S6K1 is considered a critical downstream target for mTOR and is abnormally activated in a wide range of human cancers. Overexpression of S6K1 is associated with poor prognosis in many cancer types such as esophageal squamous cell carcinoma (ESCC), non-small cell lung cancer (NSCLC), breast cancer, and nasopharyngeal carcinoma (NPC). This evidence concerns the gene MTOR and breast cancer.