We show here that FKA inhibits Cdc2 phosphorylation, increases Cdc2 kinase activity, and induces G2M arrest in HER2-overexpressing breast cancer cell lines by both (1) de-phosphorylation of Cdc25C and (2) downregulation of Cdc2 inhibitors: Myt1 and Wee1. Here, WEE1 is linked to breast cancer.