CDK4 and breast cancer: In patients with hormone receptor‐positive HER2‐negative advanced breast cancer, addition of CDK4/6 inhibitors (e.g., palbociclib, abemaciclib, or ribociclib) to endocrine therapy has been shown to improve PFS, enabling a prolonged endocrine therapy‐based period and resulting in favorable OS (as shown by the results of the MONARCH, MONALEESA, and PALOMA trials).19, 20, 21, 22