A recent study has evaluated the incidence of thromboembolic events (TEE) in patients diagnosed with advanced HR-positive, HER2-negative breast cancer. Specifically, researchers were concerned that treatment with cyclin dependent kinase (CDK) inhibitors, which are a critical treatment for this patient population, may lead to higher than expected rates of venous and arterial thrombosis.

Clinical trials for CDK4/6 inhibitors didn’t lead to increased rates of TEE. But, new data has shown there may be a cause for concern.

To better understand this potential, researchers conducted a retrospective study of one CDK inhibitor called ribociclib.

The Study

This study included 305 patients diagnosed with metastatic breast cancer. All patients were between 22 and 87 years old, and all but 3 were female. About 80% of the patients had tumors which were infiltrating ductal carcinoma. About 15% had infiltrating lobular carcinoma, and about 29% had high grade tumors.

All patients were diagnosed with metastatic disease, and 79% had visceral metastasis. All patients received the ribociclib treatment as well as either fulvestrant or letrozole. A TEE was considered related to ribociclib treatment if it occurred while patients were currently taking the treatment or the event was within 4 weeks from their final dose.

The median duration of the ribociclib treatment was 7 months, and 56 patients had the treatment for 18 months or more. 178 patients experienced complete response, partial response, or stable disease.

Researchers documented all cases of radiologically confirmed venous or arterial thrombosis.

Results

TEE cases were found in 6 patients: just 1.97%. 3 had a pulmonary embolism and 2 experienced cerebral venous sinus thrombosis. The final patient experienced limb ischemia. Rates of TEE were similar during ribociclib treatment and after. All patients who experienced a TEE were symptomatic.

All patients who experienced a TEE also had other risk factors for this condition including recent hospital admission, active smoking, or a recent cancer diagnosis. 7 patients had a TEE before starting ribociclib, and 4 had a TEE after stopping ribociclib treatment.

Every patient with a TEE was treated with LMWH and had no complications.

The researchers concluded that breast cancer patients treated with a CDK are not at any higher risk for a TEE. However, they did note that the incidence of 2 cases of cerebral venous sinus thrombosis (CVST) should be examined further. This is a very rare form of TEE and none of the known causes of the condition were found to be present in the 2 breast cancer patients who experienced the condition. This demonstrates the need for further research.

You can read more about this study and its findings here.