first three months. These findings highlight the need for careful monitoring during this period.