ERBB2 and neoplasm: Complexity in understanding the HER2/HER3 activation and signaling arises from the intricate and complex regulation of coexpression of HER2/HER3 receptors and their ligands and the broad spectrum of tumour biochemistry, heterogeneity, and range of sensitivities and resistance exhibited to drugs targeting the HER receptor system [13, 14, 17, 21].