ERBB2 and breast cancer: There are also other serum markers that are linked to breast cancer and may be used in clinical practice, including BRCA1, BRCA2, and CA 27.29 carcinoembryonic antigen (CEA), polypeptide antigen (TPA), cytokeratin 19 fragment (CIFRA-21-1), tissue polypeptide specific antigen (TPS), human epidermal growth factor receptor 2 (s-HER2), platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF) and osteopontin (OPN) [18,19].