TAA are often used in cancer vaccine development and can be primarily characterised as either (i) differentiation antigens: tissue-specific proteins that are expressed in the tumour and the analogous normal tissue, but are aberrantly expressed in the tumour due to hyperproliferation of particular cell type (e.g. PAP); or (ii) overexpressed antigens: highly expressed proteins in tumours due to malignancy, but have a baseline expression in healthy tissue (e.g. Her2/neu) [11,12]. The gene discussed is ERBB2; the disease is cancer.