ABERRANT RB GENE-EXPRESSION IN ROUTINELY PROCESSED, ARCHIVAL TUMOR-TISSUES DETERMINED BY 3 DIFFERENT ANTI-RB ANTIBODIES

The retinoblastoma (RB) susceptibility gene encodes a nuclear phosphoprotein which is likely involved in cell cycle control and cell differentiation. The RB protein is mutated or absent in a variety of human malignancies. Its role as a molecular marker for clinical tumor behavior is under extensive investigation. However, studies on the status of the RB protein in primary or metastatic tumors and their precursor lesions have been slowed by the lack of availability of a sensitive, reliable assay which allows examination of RB expression in selected cell populations within archival tissues. Thus far, meaningful immunohistochemical analysis of RB protein in formalin-fixed, paraffin-embedded specimens has been achieved only with the polyclonal antibody RB-WL-1. We now describe a method which produces excellent staining results in formalin-fixed, routinely processed tissues, using commercially available monoclonal antibodies (MAbs) in conjunction with an antigen-retrieval step. The resulting stains were superior to those on frozen sections and comparable to those obtained with RB-WL-1. Twelve of 51 random invasive bladder cancers (24%) had abnormal expression of the RB gene, as determined by immunohistochemistry. Smaller cohorts of breast, prostate and lung carcinomas had incidences of aberrant RB gene expression ranging from 9% to 24%. Since the staining method was widely applicable to essentially all formalin-fixed, archival tissues, it may expedite studies on the biological and clinical significance of altered RB expression in human neoplasia.