Palbociclib Isethionate is primarily used in the treatment of hormone receptor-positive (HR+) and human epidermal growth factor receptor 2-negative (HER2-) advanced or metastatic breast cancer. It is often prescribed in combination with other hormonal therapies, 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 cycle progression. By blocking these kinases, it helps to slow down or halt the proliferation of cancer cells. This targeted approach makes it a valuable option for patients who have not responded well to other treatments. Its use has shown significant improvement in progression-free survival, making it a key component in the management of advanced breast cancer.