ERBB2 and breast cancer: To understand the relation of CD44, CD24 and ALDH1 expression with tumorigenic cells in breast cancer, we chose six cell lines to represent the major molecular subtypes of breast cancer: MCF-7 and T47D (luminal A), BT-474 (luminal B, HER2-OE), AU-565 (HER2-OE), Hs578T and MDA-MB-231 (triple-negative/basal like).