Overexpression of HER2/neu in solid tumours: an immunohistochemical survey

Aims: Using a standardized immunohistochemical assay we have evaluated 575 primary neoplasms of different histogenesis to determine the incidence of H ER2 overexpression in some of the most common categories of human solid neo plasms. This study addresses the variable incidence of HER2 overexpression previously published for some tumour types. Methods and results: The immunohistochemical staining was performed on para ffin sections of surgical specimens and a well-defined scoring system based upon numbers of HER, receptors expressed on the cell surface was applied. Overexpression of HER2 as defined as a HER2 score of equal or greater than 2 was seen in breast cancer (22%), pulmonary adenocarcinoma (28%), colorect al adenocarcinomas (17%), pulmonary squamous (11%) and gastric adenocarcino mas (11%). As expected, the proportion of cases with a HER2 score of 3 was highest in breast cancer. Contrary to published results prostate and pancre as adenocarcinomas showed a very low incidence of HER2 overexpression. Conclusions: Overexpression of HER2 is detected immunohistochemically in a proportion of epithelial neoplasms of diverse histogenesis in addition to d uctal breast cancer. The standardized format of the assay will allow compar ative analyses of studies performed at different institutions.