Abstract PO5-05-07: Efficacy and safety of first line CDK4/6i plus endocrine therapy for patients with HR+/HER2- metastatic breast cancer:initial real-world experience at Ho Chi Minh city oncology hospital, Viet Nam

Abstract

Abstract Background The cyclin-dependent kinases (CDK)4/6 inhibitors (CDK4/6i) palbociclib and ribociclib have been available in Viet Nam since 2021 for the treatment of hormone receptor-positive metastatic breast cancer (MBC). Data regarding CDK4/6i benefit in Vietnamese MBC are sparse. This study evaluated the impact of CDK4/6i in first-line HR+/HER2− MBC using real-world experience at Ho Chi Minh City Oncology Hospital. Methods A single-institution study analyzed retrospective data from 108 patients treated with palbiciclib or ribociclib with endocrine therapy in first-line in HR+/HER2– MBC patients at Ho Chi Minh city oncology hospital. Patient characteristics, PFS, treatment response, and toxicity profiles were analyzed. Results Baseline patients’ characteristics are detailed in Table 1.The median follow-up was 12.5 months (95% CI: 10.9-13.3). Best responses by the line of therapy are in Table 2. The median PFS has still not been reached. The PFS rates at 6, 12 and 18 months were 94.4%, 93.5% and 91.5%, respectively. Patients with bone-only metastasis have a better PFS than visceral metastasis (p = 0.059). Patients with recurrent disease had shorter PFS (p = 0.083) than those presenting with de novo metastasis. The most common reasons for toxicity were neutropenia (92.6%), anemia (35.2%), thrombopenia (22.2%) and the incidence of diarrhea was only 2,8%. None were related to QTc-prolongation Conclusion The real-world effectiveness and safety with CDK4/6 inhibitors in our institution HR+/HER2– MBC patients mimics that observed in the clinical trials. This finding supports the use of CDK4/6i in combination with endocrine therapy as standard of care for HR+/HER2- MBC in Viet Nam. The study also suggests the need for more study of under-represented minority populations. Further studies are ongoing to validate these findings incorporating additional cancer centers. Keywords: advanced/metastatic breast cancer, Asia, CDK4/6 inhibitors, real world Table 1. Patient Demographics and Baseline Disease Characteristics (N=108) Characteristics N (%) Age, y: Median 52 Stage Recurrent from earlier stage, stages 0–III 67 (62) De novo, newly diagnosed stage IV at enrolment 41 (38) DFI < 12 months 5 (4.6) 12-24 months 12 (11.1) > 24 months 51 (47.2) No. of metastatic sites 1 49 (45.4) 2 37 (34.3) ≥ 3 22 (20.4) Metastasis pattern Bone only 30 (27.8) Other 78 (72.2) CDK4/6i Palbociclib 35 (32.4) Ribociclib 73 (67.6) Partner ET AIs 94 (87) Fulvestrant 14 (13) Table 2. Best responses of therapy (N=108) Best responses (N,%) CR 2 (1.9) PR 29 (26.9) SD 67 (62.1) PD 10 (9.3) Total 108 (100) ORR 31 (28.8) CBR 76 (70.3) Table. Citation Format: Hoang-Quy Nguyen, Hong-Duc Phan-Thi, Thi-Hong-Van Le. Efficacy and safety of first line CDK4/6i plus endocrine therapy for patients with HR+/HER2- metastatic breast cancer:initial real-world experience at Ho Chi Minh city oncology hospital, Viet Nam [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 PO5-05-07.