Venous thromboembolism in breast cancer patients receiving cyclin-dependent kinase inhibitors.

BACKGROUND

Venous thromboembolism (VTE) complicates several anticancer regimens including chemotherapy and antiangiogenic agents. Cyclin-dependent kinase inhibitors (CDKIs) are a new approach for hormone receptor-positive metastatic breast cancer (mBC). Reported VTE rates in randomized trials range from 0.6% to 5%, but these may underestimate actual rates observed in clinical practice.

OBJECTIVES

Evaluate VTE rate and its association with outcomes in CDKIs patients.

PATIENTS/METHODS: We conducted a retrospective cohort study of consecutive mBC patients who received any of three Food and Drug Administration (FDA)-approved CDKIs (palbociclib, ribociclib, abemaciclib) from January 2015 through December 2017. Venous thromboembolism including deep venous thrombosis (DVT), pulmonary embolism (PE), and visceral vein thrombosis (VVT) were identified by electronic medical record review. Overall survival (OS) and progression-free survival (PFS) were estimated and evaluated for association with VTE using Cox proportional hazard regression.

RESULTS

We included 424 patients, with a median age at diagnosis of 55 years. Palbociclib was the most commonly used CDKI (n = 390, 91.8%). Venous thromboembolism during CDKIs occurred in 38 patients, 6.3% at year 1, including DVT in 52.6%, PE in 18.5%, and VVT in 15.8%. Median time to VTE was 314 days. Venous thromboembolism was associated with a trend to worse PFS and OS in multivariate analysis [PFS hazard ratio (HR) 1.40, 95% confidence interval (CI) 0.83-2.38, P = .21], OS (HR 1.70, 95% CI 0.95-2.98, P = .076).

CONCLUSIONS

Venous thromboembolism rates with CDKI treatment in mBC in clinical practice are 2-fold to 5-fold greater than reported in registration trials and may be associated with worse outcomes.