Subgroup analysis revealed that combination therapy significantly improved PFS regardless of histopathological classification, endocrine resistance status, hormone receptor status, site and the number of tumor metastases, menopausal status, prior chemotherapy treatment, ET regimen, advanced disease treatment line, CDK4/6 inhibitor type, disease-free interval (DFI), and length of the treatment-free interval (TFI). The gene discussed is CDK4; the disease is neoplasm.