i-iv. primary the most common primary brain tumors are: gliomas (50.4%) meningiomas (20.8%) meningioma of the middle third of the sagittal sinus with large hyperostosis pituitary adenomas (15%) nerve sheath tumors (10%) these common tumors can also be organized according to tissue of origin as shown below: tissue of origin childrenadults astrocytespilocytic astrocytoma (pca)glioblastoma multiforme (gbm) oligodendrocytesoligodendroglioma ependymaependymoma neuronsmedulloblastoma meningesmeningioma secondary secondary tumors of the brain are metastatic and have invaded the brain from cancers originating in other organs. this means that a cancerous neoplasm has developed in another organ elsewhere in the body and that cancer cells have leaked from that primary tumor and then entered the lymphatic system and blood vessels. they then circulate through the bloodstream, and are deposited in the brain. there, these cells continue growing and dividing, becoming another invasive neoplasm of primary cancer's tissue. secondary tumors of the brain are very common in the terminal phases of patients with an incurable metastasized cancer; the most common types of cancers that bring about secondary tumors of the brain are lung cancer, breast cancer, malignant melanoma, kidney cancer, and colon cancer (in decreasing order of frequency). secondary brain tumors are more common than primary ones; in the united states, there are about 170,000 new cases every year. secondary brain tumors are the most common cause of tumors in the intracranial cavity. the skull bone structure can also be subject to a neoplasm that by its very nature reduces the volume of the intracranial cavity, and can damage the brain. by behavior brain tumors or intracranial neoplasms can be cancerous (malignant) or non-cancerous (benign). however, the definitions of malignant or benign neoplasms differ from those commonly used in other types of cancerous or non-cancerous neoplasms in the body. in cancers elsewhere in the body, three malignant properties differentiate benign tumors from malignant forms of cancer: benign tumors are self-limited and do not invade or metastasize. characteristics of malignant tumors include: uncontrolled mitosis (growth by division beyond the normal limits) anaplasia: the cells in the neoplasm have an obviously different form (in size and shape). anaplastic cells display marked pleomorphism. the cell nuclei are characteristically extremely hyperchromatic (darkly stained) and enlarged; the nucleus might have the same size as the cytoplasm of the cell (nuclear-cytoplasmic ratio may approach 1:1, instead of the normal 1:4 or 1:6 ratio). giant cells – considerably larger than their neighbors – may form and possess either one enormous nucleus or several nuclei (syncytia). anaplastic nuclei are variable and bizarre in size and shape. invasion or infiltration (medical literature uses these terms as synonymous equivalents. however, for clarity, the articles that follow adhere to a convention that they mean slightly different things; this convention is not followed outside these articles): invasion or invasiveness is the spatial expansion of the tumor through uncontrolled mitosis, in the sense that the neoplasm invades the space occupied by adjacent tissue, thereby pushing the other tissue aside and eventually compressing the tissue. often these tumors are associated with clearly outlined tumors in imaging. infiltration is the behavior of the tumor either to grow (microscopic) tentacles that push into the surrounding tissue (often making the outline of the tumor undefined or diffuse) or to have tumor cells "seeded" into the tissue beyond the circumference of the tumorous mass; this does not mean that an infiltrative tumor does not take up space or does not compress the surrounding tissue as it grows, but an infiltrating neoplasm makes it difficult to say where the tumor ends and the healthy tissue starts. metastasis (spread to other locations in the body via lymph or blood). of the above malignant characteristics, some elements do not apply to primary neoplasms of the brain: primary brain tumors rarely metastasize to other organs; some forms of primary brain tumors can metastasize but will not spread outside the intracranial cavity or the central spinal canal. due to the bbb, cancerous cells of a primary neoplasm cannot enter the bloodstream and get carried to another location in the body. (occasional isolated case reports suggest spread of certain brain tumors outside the central nervous system, e.g. bone metastasis of glioblastoma multiforme.) primary brain tumors generally are invasive (i.e. they will expand spatially and intrude into the space occupied by other brain tissue and compress those brain tissues); however, some of the more malignant primary brain tumors will infiltrate the surrounding tissue. by genetics in 2016, the who restructured their classifications of some categories of gliomas to include distinct genetic mutations that have been useful in differentiating tumor types, prognoses, and treatment responses. genetic mutations are typically detected via immunohistochemistry, a technique that visualizes the presence or absence of a targeted protein via staining. mutations in idh1 and idh2 genes are commonly found in low-grade gliomas loss of both idh genes combined with loss of chromosome arms 1p and 19q indicates the tumor is an oligodendroglioma loss of tp53 and atrx characterizes astrocytomas genes egfr, tert, and pten, are commonly altered in gliomas and are useful in differentiating tumor grade and biology specific types main article: who classification of the tumors of the central nervous system anaplastic astrocytoma, anaplastic oligodendroglioma, astrocytoma, central neurocytoma, choroid plexus carcinoma, choroid plexus papilloma, choroid plexus tumor, colloid cyst, dysembryoplastic neuroepithelial tumour, ependymal tumor, fibrillary astrocytoma, giant-cell glioblastoma, glioblastoma multiforme, gliomatosis cerebri, gliosarcoma, hemangiopericytoma, medulloblastoma, medulloepithelioma, meningeal carcinomatosis, neuroblastoma, neurocytoma, oligoastrocytoma, oligodendroglioma, optic nerve sheath meningioma, pediatric ependymoma, pilocytic astrocytoma, pinealoblastoma, pineocytoma, pleomorphic anaplastic neuroblastoma, pleomorphic xanthoastrocytoma, primary central nervous system lymphoma, sphenoid wing meningioma, subependymal giant cell astrocytoma, subependymoma, trilateral retinoblastoma. treatment a medical team generally assesses the treatment options and presents them to the person affected and their family. various types of treatment are available depending on tumor type and location, and may be combined to produce the best chances of survival: surgery: complete or partial resection of the tumor with the objective of removing as many tumor cells as possible. radiotherapy: the most commonly used treatment for brain tumors; the tumor is irradiated with beta, x rays or gamma rays. chemotherapy: a treatment option for cancer, however, it is not always used to treat brain tumors as the blood–brain barrier can prevent some drugs from reaching the cancerous cells. a variety of experimental therapies are available through clinical trials. survival rates in primary brain tumors depend on the type of tumor, age, functional status of the patient, the extent of surgical removal and other factors specific to each case. standard care for anaplastic oligodendrogliomas and anaplastic oligoastrocytomas is surgery followed by radiotherapy. one study found a survival benefit for the addition of chemotherapy to radiotherapy after surgery, compared with radiotherapy alone. surgery the primary and most desired course of action described in medical literature is surgical removal (resection) via craniotomy. minimally invasive techniques are becoming the dominant trend in neurosurgical oncology. the main objective of surgery is to remove as many tumor cells as possible, with complete removal being the best outcome and cytoreduction ("debulking") of the tumor otherwise. a gross total resection (gtr) occurs when all visible signs of the tumor are removed, and subsequent scans show no apparent tumor. in some cases access to the tumor is impossible and impedes or prohibits surgery. many meningiomas, with the exception of some tumors located at the skull base, can be successfully removed surgically. most pituitary adenomas can be removed surgically, often using a minimally invasive approach through the nasal cavity and skull base (trans-nasal, trans-sphenoidal approach). large pituitary adenomas require a craniotomy (opening of the skull) for their removal. radiotherapy, including stereotactic approaches, is reserved for inoperable cases. several current research studies aim to improve the surgical removal of brain tumors by labeling tumor cells with 5-aminolevulinic acid that causes them to fluoresce. postoperative radiotherapy and chemotherapy are integral parts of the therapeutic standard for malignant tumors. multiple metastatic tumors are generally treated with radiotherapy and chemotherapy rather than surgery and the prognosis in such cases is determined by the primary tumor, and is generally poor. radiation therapy the goal of radiation therapy is to kill tumor cells while leaving normal brain tissue unharmed. in standard external beam radiation therapy, multiple treatments of standard-dose "fractions" of radiation are applied to the brain. this process is repeated for a total of 10 to 30 treatments, depending on the type of tumor. this additional treatment provides some patients with improved outcomes and longer survival rates. radiosurgery is a treatment method that uses computerized calculations to focus radiation at the site of the tumor while minimizing the radiation dose to the surrounding brain. radiosurgery may be an adjunct to other treatments, or it may represent the primary treatment technique for some tumors. forms used include stereotactic radiosurgery, such as gamma knife, cyberknife or novalis tx radiosurgery. radiotherapy is the most common treatment for secondary brain tumors. the amount of radiotherapy depends on the size of the area of the brain affected by cancer. conventional external beam "whole-brain radiotherapy treatment" (wbrt) or "whole-brain irradiation" may be suggested if there is a risk that other secondary tumors will develop in the future. stereotactic radiotherapy is usually recommended in cases involving fewer than three small secondary brain tumors. radiotherapy may be used following, or in some cases in place of, resection of the tumor. forms of radiotherapy used for brain cancer include external beam radiation therapy, the most common, and brachytherapy and proton therapy, the last especially used for children. people who receive stereotactic radiosurgery (srs) and whole-brain radiation therapy (wbrt) for the treatment of metastatic brain tumors have more than twice the risk of developing learning and memory problems than those treated with srs alone. results of a 2021 systematic review found that when using srs as the initial treatment, survival or death related to brain metastasis was not greater than alone versus srs with wbrt. postoperative conventional daily radiotherapy improves survival for adults with good functional well-being and high grade glioma compared to no postoperative radiotherapy. hypofractionated radiation therapy has similar efficacy for survival as compared to conventional radiotherapy, particularly for individuals aged 60 and older with glioblastoma. chemotherapy patients undergoing chemotherapy are administered drugs designed to kill tumor cells. although chemotherapy may improve overall survival in patients with the most malignant primary brain tumors, it does so in only about 20 percent of patients. chemotherapy is often used in young children instead of radiation, as radiation may have negative effects on the developing brain. the decision to prescribe this treatment is based on a patient's overall health, type of tumor, and extent of cancer. the toxicity and many side effects of the drugs, and the uncertain outcome of chemotherapy in brain tumors puts this treatment further down the line of treatment options with surgery and radiation therapy preferred. ucla neuro-oncology publishes real-time survival data for patients with a diagnosis of glioblastoma multiforme. they are the only institution in the united states that displays how brain tumor patients are performing on current therapies. they also show a listing of chemotherapy agents used to treat high-grade glioma tumors. genetic mutations have significant effects on the effectiveness of chemotherapy. gliomas with idh1 or idh2 mutations respond better to chemotherapy than those without the mutation. loss of chromosome arms 1p and 19q also indicate better response to chemoradiation. other a shunt may be used to relieve symptoms caused by intracranial pressure, by reducing the build-up of fluid (hydrocephalus) caused by the blockage of the free flow of cerebrospinal fluid. prognosis the prognosis of brain cancer depends on the type of cancer diagnosed. medulloblastoma has a good prognosis with chemotherapy, radiotherapy, and surgical resection while glioblastoma multiforme has a median survival of only 12 months even with aggressive chemoradiotherapy and surgery. brainstem gliomas have the poorest prognosis of any form of brain cancer, with most patients dying within one year, even with therapy that typically consists of radiation to the tumor along with corticosteroids. however, one type, focal brainstem gliomas in children, seems open to exceptional prognosis and long-term survival has frequently been reported. prognosis is also affected by presentation of genetic mutations. certain mutations provide better prognosis than others. idh1 and idh2 mutations in gliomas, as well as deletion of chromosome arms 1p and 19q, generally indicate better prognosis. tp53, atrx, egfr, pten, and tert mutations are also useful