OC 16.2 - Hemorrhage risk in direct oral anticoagulant users receiving tamoxifen for breast cancer versus aromatase inhibitors: The STOP-Bleed Cancer study

Sunday, July 10, 2022

11:00 AM – 11:15 AM

Location: ExCel Center, ICC Capital Suite Room 8&9

Presentation Format: In-Person

Presenting Author(s)

Tzu-Fei Wang, MD, MPH

Associate professor
Department of Medicine, University of Ottawa at The Ottawa Hospital and Ottawa Hospital Research Institute, Ottawa, ON, Canada
Ottawa, Ontario, Canada

Co-Author(s)

AC

Anna Clarke

Methodologist
Ottawa Hospital Research Institute and ICES
Ottawa, Ontario, Canada
AA

Arif Awan

Assistant professor
University of Ottawa at The Ottawa Hospital and Ottawa Hospital Research Institute
Ottawa, Ontario, Canada
Marc Carrier, MD

MD, MSc
Ottawa Hospital Research Institute, Ottawa, ON, Canada
Ottawa, Ontario, Canada
MS

Manish Sood

Associate professor
University of Ottawa at The Ottawa Hospital and Ottawa Hospital Research Institute
Ottawa, Ontario, Canada

Background: Tamoxifen is commonly used as adjuvant therapy in breast cancer and is postulated to interfere with CYP3A4 and P-gp pathways. This may pose a higher hemorrhage risk with concurrent direct oral anticoagulants (DOACs) use.

Aims: To assess the risk of hemorrhage in breast cancer patients co-prescribed a DOAC and tamoxifen compared to aromatase inhibitors (AI).

Methods: This population-based, retrospective cohort study was conducted among adults of age ≥ 66 who were prescribed tamoxifen compared to AI while on a DOAC in Ontario, Canada from June 2009 to November 2020. The primary outcome is major hemorrhage requiring emergency room visit or hospitalization after prescription until censored or the end of follow-up on December 31, 2020. Overlap weighted Cox proportional hazard models, accounting for multiple covariates, were used to assess the association between hemorrhage and tamoxifen or AI use with a DOAC.

Results: Among a total of 4753 patients (98.4% women, mean age 77.4 years), 1179 (24.8%) were on tamoxifen and 3574 (75.2%) on AI. Rivaroxaban (53.2%) and apixaban (35.0%) were the most used DOACs. Patients taking AIs were younger, with higher Charlson comorbidity index score and more advanced stage (Table 1). Tamoxifen was not associated with a higher risk of major bleeding events compared to AI when combined with a DOAC [median follow-up 166 days; Tamoxifen: 29/1179 (2.5%) vs. AI: 119/3574 (3.3%), absolute risk difference 0.8%; weighted hazard ratio 0.68, 95% confidence interval 0.44-1.05]. These results were similar in additional analyses using a more liberal definition of hemorrhage, accounting for kidney function, limiting follow-up to 90 days, stratifying by incident/prevalent DOAC users, and accounting for cancer duration and the competing risk of death (Table 2).

Conclusion(s): This study suggests that in DOAC users, the concurrent use of tamoxifen poses no higher risk of hemorrhage compared to concurrent use of AI.