ERBB2 and breast cancer: For example, it was revealed that AP-2γ plays dual roles in HER2-positive breast cancer cell proliferation depending on its progression stages: proliferation was enhanced at early stages but reduced in advanced stages in comparison to control tumors.[19] Recently, a study using a tissue-specific transgenic mouse model demonstrated overexpression of AP-2γ in mammary glands resulted in hyperproliferation of epithelial cells,[26] also indicating the potential important role of AP-2γ in breast carcinoma in vivo.