in determining prognosis. glioblastoma multiforme main article: glioblastoma multiforme glioblastoma multiforme (gbm) is the most aggressive (grade iv) and most common form of a malignant brain tumor. even when aggressive multimodality therapy consisting of radiotherapy, chemotherapy, and surgical excision is used, median survival is only 12–17 months. standard therapy for glioblastoma multiforme consists of maximal surgical resection of the tumor, followed by radiotherapy between two and four weeks after the surgical procedure to remove the cancer, then by chemotherapy, such as temozolomide. most patients with glioblastoma take a corticosteroid, typically dexamethasone, during their illness to relieve symptoms. experimental treatments include targeted therapy, gamma knife radiosurgery, boron neutron capture therapy, gene therapy, and chemowafer implants. oligodendrogliomas main article: oligodendroglioma oligodendrogliomas are incurable but slowly progressive malignant brain tumors. they can be treated with surgical resection, chemotherapy, radiotherapy or a combination. for some suspected low-grade (grade ii) tumors, only a course of watchful waiting and symptomatic therapy is opted for. these tumors show a high frequency of co-deletions of the p and q arms of chromosome 1 and chromosome 19 respectively (1p19q co-deletion) and have been found to be especially chemosensitive with one report claiming them to be one of the most chemosensitive tumors. a median survival of up to 16.7 years has been reported for grade ii oligodendrogliomas. acoustic neuroma acoustic neuromas are non-cancerous tumors. they can be treated with surgery, radiation therapy, or observation. early intervention with surgery or radiation is recommended to prevent progressive hearing loss. epidemiology figures for incidences of cancers of the brain show a significant difference between more- and less-developed countries (the less-developed countries have lower incidences of tumors of the brain). this could be explained by undiagnosed tumor-related deaths (patients in extremely poor situations do not get diagnosed, simply because they do not have access to the modern diagnostic facilities required to diagnose a brain tumor) and by deaths caused by other poverty-related causes that preempt a patient's life before tumors develop or tumors become life-threatening. nevertheless, statistics suggest that certain forms of primary brain tumors are more common among certain populations. the incidence of low-grade astrocytoma has not been shown to vary significantly with nationality. however, studies examining the incidence of malignant central nervous system (cns) tumors have shown some variation with national origin. since some high-grade lesions arise from low-grade tumors, these trends are worth mentioning. specifically, the incidence of cns tumors in the united states, israel, and the nordic countries is relatively high, while japan and asian countries have a lower incidence. these differences probably reflect some biological differences as well as differences in pathologic diagnosis and reporting. worldwide data on incidence of cancer can be found at the who (world health organization) and is handled by the iarc (international agency for research on cancer) located in france. united states in the united states in 2015, approximately 166,039 people were living with brain or other central nervous system tumors. over 2018, it was projected that there would be 23,880 new cases of brain tumors and 16,830 deaths in 2018 as a result, accounting for 1.4 percent of all cancers and 2.8 percent of all cancer deaths. median age of diagnosis was 58 years old, while median age of death was 65. diagnosis was slightly more common in males, at approximately 7.5 cases per 100 000 people, while females saw 2 fewer at 5.4. deaths as a result of brain cancer were 5.3 per 100 000 for males, and 3.6 per 100 000 for females, making brain cancer the 10th leading cause of cancer death in the united states. overall lifetime risk of developing brain cancer is approximated at 0.6 percent for men and women. uk brain, other cns or intracranial tumors are the ninth most common cancer in the uk (around 10,600 people were diagnosed in 2013), and it is the eighth most common cause of cancer death (around 5,200 people died in 2012). white british patients with brain tumour are 30% more likely to die within a year of diagnosis than patients from other ethnicities. the reason for this is unknown. children in the united states more than 28,000 people under 20 are estimated to have a brain tumor. about 3,720 new cases of brain tumors are expected to be diagnosed in those under 15 in 2019. higher rates were reported in 1985–1994 than in 1975–1983. there is some debate as to the reasons; one theory is that the trend is the result of improved diagnosis and reporting, since the jump occurred at the same time that mris became available widely, and there was no coincident jump in mortality. central nervous system tumors make up 20–25 percent of cancers in children. the average survival rate for all primary brain cancers in children is 74%. brain cancers are the most common cancer in children under 19, are result in more death in this group than leukemia. younger people do less well. the most common brain tumor types in children (0-14) are: pilocytic astrocytoma, malignant glioma, medulloblastoma, neuronal and mixed neuronal-glial tumors, and ependymoma. in children under 2, about 70% of brain tumors are medulloblastomas, ependymomas, and low-grade gliomas. less commonly, and seen usually in infants, are teratomas and atypical teratoid rhabdoid tumors. germ cell tumors, including teratomas, make up just 3% of pediatric primary brain tumors, but the worldwide incidence varies significantly. in the uk, 429 children aged 14 and under are diagnosed with a brain tumour on average each year, and 563 children and young people under the age of 19 are diagnosed. research immunotherapy cancer immunotherapy is being actively studied. for malignant gliomas no therapy has been shown to improve life expectancy as of 2015. vesicular stomatitis virus