Reproducibility of p53 immunohistochemistry in bladder tumors

The National Cancer Institute Bladder Tumor Marker Network conducted a stud y to evaluate the reproducibility of immunohistochemistry for measuring p53 expression in bladder tumors, Fifty paraffin blocks (10 from each of the f ive network institutions) were chosen at random from among high-grade invas ive primary bladder tumors. Two sections from each block were sent to each laboratory for staining and scoring, and then all sections were randomly re distributed among the laboratories for a second scoring. Intra- and interla boratory reproducibility was assessed with regard to both staining and scor ing, For overall assessments of p53 positivity, the results demonstrated th at intralaboratory reproducibility was quite good. Concordance across the f ive participating laboratories was high for specimens exhibiting no or mini mal nuclear immunostaining of tumor cells or high percentages of tumor cell s with nuclear immunoreactivities. However, there was a reduced level of co ncordance on specimens with percentages of stained tumor cells in an interm ediate range. The discordancies mere due mainly to staining differences in one of the five laboratories and scoring differences in another laboratory. These results indicate that some caution must be used in comparing results across studies from different groups. Standardization of staining protocol s and selection of a uniform threshold for binary interpretation of results may improve assay reproducibility between laboratories.