First-line CDK4/6 inhibitor treatment of HR-positive, HER2-negative metastatic breast cancer: real-world data from Ho Chi Minh City Oncology Hospital, Vietnam

Abstract

Objective This study aimed to characterize the tumor response rate, progression-free survival (PFS), and overall survival (OS) among patients with HR-positive, HER2-negative metastatic breast cancer receiving CDK4/6 inhibitors plus endocrine therapy at Ho Chi Minh City Oncology Hospital. Secondary objectives included identifying clinical factors associated with survival outcomes and characterizing treatment-related toxicities. Materials and methods We conducted a retrospective cohort study enrolling 107 patients who received first-line ribociclib or palbociclib in combination with an aromatase inhibitor or fulvestrant at Ho Chi Minh City Oncology Hospital between March 1, 2021, and April 1, 2023. Results The median follow-up duration was 29 months. The median PFS was 28.0 months. The Kaplan–Meier-estimated PFS rates at 12 and 24 months were 66.4% (95% CI, 56.6%–74.4%) and 54.1% (95% CI, 44.2%–63.0%), respectively. The median OS was not reached; corresponding OS rates at 12 and 24 months were 88.8% and 87.8%, respectively. On multivariate Cox regression analysis, ER and PR expression levels emerged as independent prognostic determinants of PFS. Grade 3–4 neutropenia was observed in 58.8% of patients; all events were managed through dose interruption or reduction, and no cases of febrile neutropenia were documented. Conclusion CDK4/6 inhibitors (ribociclib or palbociclib) combined with endocrine therapy demonstrated favorable efficacy and tolerability in Vietnamese patients with HR-positive, HER2-negative metastatic breast cancer. Treatment outcomes and safety profiles were consistent with those reported in pivotal clinical trials and real-world studies. These findings should be interpreted in light of the retrospective single-center design, modest sample size, non-randomized treatment allocation, and immature OS data.