In this study, to evaluate the potential clinical activity of pertuzumab when used alone or in combination with trastuzumab, we tested six USPC primary cell lines for HER2/neu receptor expression and c-erbB2 gene amplification, and evaluated the sensitivity of these biologically aggressive tumours expressing different levels of HER2/neu to pertuzumab- and trastuzumab-mediated ADCC and complement-dependent cytotoxicity (CDC) in standard 5 h chromium release assays. The gene discussed is ERBB2; the disease is neoplasm.