ERBB2 and breast cancer: <h4>Introduction</h4>This meta-analysis was designed to compare the long-term outcomes of first-line cyclin-dependent kinase 4/6 (CDK4/6) inhibitors plus endocrine therapy (ET) versus ET in patients with HR+/HER2-metastatic or advanced breast cancer (BC).<h4>Materials and methods</h4>Four databases (Medline, Embase, Web of Science, and CENTRAL) were searched for literature comparing First-line CDK4/6 inhibitors plus ET to ET in patients with HR+/HER2-metastatic or advanced breast cancer.