Abstract PO2-04-12: From Clinical Trials to Clinical Practice; Real World Clinical Outcomes of Patients Treated with Ribociclib in Combination with Aromatase Inhibitors or Fulvestrant for HR-Positive, HER2- Negative Metastatic Breast Cancer

Abstract Background: Cyclin-dependent kinase (CDK) 4/6 inhibitors have revolutionized the treatment landscape of hormone receptor-positive (HR+), human epidermal growth factor receptor-2 (HER2)-negative metastatic breast cancer (MBC), with an impressive efficacy and safety profile. Here we report real-world clinical outcomes and toxicity data in patients treated at a tertiary care cancer center. Methods: The study is a retrospective analysis of individual patients’ data. All consecutive patients with HR+ and HER2-negative MBC, treated at our institution with ribociclib plus aromatase inhibitors (AI) or fulvestrant, between June 2017 and May 2020 were reviewed. Data were collected from patients’ electronic medical records. Progression free survival (PFS) was defined as the time from treatment initiation with CDK4/6i until the first documented progression, death from any cause or last follow-up, whichever occurred first. The Overall survival (OS) was defined as the time from treatment initiation with CDK4/6i until the date of death from any cause, or last follow-up. Results: A total of 305 patients, median age 49 (22-87) years were enrolled. Although bone metastasis was reported in 241 (79.0%) patients, bone-only metastasis was identified in 64 (20.9%). Visceral metastasis in the liver and lungs were reported in 22.0% and 25.9 % of patients, respectively. CDK4/6i combined with AI were used in first-line setting in 195 (63.9%) patients and with fulvestrant as a second line (20.7%) or beyond (15.4%). Dose reduction was required in 44 (14.14%) patients, mostly because of neutropenia (n=38, 12.5%) and abnormal liver enzymes (n=12, 3.9%), while 11 (3.6%) discontinued treatment, mostly due cardiac toxicities. Nevertheless, there were no deaths due to toxicity. Patients were followed up for a median of 31.1 months. Overall response rate (ORR) was 51.4% and median PFS, irrespective of the line of therapy, was 19.3 (17.6-23.3) months. PFS was longer in first-line setting; 23.1 (19.7-NR) months compared to 13.9 (10.2-17.6) months in second-line or beyond, p 0 .0001, and when combined with AI compared to fulvestrant; 28.6 (17.8-23.1) months versus 9.1 (4.4-NR) months, p=0.0001, and in those with bone-only metastasis; 23.1 (19.5-NR) months versus 17.3 (12.2-18.9) months for patients with visceral metastasis, p=0.0008. The median OS was not reached. Conclusions: Despite enrolling sicker patients, and outside the stringent clinical trials settings, our treatment outcomes, in real world settings, are comparable to those reported in major clinical trials, including MONALEESA-2, MONALEESA-3 and MONALEESA-7. Citation Format: Baha' Sharaf, Faris Tamimi, Sarah Edaily, Osama Salama, Hazem Abdulelah, Anas Zayed, Mahmoud Abunasser, Hala Abu-Fares, Hikmat Abdel-Razeq. From Clinical Trials to Clinical Practice; Real World Clinical Outcomes of Patients Treated with Ribociclib in Combination with Aromatase Inhibitors or Fulvestrant for HR-Positive, HER2- Negative Metastatic Breast Cancer abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-04-12.