Discrepancies across studies could derive from differences in the population of patients included (e.g., different patient- and tumor-related characteristics), diverse assessment of HER2 status, different clinical management of patients (e.g., different types of backbone ET or CDK4/6i compound used, different subsequent lines of therapy, and in particular T-DXd), or the inclusion of patients with different intrinsic BC subtypes16. Here, CDK4 is linked to breast cancer.