Glioma malignancy and its biological and histological correlates

Neoplastic transformation is a multiphasic process developing in several subsequent steps. Many things are known on oncogene activation mechanisms and oncogene cooperation in neoplastic transformation, growth factors (EGF, PDGF, etc.), antioncogenes and emerogenes. Tumor progression from benign to malignant growth has diagnostic importance. Morphologically tumor progression is represented by increased anaplasia based on genotypic heterogeneity; among human gliomas the main characteristic is represented by the lack of GFAP expression in a variable percentage of anaplastic cells. Increased cellular density and mitotic index are direct consequence of the growth fraction enhancement, whereas nuclear polymorphism and necroses are less reliable parameters. Finally tumor angiogenesis and the different meaning of endothelial proliferations in different oncotypes is discussed.