Primitive neuroectodermal tumors of the cerebrum: a histological and immunohistochemical study of 10 cases

Four males and 6 females, 5-66 (mean 27) years, with supratentorial primitive neuroectodermal tumors (PNETs) have been treated in one center in a 5-year period. Symptoms and signs had been present from 4 days to 8 years and were highly variable. The frontal hemisphere was involved in 6 cases. Seven patients have died but with a combination of surgery and radiotherapy 3 patients have survived 20 months or longer. All tumors were composed of rounded, hyperchromatic undifferentiated cells but there were focal areas of astrocytic (5 cases), mesenchymal (4 cases) or neuronal differentiation (1 case). In 9 of the 10 cases a proportion of the undifferentiated round cells stained with antibodies to GFAP. Seven of these also showed nuclear staining for S100 protein and 6 of these, plus the tumor that did not stain for GFAP, had cytoplasmic staining for neuron specific enolase. Six tumors stained with antibodies to vimentin but there was no staining for common leukocyte antibody, cytokeratin or myoglobin. These results, in particular those with GFAP, indicate that PNETs undergo differentiation even in areas of apparent morphological uniformity. Furthermore, immunohistochemistry is useful in distinguishing PNETs from other "small blue cell tumors" such as malignant lymphoma and undifferentiated secondary carcinoma.