Risk of venous and arterial thromboembolic events in women with advanced breast cancer treated with CDK 4/6 inhibitors: A systematic review and meta-analysis

Background: Cyclin-dependent kinase inhibitors (CDKIs) may increase the risk of thrombotic events of endocrine therapy (ET) in women with hormone-sensitive, HER2-negative advanced breast cancer (BC). Aim of our systematic review is the estimate of the risk of venous and arterial thromboembolism in women with advanced BC treated with CDKIs in phase III randomized controlled trials (RCTs).

Methods: Studies were identified by electronic search of MEDLINE, EMBASE and CENTRAL database until October 2021. Risk of bias was assessed according to Cochrane criteria. Differences in thrombotic outcomes among groups were expressed as pooled odds ratio (OR) and corresponding 95% confidence interval (CI), which were calculated using both a fixed-effects and a random-effects model. Statistical heterogeneity was evaluated using the I² statistic.

Results: We included 7 phase III RCTs (4415 patients) for a total of 15 papers (7 were the first published paper and 8 the follow-up papers). Reporting of thrombotic events was at high risk of bias. Women with advanced BC treated with CDKIs and ET had a two to threefold increased risk of venous thromboembolic event (VTE) compared to ET plus placebo arm [OR 2.90 (95% CI 1.32, 6.37; I² = 0%) in the main papers and OR 2.20 (95% CI 0.93, 5.20; I² = 49%) in the follow-up papers]. Women with advanced BC treated with CDKIs and ET had a non-significant mild increased risk of arterial thromboembolic event compared to ET plus placebo arm [OR 1.22 (95% CI 0.47, 3.18 I² = 0%)].

Conclusions: CDKIs in combination with endocrine therapy are associated with a two to threefold higher risk of VTE in comparison to endocrine therapy alone in women with advanced breast cancer, while the risk of arterial events is still to be defined.