Editing Brain tumor (section)

===Classification===
Tumors can be [[benign]] or [[malignant]], can occur in different parts of the brain, and may be classified as primary or secondary. A primary tumor is one that has started in the brain, as opposed to a [[metastasis|metastatic]] tumor, which is one that has spread to the brain from another area of the body.<ref>{{cite web|url=http://www.cancer.gov/cancertopics/wyntk/brain/page1|title=What you need to know about brain tumors|publisher=National Cancer Institute|archive-url=https://web.archive.org/web/20120127124137/http://www.cancer.gov/cancertopics/wyntk/brain/page1|archive-date=27 January 2012|url-status=live|access-date=25 February 2012}}</ref> The incidence of metastatic tumors is approximately four times greater than primary tumors.<ref name=Mer2012/> Tumors may or may not be [[symptomatic]]: some tumors are discovered because the patient has symptoms, others show up incidentally on an imaging scan, or at an autopsy.{{citation needed|date=December 2020}}

[[Grading of the tumors of the central nervous system]] commonly occurs on a 4-point scale (I-IV) created by the World Health Organization in 1993. Grade I tumors are the least severe and commonly associated with long-term survival, with severity and prognosis worsening as the grade increases. Low-grade tumors are often benign, while higher grades are aggressively malignant and/or metastatic. Other grading scales do exist, many based upon the same criteria as the WHO scale and graded from I-IV.<ref>{{cite journal | vauthors = Gupta A, Dwivedi T | title = A Simplified Overview of World Health Organization Classification Update of Central Nervous System Tumors 2016 | journal = Journal of Neurosciences in Rural Practice | volume = 8 | issue = 4 | pages = 629–641 | date = October 2017 | pmid = 29204027 | pmc = 5709890 | doi = 10.4103/jnrp.jnrp_168_17 | doi-access = free }}</ref>

==== Primary ====
[[File:Meningioma of the sagittal sinus isolated.jpg|thumb|Meningioma of the middle third of the sagittal sinus with large [[hyperostosis]]]]
The most common primary brain tumors are:<ref>{{Cite book|title=Meningiomas: Diagnosis, Treatment, and Outcome| vauthors = Park BJ, Kim HK, Sade B, Lee JH |publisher=Springer|year=2009|isbn=978-1-84882-910-7| veditors = Lee JH |page=11|chapter=Epidemiology}}
</ref>
* [[Gliomas]]<ref name=aans>{{cite web |title=Brain Tumors – Classifications, Symptoms, Diagnosis and Treatments |url=https://www.aans.org/en/Patients/Neurosurgical-Conditions-and-Treatments/Brain-Tumors |website=aans.org |access-date=29 January 2021 |language=en}}</ref> (50.4%)
* [[Meningiomas]]<ref name=aans/> (20.8%)
* [[Pituitary adenomas]]<ref name=aans/> (15%)
* [[Nerve sheath tumors]] (10%)

These common tumors can also be organized according to tissue of origin as shown below:<ref name="AANS 41723ct">{{cite web|url=http://www.aans.org/en/Media/Classifications-of-Brain-Tumors|title=Classifications of Brain Tumors|website=AANS|publisher=American Association of Neurological Surgeons|archive-url=https://web.archive.org/web/20170424085734/http://www.aans.org/en/Media/Classifications-of-Brain-Tumors|archive-date=24 April 2017|url-status=live|access-date=23 April 2017}}</ref>
{| class="wikitable"
|-
!
Tissue of origin
! Children !! Adults
|-
|[[Astrocytes]]||[[Pilocytic astrocytoma|Pilocytic Astrocytoma]] (PCA) ||[[Glioblastoma]]
|-
|[[Oligodendrocytes]]||  ||[[Oligodendroglioma]]
|-
|[[Ependyma]]||[[Ependymoma]]||
|-
|[[Neurons]]||[[Medulloblastoma]]||
|-
|[[Meninges]]||  ||[[Meningioma]]
|}

====Secondary====
Secondary tumors of the brain are [[metastasis|metastatic]] and have spread to the brain from [[cancer]]s originating in another organ. Metastatic spread is usually by the blood. The most common types of cancers that spread to the brain are [[lung cancer]] (accounting for over half of all cases), [[breast cancer]], [[melanoma]] skin cancer, [[kidney cancer]] and [[colon cancer]].<ref name="Brenner 2022">{{cite journal |last1=Brenner |first1=Alex W. |last2=Patel |first2=Akash J. |title=Review of Current Principles of the Diagnosis and Management of Brain Metastases |journal=Frontiers in Oncology |date=24 May 2022 |volume=12 |doi=10.3389/fonc.2022.857622|doi-access=free |pmid=35686091 |pmc=9171239 }}</ref>

=====By behavior=====
Brain tumors 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:<ref>{{cite journal | vauthors = Louis DN, Perry A, Wesseling P, Brat DJ, Cree IA, Figarella-Branger D, Hawkins C, Ng HK, Pfister SM, Reifenberger G, Soffietti R, von Deimling A, Ellison DW | title = The 2021 WHO Classification of Tumors of the Central Nervous System: a summary | journal = Neuro-Oncology | volume = 23 | issue = 8 | pages = 1231–1251 | date = August 2021 | pmid = 34185076 | pmc = 8328013 | doi = 10.1093/neuonc/noab106 }}</ref>
* 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 (cytology)|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 ([[syncytium|syncytia]]). Anaplastic nuclei are variable and bizarre in size and shape.
* invasion or infiltration:
** 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.
* [[metastasis]] (spread to other locations in the body via lymph or blood).

==== By genetics ====
In 2016, the WHO restructured their classifications of some categories of [[glioma]]s 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]].<ref name=":4" />
* 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]]<ref>{{cite web |url= https://www.lecturio.com/concepts/oligodendroglioma/| title= Oligodendroglioma|website=The Lecturio Medical Concept Library |access-date= 21 August 2021}}</ref>
* Loss of [[P53|TP53]] and [[ATRX]] characterizes [[astrocytoma]]s
* Genes [[Epidermal growth factor receptor|EGFR]], [[Telomerase reverse transcriptase|TERT]], and [[PTEN (gene)|PTEN]], are commonly altered in gliomas and are useful in differentiating tumor grade and biology<ref name=":4" />

====Specific types====
{{main|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]], [[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]].