Alpelisib is primarily used in the treatment of advanced or metastatic breast cancer, specifically in cases where the cancer is hormone receptor-positive (HR+), HER2-negative, and has a PIK3CA mutation. It is often prescribed in combination with fulvestrant, an estrogen receptor antagonist, to enhance its efficacy. The drug works by inhibiting the PI3K pathway, which is often overactive in these types of cancers, thereby slowing tumor growth and progression. Alpelisib is particularly beneficial for patients who have previously undergone endocrine therapy but have seen their cancer progress. Its targeted approach helps in managing the disease more effectively, offering a therapeutic option for those with specific genetic mutations.