ERBB2 and breast cancer: Additionally, ER + and/or PR+, HER2 + breast cancers are classified as another type of luminal B breast cancer.[5,12] Therefore, luminal B breast cancers can be either ER + and/or PR + , HER2−, high Ki67 index, or ER + and/or PR + , HER2 + , with either high or low Ki67.