Immunohistochemical performance of antibodies on previously frozen tissue

Immunohistochemical stains are occasionally performed on paraffin-embedded, fixed material that was previously frozen, most frequently for an intraope rative frozen section diagnosis. A retrospective study comparing immunohist ochemistry on previously frozen then fixed tissue with freshly fixed tissue was designed. Of 43 cases identified during the period 1994-1996 in which immunohistochemistry was performed on frozen section blocks, 19 met criteri a for inclusion. Immunohistochemistry using antibodies to S-100, HMB-45, sy naptophysin, chromogranin, neuron-specific enolase (NSE), neurofilament, gl ial fibrillary acidic protein, vimentin, and carcinoembryonic antigen (CEA) was compared. Staining for cytokeratins was unchanged. Staining for S-100, HMB-45, synaptophysin, and NSE were negative in frozen/fixed tissue and po sitive in comparable fresh/fixed tissue in at least one case each. Chromogr anin and CEA exhibited a significant decrease in the frozen/fixed tissue. W e conclude that caution must be exercised in interpreting immunohistochemic al results using tissue that was frozen for intraoperative consultation bef ore formalin fixation and paraffin embedding.