Earlier clinical studies indicated that metformin could improve chemotherapy outcomes, reduce the mortality rate, and increase the overall survival rate of patients with breast cancer (NCT00930579, NCT00984490) [18], prostate cancer (NCT00881725) [18], non-small cell lung cancer [19,20], and head and neck cancer [21] by activating AMPK, inhibiting PI3K/AKT/mTOR, and inactivating MAPK. Here, PIK3CA is linked to breast cancer.