In the real-world setting, patients with metastatic breast cancer treated with ribociclib plus aromatase inhibitors or fulvestrant are not at higher risk for thromboembolic events, according to a study presented at the 2021 San Antonio Breast Cancer Symposium.

CDK4/6 inhibitors, like ribociclib, are widely used in routine clinical practice, and were not largely associated with thromboembolic events among patients treated on clinical trials. However, recent data have reported higher than expected rates of both arterial and venous thrombosis for patients receiving CDK4/6 inhibitors.

Thus, this study aimed to use real-world data to examine rates of thromboembolic events in patients treated with ribociclib in the real-world setting.

Patients with metastatic breast cancer who were treated with ribociclib plus aromatase inhibitors or fulvestrant were reviewed and data were collected using electronic medical records and radiology department archives. All episodes of radiology confirmed arterial or venous thrombosis were reported. Researchers considered thromboembolic events ribociclib-related if diagnosed while patients were on drug or within 4 weeks of the last dose.

A total of 305 patients were included in the study. The median age of patients was 49 years. All 305 patients had metastatic disease and 168 (55.1%) were de novo metastasis. At the time of ribociclib therapy, 241 (79%) patients had visceral metastasis and 195 (63.9%) patients had bone-only disease.

In first-line setting, ribociclib was used in combination with letrozole in 195 (63.9%) patients. In those who failed one or more lines of endocrine therapy or chemotherapy, ribociclib was used in combination with fulvestrant or letrozole in 110 (35.9%) patients. The median duration of ribociclib therapy was 7 months.

There were 5 (1.6%) confirmed episodes of venous thromboembolism; 3 were pulmonary embolism with or without deep vein thrombosis and 2 were lower extremity deep vein thrombosis. All episodes were symptomatic. An additional patients had arterial thrombosis.

During chart review, 7 (2.3%) additional patients had a confirmed diagnosis of venous thromboembolism prior to ribociclib and 4 (1.3%) patients had a confirmed episode 2-7 months after stopping ribociclib. All patients were treated with low-molecular heparin with no complications.

“In real-world settings, and contrary to recent reports, breast cancer patients treated with ribociclib with aromatase inhibitors or fulvestrant are not at higher risk for arterial or venous thromboembolic events. Patients had similar rates prior to initiation, and after stopping ribociclib,” concluded study authors.

Abdel-Razeq H, Tamimi F, Edaily S, et al. Thromboembolic events (TEE) in patients with HER2-negative, hormone receptor-positive metastatic breast cancer treated with Ribociclib combined with Letrozole or Fulvestrant. Real-world data. Presented at: 2021 San Antonio Breast Cancer Symposium; December 7-10, 2021; virtual. Abstract P4-02-15.