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==Overview==
==Overview==
==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.
Precancerous lesions of the oropharynx include leukoplakia, erythroplakia, and mixed erythroleukoplakia.[1] Leukoplakia, the most common of the three conditions, is defined by the World Health Organization as “a white patch or plaque that cannot be characterized clinically or pathologically as any other disease.”[2] The diagnosis of leukoplakia is one of exclusion; conditions such as candidiasis, lichen planus, leukoedema, and others must be ruled out before a diagnosis of leukoplakia can be made.[1]
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.
The prevalence of leukoplakia in the United States is decreasing; this decline has been related to reduced tobacco consumption.[3] Although erythroplakia is not as common as leukoplakia, it is much more likely to be associated with dysplasia or carcinoma. The development of oral squamous cell carcinoma (OSCC) is a multistep process requiring the accumulation of multiple genetic alterations, influenced by a patient’s genetic predisposition as well as by environmental influences, including tobacco, alcohol, chronic inflammation, and viral infection. Tumorigenic genetic alterations consist of two major types: tumor suppressor genes, which promote tumor development when inactivated; and oncogenes, which promote tumor development when activated. Tumor suppressor genes can be inactivated through genetic events such as mutation, loss of heterozygosity, or deletion, or by epigenetic modifications such as DNA methylation or chromatin remodeling. Oncogenes can be activated through overexpression due to gene amplification, increased transcription, or changes in structure due to mutations that lead to increased transforming activity. This review focuses on the molecular mechanisms of oral carcinogenesis and the use of biologic therapy to specifically target molecules altered in OSCC. The rapid progress that has been made in our understanding of the molecular alterations contributing to the development of OSCC is leading to improvements in the early diagnosis of tumors and the refinement of biologic treatments individualized to the specific characteristics of a patient’s tumor. This review focuses on the molecular mechanisms of oral carcinogenesis and the use of biologic therapy to specifically target molecules altered in oral squamous cell carcinoma.


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].
Oral squamous carcinogenesis is a multistep process in which multiple genetic events occur that alter the normal functions of oncogenes and tumour suppressor genes. This can result in increased production of growth factors or numbers of cell surface receptors, enhanced intracellular messenger signalling, and/or increased production of transcription factors. In combination with the loss of tumour suppressor activity, this leads to a cell phenotype capable of increased cell proliferation, with loss of cell cohesion, and the ability to infiltrate local tissue and spread to distant sites. Recent advances in the understanding of the molecular control of these various pathways will allow more accurate diagnosis and assessment of prognosis, and might lead the way for more novel approaches to treatment and prevention.
 
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==
{{Reflist|2}}


==References=={{Reflist|2}}
[[Category:Oral and maxillofacial surgery]]
[[Category:Oral and maxillofacial surgery]]
[[Category:Otolaryngology]]
[[Category:Otolaryngology]]

Revision as of 03:59, 3 September 2015

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1];{{AE}] Simrat Sarai, M.D. [2]

Overview

Pathophysiology

Precancerous lesions of the oropharynx include leukoplakia, erythroplakia, and mixed erythroleukoplakia.[1] Leukoplakia, the most common of the three conditions, is defined by the World Health Organization as “a white patch or plaque that cannot be characterized clinically or pathologically as any other disease.”[2] The diagnosis of leukoplakia is one of exclusion; conditions such as candidiasis, lichen planus, leukoedema, and others must be ruled out before a diagnosis of leukoplakia can be made.[1]

The prevalence of leukoplakia in the United States is decreasing; this decline has been related to reduced tobacco consumption.[3] Although erythroplakia is not as common as leukoplakia, it is much more likely to be associated with dysplasia or carcinoma. The development of oral squamous cell carcinoma (OSCC) is a multistep process requiring the accumulation of multiple genetic alterations, influenced by a patient’s genetic predisposition as well as by environmental influences, including tobacco, alcohol, chronic inflammation, and viral infection. Tumorigenic genetic alterations consist of two major types: tumor suppressor genes, which promote tumor development when inactivated; and oncogenes, which promote tumor development when activated. Tumor suppressor genes can be inactivated through genetic events such as mutation, loss of heterozygosity, or deletion, or by epigenetic modifications such as DNA methylation or chromatin remodeling. Oncogenes can be activated through overexpression due to gene amplification, increased transcription, or changes in structure due to mutations that lead to increased transforming activity. This review focuses on the molecular mechanisms of oral carcinogenesis and the use of biologic therapy to specifically target molecules altered in OSCC. The rapid progress that has been made in our understanding of the molecular alterations contributing to the development of OSCC is leading to improvements in the early diagnosis of tumors and the refinement of biologic treatments individualized to the specific characteristics of a patient’s tumor. This review focuses on the molecular mechanisms of oral carcinogenesis and the use of biologic therapy to specifically target molecules altered in oral squamous cell carcinoma.

Oral squamous carcinogenesis is a multistep process in which multiple genetic events occur that alter the normal functions of oncogenes and tumour suppressor genes. This can result in increased production of growth factors or numbers of cell surface receptors, enhanced intracellular messenger signalling, and/or increased production of transcription factors. In combination with the loss of tumour suppressor activity, this leads to a cell phenotype capable of increased cell proliferation, with loss of cell cohesion, and the ability to infiltrate local tissue and spread to distant sites. Recent advances in the understanding of the molecular control of these various pathways will allow more accurate diagnosis and assessment of prognosis, and might lead the way for more novel approaches to treatment and prevention.

==References==

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