Glioblastoma multiforme: morphology and biology.

Glioblastoma multiforme, representing about 50% of all gliomas, encompasses a group of intrinsic tumours of the brain in later years (age peak around 50 years), the morphological hallmarks of which are an ensemble of variations in tumour cell and tissue structure featuring its biological malignancy. Glioblastoma, while sometimes appearing as a distinct "primary" tumour type, is usually accepted as an extreme manifestation of anaplasia and dedifferentiation of glia, mostly astrocytic. The astrocytic nature of most glioblastomas has been confirmed by ultrastructural studies and progressive differentiation of tumours maintained in organotypic tissue culture. Reproducible experimental models are particularly induced by oncogenic RNA (oncorna) viruses. The cell kinetic parameters are similar to those of other solid malignant tumours except for a comparatively low growth fraction of glioblastoma. The frequent occurrence of giant cells as well as of regressive changes with necrosis and vascular responses are indirect (secondary) indicators of malignancy which coincide with histochemical (enzymatic anisochronia) and biochemical data (lower level of glia specific S100 protein than in differentiated gliomas). Vascular proliferation, a characteristic feature of glioblastoma, may occasionally progress to sarcomatous transformation with development of gliosarcomas (mixed glial-mesenchymal tumours). While dissemination of glioblastoma through the cerebrospinal pathways is not uncommon, extraneural distant metastatic spread is rare, and usually observed after craniotomy. The results of modern neuro-oncology support the pathogenetic view that glioblastoma results from neoplastic transformation of glial elements with continuing dedifferentiation. This transformation can be experimentally induced by various factors including oncogenic DNA (oncorna) viruses by using a reverse transcriptase, while there is indirect evidence for an oncorna-virus information in human glioblastoma. The significance of immunological factors in the pathogenesis of brain tumours and in the course of neoplastic transformation of glia is not yet understood, but both morphological and immunological data are in favour of a cell mediated immunological reaction against tumour-specific antibodies. Since immunological factors and changes in cytokinetics are apparently active after the transformed tumour cells proliferate, all available therapeutic methods, including radiation, chemotherapy, and immunotherapy of glioblastoma only influence the final stages of neoplastic development with clinical manifestation of the tumour. In spite of modern combination and multimodality therapy schemes the prognosis of glioblastoma is still poor.