The use of CDK4/6 inhibitors, such as palbociclib, ribociclib, and abemaciclib, to treat HR+ breast cancer is another encouraging advancement in breast cancer targeted therapy [17]. CDK4-6 inhibitors improve median progression-free survival and delay progression of disease, with ribociclib also showing an improvement in overall survival [18,19]. Another significant development is the introduction of immunotherapy as a potential breast cancer treatment strategy. Here, CDK4 is linked to breast cancer.