Immunohistochemistry in childhood brain tumors: what are the facts?

In the past, contradictory results have been reported concerning the specificity of neuronal or glial cell markers. However, we have investigated this aspect in a large group of more than 550 brain tumors (among them 60 medulloblastomas). These contradictions can easily be explained by considering two basic facts. First, every neoplastic cell population, especially in embryonic tumors, diffusely infiltrates the brain tissue: non-neoplastic cells, intermingled with tumor cells, can therefore give rise to immunohistochemical and histogenetic misinterpretations. Second, different cell markers can be expressed by one and the same cell (e.g., GFAP, NSE, vimentin), making nosological interpretation of the tumor difficult, impossible, or at best rather subjective. Clear-cut marker positivity is mostly found in the differentiated tumors for which the nosological classification is already clear by the usual histological methods. Only synaptophysin seems to be a reliable marker for neurogenic cells. In embryonic brain tumors (so-called PNET), no correlations between the presence of a given cell marker and the biological behavior of the tumor have so far been detected.