Abemaciclib is a medication used to treat certain types of breast cancer, particularly hormone receptor-positive breast cancer that has spread to other parts of the body. It works by inhibiting specific proteins called cyclin-dependent kinases (CDK4 and CDK6), which are involved in cell division. By blocking these proteins, abemaciclib helps slow down or stop the growth of cancer cells. This drug is often prescribed in combination with other treatments, such as aromatase inhibitors or hormonal therapies, to enhance its effectiveness. Patients taking abemaciclib may experience side effects, including fatigue, diarrhea, and low blood cell counts, which require monitoring by healthcare professionals.