Glioma - Pathophysiology

Pathophysiology

High-grade gliomas are highly-vascular tumors and have a tendency to infiltrate. They have extensive areas of necrosis and hypoxia. Often tumor growth causes a breakdown of the blood–brain barrier in the vicinity of the tumor. As a rule, high-grade gliomas almost always grow back even after complete surgical excision, and so are commonly called recurrent cancer of the brain.

On the other hand, low-grade gliomas grow slowly, often over many years, and can be followed without treatment unless they grow and cause symptoms.

Several acquired (not inherited) genetic mutations have been found in gliomas. Tumor suppressor protein 53 (p53) is an early mutation. p53 is the "guardian of the genome," which, during DNA and cell duplication, makes sure that the DNA is copied correctly and destroys the cell (apoptosis) if the DNA is mutated and can't be fixed. When p53 itself is mutated, other mutations can survive. Phosphatase and tensin homolog (PTEN), another protein that also helps destroy cells with dangerous mutations, is itself lost or mutated. Epidermal growth factor receptor (EGFR), a growth factor that normally stimulates cells to divide, is amplified and stimulates cells to divide too much. Together, these mutations lead to cells dividing uncontrollably, a hallmark of cancer. Recently, mutations in IDH1 and IDH2 were found to be part of the mechanism and associated with a more favorable prognosis. The IDH1 and IDH2 genes are significant because they are involved in the citrate cycle in mitochondria. Mitochondria are involved in apoptosis. Furthermore, the altered glycolysis metabolism in some cancer cells leads to low oxygen (hypoxia). The normal response to hypoxia is to stimulate the growth of new blood vessels (angiogenesis). So these two genes may contribute to both the lack of apoptosis and vascularization of gliomas.

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