Glioblastoma, also known as glioblastoma multiforme (GBM), is the most aggressive cancer that begins within the brain. Initially, signs and symptoms of glioblastoma are nonspecific. They may include headaches, personality changes, nausea, and symptoms similar to those of a stroke. Worsening of symptoms often is rapid, and may progress to unconsciousness.
Despite maximum treatment, the cancer usually recurs. The typical length of survival following diagnosis is 12 to 15 months, with fewer than 3 to 7% of people surviving longer than five years. Without treatment, survival is typically three months. It is the most common cancer that begins within the brain and the second-most common brain tumor, after meningioma. About three per 100,000 people develop the disease a year. It most often begins around 64 years of age and occurs more commonly in males than females.Immunotherapy is being studied.
Signs and symptoms
Common symptoms include seizures, headaches, nausea and vomiting, memory loss, changes to personality, mood or concentration, and localized neurological problems. The kind of symptoms produced depends more on the location of the tumor than on its pathological properties. The tumor can start producing symptoms quickly, but occasionally is an asymptomatic condition until it reaches an enormous size.
The cause of most cases is unclear. About 5% develop from another type brain tumor known as a low-grade astrocytoma.
Uncommon risk factors include genetic disorders such as neurofibromatosis, Li-Fraumeni syndrome, tuberous sclerosis, or Turcot syndrome. Previous radiation therapy is also a risk. For unknown reasons, it occurs more commonly in males.
Glioblastomas are characterized by the presence of small areas of necrotizingtissue that are surrounded by anaplastic cells. This characteristic, as well as the presence of hyperplastic blood vessels, differentiates the tumor from grade 3 astrocytomas, which do not have these features.
GBMs usually form in the cerebral white matter, grow quickly, and can become very large before producing symptoms. Fewer than 10% form more slowly following degeneration of low-grade astrocytoma or anaplastic astrocytoma. These are called secondary GBMs and are more common in younger patients (mean age 45 versus 62 years). The tumor may extend into the meninges or ventricular wall, leading to high protein content in the cerebrospinal fluid (CSF) (> 100 mg/dl), as well as an occasional pleocytosis of 10 to 100 cells, mostly lymphocytes. Malignant cells carried in the CSF may spread (rarely) to the spinal cord or cause meningeal gliomatosis. However, metastasis of GBM beyond the central nervous system is extremely unusual. About 50% of GBMs occupy more than one lobe of a hemisphere or are bilateral. Tumors of this type usually arise from the cerebrum and may exhibit the classic infiltration across the corpus callosum, producing a butterfly (bilateral) glioma.
The tumor may take on a variety of appearances, depending on the amount of hemorrhage, necrosis, or its age. A CT scan usually shows an inhomogeneous mass with a hypodense center and a variable ring of enhancement surrounded by edema. Mass effect from the tumor and edema may compress the ventricles and cause hydrocephalus.
Four subtypes of glioblastoma have been identified based on gene expression:
Classical: Around 97% of tumors in this subtype carry extra copies of the epidermal growth factor receptor (EGFR) gene, and most have higher than normal expression of EGFR, whereas the geneTP53 (p53), which is often mutated in glioblastoma, is rarely mutated in this subtype.Loss of heterozygosity in chromosome 10 is also frequently seen in the classical subtype alongside chromosome 7 amplification.
The mesenchymal subtype is characterized by high rates of mutations or other alterations in NF1, the gene encoding neurofibromin 1 and fewer alterations in the EGFR gene and less expression of EGFR than other types.
The neural subtype was typified by the expression of neuron markers such as NEFL, GABRA1, SYT1, and SLC12A5, while often presenting themselves as normal cells upon pathological assessment.
Many other genetic alterations have been described in glioblastoma, and the majority of them are clustered in two pathways, the RB and the PI3K/AKT. Glioblastomas have alterations in 68-78% and 88% of these pathways, respectively.
Another important alteration is methylation of MGMT, a "suicide" DNA repair enzyme. Methylation impairs DNA transcription and expression of the MGMT gene. Since the MGMT enzyme can repair only one DNA alkylation due to its suicide repair mechanism, reverse capacity is low and methylation of the MGMT gene promoter greatly affects DNA-repair capacity. Indeed, MGMT methylation is associated with an improved response to treatment with DNA-damaging chemotherapeutics, such as temozolomide.
Glioblastoma stem-like cells
Tumorigenic glioblastoma cells (i.e. cancer stem-like cells) are identifiable in glioblastoma. Their presence, coupled with the glioblastomas diffuse nature results in difficulty in removing them completely by surgical intervention, and is therefore believed to be the possible cause behind resistance to conventional treatments, and the high recurrence rate . These glioblastoma stem-like cells reside in a niche around arterioles, protecting these cells against therapy by maintaining a relatively hypoxic environment. .Glioblastoma stem-like cells share some resemblance with neural progenitor cells, both expressing the surface receptor CD133. Additionally, transcription factors that have roles in proliferation in progenitor cells - OLIG2 and Hes3 have been shown to be markers of glioblastoma cancer stem cells. CD44 can also be used as a cancer stem cell marker in a subset of glioblastoma tumour cells
The IDH1 gene encodes for the enzyme isocitrate dehydrogenase 1 and is uncommonly mutated in glioblastoma (primary GBM: 5%, secondary GBM >80%). By producing very high concentrations of the "oncometabolite" D-2-hydroxyglutarate and dysregulating the function of the wild-type IDH1 enzyme, it induces profound changes to the metabolism of IDH1-mutated glioblastoma, compared with IDH1 wild-type glioblastoma or healthy astrocytes. Among others, it increases the glioblastoma cells' dependence on glutamine or glutamate as an energy source.IDH1-mutated glioblastomas are thought to have a very high demand for glutamate and use this amino acid and neurotransmitter as a chemotactic signal. Since healthy astrocytes excrete glutamate, IDH1-mutated glioblastoma cells do not favor dense tumor structures, but instead migrate, invade, and disperse into healthy parts of the brain where glutamate concentrations are higher. This may explain the invasive behavior of these IDH1-mutated glioblastoma.
Furthermore, GBM exhibits numerous alterations in genes that encode for ion channels, including upregulation of gBK potassium channels and ClC-3 chloride channels. By upregulating these ion channels, glioblastoma tumor cells are hypothesized to facilitate increased ion movement over the cell membrane, thereby increasing H2O movement through osmosis, which aids glioblastoma cells in changing cellular volume very rapidly. This is helpful in their extremely aggressive invasive behavior, because quick adaptations in cellular volume can facilitate movement through the sinuous extracellular matrix of the brain.
GBM in the frontal right lobe as seen on CT scan
Sagittal MRI with contrast of a glioblastoma WHO grade IV in a 15-year-old boy
Glioblastoma (histology slide)
Axial post-contrast T1 (top) and T2 (bottom) weighted MRI showing an IDH1 mutant frontal lobe glioblastoma with sparse enhancement despite large size.
When viewed with MRI, glioblastomas often appear as ring-enhancing lesions. The appearance is not specific, however, as other lesions such as abscess, metastasis, tumefactive multiple sclerosis, and other entities may have a similar appearance. Definitive diagnosis of a suspected GBM on CT or MRI requires a stereotactic biopsy or a craniotomy with tumor resection and pathologic confirmation. Because the tumor grade is based upon the most malignant portion of the tumor, biopsy or subtotal tumor resection can result in undergrading of the lesion. Imaging of tumor blood flow using perfusion MRI and measuring tumor metabolite concentration with MR spectroscopy may add diagnostic value to standard MRI in select cases by showing increased relative cerebral blood volume and increased choline peak, respectively, but pathology remains the gold standard for diagnosis and molecular characterization.
Distinguishing primary glioblastoma from secondary glioblastoma is important. These tumors occur spontaneously (de novo) or have progressed from a lower-grade glioma, respectively. Primary glioblastomas have a worse prognosis and different tumor biology, and may have a different response to therapy, which makes this a critical evaluation to determine patient prognosis and therapy. Over 80% of secondary glioblastomas carry a mutation in IDH1, whereas this mutation is rare in primary glioblastoma (5-10%). Thus, IDH1 mutations are a useful tool to distinguish primary and secondary glioblastomas, since histopathologically they are very similar and the distinction without molecular biomarkers is unreliable.
There are no known methods to prevent glioblastoma.
Treating glioblastoma is very difficult due to several complicating factors:
The tumor cells are very resistant to conventional therapies.
The brain is susceptible to damage from conventional therapy.
The brain has a very limited capacity to repair itself.
Treatment of primary brain tumors consists of palliative (symptomatic) care and therapies intended to improve survival.
Supportive treatment focuses on relieving symptoms and improving the patient's neurologic function. The primary supportive agents are anticonvulsants and corticosteroids.
Historically, around 90% of patients with glioblastoma underwent anticonvulsant treatment, although only an estimated 40% of patients required this treatment. Recently, neurosurgeons have been recommended that anticonvulsants not be administered prophylactically, and should wait until a seizure occurs before prescribing this medication. Those receiving phenytoin concurrent with radiation may have serious skin reactions such as erythema multiforme and Stevens-Johnson syndrome.
Corticosteroids, usually dexamethasone, can reduce peritumoral edema (through rearrangement of the blood-brain barrier), diminishing mass effect and lowering intracranial pressure, with a decrease in headache or drowsiness.
Surgery is the first stage of treatment of glioblastoma. An average GBM tumor contains 1011 cells, which is on average reduced to 109 cells after surgery (a reduction of 99%).
Benefits of surgery include resection for a pathological diagnosis, alleviation of symptoms related to mass effect, and potentially removing disease before secondary resistance to radiotherapy and chemotherapy occurs.
The greater the extent of tumor removal, the better. In retrospective analyses, removal of 98% or more of the tumor has been associated with a significantly longer healthier time than if less than 98% of the tumor is removed. The chances of near-complete initial removal of the tumor may be increased if the surgery is guided by a fluorescent dye known as 5-aminolevulinic acid. GBM cells are widely infiltrative through the brain at diagnosis, so despite a "total resection" of all obvious tumor, most people with GBM later develop recurrent tumors either near the original site or at more distant locations within the brain. Other modalities, typically radiation and chemotherapy, are used after surgery in an effort to suppress and slow recurrent disease.
Subsequent to surgery, radiotherapy becomes the mainstay of treatment for people with glioblastoma. It is typically performed along with giving temozolomide. A pivotal clinical trial carried out in the early 1970s showed that among 303 GBM patients randomized to radiation or nonradiation therapy, those who received radiation had a median survival more than double those who did not. Subsequent clinical research has attempted to build on the backbone of surgery followed by radiation. On average, radiotherapy after surgery can reduce the tumor size to 107 cells. Whole-brain radiotherapy does not improve when compared to the more precise and targeted three-dimensional conformal radiotherapy. A total radiation dose of 60-65 Gy has been found to be optimal for treatment.
Most studies show no benefit from the addition of chemotherapy. However, a large clinical trial of 575 participants randomized to standard radiation versus radiation plus temozolomide chemotherapy showed that the group receiving temozolomide survived a median of 14.6 months as opposed to 12.1 months for the group receiving radiation alone. This treatment regimen is now standard for most cases of glioblastoma where the person is not enrolled in a clinical trial. Temozolomide seems to work by sensitizing the tumor cells to radiation, and appears more effective for tumors with MGMT promoter methylation. High doses of temozolomide in high-grade gliomas yield low toxicity, but the results are comparable to the standard doses.Antiangiogenic therapy with medications such as bevacizumab control symptoms, but do not appear to affect overall survival in those with glioblastoma. The overall benefit of anti-angiogneic therapies as of 2019 is unclear.
Alternating electric field therapy is an FDA-approved therapy for newly diagnosed and recurrent glioblastoma. In 2015, initial results from a phase-three randomized clinical trial of alternating electric field therapy plus temozolomide in newly diagnosed glioblastoma reported a three-month improvement in progression-free survival, and a five-month improvement in overall survival compared to temozolomide therapy alone, representing the first large trial in a decade to show a survival improvement in this setting. Despite these results, the efficacy of this approach remains controversial among medical experts.
The most common length of survival following diagnosis is 12 to 15 months, with fewer than 3 to 7% of people surviving longer than five years. In the United States between 2012 and 2016 five year survival was 6.8%. Without treatment, survival is typically 3 months.
A good initial Karnofsky performance score (KPS) and MGMTmethylation are associated with longer survival. A DNA test can be conducted on glioblastomas to determine whether or not the promoter of the MGMTgene is methylated. Patients with a methylated MGMT promoter have longer survival than those with an unmethylated MGMT promoter, due in part to increased sensitivity to temozolomide. This DNA characteristic is intrinsic to the patient and currently cannot be altered externally. Another positive prognostic marker for glioblastoma patients is mutation of the IDH1 gene, which can be tested by DNA-based methods or by immunohistochemistry using an antibody against the most common mutation, namely IDH1-R132H.
More prognostic power can be obtained by combining the mutational status of IDH1 and the methylation status of MGMT into a two-gene predictor. Patients with both IDH1 mutations and MGMT methylation have the longest survival, patients with an IDH1 mutation or MGMT methylation an intermediate survival, and patients without either genetic event have the shortest survival.
Long-term benefits have also been associated with those patients who receive surgery, radiotherapy, and temozolomide chemotherapy. However, much remains unknown about why some patients survive longer with glioblastoma. Age under 50 is linked to longer survival in GBM, as is 98%+ resection and use of temozolomide chemotherapy and better KPSs. A recent study confirms that younger age is associated with a much better prognosis, with a small fraction of patients under 40 years of age achieving a population-based cure. Cure is thought to occur when a person's risk of death returns to that of the normal population, and in GBM, this is thought to occur after 10 years.
UCLA Neuro-oncology publishes real-time survival data for patients with this diagnosis. They are the only institution in the United States that shows how their patients are performing. They also show a listing of chemotherapy agents used to treat GBM tumors. Despite a poor prognosis, a small number of survivors have been GBM free for more than 10 years.
According to a 2003 study, GBM prognosis can be divided into three subgroups dependent on KPS, the age of the patient, and treatment.
Age >= 50, KPS >= 70, surgical removal with good neurologic function
V + VI
Age >= 50, KPS >= 70, surgical removal with poor neurologic function
Age >= 50, KPS >= 70, no surgical removal
Age >= 50, KPS < 70
About three per 100,000 people develop the disease a year, although regional frequency may be much higher. The frequency in England has doubled between 1995 and 2015.
It is the second-most common central nervous system cancer after meningioma. It occurs more commonly in males than females. Although it most often begins around 64 years of age, in 2014, the broad category of brain cancers was second only to leukemia in people in the United States under 20 years of age.
The term glioblastoma multiforme was introduced in 1926 by Percival Bailey and Harvey Cushing, based on the idea that the tumor originates from primitive precursors of glial cells (glioblasts), and the highly variable appearance due to the presence of necrosis, hemorrhage, and cysts (multiform).
As of 2012, RNA interference, usually microRNA, was under investigation in tissue culture, pathology specimens, and preclinical animal models of glioblastoma. Additionally, experimental observations suggest that microRNA-451 is a key regulator of LKB1/AMPK signaling in cultured glioma cells  and that miRNA clustering controls epigenetic pathways in the disease.
Gene therapy has been explored as a method to treat glioblastoma, and while animal models and early-phase clinical trials have been successful, as of 2017, all gene-therapy drugs that had been tested in phase III clinical trials for glioblastoma had failed.
Intranasal drug delivery
Direct nose-to-brain drug delivery is being explored as a means to achieve higher, and hopefully more effective, drug concentrations in the brain. A clinical phase I/II study with glioblastoma patients in Brazil investigated the natural compound perillyl alcohol for intranasal delivery as an aerosol. The results were encouraging and, as of 2016, a similar trial has been initiated in the United States.
Research has been done to see if consumption of cured meat is a risk factor. No risk had been confirmed as of 2013. Similarly, exposure to radiation during medical imaging, formaldehyde, and residential electromagnetic fields, such as from cell phones and electrical wiring within homes, have been studied as risk factors. As of 2015, they had not been shown to cause GBM. However, a meta-analysis published in 2007 found a correlation between the rate of GBMs and use of a cell phone for longer than 10 years, especially among those who always held the phone on one side of their heads.
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