Paraffin immunohistochemical detection of CD56, a useful marker for neural cell adhesion molecule (NCAM), in normal and neoplastic fixed tissues

CD56, the neural cell adhesion molecule (NCAM), is a natural killer (NK) cell-associated antigen that has been identified as a neuroendocrine marker. CD56 is present in carcinoid tumors, paragangliomas, and neuroendocrine carcinomas, and may be seen in nonneuroendocrine carcinomas, myeloid leukemias, some T cell lymphomas, and multiple myeloma. To date, most studies detecting this antigen have been performed on fresh or frozen tissue. We applied either of two monoclonal CD56 antibodies to routinely-fixed, paraffin-embedded sections of various normal (autopsy) tissues and tumors using the avidin-biotin-peroxidase complex method with an automated immunostainer. We found optimal reactivity of CD56 using microwave-based epitope retrieval, as reactivity was markedly decreased with enzymatic pretreatment. Autopsy tissues showed strong marking of peripheral nerve, adrenal zona glomerulosa and medulla, and synapses in cerebral cortex. CD56 marked thyroid follicular epithelium, proximal renal tubules, hepatocytes, gastric parietal cells, and pancreatic islet cells. Merkel cell carcinoma, neuroblastoma, ganglioglioma, oligodendroglioma, glioblastoma multiforme, pheochromocytoma, retinoblastoma, laryngeal and pulmonary squamous cell carcinomas, pulmonary and intestinal carcinoids, pulmonary small-cell undifferentiated carcinoma, pancreatic islet cell tumor, hepatocellular carcinoma, renal cell carcinoma, follicular and papillary thyroid carcinoma, NK cell lymphoma and NK-like T-cell lymphoma marked positively. We conclude that CD56 can be detected in paraffin-embedded tissues following nonenzymatic epitope retrieval in some normal tissues, tumors of neuroendocrine origin, and other neoplasms known to express NCAM.