Abstract P4-02-15: 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
Authors: Abdel-Razeq Hikmat , Tamimi Faris , Edaily Sarah , Sharaf Baha' , Abunasser Mahmoud , Salama Osama , Abdel-Razeq Rashid , Abdulelah Hazem , Bater Rayan 
Published: March 2022

Abstract
Background: Breast cancer is the most common cancer diagnosed among women worldwide. More than 70% of breast cancers are hormone receptor (HR)-positive, for which endocrine therapy (ET) is the preferred initial treatment especially so for those with low burden disease. Majority of patients with HR-positive metastatic breast cancer (mBC) acquire resistance to endocrine therapy. CDK4/6 inhibitors modulate this resistance and are integral treatment for patients with advanced HR-positive, HER2-negative breast cancer. Since their approval, CDK4/6 inhibitors are widely used in clinical practice. Thromboembolic events (TEE) were not a major issue among patients treated on clinical trials. However, conflicting data starts to emerge describing higher than expected rates of both arterial and venous thrombosis in patients treated with CDK4/6 inhibitors. In this study, we use real world data to study TEE rates in patients treated with ribociclib in real-world settings.Methods: The study is a retrospective analysis of individual patients’ data. All consecutive patients with mBC treated with ribociclib combined with aromatase inhibitors or fulvestrant were reviewed. Data were collected from patients’ electronic medical records and from radiology department archives. All episodes of radiology confirmed arterial or venous thrombosis were recorded. TEE was considered ribociclib related if diagnosed while patients on the drug or withing 4 weeks after the last dose.Results: During the study period, a total of 305 patients were enrolled. Median age (range) was 49 (22-87) years. All patients had metastatic disease and 168 (55.1%) were de novo metastasis. Most (n=241, 79.0%) of the patients had visceral metastasis at time of ribociclib therapy; only 64 (20.9%) had bone-only disease. Ribociclib was used in combination with letrozole in first-line setting in 195 (63.9%) and with fulvestrant or letrozole in 110 (35.9%) patients who failed one or more lines of ET or chemotherapy. Median duration (range) of ribociclib therapy was 7 (1-45) months. Episodes of venous thromboembolism were confirmed in only 5 (1.6%) patients; 3 were PE with or without DVT and 2 were lower extremity DVT and all were symptomatic. Another patient had arterial thrombosis (lower limb ischemia). During the chart review, 7 (2.3%) more patients had a confirmed diagnosis of VTE prior to ribociclib and another 4 (1.3%) patients had a confirmed episode after (range: 2-7 months) stopping it. All patients were treated with low-molecular heparin (LMWH) with no complications. Given the small number of patients with TEE, no clinical or pathological predictors could be used to identify subgroups of patients at higher risk for TEE while on ribociclib.Conclusions: In real-world settings, and contrary to recent reports, breast cancer patients treated with ribociclib with AI or fulvestrant are not at higher risk for arterial or venous thromboembolic events. Patients had similar rates prior to initiation, and after stopping ribociclib.
Citation Format: Hikmat Abdel-Razeq, Faris Tamimi, Sarah Edaily, Baha' Sharaf, Mahmoud Abunasser, Osama Salama, Rashid Abdel-Razeq, Hazem Abdulelah, Rayan Bater. 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 [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P4-02-15.