Diagnostic revision of 206 adult gliomas (including 40 oligoastrocytomas) based on ATRX, IDH1/2 and 1p/19q status.

The diagnosis of 206 low and high grade adult gliomas, including 40 oligoastrocytomas, was revised based on the immunohistochemical reactivity for the ATRX protein, IDH1/2 mutation status and 1p/19q chromosomal status. All oligodendrogliomas kept the initial diagnosis. Astrocytomas did not change diagnosis in 30 of 36 cases (83.3 %); four of 36 (11.1 %) cases were reclassified as oligodendroglioma, one (2.8 %) as DNT and the other (2.8 %) as reactive gliosis. Oligoastrocytomas changed diagnosis in 35 of 40 (87.5 %) cases, being reclassified 22 of 40 (55 %) as astrocytoma, 11 of 40 (27.5 %) as oligodendroglioma and two of 40 (5 %) as reactive gliosis. Four (10 %) remained unclassifiable. In one case only (2.5 %), the diagnosis of oligoastrocytoma could not be excluded since tumor astrocytes and tumor oligodendrocytes coexisted in mixed tumor areas. In the GBM tumor subgroup, GBMO disappeared because they were not substantiated by molecular genetics. Pilocytic astrocytomas retained ATRX expression. Loss of nuclear ATRX protein expression was strongly associated to IDH1/2 mutations (p = 0.0001) and mutually exclusive with total 1p/19q co-deletion (p = 0.0001). In astrocytic tumors, loss of immunoreactivity for the ATRX protein was significantly associated to the ALT phenotype (p = 0.0003). The constitutive ATRX expression in microglia/macrophages may be misleading, especially in the identification of an oligodendroglial tumor infiltration. Of paramount importance in the recognition of oligodendroglial and astrocytic tumor cells were the double immunostainings for ATRX/GFAP, ATRX/IDH1R132H, ATRX/Iba-1 and ATRX/CD68.

The Microenvironment in Gliomas: Phenotypic Expressions.

The microenvironment of malignant gliomas is described according to its definition in the literature. Beside tumor cells, a series of stromal cells (microglia/macrophages, pericytes, fibroblasts, endothelial cells, normal and reactive astrocytes) represents the cell component, whereas a complex network of molecular signaling represents the functional component. Its most evident expressions are perivascular and perinecrotic niches that are believed to be the site of tumor stem cells or progenitors in the tumor. Phenotypically, both niches are not easily recognizable; here, they are described together with a critical revision of their concept. As for perinecrotic niches, an alternative interpretation is given about their origin that regards the tumor stem cells as the residue of those that populated hyperproliferating areas in which necroses develop. This is based on the concept that the stem-like is a status and not a cell type, depending on the microenvironment that regulates a conversion of tumor non-stem cells and tumor stem cells through a cell reprogramming.