ERBB2 and breast cancer: A total of 70 different anti-HER2 mAbs were tested in vitro for their efficacy in inhibiting cell proliferation and inducing apoptosis of SK-BR-3 (strong HER2 gene amplification, HER2/CEP17 ratio: 4.8, HER2 protein overexpression, moderately trastuzumab sensitive), MDA-MB-361 (moderate HER2 gene amplification, HER2/CEP17 ratio: 3.6, intermediate HER2 expression, trastuzumab insensitive), and MDA-MB-453 (moderate HER2 gene amplification, borderline HER2 gene ratio 2.1, intermediate HER2 protein expression, trastuzumab insensitive) BC cell lines.