ERBB2 and cancer: HER2 activates multiple signaling axes, especially in MAPK signaling system and STAT3; leading to rapid tumor proliferation and cancer metastasis.15 HER2 also promotes epithelial-mesenchymal transition (EMT) by upregulating TGFβ/SNAIL-ZEB1, activates a Wnt-dependent EMT-like dissemination program, and downregulates E-cadherin expression.16,17 Interestingly, the increase of HER2 expression could be observed in metastatic cancer cells even though the primary tumor is HER2 negative.15,18