Loss of expression of the Neural Cell Adhesion Molecule 1 (NCAM1) in atypical teratoid/rhabdoid tumors: a new diagnostic marker?

Background: Atypical teratoid/rhabdoid tumors (AT/RT) are aggressive embryonal tumors of the central nervous system. They are largely characterized by inactivating mutations of the SMARCB1 tumor suppressor gene. AT/RT patients have a very poor prognosis and no standard therapeutic protocol has been defined yet. Recently, multimodal therapy with multiple drug combinations has slightly improved the overall survival, however drug toxicity remains high. In this scenario, a better understanding of the pathophysiology of the disease is needed. Methods: We evaluated the gene expression profile of AT/RT samples to find new genetic factors contributing to the pathophysiology of the disease. We found target genes significantly differentially expressed between AT/RT and medulloblastoma (MB), the most common embryonal brain tumor. The mRNA expression was validated by quantitative real-time PCR and, at the protein level, expression was validated by immunohistochemistry in an independent set of tumors. Results: The Neural cell adhesion molecule 1 (NCAM1) gene was found to be consistently downregulated in AT/RT samples when compared to MB and normal brain tissue. Immunohistochemistry showed that the expression of NCAM1 in AT/RT was significantly lower than that of MB. Conclusion: NCAM1 is an important molecule involved in neuron-to-neuron and neuron-to-muscle adhesion during development. Downregulation of NCAM1 has been implicated in several human cancers suggesting that it might have a tumor repressor role. In this study we found a significantly reduced expression of NCAM1 in AT/RT when compared to MB and we suggest that this feature can be used as a diagnostic marker, along with demonstration of SMARCB1 (INI1) or SMARCA4 (BRG1) inactivation. The roles of NCAM1 in the pathophysiology of AT/RT are still to be determined.