Recurrence is the reoccurrence of cancer after treatment. When breast cancer has spread to lymph nodes and/or other tissues in the breast area without spreading farther to other parts of the body, it is called locally advanced breast cancer (stage III). When the cancer has spread to other parts of the body, such as the bones or liver, it is called metastatic breast cancer (stage IV) and is the most severe state of the disease. Locally advanced and metastatic breast cancer are collectively referred to as advanced breast cancer. Distant recurrence is the leading cause of death from breast cancer. Aromatase inhibitors are often prescribed by physicians to prevent recurrence in patients initially diagnosed with advanced breast cancer and in postmenopausal women with hormone-sensitive early-stage breast cancer. Aromatase inhibitor drugs reduce hormone levels in the body, such as estrogen, and are a form of endocrine therapy. Aromatase inhibitor drugs are an important advance in the treatment of women with HR+ breast cancer and have been shown to reduce the risk of recurrence in patients with HR+ breast cancer after surgical removal of the tumor. Endocrine therapy remains an important modality of treatment for women with HR+ breast cancer, most of whom will eventually progress to treatment resistance. Treatment resistance is associated with excessive activation of the PI3K/Akt / mTOR pathway.