Brain tumor
A brain tumor occurs when abnormal cells form within the brain.[2] There are two main types of tumors: malignant (cancerous) tumors and benign (non-cancerous) tumors.[2] These can be further classified as primary tumors, which start within the brain, and secondary tumors, which most commonly have spread from tumors located outside the brain, known as brain metastasis tumors.[1] All types of brain tumors may produce symptoms that vary depending on the size of the tumor and the part of the brain that is involved.[2] Where symptoms exist, they may include headaches, seizures, problems with vision, vomiting and mental changes.[1][2][7] Other symptoms may include difficulty walking, speaking, with sensations, or unconsciousness.[1][3]
The cause of most brain tumors is unknown, though up to 4% of brain cancers may be caused by CT scan radiation.[2][8] Uncommon risk factors include exposure to vinyl chloride, Epstein–Barr virus, ionizing radiation, and inherited syndromes such as neurofibromatosis, tuberous sclerosis, and von Hippel-Lindau Disease.[1][2][3] Studies on mobile phone exposure have not shown a clear risk.[3] The most common types of primary tumors in adults are meningiomas (usually benign) and astrocytomas such as glioblastomas.[1] In children, the most common type is a malignant medulloblastoma.[3] Diagnosis is usually by medical examination along with computed tomography (CT) or magnetic resonance imaging (MRI).[2] The result is then often confirmed by a biopsy. Based on the findings, the tumors are divided into different grades of severity.[1]
Treatment may include some combination of surgery, radiation therapy and chemotherapy.[1] If seizures occur, anticonvulsant medication may be needed.[1] Dexamethasone and furosemide are medications that may be used to decrease swelling around the tumor.[1] Some tumors grow gradually, requiring only monitoring and possibly needing no further intervention.[1] Treatments that use a person's immune system are being studied.[2] Outcomes for malignant tumors vary considerably depending on the type of tumor and how far it has spread at diagnosis.[3] Although benign tumors only grow in one area, they may still be life-threatening depending on their size and location.[9] Malignant glioblastomas usually have very poor outcomes, while benign meningiomas usually have good outcomes.[3] The average five-year survival rate for all (malignant) brain cancers in the United States is 33%.[4]
Secondary, or metastatic, brain tumors are about four times as common as primary brain tumors,[2][10] with about half of metastases coming from lung cancer.[2] Primary brain tumors occur in around 250,000 people a year globally, and make up less than 2% of cancers.[3] In children younger than 15, brain tumors are second only to acute lymphoblastic leukemia as the most common form of cancer.[11] In NSW Australia in 2005, the average lifetime economic cost of a case of brain cancer was AU$1.9 million, the greatest of any type of cancer.[12]
Cause[edit]
The best known cause of brain cancers is ionizing radiation.[8][26] Approximately 4% of brain cancers in the general population are caused by CT scan radiation.[8] For brain cancers that follow a CT scan at lags of 2 years or more, it has been estimated that 40% are attributable to CT scan radiation.[8] The relationship between ionizing radiation and brain cancers can be best explained by radiation carcinogenesis, and traditional models of oncogenesis. The stochastic effects of ionizing radiation demonstrate a dose-response relationship to the probability of occurrence, but no dose-response relationship to severity of disease. The majority of radiation-induced brain cancers are caused by ionizing radiation from medical sources such as CT scans.
Mutations and deletions of tumor suppressor genes, such as P53, are thought to be the cause of some forms of brain tumor.[27] Inherited conditions, such as Von Hippel–Lindau disease, tuberous sclerosis, multiple endocrine neoplasia, and neurofibromatosis type 2 carry a high risk for the development of brain tumors.[1][28][29] People with celiac disease have a slightly increased risk of developing brain tumors.[30] Smoking has been suggested to increase the risk but evidence remains unclear.[31]
Although studies have not shown any link between cell phone or mobile phone radiation and the occurrence of brain tumors,[32] the World Health Organization has classified mobile phone radiation on the IARC scale into Group 2B – possibly carcinogenic.[33] The claim that cell phone usage may cause brain cancer is likely based on epidemiological studies which observed a slight increase in glioma risk among heavy users of wireless phones. When those studies were conducted, GSM (2G) phones were in use. Modern, third-generation (3G) phones emit, on average, about 1% of the energy emitted by those GSM (2G) phones, and therefore the finding of an association between cell phone usage and increased risk of brain cancer is not based upon current phone usage.[3]
Research[edit]
Immunotherapy[edit]
Cancer immunotherapy is being actively studied. For malignant gliomas no therapy has been shown to improve life expectancy as of 2015.[111]