ERBB2 and breast cancer: The 4T1 cell line (triple-negative mouse breast cancer), MDA-MB-231 (triple-negative human breast cancer), SK-BR-3 (overexpressed HER2 breast cancer), T-47D (luminal A human breast cancer), MCF7 (luminal A human breast cancer), and the nontumorigenic MCF10A cell line (epithelial cell line from mammary gland) were used.