To determine whether the high, moderate, or low expression of the HER2/neu receptor detected on USPC tissue blocks may differ in the primary USPC cell lines because of the potential selection of a sub-population of cancer cells present in the original tumour, or whether in vitro expansion conditions may have modified receptor expression, we performed additional immunohistochemical analysis of HER2/neu on the cell blocks obtained from all six primary USPC culture cell lines used in cytotoxicity experiments. The gene discussed is ERBB2; the disease is neoplasm.