Glioblastoma, also known as glioblastoma multiforme (GBM), is the most aggressive cancer that begins within the brain. Initially, signs and symptoms of glioblastoma are non-specific. They may include headaches, personality changes, nausea, and symptoms similar to those of a stroke. Worsening of symptoms often is rapid. This may progress to unconsciousness.
The cause of most cases is unclear. Uncommon risk factors include genetic disorders such as neurofibromatosis and Li-Fraumeni syndrome, and previous radiation therapy. Glioblastomas represent 15% of brain tumors. They can either start from normal brain cells or develop from an existing low-grade astrocytoma. The diagnosis typically is made by a combination of CT scan, MRI scan, and tissue biopsy.
There is no clear way to prevent the disease. Typically, treatment involves surgery, after which chemotherapy and radiation therapy are used. The medication temozolomide is used frequently as part of chemotherapy. High dose steroids may be used to help reduce swelling and decrease symptoms. It is unclear whether trying to remove all or simply most of the cancer is better.
Despite maximum treatment, the cancer usually recurs. The most common length of survival following diagnosis is 12 to 15 months, with fewer than 3% to 5% 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 3 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 in glioblastoma with promising results.
Signs and symptoms
Common symptoms include seizure, 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, GBM occurs more commonly in males.
Other associations include exposure to smoking, pesticides, and working in petroleum refining or rubber manufacturing.
Glioblastoma has been associated with the viruses SV40, HHV-6, and cytomegalovirus.
The cellular origin of glioblastoma is unknown. Because of the similarities in immunostaining of glial cells and glioblastoma, it has long been assumed that gliomas such as glioblastoma originate from glial type cells. However more recent studies suggest that astrocytes, oligodendrocyte progenitor cells and neural stem cells could also serve as the cell of origin.
Glioblastoma multiforme tumors are characterized by the presence of small areas of necrotizing tissue 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 will usually show 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:
- Classical: Ninety-seven percent of tumors in the 'classical' subtype carry extra copies of the epidermal growth factor receptor (EGFR) gene, and most have higher than normal expression of epidermal growth factor receptor (EGFR), whereas the gene TP53 (p53), which is often mutated in glioblastoma, is rarely mutated in this subtype. Loss of heterozygosity (LOH) in chromosome 10 is also frequently seen in the classical subtype alongside chromosome 7 amplification.
- The Proneural subtype often has high rates of alterations in TP53 (p53), and in PDGFRA, the gene encoding a-type platelet-derived growth factor receptor, and in IDH1, the gene encoding isocitrate dehydrogenase-1.
- 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 is described to impair DNA transcription and therefore, expression of the MGMT enzyme. Since an 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
Cancer cells with properties similar to stem cells have been found in glioblastomas (this may be a cause of their resistance to conventional treatments, and high recurrence rate). These so-called glioblastoma stem-like cells reside in a niche around arterioles, protecting these cells against therapy by maintaining a relatively hypoxic environment. A biomarker for cells in glioblastomas that exhibit cancer stem cell properties, the transcription factor Hes3, has been shown to regulate their number when placed in culture.
The IDH1 gene encodes for the enzyme isocitrate dehydrogenase 1 and is frequently 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. It has been hypothesized that IDH1-mutated glioblastoma are in 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 behaviour of these IDH1-mutated glioblastoma.
Furthermore, glioblastoma multiforme exhibits numerous alterations in genes that encode for ion channels, including upregulation of gBK potassium channels and ClC-3 chloride channels. It has been hypothesized that by upregulating these ion channels, glioblastoma tumor cells can 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.
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 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.
It is important to distinguish primary glioblastoma from secondary glioblastoma. These tumors occur spontaneously (de novo) or have progressed from a lower-grade glioma, respectively. Primary glioblastomas have a worse prognosis, 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 glioblastoma carries 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.
It is very difficult to treat glioblastoma due to several complicating factors:
- The tumor cells are very resistant to conventional therapies.
- The brain is susceptible to damage due to conventional therapy.
- The brain has a very limited capacity to repair itself.
- Many drugs cannot cross the blood-brain barrier to act on the tumor.
Treatment of primary brain tumors and brain metastases consists of both symptomatic and palliative therapies.
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 it has been estimated that only approximately 40% of patients required this treatment. Recently, it has been recommended that neurosurgeons not administer anticonvulsants 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 given 4 to 8 mg every 4 to 6 h, 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.
Palliative treatment usually is conducted to improve quality of life and to achieve a longer survival time. It includes surgery, radiation therapy, and chemotherapy. A maximally feasible resection with maximal tumor-free margins is usually performed along with external beam radiation and chemotherapy. Gross total resection of tumor is associated with a better prognosis.
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. 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 in retrospective analyses. 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, and 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 (TMZ). 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.
GBM tumors are well known to contain zones of tissue exhibiting hypoxia which are highly resistant to radiotherapy. Various approaches to chemotherapy radiosensitizers have been pursued with limited success as of 2016. As of 2010 newer research approaches included preclinical and clinical investigations into the use of an oxygen diffusion-enhancing compound such as trans sodium crocetinate (TSC) as radiosensitizers, and as of 2015 a clinical trial was underway.
Boron neutron capture therapy has been tested as an alternative treatment for glioblastoma multiforme but is not in common use.
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 regime 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.
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 affect overall survival.
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 5% of people surviving longer than five years. Without treatment survival is typically 3 months.
Increasing age (> 60 years of age) carries a worse prognostic risk. Death is usually due to widespread tumor infiltration with cerebral edema and increased intracranial pressure.
A good initial Karnofsky Performance Score (KPS) and MGMT methylation are associated with longer survival. A DNA test can be conducted on glioblastomas to determine whether or not the promoter of the MGMT gene 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 of under 50 is linked to longer survival in glioblastoma multiforme, as is 98%+ resection and use of temozolomide chemotherapy and better Karnofsky performance scores. 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. The population-based cure is thought to occur when a population'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, there is a small number of survivors who have been GBM free for more than 10-20 years.
According to a 2003 study, glioblastoma multiforme prognosis can be divided into three subgroups dependent on KPS, the age of the patient, and treatment.
About 3 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. It is the second most common central nervous system cancer after meningioma.
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 in preclinical animal models of glioblastoma.
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 increased incidence of GBM and use of a cell phone for longer than 10 years, especially among those who always held the phone on one side of their head.
- List of people with brain tumors
- Information about Glioblastoma Multiforme (GBM) from the American Brain Tumor Association
- AFIP Course Syllabus - Astrocytoma WHO Grading Lecture Handout
- Image Database - MR & CT of Glioblastoma
Source of the article : Wikipedia