Fig. 1.

A Paraffin block of a tissue array which is used in the immunohistochemical quality assurance trial; B 30 different tumour samples with defined target expression are assembled in one slide which has been stained for cytokeratin. Up to 200 slides can be produced from one tissue array assuring that all participants in the trial obtain almost identical material and that results among different laboratories become comparable. In the quality network of the German Society for Pathology and the Berufsverband Deutscher Pathologen (‘QuIP’, www.ringversuch.de; www99.mh-han-nover.de/institute/pathologie/dgp), quality assurance trials based on tissue arrays have been set up for different target molecules (ER, PR, HER2, c-kit).