ERBB2 and neoplasm: USPC ARK-2 and USPC ARK-10, two Her2/neu FISH-positive tumours shedding Her2/neu ECD in the supernatants but showing different levels of Her2/neu surface expression by flow cytometry (Table 2), were representatively tested for their sensitivity to natural killer (NK) cytotoxicity when challenged with heterologous PBLs collected from several healthy donors in a standard 5-h 51Cr-release assay.