Expression of diagnostic neuronal markers and outcome in glioblastoma

Background: High-grade gliomas featuring giant cells, often demonstrate immunoreactivity for neuronal markers, a finding prognostically significant according to some studies. We investigated this event in glioblastomas (GBM). Methods: Immunoexpression for synaptophysin, neurofilament protein, neuronal nuclear antigen, chromogranin and glial fibrillary acidic protein was analysed in 82 GBM including 11 fibrillary, 8 gemistocytic, 40 giant cell and 23 small cell examples. Survival was compared between tumours exhibiting (GBMpos) or lacking (GBMneg) neuronal markers and also between tumours expressing only one vs. two or more neuronal markers. Results: Forty-five of the 82 tumours (54.8%) including 5 fibrillary, 5 gemistocytic, 30 giant cell and 5 small cell GBMs expressed at least one neuronal marker, synaptophysin being the most frequent (96%). There was no statistically significant difference in survival between GBMpos and GBMneg tumours, all cytologic subtypes combined (P = 0.22). The same was true when cytologic categories were compared. When only GBMpos tumours were analysed, there was a marginally significant difference in outcome between tumours positive for one vs. multiple markers (P = 0.05). This difference was influenced primarily by giant cell GBMs among which the survival time was significantly shorter in the multiple vs. single marker category (median 123 vs. 295 days, P = 0.014). This difference was not observed in the other GBM cell types. Ultrastructurally, rare neurosecretory granules in glial filament-rich cells were identified in one of four tumours studied. Conclusions: Neuronal marker expression is a frequent feature of GBM. Its prognostic significance is limited to the giant cell GBMs expressing two or more neuronal markers, these being associated with shorter survival.