CDK 4/6 inhibitors are primarily used in the treatment of certain types of breast cancer, particularly hormone receptor-positive (HR+) and human epidermal growth factor receptor 2-negative (HER2-) breast cancer. These inhibitors work by blocking the activity of cyclin-dependent kinases 4 and 6, which are proteins involved in cell division. By inhibiting these proteins, the progression of the cell cycle is halted, preventing the proliferation of cancer cells. In clinical practice, CDK 4/6 inhibitors are often combined with endocrine therapy, such as aromatase inhibitors or fulvestrant, to enhance their effectiveness. This combination has shown significant improvement in progression-free survival and overall survival rates in patients with advanced or metastatic breast cancer. Commonly used CDK 4/6 inhibitors include palbociclib, ribociclib, and abemaciclib. These drugs are typically administered orally and are part of a comprehensive treatment plan that may include other therapies depending on the patient's specific condition and response to treatment. Overall, CDK 4/6 inhibitors represent a critical advancement in targeted cancer therapy, offering a more effective and tailored approach to managing certain types of breast cancer.