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 Table of Contents  
REVIEW ARTICLE
Year : 2012  |  Volume : 8  |  Issue : 6  |  Page : 57-66

Oral cancer: Premalignant conditions and screening - an update


1 Department of Head and Neck Surgical Oncology, Tata Memorial Centre, Dr. Ernest Borges Marg, Parel, Mumbai - 400 012, India
2 Department of Surgical Oncology, Tata Memorial Centre, Dr. Ernest Borges Marg, Parel, Mumbai - 400 012, India

Date of Web Publication24-Jan-2012

Correspondence Address:
Deepa R Nair
Room no. 43, Private OPD, Head and Neck Services, Surgical Oncology, Tata Memorial Centre, Parel, Dr Ernest Borges Marg, Mumbai - 400012
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0973-1482.92217

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 > Abstract 

Oral cancers form a significant portion of the cancer burden seen in our country. Typically, they tend to be preceded by a premalignant state for a long time. This article discusses the various types of premalignant disorders commonly seen in daily practice. Also, it is important to screen patients for these conditions so as to detect malignant changes early. Previously, the screening of patients for oral cancer and precancerous lesions has relied mainly on conventional oral examination. Nowadays, many newer techniques are available to potentially assist in the screening of healthy patients for evidence of oral cancer. This article attempts to review the current literature for screening methods and adjuncts such as toluidine blue, brush cytology, tissue chemiluminescence and autofluorescence.

Keywords: Oral cancer, premalignant disorders, screening


How to cite this article:
Nair DR, Pruthy R, Pawar U, Chaturvedi P. Oral cancer: Premalignant conditions and screening - an update. J Can Res Ther 2012;8:57-66

How to cite this URL:
Nair DR, Pruthy R, Pawar U, Chaturvedi P. Oral cancer: Premalignant conditions and screening - an update. J Can Res Ther [serial online] 2012 [cited 2017 Mar 26];8:57-66. Available from: http://www.cancerjournal.net/text.asp?2012/8/6/57/92217


 > Introduction Top


Oral cancers are one of the leading cancers in India today, with an age standardized incidence rate of 12.6 per 100 000 population. It is one of the leading cancers in Indian males accounting for approximately 30% of the cancer burden. A significant number of these cases would present initially with precursor lesions that are further classified as precancerous lesions and precancerous conditions.

A precancerous lesion is a morphologically altered tissue in which oral cancer is more likely to occur than in its apparently normal counterpart, for example, Leukoplakia, Erythroplakia etc. A precancerous condition is a generalized state associated with a significantly increased risk of cancer, for example, submucous fibrosis, Lichen planus etc. However, in a World Health Organization (WHO) Workshop, held in 2005, it was decided to use the term "potentially malignant disorders (PMD)" as it conveys that not all disorders described under this term may transform into cancer. [1]

The following were identified as Potentially Malignant Disorders by the World Health Organisation's working group on Oral Cancer. [2]

  • Leukoplakia
  • Erythroplakia
  • Palatal lesion of reverse cigar smoking
  • Oral lichen planus
  • Oral submucous fibrosis (SMF)
  • Discoid lupus erythematosus
Hereditary disorders such as dyskeratosis congenita and epidermolysis bullosa.


 > Leukoplakia Top


The term "leukoplakia" was coined by Schwimmer of Budapest in 1877, for white changes on the tongue, seen prior to lingual cancer development in tertiary syphilis. It is the most common premalignant lesion and the most studied PMD. The WHO working group defines leukoplakia as "a keratotic white patch or plaque that cannot be scraped off and cannot be characterized clinically or pathologically as any other disease." Therefore, a process of exclusion establishes the diagnosis of the disease.

Incidence

The estimated prevalence of oral leukoplakia, worldwide, is approximately 2%. [3] Petti, [3] in a systematic review, summarized the world prevalence of leukoplakia based on 23 studies from 17 countries published between 1986 and 2002. Using statistical techniques, he calculated a global prevalence of 2.6%. In India, a striking variation has been observed with 0.2% in Bihar and 4.9% in Andhra Pradesh. [4] Gujarat has shown a prevalence rate of 11.7% owing to the high prevalence of tobacco or guthka chewing practices. The systematic review by Petti [3] also confirmed that oral PMD affects males at least three times as often as females.

Etiopathogenesis

The etiology of leukoplakia remains unknown. Many physical agents have been proposed, including tobacco, alcohol, chronic friction, electro galvanic reaction between unlike restorative metals, and ultraviolet radiation. [5],[6] Tobacco smoking is by far the most accepted factor and smokers are six times more prone to leukoplakia than nonsmokers. There are conflicting results of studies related to the possible role of human papilloma virus infection. [7]

Clinically, leukoplakia can be subdivided into a homogeneous type (flat, thin, uniform white in color) and a nonhomogeneous type. The nonhomogeneous type has been defined as a white lesion, that may be either irregularly flat (speckled) or nodular. Verrucous leukoplakia is yet another type of non-homogeneous leukoplakia. Although verrucous leukoplakia usually has a uniform white appearance, its verrucous texture is the distinguishing feature from homogeneous (flat) leukoplakia. Verrucous leukoplakia is clinically indistinguishable from the clinical aspect of verrucous carcinoma. [8] Proliferative verrucous leukoplakia (PVL) is a subtype of verrucous leukoplakia, being characterized by multifocal presentation, resistance to treatment and a high rate of malignant transformation. [9],[10] PVL seems more prevalent among elderly women.

Various phases of leukoplakia have been described:

Phase 1: Thin gray white translucent plaques which are soft and flat.

Phase 2: Homogenous thick smooth or fissured leukoplakias.

Phase 3: Nodular or granular surface or verruciform leukoplakia

Phase 4: Erythroplakia, speckled leukoplakia, nonhomogenous leukoplakia

Leukoplakias are known to occur at almost all places in oral cavity. However, they are most frequent in buccal mucosa and mandibular mucosa. Two-third of the oral leukoplakias occurs at the vermillion, buccal mucosa and gingival surface. In Gujarat, where smoking is common, 43.9% of leukoplakias occurred on the buccal mucosa while 35.4% at the commissure, whereas in Kerala where tobacco chewing is common, 64.8% were on the buccal mucosa, 24.3% at the commissures and 6% on the tongue. In Andhra Pradesh, where smoking is common, 71.3% were on palate, 8.1% on the commissure, 16.9% on the buccal mucosa and 2.7 on tongue. [4] In a Swedish study, the buccal mucosa or commissure was involved in 90% of cases. [11] In a Hungarian study, the tongue was involved in 36.5%, buccal mucosa in 27.9%, alveolar ridge in in 13.6% and commissure in 12.5%.

Prognosis and malignant transformation

The prognosis of leukoplakia varies. In a study conducted in Mumbai, 42.5% untreated leukoplakias diseappeared in 5 years and 45.3% in 10 years in the tobacco chewing group. [12] In Gujarat, 11% of leukoplakias re-examined after 2 years had increased in the size, 31.6% had decreased in size or disappeared and 57.3% had remained unchanged. [13] In a study from developed world only 20.1% had disappeared, 17.8% had reduced in size and 3.3% had increased at 10 years follow up. [14]

The frequency of dysplastic or malignant alterations in oral leukoplakia has ranged from 15.6 to 39.2% in several studies. In Indian studies, the rate of malignant transformation ranges from 0.13% to 2.2% per year. [12],[13] In a Swedish study, 0.2% developed oral cancer in 2 years, 0.4% in 5 years in tobacco users while in non tobacco users the transformation rate was 1.15 and 3.1% at 2 and 5 years respectively. [15] In systematic review, Petti has calculated a global transformation rate for oral leukoplakia of 1.36% per year. [3] The lesions that are present in the floor of mouth, lateral tongue and lower lip are more likely to show dysplastic or malignant changes.

The possibility of malignant transformation of leukoplakias depends on multiple factors:

  • Female gender
  • Long duration of leukoplakia
  • Leukoplakia in nonsmokers (idiopathic leukoplakia)
  • Location on the tongue and/or floor of the mouth
  • Size > 200 mm 2
  • Nonhomogeneous type
  • Presence of Candida albicans
  • Presence of epithelial dysplasia.



 > Erythroplakia Top


Erythroplakia is defined as "a fiery red patch or bright red velvety plaques that cannot be characterized clinically or pathologically as any other definable disease." [16] There are various clinical variations such as:

  • Homogeneous erythroplakia.
  • Erythroplakia interspersed with patches of leukoplakia (erythroleukoplakia).
  • Granular or speckled erythroplakia (embracing the lesion described as speckled leukoplakia).
Erythroplakia is not as common as leukoplakia and has an incidence reported between 0.02% and 0.83%. [17] It mainly occurs in the middle aged and the elderly. There is no distinct gender preference. This lesion has been called "the dangerous oral mucosa" because it typically presents as carcinoma in situ, severe epithelial dysplasia or superficially invasive carcinoma under the microscope. In very high risk settings, such as floor of mouth lesions in heavy smokers and alcohol abusers, 80% of these red patches already may contain focal areas of microinvasive cancer at the time of initial biopsy. Any site of the oral and oropharyngeal cavity may become involved, usually in a solitary fashion. This solitary presentation is often helpful in clinically distinguishing erythroplakia from erosive lichen planus, lupus erythematosus and erythematous candidiasis, since these lesions occur almost always in a bilateral, more or less in a symmetrical pattern.

In a sister study, to their large series of leukoplakia cases, Shafer and Waldron also analyzed their biopsy experience with 65 cases of erythroplakia. [18] All the erythroplakia cases showed some degree of epithelial dysplasia; 51 % showed invasive squamous cell carcinoma, 40% were carcinoma in situ or severe epithelial dysplasia, and the remaining 9% demonstrated mild-to-moderate dysplasia. Therefore, true clinical erythroplakia is a much more worrisome lesion than leukoplakia.


 > Oral Submucous Fibrosis Top


Oral submucous fibrosis (OSMF) is a chronic disorder characterized by fibrosis of the lining mucosa of the upper digestive tract involving the oral cavity, oropharynx and frequently the upper third of the oesophagus. Except in early forms of the disease, the clinical presentation is characteristic due to fibrosis of lamina propria and submucosa with an increasing loss of tissue mobility. OSMF is particularly associated with areca nut chewing, the main component of betel quid. [19] Hence, it is the most common precancerous lesion that is a unique problem in South East Asia especially India. Factors including areca nut chewing, ingestion of chilies, genetic and immunologic processes, nutritional deficiencies, and other factors have been incorporated in causation of OSMF. Patients with OSMF have been found to have an increased frequency of HLA 10, DR3, and DR7. [20]

Clinically, OSMF is characterized by a burning sensation, blanching and stiffening of the oral mucosa and oropharynx, and trismus. The most characteristic feature is the marked vertical fibrous ridge formation within the cheeks, and board like stiffness of the buccal mucosa. The fibrosis in the soft tissue leads to trismus, difficulty in eating, and even dysphagia. In advanced stages vertical fibrous bands appear in the cheeks, faucial pillars, and encircle the lips. Through an as yet unknown process, fibrosis and hyalinization occur in the lamina propria, which results in atrophy of the overlying epithelium. The atrophic epithelium apparently predisposes to the development of a squamous cell carcinoma in the presence of carcinogens. Biopsy of the tissue is rarely performed due to the observation that such investigation results in further fibrous scar formation and worsening of the symptoms.

The clinical presentation can be summarized into early and forms:

  • Early forms are characterized by burning sensation exacerbated by spicy foods, vesiculation, blanching of mucosa, and leathery mucosa.
  • Late forms are characterized by fibrous bands within the mucosa, limitation of mouth opening, narrowing of the oropharyngeal orifice with distortion of uvula and woody changes of the mucosa and tongue.
In India, it affects between 0-2% and 1.2% of an urban population attending dental clinics. [21] There is a positive association between the incidence of leukoplakia and oral cancer with OSMF. The frequency of malignant change has been reported from 3% to 6%. The possible precancerous nature of OSMF was first described by Paymaster, who observed the occurrence of squamous cell carcinoma in one third of his patients with OSMF. [22] In a long-term follow-up study over a period of 17 years by Murti et al., [23] the annual malignant transformation rate was approximately 0.5% or 7.6% over 17 years. [23]


 > Oral Lichen Planus Top


Lichen planus is an autoimmune disorder of the skin and/or mouth membranes which usually affects middle-aged persons but may occur at any age with a strong female predilection (M:F = 1:2). Persons with oral lesions seldom have skin lesions. Oral lichen planus is a T-cell-mediated autoimmune disease in which autocytotoxic CD8 + T cells trigger apoptosis of oral epithelial cells. [24],[25] Oral mucosal lichenoid lesions may occur after the administration of systemic drugs such as nonsteroidal anti-inflammatory drugs (NSAIDs), sulfonylureas, antimalarials, beta-blockers, and some angiotensin-converting enzyme (ACE) inhibitors. The period between the commencement of the drug therapy and the clinical appearance of oral lichen planus-like disease varies.

The buccal mucosa, tongue, and gingiva are the most common sites, whereas palatal lesions are uncommon; with intertwining white streaks forming a reticular pattern similar to a spider web, any oral area can be affected. The background membrane may be red, and some persons might have blisters and ulcers with the white lines. There may be a metallic taste, and ulcers may be somewhat tender. The lesions tend to bilateral and symmetrical that distinguishes them from erythroleukoplakia. Andreasen [26] divided oral lichen planus into six types: reticular, papular, plaque-like, erosive, atrophic, and bullous. The reticular, papular, and plaque-like forms are usually painless and appear clinically as white keratolic lesions. The erosive, atrophic, and bullous forms are often associated with a burning sensation and in many cases can cause severe pain.

There is still no consensus in the literature whether patients with oral lichen planus (OLP) carry an increased risk of developing squamous cell carcinomas, with majority favoring it. Most of the assumptions are based on retrospective studies with only few prospective studies. [27],[28],[29],[30] The reported annual malignant transformation rate is usually well below 1%. There is no data to conclude which variety of OLP would eventually develop into squamous carcinoma, though some studies attribute a higher rate in specially the atrophic and erosive-ulcerative types. [31],[32] The present lack of clinicopathologic correlation in the diagnosis also adds to the confusion. [33],[34] Another entity, described as lichenoid dysplasia [35] adds to the confusion. As there is no particular treatment to prevent the malignant transformation, some authors [36] recommend keeping patients on close surveillance.


 > Nicotine Stomatitis Top


Nicotine stomatitis is a thickened, hyperkeratotic alteration of the palatal mucosa that is most frequently related to pipe smoking or reverse smoking. The palatal mucosa becomes thickened and hyperkeratotic, sometimes developing a fissured surface. The surface often develops popular elevations with red centers, which represent the inflamed openings of the minor salivary gland ducts. The term nicotine stomatitis is actually a misnomer because it is not the nicotine that causes the changes; the changes are caused by the intense heat generated from the smoking. Although nicotine stomatitis is a tobacco related it is not considered to be premalignant and it is readily reversible with discontinuation of the tobacco habit.


 > Palatal Lesions in Reverse Cigar Smokers Top


In some Southeast Asian and South American countries, individuals practice a habit known as reverse smoking in which the lit end of the cigarette or cigar is placed inside the mouth. This habit creates a more severe heat-related alteration of the palatal mucosa known as reverse smoker's palate, which has been associated with a significant risk of malignant transformation. [37],[38]


 > Actinic Keratosis Top


Actinic keratosis is considered to represent a potentially malignant condition that arises in many sites including lips. It is commonly associated with exposure to sun. In Actinic keratosis, the average rate of progression to invasive cancer ranges from 0.025% to 16% per year. [39] Actinic cheilitis is a clinical term for an ulcerative, sometimes crust-forming lesion of the mucosa of part or entire vermilion border of the lower lip. The histopathology can vary from hyperkeratosis with or without epithelial dysplasia to early squamous cell carcinoma.


 > Tobacco Pouch Keratosis Top


Another specific tobacco-related oral mucosal alteration occurs in association with smokeless tobacco use, either from snuff or chewing tobacco. Such lesions typically occur in the buccal or labial vestibule where the tobacco is held, but they can also extend onto the adjacent gingiva and buccal mucosa. Overall, it is estimated that 15% of chewing tobacco users and 60% of snuff users will develop clinical lesions. Microscopically, smokeless tobacco keratoses show hyperkeratosis and acanthosis of the mucosal epithelium. True epithelial dysplasia is uncommon; when dysplasia is found, it is usually mild in degree. [40] Most tobacco pouch keratoses are readily reversible within 2 to 6 weeks after cessation of the tobacco habit.


 > Hereditary Disorders with Increased Risk of Malignant Transformation Top


Two conditions that may have an increased risk of malignancy in the mouth are Dyskeratosis Congenital (DC) and Epidermolysis Bullosa. They are rare hereditary conditions. Most cases of DC are X-linked and affect males. Patients with DC often develop white plaques on the dorsal tongue that may be confused with leukoplakia, but the absence of habits and their young age may point to the hereditary nature of this disorder. Malignant change within the areas of white patches is reported. In Xeroderma pigmentosum and Fanconi's anemia, there is an increased incidence of malignancies, including oral cancer.


 > Management of Potentially Malignant Disorders Top


Most PMD are asymptomatic and the main aim of treatment is to prevent and/or to detect cancer development early. Treatment of PMD can be in three categories namely close observation, surgical excision/ablation, and medical treatment.

Observation: patients with early small lesions that are clinically benign looking and appear at favorable sites can be observed. However, the need for frequent follow-ups and possibility of malignant transformation has to be explained to the patient.

Conservative surgical excision with negative margins remains the treatment of choice for leukoplakia. Surgical resection is performed to remove areas at high risk to progress to early carcinoma or to undergo early malignant transformation. Attempts to remove all clinically apparent areas of leukoplakia, or histologically diagnosed areas of dysplasia, are impractical in most circumstances and produce scarring and contracture that result in more morbidity than benefit to the patient. This inability to successfully eradicate all precancerous areas with surgery is due to the widespread 'field effect' commonly found in the oral cavity, in which exposure to carcinogens creates premalignant changes over large areas of mucosa. Also excision is associated with high recurrence rates. [41],[42] However, excision of leukoplakia has not shown to decrease the rate of malignant transformation in some studies. [43]

Laser ablation has also been advocated for eradication of OPLs. This approach offers the potential advantage of reduced scarring, but a major disadvantage is the lack of a resected specimen for histopathologic and genetic studies. A study comparing different laser techniques CO2 laser, NdYAG laser, and KTP, demonstrated differences in recurrence rates as 34.2%, 28.9%, and 17.0%, respectively. [44]

Cryosurgery does not seem to be of particular benefit. Recurrence rates of 20-71.4% have being reported, along with malignant transformation rates of 7-25%. [45]

Photodynamic therapy is another ablative method being investigated for management of PMD. A photosensitizing agent, such as hematoporphyrin derivatives or 5-ALA, which preferentially targets neoplastic cells is administered either intravenously or topically. The tissue to be targeted is then exposed to a specific wavelength of light, which activates the photosensitizer, causing it to transfer energy to molecular oxygen, generating reactive oxygen species locally, and subsequent tissue damage. [46] Several small clinical studies have shown promising results for treating epithelial premalignant lesions and superficial carcinomas. [47],[48],[49] The major limiting side effect has been cutaneous photosensitivity, but newer photosensitizing agents such as 5-ALA, have markedly reduced the incidence and severity of this complication. There is a need for further studies before making a definitive comment on this treatment modality.

In case of erythroplakias, surgery, either by cold knife or by laser, is the recommended treatment modality. Without therapy this disease transforms into invasive carcinoma in 60-90% of the cases within 5-10 years after initial diagnosis. As for excision of leukoplakia, no guidelines are available with regard to the width of the surgical margins. There are no data from the literature about the recurrence rate after excision of erythroplakias.

At this time there is no cure for OSMF and management consists of elimination of the ingestion of implicated irritants. Successful prevention in the early stages of the condition has been shown to produce improvement in symptoms


 > Screening for Potentially Malignant Disorders Top


The entire mucosa of the upper aerodigestive tract when exposed to the various carcinogens tends to undergo and accumulate various cytogenetic changes which ultimately lead to the formation of various malignant lesions (Slaughter's concept of field cancerization). This means the majority of cancers are preceded by a detectable preclinical phase.

The overall malignant transformation rates for various PMDs vary from approximately 5% for leukoplakia to ~85 % for erythroplakia. [50] Early detection of these lesions may help in preventing their malignant transformation or down staging the disease. This is the entire idea behind screening of populations with high-risk behavior for oral cancer.

The National Screening Committee defines screening as "a process of identifying apparently healthy people who may be at increased risk of a disease or condition." Screening programs can be undertaken for a population at large, or targeting high risk groups, for example, tobacco and alcohol users for oral cancer.

An ideal screening test must be easily applicable and acceptable to the population, cost effective, detect disease early in its natural history and have a high positive predictive value and low false negatives (high sensitivity). [51],[52]


 > Methods of Screening Top


Oral examination

Conventional oral examination

Conventional oral examination using normal (incandescent) light is the most commonly applied and accepted screening method for oral squamous cell carcinoma. This easily available and cheap method has found to be equally effective in detecting PMDs across all levels of training, including junior and senior dentists as well as trained healthcare workers or auxiliaries. It is particularly useful for screening accessible sites such as buccal mucosa, tongue, and floor of mouth. However, COE tends to pick up lesions that in a majority of cases that are clinically and histopathologically benign, that is, the conventional leukoplakias, with a small number that are progressive or definitely malignant. Conversely, COE may also miss areas of histological changes that appear clinically normal (false negative).

Systematic studies have been undertaken to assess the reliability and reproducibility of COE. [52],[53],[54],[55],[56],[57] A meta-analysis of this data showed a weighted pooled sensitivity of 0.848 (95% CI 0.73, 0.92) and specificity of 0.965 (95% CI 0.93, 0.98) indicating a satisfactory test performance for an oral examination. [58] A meta-regression analysis of heterogeneity indicated no differences between studies suggesting that trained auxiliaries are able to screen with a degree of accuracy similar to dental practitioners.

Only one prospective randomized controlled trial (RCT) to evaluate the efficacy of COE in screening a population is present in the literature. This study conducted by Sankarnarayan et al.[59],[60] is a cluster randomized, population-based screening trial carried out in the Trivandarum district, Kerala, from 1995 - 2004. The participants (n = 191,873) were randomized to and intervention arm (seven clusters) and a control arm (six clusters). The initial evaluation after the first and second rounds showed a surrogate marker of improved outcomes including better 3-year survival, earlier stage of presentation and yield in the intervention arm, which was considered to be due to the lead time bias. [61] However, the long term results at 9 years showed that though, there was no increase in survival in the overall population, a significant increase in survival was seen among males with high-risk habits, such as tobacco use. [62] This was the first clear evidence to support the efficacy of an oral cancer screening program, as measured by reduced mortality.

A Cochrane review of visual oral examination identified several serious potential biases in the study. [63] These included a lack of standardized diagnostic criteria, the absence of outcome data blinding, only a 63% rate of compliance with the referral and no active follow-up, and only a minority of subjects being biopsied to confirm the diagnosis of a potentially malignant oral disorder. They concluded that there is insufficient evidence to recommend inclusion or exclusion of screening for oral cancer using a visual examination in the general population.

In a cost analysis, Subramanian et al.[64] found that the benefit produced by a screen was 269.31 life years saved per 100,000 for all the individuals and 1437.64 for those at high risk, whilst the incremental cost per life-year saved was US$835 for all individuals, which is reduced to US$156 for high-risk individuals, which is cost effective as per WHO. In a similar study in a hypothetical population, Speight et al.[65] used a decision-tree analysis based on probabilities of prevalence, malignant transformation and survival and found that 312 quality-adjusted life years could be saved by screening adults who smoke and/or use alcohol. Further analyses to determine the incremental cost-effectiveness of different screening programs found that the costs per life saved was GBP £18,919 for an opportunistic high risk screen by a primary care dentist (PCD), GBP £19,703 for a high-risk screen by a general medical practitioner (GMP), and GBP £21,623 for an opportunistic population screen, which compared well to other current running screening programs.

Mouth self-examination

As most of the cancers in the oral cavity, especially in the buccal mucosa, tongue, hard palate, gingival, and lips are easily accessible for self-examination, a lot of authors have recommended that high-risk persons with history of tobacco and alcohol abuse be taught MSE. [66],[67],[68] However, the efficacy of MSE in early detection is still to be proven.

Mathew et al.[69] evaluated the feasibility of MSE within a high-risk population. Brochures describing the risk factors of oral cancer, the appearance of premalignant and malignant lesions of the oral cavity, and the method of MSE were distributed to participants who smoked and/or were 30-year old or older. Out of the approximately 22,000 eligible subjects, 8028 (36%) practiced MSE. Of those who identified a change in their mouth and presented to the clinic, 21% had mistaken anatomic landmarks or normal variations for lesions, 39% had benign lesions, 34% had clinical pathology, and 6% had new or recurrent oral cancer. Mathew et al. concluded that MSE is feasible, but larger studies are required to evaluate whether health education could result in a sustained practice of MSE resulting in reduction in incidence of and mortality from oral cancer.

As the previous studies reported the outcomes only of those patients who presented to the clinic after noticing changes while practicing MSE, Scott et al.[70] conducted a pilot study to assess the accuracy of MSE. The proportion of correct diagnosis was 51%. The sensitivity of MSE was 33% (95% confidence interval [CI], 11% to 65%), and the specificity of MSE was 54% (95% CI, 38% to 69%). The PPV of MSE was 17% (95% CI, 6% to 40%), while the NPV was 73% (95% CI, 54% to 87%). Thus, compared to other self-examination like for skin or breast cancer, MSE seems to be a less accurate method of detection. The low sensitivity and specificity found for MSE may have occurred due to the patients' lack of knowledge of the appearance of oral changes, a need for good lighting conditions, an unfamiliarity of the 'usual' appearance of their oral cavity, and an inability to differentiate between normal anatomic landmarks and oral mucosal changes. Further education and training of patients in identifying lesions is required.

Histopathological examination

Biopsy and histopathology

Biopsy and fistopathology of suspicious lesions is the gold standard for detecting early cancer in PMDs. However, it being an invasive technique cannot be employed for mass screening where it should be used for confirmatory as an adjunct to other screening methods. Also, in cases of multiple/ extensive lesions (field cancerization) it is imperative to target the most representative area to avoid diagnostic errors. Also, there is a high inter observer variability especially in gradation of dysplasias.

Brush cytology

Exfoliative cytology is advocated for clinically suspicious lesions that are detected by screening by visual examination. Any lesion suspicious on brush biopsy however would need confirmation by histopathology, as the use of brush cytology does not provide a definitive diagnosis. But it may be useful in those lesions that are not clinically suspicious, but would still need to be kept under surveillance. Being noninvasive, there is more chance of compliance with screening by this method in the general population.

Several studies have shown encouraging results with oral brush cytology for evaluation of oral precancerous lesions. Cytopathologic evaluation of oral brush biopsies from leukoplakias and erythroplakias as a single method yields sensitivities for the detection of oral cancer, ranging from 92-100% and specificity between 92-94%. [71],[72],[73],[74]

In Navone [75] study of 2006, results of conventional exfoliative cytology and liquid-based cytology (by using dermatologic curette) were compared with scalpel biopsy. Both sensitivity and specificity were better in LBC group than in conventional cytology. The false negative and positive results were 7/89 and 2/89 in conventional smear group and 4/384 and 3/384 in the LBC group. Thus, LBC gives better results and enhances sensitivity and specificity compared to conventional cytology.

OralCDx® brush biopsy (OralCDx® Laboratories Inc., Suffern, NY, USA) is an oral transepithelial ''biopsy" system that uses computer-assisted brushing. [76] This technique was designed to screen nonsuspicious oral epithelial abnormalities for dysplasia or cancer. When an abnormal result is reported (atypical or positive), the clinician must follow-up with a scalpel biopsy of the lesion, as the use of brush cytology does not provide a definitive diagnosis. The sensitivity of this system for the detection of abnormal cells has been of 52-100% and the specificity of 29-100%. Overall, the OralCDx technique appears to overestimate dysplastic lesions and produce a high number of false-positive results and has a low positive predictive value (PPV). [77]

The problem with various oral brush biopsy studies are that they have compared the role of brush biopsy against the gold standard - scalpel biopsy and histopathology in Class I lesions (clinically suspicious) but not so in Class II lesions (clinically innocuous). Hence, the true accuracy and negative predictive value of brush biopsy is unknown. In this scenario, the role of brush biopsy may be limited to patients with multiple precursor lesions, aiding in targeting the most suspicious sites, thus improving compliance for follow up in such patients.

The use of DNA image cytometry, argyrophilic nucleolar organizing regions (AgNOR) analysis, and multimodal cell analysis has been shown to significantly increase diagnostic accuracy of oral cytology. [78],[79],[80]

Epigenetic alterations (promoter hypermethylation), genomic instability and loss of heterozygosity (LOH), microsatellite instability (MSI), and restriction fragment length polymorphism (RFLP) are other molecular markers that are now being studied to increase the yield in exfoliative cytology.

Toluidine blue

Toluidine blue (also known as tolonium chloride) is a vital dye that may stain nucleic acids and abnormal tissues. It has been used as an aid to the identification of mucosal abnormalities of the oral cavity. Many surgeons prefer to use toludine blue to demarcate the lesion prior to excision. There is evidence to suggest that toluidine blue can be of help in detecting premalignant lesions. Warnakulasuriya and Johnson [81] evaluated 102 patients with undiagnosed oral mucosal lesions. Eighteen patients proved to have oral carcinomas and all of their respective malignant lesions stained with toluidine blue (sensitivity = 100% for detection of oral cancer). However, the overall specificity was low at 0.62. Also, the sensitivity to assess dysplasia was low -79.5%. The authors also reported 12 oral sites with no clinical evidence of abnormality that were dye-positive and five of these sites showed dysplasia on biopsy. They conclude that the method was valuable for surveillance of high-risk individuals and sensitive for detecting carcinomas. Onofre et al.[82] found that all carcinomas stained positively, but only 50% of dysplasias were positive and that 13 of 37 (35%) benign lesions also stained. The overall sensitivity and specificity was 0.77 and 0.67, respectively. This was also similar to findings by Martin et al.[83] suggesting that toluidine blue is sensitive to detect carcinomas but not as good to detect dysplasia.

Zhang et al.[84] in a pilot study have shown that it may be useful in determining which clinically evident oral lesion is more likely to progress to oral cancer, by preferentially staining lesions with higher degrees of dysplasia and recognizing lesions with high risk molecular patterns. In their study, staining status strongly associated with outcome. More importantly, it predicted risk and outcome of visible oral lesions with little to no microscopic evidence of dysplasia.

A recent review by Epstein et al.[85] suggests that Toluidine blue has utility as an adjunct in the detection of premalignant and malignant oral mucosal lesions and in identifying high-risk areas of lesions for biopsy in patients at increased risk of cancer when evaluated by experienced healthcare workers. However, there is no evidence that toluidine blue is effective as a screening test in a primary care setting. The high rate of false positive stains and the low specificity in staining dysplasia likely outweigh the potential benefits of any additional cancers detected.

Light-based detection systems

Light-based detection systems are based on the assumption that the structural and metabolic changes that take place in the mucosa during carcinogenesis give rise to distinct profiles of absorption and refraction when exposed to different types of light or energy. There are basically two main systems of detection:

Chemiluminisence

Chemiluminisence or reflective tissue fluorescence has been previously used as 1% acetic acid washes to detect the "acetowhite'' areas for detection of premalignant and malignant conditions in cervix and oral mucosa. Recently, this technology has been adapted and two systems are available for early detection based on it - Vizilite® (Zila Pharmaceuticals, Phoenix, AZ, USA) and Microlux/DL® (AdDent Inc., Danbury, CT, USA).

In both of these, the patient must rinse the mouth with a 1% acetic acid solution followed by direct visual examination of the oral cavity using a blue-white light source. The 1% acetic acid wash is used to help remove the glycoprotein layer and may increase the visibility of epithelial cell nuclei by dehydration. ViziLite Plus uses a disposable chemiluminescent light packet, while the MicroLux unit offers a reusable, battery-powered light source. Normal cells absorb the light and have a bluish color, whereas the light is reflected by abnormal cells with a higher nucleus: cytoplasm ratio and by epithelium with excessive keratinisation, hyperparakeratinisation, and/or significant inflammatory infiltrate, which appear acetowhite with brighter, more marked and more distinguishable borders.

Most of the studies conducted with these systems are in patients with oral lesions and not the general population. Hence, the reported sensitivities in all these studies is nearly 100%, but other accuracy values were inconsistent: zero to 14% specificity, PPVs of 18% to 80% and NPVs of zero to 100%. [86],[87],[88] The results of these studies suggested enhancement in visual parameters of the lesions in brightness, sharpness (margin delineation), surface texture and, in some cases, size of lesion compared with results of examination by means of standard illumination, although no previously unidentified lesions were reported. To further increase the yield, now the test is combined with toludine blue staining. Toluidine blue stain retention was associated with a large reduction in biopsies showing benign histology (false positive biopsy results), while maintaining a 100% NPV for the presence of severe dysplasia or cancer. [88] Similar findings were seen by others, that is, though the acid rinse accentuated some lesions, the overall detection rate was not significantly improved. [89],[90]

Tissue fluorescence imaging

The principle of tissue autofluorescence is that some biofluorophores within tissue get excited and emitfluorescence when exposed to a light source of particular wavelength. The VELscope® system (Visually Enhanced Lesion Scope; LED Dental Inc., White Rock, BC, Canada) is a portable device which detects the loss of fluorescence in visible and nonvisible high-risk oral lesions such as cancers and precancers, by applying direct fluorescence. Under intense blue excitation light (400 to 460 nm), normal oral mucosa emits a pale green autofluorescence when viewed through the selective (narrow-band) filter incorporated within the instrument. Whereas abnormal tissue (cancer or precancer), due to a disruption in the biofluorophores, do not reflect as much light and appear darker than the surrounding normal tissue.

A few studies have been done using VELscope® for early detection of PMDs with reported sensitivity values of 97-100% and specificities of 94-100%. [91],[92] However, a recent study by Awan et al.[93] found the sensitivity and specificity of autofluorescence for the detection of a dysplastic lesion was 84.1% and 15.3%, respectively. ROC curve for autofluorescence as a tool for the detection of dysplasia group also showed a poor diagnostic value (AUC = 0.49, 95% CI: 0.39-0.61, P = 0.96).

A small study investigating the role of fluorescence visualization for the detection of surgical tumor margins for oral cancer when used in the operating room, found that the loss of autofluorescence could extend as much as 25 mm beyond the clinically evident tumors. [94] Histology of these areas revealed either cancer or dysplasia and in 63% loss of heterozygosity studies found loss of either 3p and/or 9p. However, these results need to be validated in a larger group as well as for population based screening.

In summary, there is no evidence that supports the use of reflective tissue fluorescence systems to help in the detection of oral premalignant lesions. Further trials are needed that specifically investigate the ability of these devices to detect precancerous lesions that are invisible by COE alone.


 > Conclusion Top


Potentially malignant disorders are an important spectrum of diseases that need to be identified and followed up closely. Correct identification of their malignant potential may help in early diagnosis of cancer and down staging of the disease. Clinical examination and histopathology remain the "gold standard" for the detection of oral cancer. However, other than visual examination, no single method for screening seems to be applicable and cost effective in the general population. Further studies are needed for the same.

 
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