Central nervous system primitive neuroectodermal tumor: Difference between revisions

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{{Orphan|date=March 2019}}

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|caption = Primitive neuroectodermal tumor of the [[central nervous system]] in a 5-year-old

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A '''central nervous system primitive neuroectodermal tumor''', often abbreviated as '''PNET''', '''supratentorial PNET''', or '''CNS-PNET''',<ref name=":0">{{Cite journalbook|date=2015|editor-last=Karajannis|editor-first=Matthias A.|editor2-last=Zagzag|editor2-first=David|title=Molecular Pathology of Nervous System Tumors|journal=Molecular Pathology Library|volume=8|doi=10.1007/978-1-4939-1830-0|issn=1935-987X|isbn=978-1-4939-1829-4 |title=Molecular Pathology of Nervous System Tumors |series=Molecular Pathology Library }}</ref> is one of the 3 types of embryonal central nervous system tumors defined by the [[World Health Organization]] ([[medulloblastoma]], [[atypical teratoid rhabdoid tumor]], and PNET).<ref name=":1">{{Cite journalbook|date=2014|editor-last=Hayat|editor-first=M.A.|title=Tumors of the Central Nervous System, Volume 13|journal=Tumors of the Central Nervous System|volume=13|doi=10.1007/978-94-007-7602-9|issn=2215-096X|isbn=978-94-007-7601-2 |title=Tumors of the Central Nervous System, Volume 13 }}</ref> It is considered an embryonal tumor because it arises from cells partially differentiated or still undifferentiated from birth.<ref name=":0" /> Those cells are usually [[neuroepithelial cell]]s,<ref name=":0" /><ref name=":1" /><ref name=":2">{{Citation|last=Fuller|first=Christine E.|chapter=Oligodendroglial Tumors|date=2009-10-23|pages=39–46|publisher=Springer New York|isbn=9781441910615|doi=10.1007/978-1-4419-1062-2_4|title=Atlas of Pediatric Brain Tumors}}</ref> stem cells destined to turn into [[glia]] or [[neuron]]s.<ref name=":3">{{Cite journal|last=Nelesen|first=Richard A|date=March 2000|title= Biological Psychology: An Introduction to Behavioral, Cognitive, and Clinical Neuroscience, 2nd edition. Mark R. Rosenweig, Arnold L. Leiman, and S. Marc Breedlove, Sinauer Associates, Inc., Sunderland MA, 1999. 561+92 pp. ISBN 0-87893-791-9|journal=Biological Psychology|volume=52|issue=2|pages=185–186|doi=10.1016/s0301-0511(99)00025-3|s2cid=54349873|issn=0301-0511}}</ref> It can occur anywhere within the [[spinal cord]] and [[cerebrum]] and can have multiple sites of origins, with a high probability of [[metastasis]] through [[cerebrospinal fluid]] (CSF).<ref name=":0" /><ref name=":1" />

PNET has five subtypes of tumors: [[neuroblastoma]], [[ganglioneuroblastoma]], [[medulloepithelioma]], ependymoblastoma, and not otherwise specified PNET.<ref name=":0" /> It is similar to [[medulloblastoma]] regarding histology but different regarding genetic factors and tumor site. It is a rare disease occurring mostly among children,<ref name=":0" /><ref name=":1" /> accounting for 1.9 to 7% of childhood brain tumors.<ref name=":1" /> Symptoms involve emotional, visual, motor, and speech defects.<ref name=":1" /> [[Magnetic resonance imaging]] (MRI) and [[CT scan|computed tomography]] (CT) are used to diagnose PNETs.<ref name=":1" /> Even though a universal treatment plan hasn't been stablished yet, common strategies involve [[chemotherapy]] and [[Radiation therapy|radiotherapy]] for individuals older than 3 years of age.<ref name=":0" /><ref name=":1" /> Their efficacy, however, is still controversial.<ref name=":1" /> Surgery can be used to remove mass affected by tumorous cells.<ref name=":1" /> The prognosis of the disease is more positive for adults than for children, who have a higher probability of having sequelae from the tumor.<ref name=":0" /><ref name=":1" />

It is important to note that this classification term has been removed from the latest WHO classification of CNS tumors as of 2016. Instead PNETs are now included into the category of "Embryonal Tumors with Multilayered Rosettes" along with ependymoblastoma and embryonal tumor with abundant neuropil and true rosettes (ETANTR). <ref>Louis DN, Ohgaki H, Wiestler OD, Cavenee WK "WHO Classification of Tumours of the Central Nervous System. 4th Edition Revised"</ref>

== Classification ==

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[[File:Ependymoblastomatous Rosette.jpg|thumb|Rosettes in Ependymoblastoma histology]]

Further classification types have come up but not yet approved by the [[World Health Organization]].<ref name=":0" /> The term "embryonal tumor with abundant neuropil and true rosettes", or ETANTR, has been proposed as a sixth subtype of PNET.<ref name=":0" /> However, the still unofficial term "embryonal tumor with multilayered rosettes" (ETMR) has been more frequently used and encompasses ETANTRs, [[medulloepithelioma]]s, ependymoblastomas, and variants of PNETs with presence of rosettes and with no well defined classification.<ref name=":2" />

=== PNET vs. medulloblastoma ===

The differentiation between primitive neuroectodermal tumor in the central nervous system and [[medulloblastoma]] is recent.<ref name=":0" /><ref name=":1" /> According to the [[World Health Organization]], both tumors have the same histology but primitive neuroectodermal tumors occur outside the [[cerebellum]].<ref name=":1" /> Moreover, it has been documented that both have different genetic expression and mutations.<ref name=":0" /><ref name=":1" /> Another essential difference between them is the ___location of their respective blood vessels within the brain.<ref name=":1" /> It has also been theorized that PNETs influence mainly [[glia]] cells while [[medulloblastoma]]s influence mainly [[Neuron|neural]] behavior, however such theory hasn't been confirmed yet.<ref name=":0" /> [[Medulloblastoma]]s are more frequent than PNETs, representing 10% of all child deaths caused by cancer.<ref name=":1" /> They also present better prognosis: children affected by [[medulloblastoma]] reach the 5 year survival mark in 70-80% of cases, while children affected by PNET reach the 5 year survival mark in less than 50% of cases.<ref name=":0" />

== Risk factors ==

The rate of PNETs in not correlated with sex, but it shows a correlation with age.<ref name=":0" /> Most cases occur in children around 5 years of age, having a very low frequency in adults.<ref name=":0" /> Regarding genetic mutations, a specific type of gene alteration that directly leads to this tumor hasn't been defined yet.<ref name=":0" /> However, a positive correlation between individuals with [[Li–Fraumeni syndrome|Li-Fraumeni syndrome]] with a mutation in the [[P53|gene ''p53'']] and PNET has been reported.<ref name=":1" /> A significant number of individuals with mutations on the [[Retinoblastoma protein|''rb'' tumor suppressor gene]] have also developed the tumor.<ref name=":1" /> Such gene encodes for the protein Rb responsible for stopping the cell cycle at the [[G1 phase]].<ref name=":4">{{Cite journal|last=Baker|first=Henry V|date=June 2003|title= ''Essential Genetics: A Genomics Perspective'' . ''Third Edition. By '' Daniel L Hartl '' and '' , Elizabeth W Jones. ''Sudbury (Massachusetts): Jones and Bartlett Publishers'' . $78.95 (paperPaper). xxviXxvi + 613 p; ill.; index. ISBN: 0–7637–1852–1. 2002.|isbn=0-7637-1852-1|journal=The Quarterly Review of Biology|volume=78|issue=2|pages=[https://archive.org/details/essentialgenetic0000hart/page/225 225–226]|doi=10.1086/377959|issn=0033-5770|url-access=registration|url=https://archive.org/details/essentialgenetic0000hart/page/225}}</ref> Another possible contributing factor are mutations in the [[CREB-binding protein]], whose function includes activating transcription,<ref name=":4" /> but this interaction still need to be studied further.<ref name=":1" /> It has also been presumed that the tumor can arise from cranial irradiation.<ref name=":1" />

== Diagnosis ==

[[File:MRI of PNET.jpg|thumb|[[Magnetic resonance imaging|Magnetic resonance]] image of PNET]]

Most children that develop primitive neuroectodermal tumors are diagnosed early in life, usually at around 3-63–6.8 years of age.<ref name=":1" /> Symptoms patients present at time of diagnosis include irritable mood, visual difficulties, [[lethargy]], and [[ataxia]].<ref name=":1" /> The circumference of the patient's head might also sufferbecome an enlargementenlarged and they might be subject to seizures, especially if they have less than one year of life.<ref name=":1" />

Several analysis can be used to determine the presence of the disease. Physical examinations showing [[papilledema]], visual field defects, cranial nerves [[Cerebral palsy|palsy]], dysphasia, and focal neurological deficits are evidences for possible tumor.<ref name=":1" /> PNETs can also be spotted through [[CT scan|computed tomography]] (CT) and [[magnetic resonance imaging]] (MRI).<ref name=":1" /> In images produced by [[Magnetic resonance imaging|MRIs]], an irregular augmentation among a solid mass will indicated the presence of tumor.<ref name=":2" /> However, the results of MRIs are usually ambiguous in defining the presence for this specific tumor.<ref name=":1" /> In [[CT scan]]s, the presence of PNETs will be indicated by an elevated density and an increase in volume of the brain.<ref name=":1" /> The [[CT scan]] can also show [[calcification]],<ref name=":2" /> which is present in 41-44% of PNET cases.<ref name=":1" /> Since the tumor can be replicated in other parts of the nervous system through the [[cerebrospinal fluid]] (CSF), a CSF analysis can also be conducted.<ref name=":1" /> A spinal MRI is a fourth type of analysis that is useful in investigating the level of tumor propagation to the [[spinal cord]].<ref name=":1" />

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The probability of primitive neuroectodermal tumors to have recurrence and [[Metastasis|metastasize]] through [[cerebrospinal fluid]] is relatively high.<ref name=":2" /> The outcome of PNET is more positive when the individual is an adult, independent of age subgroups, or an older child.<ref name=":1" /> Less than 50% of children survive more than 5 years,<ref name=":0" /> while the majority of adults live to 7 years.<ref name=":1" /> The reason the prognosis for such tumor is worst in children is due to the higher probability of the tumor spreading to the rest of the [[nervous system]] through the [[cerebrospinal fluid]] and growing again.<ref name=":1" /> Moreover, children have the probability of developing deficiencies in cognitive processes, problems in the [[endocrine system]], and psychological obstacles after the disease.<ref name=":1" /> Adults, on the other hand, don't show such propensity.<ref name=":1" /> As a consequence, 37.7% of children affected by the tumor live to 4 years.<ref name=":1" />

The effect of treatment strategies such as [[chemotherapy]] and [[radiation therapy]] on the prognosis of the disease is still controversial, with studies claiming either their benefits or their ineffectiveness.<ref name=":1" /> The same holds true for the relationship between volume of tumor removed by surgery and survival.<ref name=":1" /> Furthermore, factors such as tumor size, ___location of origin, race, and sex of individual don't show any influence on the outcome of the disease.<ref name=":1" /> However, interactions of some factors such as tumor site, age, and treatment strategy can affect one's prognosis.<ref name=":1" /> For instance, when younger children below the age of 3three suffering fromdevelop tumors originating in places other than the [[pineal gland]] are treated with [[chemotherapy]], they present better outcomes than those suffering fromwith [[Pineal gland|pineal]] tumors and treated with [[chemotherapy]].<ref name=":1" />

== References ==