Key result
CDK4/6 inhibitors in breast cancer are linked to ~263% higher CV event risk versus matched controls.
Why the study?
CDK4/6 inhibitors improve outcomes in hormone receptor-positive, HER2-negative breast cancer, but real-world data on cardiovascular toxicity are limited.
Does CDK4/6 inhibitor treatment increase the risk of cardiovascular events in women with breast cancer compared to a matched cancer-free population?
Cohort (n=1,072)
No
Does CDK4/6 inhibitor treatment increase the risk of cardiovascular events in women with breast cancer compared to a matched cancer-free population?
Women with breast cancer treated with CDK4/6 inhibitors have a significantly higher burden of cardiovascular events, particularly venous thromboembolism and atrial fibrillation, compared to a matched cancer-free population.
Answers are grounded in this paper and cite their sources.
Increased CV monitoring may be prudent in CDK4/6-treated patients; leaves open need for prospective trials to confirm causality and guide practice.
Background Cyclin-dependent kinase (CDK) 4/6 inhibitors improve outcomes in hormone receptor–positive, HER2-negative breast cancer, but real-world data on cardiovascular (CV) toxicity are limited. Methods In this single-centre retrospective matched cohort study, women with breast cancer treated with a CDK4/6 inhibitor at University Hospitals Leuven between 2016 and 2022 constituted the index cohort. Age- and BMI-matched women without active cancer, selected from the population-based FLEMENGHO study, constituted the reference cohort. CV events were identified from medical records, and follow-up in the reference cohort was truncated to the maximum follow-up duration of the index cohort to improve comparability. Results Among 536 matched pairs, the index cohort had a significantly higher observed incidence of CV events than the reference cohort (67.7 vs 17.2 per 1,000 person-years; P < 0.0001), including the cardiac composite (28.0 vs 9.6 per 1,000 person-years; P < 0.0001). Venous thromboembolism (11.6% vs 0.75%) and atrial fibrillation/flutter (4.7% vs 1.5%) were more frequent in the index cohort. Coronary events, stroke, and heart failure did not differ significantly. After adjustment for measured baseline CV risk factors, index-cohort membership remained associated with higher risks of CV events (HR, 3.63; 95% CI, 2.57–5.13) and cardiac events (HR, 3.25; 95% CI, 1.97–5.35). Conclusions Women with breast cancer receiving CDK4/6 inhibitors had a substantially higher observed burden of venous thromboembolism and atrial arrhythmias than the age- and BMI-matched population reference cohort without active cancer. These findings support cardiovascular awareness in this population. However, the comparison cannot isolate a drug-specific effect because active malignancy, previous cancer therapies, baseline differences, and surveillance intensity may also contribute. Trial registration This retrospective single-centre matched cohort study was approved by the Ethics Committee UZ/KU Leuven (approval numbers s68763 and s64406). As a retrospective observational study, prospective trial registration was not required.
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Leenaerts et al. (2026) conducted a cohort in Breast cancer (n=1,072). CDK4/6 inhibitors vs. Age- and BMI-matched women without active cancer was evaluated on Cardiovascular events (HR 3.63, 95% CI 2.57-5.13, p=<0.0001). CDK4/6 inhibitors in women with breast cancer were associated with a higher risk of cardiovascular events compared to matched controls without active cancer.
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