Oral cancer pathophysiology

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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]

Overview

Pathophysiology

  • It is understood that oral cavity carcinoma is the result of dysfunction of either :

Tumor suppressor genes (TSGs)

  • Oral cavity cancer may be the result of 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 (TSGs).
  • Normally TSGs modulate normal growth.
  • Mutation of these TSGs leads to dysfunctional growth control.
  • Mutation most commonly occurs in either of the following:
    • Short arm of chromosome 3
    • TSG termed P16 on chromosome 9
    • TSG termed TP53 on chromosome 17
  • Cytochrome P450 genotypes is related to mutations in some TSGs and lead to oral squamous cell carcinoma.
  • In western countries (eg, United Kingdom, United States, Australia) TP53 mutations are the most common molecular change that leads to oral squamous cell carcinoma.

Oncogenes

  • Cancer may also occur if there is mutation to other genes that control cell growth, mainly oncogenes.
  • Oncogenes most commonly involved are:
    • Chromosome 11 (PRAD1)
    • Chromosome 17 (Harvey ras [H-ras])
  • In eastern countries (eg, India, Southeast Asia), ras oncogenes is a more common cause of oral squamous cell carcinoma.

Carcinogen-metabolizing enzymes

  • Carcinogen-metabolizing enzymes are known to cause cancer in some patients.
  • Cytotoxic enzymes such as alcohol dehydrogenase result in the production of:
    • Free radicles
    • DNA hydroxylated bases
  • These cytotoxic enzymes especially predispose oral squamous cell carcinoma.

Alcohol

  • Alcohol dehydrogenase oxidizes ethanol to acetaldehyde which is cytotoxic in nature.
  • cytochrome P450 IIEI (CYP2E1) also metabolizes ethanol to acetaldehyde.
  • Alcohol dehydrogenase type 3 genotype predisposes to oral squamous cell carcinoma.
  • 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.
  • This makes saliva to loose its antioxidant potential and become a potent pro-oxidant milieu.[1]

Pathology of classical or conventional SCC

  • Most cancers of the oral cavity are classical or conventional squamous cell carcinoma.
  • This type of SCC starts in the squamous epithelium that lines the oral cavity and occurs most often on the lower lip, tongue and floor of the mouth.
  • The microscopic features of classical SCC include:
    • Epithelial pearls
      • These are circular layers of squamous cells around a collection of keratin (a tough fibrous protein) in the centre.
  • The cancer starts in the squamous cells of the epithelium and invades the deeper layers of the oral cavity.

Pathology of variants of SCC

  • These squamous cell carcinomas have distinct microscopic features that make them look and behave differently from classical SCC.
  • Verrucous carcinoma
    • These tumours make up less than 5% of all oral cavity tumours.
    • 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 subtype of squamous cell carcinoma.
    • It is more common in men older than 60 years.
  • Papillary SCC
    • This is a rare subtype of squamous cell carcinoma that grows outward from the surface of the epithelium (exophytic).
    • HPV infection 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 cells break down.
    • This results in microscopic spaces in the tumour 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-containing gland cells.
  • Lymphoepithelial carcinoma
    • This is a rare subtype of squamous cell carcinoma.
    • The microscopic appearance is similar to undifferentiated nasopharyngeal carcinoma.
    • It is also called undifferentiated carcinoma.

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.


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