ERBB2 and neoplasm: The stronger correlation between HER2 protein overexpression and response to anti-HER2 therapy is likely to reflect the fact that HER2 oncogenic pathways are driven by HER2 protein overexpression and not merely by HER2 gene copy number independent of the HER2 protein level as is the case in HER2 IHC 2 + /Amplified tumours.