ERBB2 and breast carcinoma: HER2 signalling in breast cancer cells is critical in heregulin β1-induced up-regulation of vascular endothelial growth factor-C, an important regulator of tumour lymphangiogenesis33, and the HER2 protein expression level is significantly associated with vascular endothelial growth factor-C expression and tumour lymphangiogenesis in human breast cancer tissues34.