As a rule, high-grade gliomas almost always grow back even after complete surgical excision, so are commonly called recurrent cancer of the brain.Conversely, 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 mutated early in the disease. p53 is the "guardian of the genome", which, during DNA and cell duplication, makes sure the DNA is copied correctly and destroys the cell (apoptosis) if the DNA is mutated and cannot be fixed. When p53 itself is mutated, other mutations can survive. Phosphatase and tensin homolog (PTEN), another tumor suppressor gene, is itself lost or mutated. Epidermal growth factor receptor, 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. In 2009, mutations in IDH1 and IDH2 were found to be part of the mechanism and associated with a less favorable prognosis. Diagnosis
Classification
Gliomas are classified by cell type, by grade, and by location. By type of cell
Gliomas are named according to the specific type of cell with which they share histological features, but not necessarily from which they originate. The main types of glioma are:
Ependymomas: ependymal cells
Astrocytomas: astrocytes (glioblastoma multiforme is a malignant astrocytoma and the most common primary brain tumor among adults).
Results show the evidence is insufficient to make a reliable decision. The relative effectiveness of surgical resection compared to biopsy for people with malignant glioma (high-grade) is unknown.For high-grade gliomas, a 2003 meta-analysis compared radiotherapy with radiotherapy and chemotherapy. It showed a small but clear improvement from using chemotherapy with radiotherapy. A 2019 meta-analysis suggested that for people with less aggressive gliomas, radiotherapy may increase the risk of long term neurocognitive side effects. Whilst, evidence is uncertain on whether there are long term neurocognitive side effects associated with chemoradiotherapy.Temozolomide is effective for treating Glioblastoma Multiforme (GBM) compared to radiotherapy alone. A 2013 meta-analysis showed that Temozolomide prolongs survival and delays progression, but is associated with an increase in side effects such as blood complications, fatigue, and  infection. For people with recurrent GBM, when comparing temozolomide with chemotherapy, there may be an improvement in the time-to-progression and the persons quality of life, but no improvement in overall survival, with temozolomide treatment. Evidence suggests that for people with recurrent high-grade gliomas who have not had chemotherapy before, there are similar survival and time-to-progression outcomes between treatment with temozolomide or the chemotherapy multidrug known as PCV (procarvazine, lomustine and vincristine).A mutational analysis of 23 initial low-grade gliomas and recurrent tumors from the same patients has challenged the benefits and usage of Temozolomide. The study showed that when lower-grade brain tumors of patients are removed and patients are further treated with Temozolomide, 6 out of 10 times the recurrent tumors were more aggressive and acquired alternative and more mutations.