Palbociclib is primarily used in the treatment of hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) advanced or metastatic breast cancer. It is often prescribed in combination with other medications, such as letrozole or fulvestrant, to enhance its effectiveness. The drug works by inhibiting cyclin-dependent kinases 4 and 6 (CDK4/6), which play a crucial role in cell division and cancer progression. By blocking these enzymes, palbociclib helps to slow down or stop the growth of cancer cells, thereby improving progression-free survival in patients. It is particularly beneficial for postmenopausal women with advanced breast cancer, offering a targeted therapy option that can be less harsh than traditional chemotherapy. Regular monitoring of blood counts is essential during treatment, as palbociclib can lower white blood cell levels, increasing the risk of infections.