Glial fibrillary acidic protein in medulloblastomas and other embryonic CNS tumours of children.

Investigation of GFAP in 50 medulloblastomas showed a few GFAP-positive tumour cells in 5 cases only; 17 tumours were negative, and 28 showed a "pseudopositivity", i.e. GFAP-bearing cells were identified as reactive or degenerating astrocytes, intermingled with tumour elements. A high GFAP content was seen in 2 small-cell gliomas of the cerebellum, whereas 3 pineoblastomas, 2 neuroblastomas of CNS, and one medulloepithelioma were negative. GFAP is a very good method for identificating astrocytes, but does not seem to be reliable for identifying the origin of undifferentiated tumours such as medulloblastomas. In these neoplasms glial differentiation is lacking or extremely rare, GFAP-positivity being mostly an artifact. The investigation of small tumour samples or the positivity of a single cell are inadequate data for a correct evaluation of the findings, especially taking in mind that GFAP of degenerated astrocytes can be phagocytised by cells other than glial (e.g., macrophages, epithelial and meningioma cells). The importance of carefully checking the whole structure of the tumour is stressed, GFAP positivity or negativity being not a sufficient criterion for its nosological classification.