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{{Oral cancer}}
{{Oral cancer}}
{{CMG}};{{AE}] {{Simrat}}
{{CMG}}; {{AE}} {{SSW}}, {{Simrat}}; {{GRR}} {{Nat}}
==Overview==
==Overview==
It is understood that oral cancers occur as a the result of [[carcinogen]]-[[Metabolize|metabolizing]] [[enzymes]], [[alcohol]], [[tobacco]] and [[Genetics|genetic factors]]. [[Cytotoxicity|Cytotoxic]] [[enzymes]] such as [[alcohol dehydrogenase]] result in the production of [[free radicals]] and [[hydroxylation]] of [[DNA]] base units. [[Alcohol dehydrogenase]] oxidizes [[ethanol]] to [[acetaldehyde]] which is [[Cytotoxicity|cytotoxic]] in nature. Cigarette smoke has various [[carcinogens]], which can lead to oral cancers. Low-reactive [[free radicals]] in [[cigarette smoke]] interact with [[redox]]-active [[metals]] in [[saliva]].The development of oral cancer is the result of multiple [[genetic mutations]]. These [[mutations]] occur in [[Tumor suppressor genes|tumor suppressor genes (TSGs)]] and [[Oncogene|oncogenes]]. [[Squamous cell carcinoma]] is the most common [[malignancy]] of the oral cavity. It typically has three gross morphological growth patterns, which are exophytic, [[Ulcerated lesion|ulcerative]], and infiltrative. [[Microscopic|Microscopically]], oral cancers are broadly based and invasive through [[papillary]] fronds. Oral cancer consists of highly [[Differentiate|differentiated]] [[Squamous cell|squamous cells]] lacking frank [[Cytological|cytologic]] criteria of [[malignancy]] with rare [[Mitosis|mitoses]].The surface of the lesion is covered with compressed invaginating folds of [[keratin]] layers. A stroma-like [[Inflammatory response|inflammatory reaction]] and a blunt pushing margin may be seen.
==Pathophysiology==
==Pathophysiology==
Oral carcinogenesis like any other cancer is a progressive disease and normal epithelium passes through stages starting from dysplasia to finally transforming into invasive phenotypes. Although all types of carcinomas are seen in oral cavity, the most common form of Oral carcinogenesis is squamous cell carcinoma. Use of genetic and proteomic approach in recent years have revealed the molecular pathological picture of oral carcinogenesis  There is active search to identify genetic alterations in oncogenes or tumour suppressor genes, role of genomic instability and epigenetic modifications and to generate a gene expression profile in oral oncogenesis [20]. Understanding these genetic changes and gene expression patterns are keys to the understanding of molecular pathogenesis of OC. Though, there are some significant leads achieved, the complete understanding of molecular pathology of OC and its association with causative agent will require another decade of intensive research. We have discussed some of the important updates in this area of active research.
It is understood that oral cancer occurs as a the result of [[carcinogen]]-[[Metabolize|metabolizing]] [[enzymes]], [[alcohol]], [[tobacco]] and [[Genetics|genetic factors]].
Genetic Susceptibility


It is now established that up to 10% of all cancers have a strong hereditary component. Role of genetic component in the development of OC is being suggested by several studies showing familial clustering [21]. A clustering of OC has been seen in certain ethnic groups, like Askenazi group in Israel; with incidence being double as compared to other Jewish population in that country. However, the basis of this genetic susceptibility is not well understood, as yet.
===Carcinogen-metabolizing enzymes===
*[[Carcinogen]]-[[Metabolize|metabolizing]] [[enzymes]] are known to cause [[cancer]] in some patients.
*[[Cytotoxicity|Cytotoxic]] [[enzymes]] such as [[alcohol dehydrogenase]] result in the production of:
**[[Free radicals]]
**[[DNA]] hydroxylated [[Base (chemistry)|bases]]
*These [[cytotoxic]] [[enzymes]] dominantly play a key role in the development of oral squamous cell carcinoma.
===Alcohol===
*[[Alcohol dehydrogenase]] oxidizes [[ethanol]] to [[acetaldehyde]], which is [[cytotoxic]] in nature.
*[[CYP2E1|Cytochrome P450 IIEI]] ([[CYP2E1]]) also [[Metabolize|metabolizes]] [[ethanol]] to [[acetaldehyde]].
*[[Alcohol dehydrogenase]] type 3 genotype predisposes to oral squamous cell carcinoma.
*[[Carcinogen|Carcinogenic]] potential increases when combined with [[tobacco]] use.
===Tobacco===
*[[Cigarette smoke]] has various [[carcinogens]], which can lead to oral cancers.
*Low reactive [[free radicals]] in [[cigarette smoke]] interact with [[redox]]-active metals in [[saliva]].
*[[saliva]] then looses its [[antioxidant]] potential and becomes a potent pro-oxidant milieu.<ref name="pmid17344667">{{cite journal |vauthors=Nagler R, Dayan D |title=The dual role of saliva in oral carcinogenesis |journal=Oncology |volume=71 |issue=1-2 |pages=10–7 |year=2006 |pmid=17344667 |doi=10.1159/000100445 |url=}}</ref>
==='''Pathology of classical or conventional squamous cell carcinoma'''===
* Most cancers of the [[oral cavity]] are classical or conventional squamous cell carcinoma.
* This type of SCC starts in the [[squamous epithelium]], which lines the [[oral cavity]] and occurs most often on the [[lower lip]], [[tongue]] and floor of the mouth.
* The [[microscopic]] features of classical SCC involve
** Keratin pearls
*** These are circular layers of [[Squamous cell|squamous cells]] that surround [[keratin]] (a tough fibrous [[protein]]).


Evaluation of specific genetic polymorphism in key genes involved in oral carcinogenesis has been the major area of study. Glutathione S-transferase M1 (GSTM1) null genotype appears to be the most consistent polymorphic susceptibility marker for head and neck cancer including OC. Meta-analyses by Tripathy and Roy showed that the GSTM1 null genotype conferred a 20–50% significantly increased HNSCC risk [22].
*Cancer starts in the [[Squamous cell|squamous cells]] of the [[epithelium]], and then invades the deeper layers of the [[oral cavity]].
==='''Pathology of squamous cell carcinoma variants'''===
* The following [[squamous cell carcinomas]] have distinct [[microscopic]] features that make them look and behave differently from classical SCC:
 
*'''Verrucous carcinoma'''
**These [[tumors]] make up less than 5% of all oral cavity tumors.
**They have a wart-like appearance and develop most often on the [[gums]] ([[gingiva]]), lining of the cheeks ([[buccal mucosa]]) and [[larynx]].
**Verrucous carcinomas are low grade, slow-growing and rarely spread.
**They are associated with the chronic use of snuff or chewing [[tobacco]].
*'''Basaloid SCC'''
**This is a rare but aggressive sub-type of squamous cell carcinoma.
**It is more common in men older than 60 years old.
*'''Papillary SCC'''
**This is a rare sub-type of squamous cell carcinoma that grows outward from the surface of the [[epithelium]] (exophytic).
**[[Human papillomavirus|HPV]] infections may have a role in the development of this type of cancer.
*'''Spindle cell carcinoma (SpCC)'''
**This is an aggressive, rare variant of squamous cell carcinoma.
**These [[tumors]] contain a mixture of conventional squamous cell carcinoma and spindle cells that resemble a [[sarcoma]].
**It is also known as sarcomatoid carcinoma, pseudosarcoma, carcinosarcoma, pleomorphic carcinoma, metaplastic carcinoma, collision tumor and Lane tumor.
 
*'''Acantholytic SCC'''
**This is a rare variant of SCC in which the connections between the [[malignant]] [[Squamous cell|squamous cells]] are broken down.
**This results in [[microscopic]] spaces in the tumor tissue, which appear like [[glands]] or [[vascular]] spaces.
*'''Adenosquamous carcinoma'''
**This is a very rare, aggressive type of squamous cell carcinoma.
**It looks like classical squamous cell carcinoma but also has [[mucus]]-producing [[gland]] cells.
*'''Lymphoepithelial carcinoma'''
**This is a rare sub-type of squamous cell carcinoma.
**The [[microscopic]] appearance is similar to undifferentiated [[nasopharyngeal carcinoma]].
**It is also known as [[undifferentiated]] carcinoma.
 
== Genetics ==
* The development of oral cancer is the result of multiple [[genetic mutations]].
* These [[mutations]] include:
** [[Tumor suppressor genes]] (TSGs)
** [[Oncogenes]]
 
====Tumor suppressor genes (TSGs)====
*Oral cavity cancer may be the result of an [[Allele|allelic]] imbalance, which is caused by [[chromosomal]] changes- particularly in [[chromosome]] 3, 9, 11 and 17.
*These changes lead to [[mutation]] in [[tumor suppressor genes]] ([[Tumor suppressor genes|TSGs]]).
*In non-cancerous situations, [[Tumor suppressor genes|TSGs]] modulate normal growth.
*Mutation of these [[Tumor suppressor genes|TSGs]] lead to dysfunctional growth control.
*Mutation most commonly occurs in one of the following:
**Short arm of [[Chromosome 3 (human)|chromosome 3]]
**TSG termed ''[[P16 (gene)|P16]]'' on [[chromosome 9]]
**TSG termed ''[[TP53]]'' on [[chromosome 17]]
*The [[Cytochrome P450]] [[genotype]] is related to [[mutations]] in some [[Tumor suppressor genes|TSGs]] and leads to oral squamous cell carcinoma.
*In western countries (eg. United Kingdom, United States, or Australia), ''[[TP53]]'' [[Mutation|mutations]] are the most common molecular change that leads to oral [[squamous cell carcinoma]].
====Oncogenes====
*Cancer may also occur if there is mutation in other [[genes]] that control [[cell growth]], typically [[oncogenes]].
*[[Oncogenes]] most commonly involved are:
**[[Chromosome 11]] (''PRAD1)''
**[[Chromosome 17]] (Harvey ras [H-''ras''])
*In eastern countries (eg. India or Southeast Asia), ''[[Ras gene|ras]]'' [[oncogenes]] is a more common cause of oral squamous cell carcinoma.
==Gross Pathology==
* [[Squamous cell carcinoma]] is the most common [[Bone or cartilage mass|malignancy]] of the oral cavity.
* It typically has three gross morphological growth patterns, which are exophytic, [[Ulcerated lesion|ulcerative]], and infiltrative.
* The infiltrative and [[Ulceral|ulcerative]] are the growth patterns most commonly observed in the oral cavity.
* The [[macroscopic]] appearance of oral cancer depends on the following:
**Duration of the [[lesion]]
**The amount of [[keratinization]]
**The changes in the adjoining [[Mucosal|mucosa]]
**A fully developed oral cavity lesion appears as an exophytic bulky lesion that is gray to grayish-red and has a rough, shaggy, or [[Papilloma|papillomatous]] surface
[[File:PLoS oral cancer.png|300px|center|thumb|Gross pathology of oral SCC, source: By Luca Pastore, Maria Luisa Fiorella, Raffaele Fiorella, Lorenzo Lo Muzio - http://www.plosmedicine.org/article/showImageLarge.action?uri=info%3Adoi%2F10.1371%2Fjournal.pmed.0050212.g001, CC BY 2.5, https://commons.wikimedia.org/w/index.php?curid=15252632]]
 
==Microscopic Pathology==
*[[Microscopic|Microscopically]], oral cancers are broadly based and invasive through [[papillary]] fronds.
*Oral cancer constitutes of highly-[[Differentiate|differentiated]] squamous cells lacking frank cytologic criteria of [[malignancy]] with rare [[mitoses]].
*The surface of the lesion is covered with compressed invaginating folds of [[keratin]] layers.
*A stroma-like inflammatory reaction and a blunt pushing margin may be seen.
 
* SCC is subdivided by the WHO into:<ref name="pmid23015393">{{cite journal| author=Peterson BR, Nelson BL| title=Nonkeratinizing undifferentiated nasopharyngeal carcinoma. | journal=Head Neck Pathol | year= 2013 | volume= 7 | issue= 1 | pages= 73-5 | pmid=23015393 | doi=10.1007/s12105-012-0401-4 | pmc=3597164 | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=23015393  }}</ref>
**[[Keratinized|Keratinizing]] type: Worst [[prognosis]]
**Undifferentiated type: Intermediate prognosis and [[Epstein Barr virus|EBV]] association<ref name="pmid7778675">{{cite journal| author=Pathmanathan R, Prasad U, Chandrika G, Sadler R, Flynn K, Raab-Traub N| title=Undifferentiated, nonkeratinizing, and squamous cell carcinoma of the nasopharynx. Variants of Epstein-Barr virus-infected neoplasia. | journal=Am J Pathol | year= 1995 | volume= 146 | issue= 6 | pages= 1355-67 | pmid=7778675 | doi= | pmc=1870892 | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=7778675  }}</ref>
**Non-keratinizing type: Good [[prognosis]] and [[Epstein Barr virus|EBV]] association
[[File:Oral cancer (1) squamous cell carcinoma histopathology.jpg|300px|center|thumb|Microscopic picture of oral SCC, source: By No machine-readable author provided. KGH assumed (based on copyright claims). - No machine-readable source provided. Own work assumed (based on copyright claims)., CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=486166]]


The variant val allele of the CYP1A1 (Cytochrome P450, family 1, member A1) polymorphism is another fairly consistent susceptibility marker with a 35% increased risk in a meta- analysis of 12 studies [21]. The studies on many other gene polymorphisms have been inconclusive. Brennan et al. [23] found that ALDH1B and ALDH2 (Aldehyde dehydrogenase 2) genes were associated with HNSCC and showed significant correlation with alcohol consumption.
==References==
==References==
{{Reflist|2}}
{{Reflist|2}}
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Latest revision as of 12:49, 11 April 2019

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Sargun Singh Walia M.B.B.S.[2], Simrat Sarai, M.D. [3]; Grammar Reviewer: Natalie Harpenau, B.S.[4]

Overview

It is understood that oral cancers occur as a the result of carcinogen-metabolizing enzymes, alcohol, tobacco and genetic factors. Cytotoxic enzymes such as alcohol dehydrogenase result in the production of free radicals and hydroxylation of DNA base units. Alcohol dehydrogenase oxidizes ethanol to acetaldehyde which is cytotoxic in nature. Cigarette smoke has various carcinogens, which can lead to oral cancers. Low-reactive free radicals in cigarette smoke interact with redox-active metals in saliva.The development of oral cancer is the result of multiple genetic mutations. These mutations occur in tumor suppressor genes (TSGs) and oncogenes. Squamous cell carcinoma is the most common malignancy of the oral cavity. It typically has three gross morphological growth patterns, which are exophytic, ulcerative, and infiltrative. Microscopically, oral cancers are broadly based and invasive through papillary fronds. Oral cancer consists of highly differentiated squamous cells lacking frank cytologic criteria of malignancy with rare mitoses.The surface of the lesion is covered with compressed invaginating folds of keratin layers. A stroma-like inflammatory reaction and a blunt pushing margin may be seen.

Pathophysiology

It is understood that oral cancer occurs as a the result of carcinogen-metabolizing enzymes, alcohol, tobacco and genetic factors.

Carcinogen-metabolizing enzymes

Alcohol

Tobacco

Pathology of classical or conventional squamous cell carcinoma

Pathology of squamous cell carcinoma variants

  • Verrucous carcinoma
    • These tumors make up less than 5% of all oral cavity tumors.
    • They have a wart-like appearance and develop most often on the gums (gingiva), lining of the cheeks (buccal mucosa) and larynx.
    • Verrucous carcinomas are low grade, slow-growing and rarely spread.
    • They are associated with the chronic use of snuff or chewing tobacco.
  • Basaloid SCC
    • This is a rare but aggressive sub-type of squamous cell carcinoma.
    • It is more common in men older than 60 years old.
  • Papillary SCC
    • This is a rare sub-type of squamous cell carcinoma that grows outward from the surface of the epithelium (exophytic).
    • HPV infections may have a role in the development of this type of cancer.
  • Spindle cell carcinoma (SpCC)
    • This is an aggressive, rare variant of squamous cell carcinoma.
    • These tumors contain a mixture of conventional squamous cell carcinoma and spindle cells that resemble a sarcoma.
    • It is also known as sarcomatoid carcinoma, pseudosarcoma, carcinosarcoma, pleomorphic carcinoma, metaplastic carcinoma, collision tumor and Lane tumor.
  • Acantholytic SCC
  • Adenosquamous carcinoma
    • This is a very rare, aggressive type of squamous cell carcinoma.
    • It looks like classical squamous cell carcinoma but also has mucus-producing gland cells.
  • Lymphoepithelial carcinoma

Genetics

Tumor suppressor genes (TSGs)

Oncogenes

Gross Pathology

  • Squamous cell carcinoma is the most common malignancy of the oral cavity.
  • It typically has three gross morphological growth patterns, which are exophytic, ulcerative, and infiltrative.
  • The infiltrative and ulcerative are the growth patterns most commonly observed in the oral cavity.
  • The macroscopic appearance of oral cancer depends on the following:
    • Duration of the lesion
    • The amount of keratinization
    • The changes in the adjoining mucosa
    • A fully developed oral cavity lesion appears as an exophytic bulky lesion that is gray to grayish-red and has a rough, shaggy, or papillomatous surface
Gross pathology of oral SCC, source: By Luca Pastore, Maria Luisa Fiorella, Raffaele Fiorella, Lorenzo Lo Muzio - http://www.plosmedicine.org/article/showImageLarge.action?uri=info%3Adoi%2F10.1371%2Fjournal.pmed.0050212.g001, CC BY 2.5, https://commons.wikimedia.org/w/index.php?curid=15252632

Microscopic Pathology

  • Microscopically, oral cancers are broadly based and invasive through papillary fronds.
  • Oral cancer constitutes of highly-differentiated squamous cells lacking frank cytologic criteria of malignancy with rare mitoses.
  • The surface of the lesion is covered with compressed invaginating folds of keratin layers.
  • A stroma-like inflammatory reaction and a blunt pushing margin may be seen.
Microscopic picture of oral SCC, source: By No machine-readable author provided. KGH assumed (based on copyright claims). - No machine-readable source provided. Own work assumed (based on copyright claims)., CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=486166

References

  1. ↑ Nagler R, Dayan D (2006). "The dual role of saliva in oral carcinogenesis". Oncology. 71 (1–2): 10–7. doi:10.1159/000100445. PMID 17344667.
  2. ↑ Peterson BR, Nelson BL (2013). "Nonkeratinizing undifferentiated nasopharyngeal carcinoma". Head Neck Pathol. 7 (1): 73–5. doi:10.1007/s12105-012-0401-4. PMC 3597164. PMID 23015393.
  3. ↑ Pathmanathan R, Prasad U, Chandrika G, Sadler R, Flynn K, Raab-Traub N (1995). "Undifferentiated, nonkeratinizing, and squamous cell carcinoma of the nasopharynx. Variants of Epstein-Barr virus-infected neoplasia". Am J Pathol. 146 (6): 1355–67. PMC 1870892. PMID 7778675.


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