ERBB2 and breast cancer: Seven studies (169,586 participants and 8,153 BC cases) classified the type of BC by estrogen receptor (ER), five studies (13,244 participants and 6,507 BC cases) classified according to progesterone receptor (PR), and five studies (166,471 participants and 6,618 BC cases) classified according to human epidermal growth factor receptor 2 (HER2).