ERBB2 and breast neoplasm: Luminal A and Luminal B BCs are both positive for hormone receptors (ER+ and PR+) but differ in the HER2 status (Luminal A is HER2-, whereas Luminal B is HER2+) and in the expression levels of the cell differentiation marker Ki67 (> in Luminal B vs. Luminal A), so that the Luminal A subtype is a low-grade breast tumor, whereas the Luminal B subtype is more aggressive [7]; Luminal B tumors, expressing both hormone receptors and overexpressing HER2, are also named triple positive (TPBC).