Cancers of the Oral Mucosa

Updated: Jun 29, 2017
  • Author: Chelsia Q Sim, DDS, MSc; Chief Editor: Dirk M Elston, MD  more...
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Overview

Background

The image below shows early oral squamous cell carcinoma (OSCC) on the lateral border of the tongue.

Different clinical presentations of oral squamous Different clinical presentations of oral squamous cell carcinoma (OSCC) on the anterior and posterior lateral border of the tongue illustrate the importance of differential diagnosis. This first case was thought to be an allergic reaction to amalgam. Therefore, the importance of a good differential diagnosis.

 

Mouth (oral) cancer is a major neoplasm worldwide and accounts for most head and neck cancers. It theoretically should be largely preventable or detectable at an early stage. [1] Approximately 90% of oral cancers are SCC, which is seen typically on the lateral border of the tongue, oropharynx, and floor of the mouth, as a red lesion (erythroplakia), white lesion (leukoplakia), or a mix of the two (erythroleukoplakia) with an ulcer. See the image below.

Oral squamous cell carcinoma in the most common in Oral squamous cell carcinoma in the most common intraoral site manifesting as a chronic, indurated ulcer.

Early oral cancer is asymptomatic, which contributes to delayed diagnosis. Any single ulcerated lesion persisting for more than 3 weeks should be regarded with suspicion, and a biopsy should be performed. The mnemonic RULE (red, ulcerated, lump, extending for 3 or more weeks) is an aid to diagnosis. [2, 3]

OSCC is particularly common in the developing world, mostly in older males. There is concern about an ongoing increase in younger patients and in women in particular, as well as in the oropharynx, possible due to human papillomavirus (HPV) infection. [4] The etiology of OSCC appears to be multifactorial and strongly related to lifestyle, mostly habits and diet (particularly tobacco alone or in combination with betel, and alcohol use). Other factors such as infective agents may also be implicated, particularly in oropharyngeal cancer (HPV). Immune defects or immunosuppression, defects of carcinogen metabolism, or defects in DNA-repair enzymes underlie some cases of SCC. Sunlight exposure predisposes to lip cancer.

Findings from the history and clinical examination by a trained dentist are the primary indicators of OSCC, but the diagnosis must always be confirmed histologically with tissue biopsies, even if the clinical picture is consistent with OSCC.

 

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Pathophysiology

In oral squamous cell carcinoma (OSCC), modern DNA technology, especially allelic imbalance (loss of heterozygosity) studies, have identified chromosomal changes suggestive of the involvement of tumor suppressor genes (TSGs), particularly in chromosomes 3, 9, 11, and 17. Functional TSGs seem to assist growth control, while their mutation can unbridle these control mechanisms.

The regions most commonly identified thus far have included some on the short arm of chromosome 3, a TSG termed P16 on chromosome 9, and the TSG termed TP53 on chromosome 17, but multiple other genes are being discovered.

As well as damage to TSGs, cancer may also involve damage to other genes involved in growth control, mainly those involved in cell signaling (oncogenes), especially some on chromosome 11 (PRAD1 in particular) and chromosome 17 (Harvey ras [H-ras]). Changes in these and other oncogenes can disrupt cell growth control, ultimately leading to the uncontrolled growth of cancer. H-ras was one of the oncogenes that first caught the attention of molecular biologists interested in cell signaling, cell growth control, and cancer. It and the gene for epidermal growth factor receptor (EGFR) are involved in cell signaling.

The genetic aberrations involve, in order of decreasing frequency, chromosomes 9, 3, 17, 13, and 11 in particular, and probably other chromosomes, and involve inactivated TSGs, especially P16, and TP53 and overexpressed oncogenes, especially PRAD1.

The molecular changes found in OSCC from Western countries (eg, United Kingdom, United States, Australia), particularly TP53 mutations, are infrequent in Eastern countries (eg, India, Southeast Asia), where the involvement of ras oncogenes is more common, suggesting genetic differences that might be involved in explaining the susceptibility of certain groups to OSCC.

Carcinogen-metabolizing enzymes are implicated in some patients. Alcohol dehydrogenase oxidizes ethanol to acetaldehyde, which is cytotoxic and results in the production of free radicals and DNA hydroxylated bases; alcohol dehydrogenase type 3 genotypes appear predisposed to OSCC. Cytochrome P450 can activate many environmental procarcinogens. Ethanol is also metabolized to some extent by cytochrome P450 IIEI (CYP2E1) to acetaldehyde. Mutations in some TSGs may be related to cytochrome P450 genotypes and predispose to OSCC. Glutathione S transferase (GST) genotypes may have impaired activity; for example, the null genotype of GSTM1 has a decreased capacity to detoxify tobacco carcinogens. Some GSTM1 and GSTP1 polymorphic genotypes and GSTM1 and GSTT1 null genotypes have been shown to predispose to OSCC. N-acetyltransferases NAT1 and NAT2 acetylate procarcinogens. N-acetyl transferase NAT1*10 genotypes may be a genetic determinant of OSCC, at least in some populations.

Tobacco is a potent risk factor for oral cancer. An interaction occurs between redox-active metals in saliva and the low reactive free radicals in cigarette smoke. The result may be that saliva loses its antioxidant capacity and instead becomes a potent pro-oxidant milieu. [5]

DNA repair genes are clearly involved in the pathogenesis of some rare cancers, such as those that occur in association with xeroderma pigmentosum, but, more recently, evidence of defective DNA repair has also been found to underlie some OSCCs.

An immune deficiency state may predispose one to a higher risk of developing OSCC, especially lip cancer.

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Epidemiology

The oral cavity is one of the 10 most frequent sites of cancer internationally, with three quarters of cases affecting people in the developing world, where, overall, oral cancer is the third most common cancer after stomach and cervical cancer. An estimated 378,500 new cases of intraoral cancer are diagnosed annually worldwide. [4]

Unfortunately, the parts of the world where oral cancer is most common are also those where descriptive information (ie, incidence, mortality, prevalence) is least available. In certain countries, such as Sri Lanka, India, Pakistan, and Bangladesh, oral cancer is the most common cancer. In parts of India, oral cancer can represent more than 50% of all cancers.

The worldwide incidence of oral cancer is estimated to be around 260,000 cases annually, although there is great variation in the incidences across the world. Countries like Taiwan, Hungary, Brazil, France, and parts of South Africa have higher incidences compared with some other countries, such as Japan. In developed countries, oral cancer is less common but is the eighth most common form of cancer overall. For example, in areas of northern France, oral cancer is the most common form of cancer in men. Estimates show that in 1980, more than 32,000 new cases of oral cancer were diagnosed throughout the European community. The prevalence of lip cancer appears to be decreasing, but the prevalence of intraoral cancer appears to be rising in many countries, especially in younger people. This is especially true in Central and Eastern Europe, especially Hungary and Northern France. Within the United States, oral cancer represents the eleventh most common cancer in males and the sixteenth most common in females. Approximately 27,000 new cases of oral cancer are diagnosed each year, with about 5,500 patients succumbing to the disease annually. [4]

Race

The prevalence of tongue cancer is consistently found to be higher (by approximately 50%) in blacks compared with whites within the same regions of the United States. [6] The prevalence of oral cancer is also generally higher in ethnic minorities in other developed countries. [7]

Sex

Oral cancer affects males more frequently than females, although the ratio is equalizing.

Age

Oral cancer is predominantly found in middle-aged and older persons. However, in recent years, an increase in younger patients has been observed.

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Prognosis

In general, the prognosis for oral cancer depends on tumor staging and the location of the tumor. At most times, the staging of the tumor is associated with the timing of the diagnosis. The earlier the diagnosis, the lower the tumor stage, and hence, a better survival rate (83.7%) is noted compared with a lower survival rate with a late diagnosis, leading to a higher stage III-IV (38.5%). However, other factors also have to be taken into account, such as the location of the tumor, the patient’s general health, age, tobacco usage, and the presence of human papillomavirus (HPV) infection.

Based on 2017 data from the United States, the estimated 5-year survival rate for oral and pharyngeal cancers is approximately 66%. Lip carcinomas generally has the best 5-year survival rate (88%) and the floor of mouth has the worst (54%). [4] Tumor staging is the best prognostic factor for intraoral cancers and lip carcinomas, while the status of transcriptionally active HPV is considered the most important prognostic factor for oropharyngeal cancers. Those with HPV-positive tumors tend to respond better to chemotherapy and/or radiation therapy compared with those with HPV-negative tumors.

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Patient Education

Unfortunately, little has been done in regard to patient education as it concerns oral cancer. Like melanoma, oral cancer can be easily seen, except those in the posterior regions of the tongue, by the patient and the primary care physician. However, this is true only if they know how to identify it. Of interest, the National Cancer Institute (NCI) estimates 87,110 new cases of melanoma for 2017, with 9,730 estimated deaths, while for oral cancer, they estimate 49,670 new cases, with a mortality of 9,700. This difference can only be explained by the aggressive campaign sponsored by the America Academy of Dermatology (AAD) against melanoma, which produced and distributed visual teaching material for patients about the risk of melanoma and the typical clinical presentation. Increased awareness instituted by relevant dental societies to educate the public on the risks and typical clinical presentation of oral squamous cell carcinoma (OSCC) is recommended.

Educate patients regarding lifestyle changes, including a diet richer in vegetables and fruits, discontinued smoking, and moderation of alcohol consumption. Furthermore, patients should be encouraged to learn about their oral condition, prevention, treatment options, and complications from therapy. For patient education resources, see the following:

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