Flow cytometric analysis of nuclear DNA content in oral leukoplakia: relation to clinicopathologic findings

Aneuploidy and loss of heterozygosity as risk markers for malignant transformation in oral mucosa

The ability to predict malignant transformation in oral potentially malignant disorders would inform targeted treatment, provide prognostic information and allow secondary prevention. DNA ploidy and loss of heterozygosity assays are already in clinical use, and loss of heterozygosity has been used in prospective clinical trials. This review appraises published evidence of predictive ability and explores interpretation of heterogeneous studies, with different diagnostic methods, criteria and intention. Both methods have a sound biological foundation and have predictive value independent of dysplasia grading and clinical parameters. The application of these two techniques cannot be directly compared because of differences in expression of results and application to populations of different risk. Predicting malignant transformation accurately on an individual patient basis is not yet possible with either technique. However, they are valuable applications to stratify patients for inclusion in trials, identify the lowest risk patients and exclude risk when biopsy results are indeterminate for dysplasia.

The genetic basis of oral leukoplakia and its key role in understanding oral carcinogenesis

Oral leukoplakia (OL) is the most common oral potentially malignant disorder, with a global prevalence of 2%-3%, variable malignant transformation rate and incompletely understood aetiology. Considering the subjectivity in oral dysplasia grading, other evaluation methods have been tested as predictors of malignant transformation. DNA ploidy status and loss of heterozygosity signatures have been shown to be good predictive markers of malignant transformation. However, effective markers to predict which lesions will progress to invasive carcinoma and by which mechanisms remain unclear. Recent evidence suggests that dysplasia progression to carcinoma occurs through neutral clonal evolution (i.e. randomly). We focus on the genetic basis of OL, encompassing the gross chromosomal alterations and single-gene mutations, and discuss such alterations in the context of aetiology, clinical presentation and progression. The deeper we understand the genetic basis of OL, the more we approach a better comprehension of the complex and poorly understood process of oral carcinogenesis.

Predicting malignant progression in clinically high-risk lesions by DNA ploidy analysis and dysplasia grading

The value of image cytometry DNA ploidy analysis and dysplasia grading to predict malignant transformation has been determined in oral lesions considered to be at ‘high’ risk on the basis of clinical information and biopsy result. 10-year follow up data for 259 sequential patients with oral lesions clinically at ‘high’ risk of malignant transformation were matched to cancer registry and local pathology database records of malignant outcomes, ploidy result and histological dysplasia grade. In multivariate analysis (n = 228 patients), 24 developed carcinoma and of these, 14 prior biopsy samples were aneuploid. Aneuploidy was a significant predictor (hazard ratio 7.92; 95% CI 3.45, 18.17) compared with diploidy (p < 0.001). The positive predictive value (PPV) for severe dysplasia was 50% (95% CI 31.5, 68.5) and for aneuploid lesions, 33.3% (95% CI 19.0, 47.6). Combined DNA aneuploidy and severe dysplasia increased PPV to 56.3% (95% CI 31.9, 80.6). Diploid-tetraploid and non-dysplastic status had high negative predictive values (NPV) of 94.6% (95% CI 91.4, 97.8) and 99.17% (95% CI 97.4, 100.8) respectively. DNA ploidy predicts malignant transformation well and combining it with dysplasia grading gave the highest predictive value. The predictive values reported here exceed those from other investigations to date.

Genomic DNA Copy Number Aberrations, Histological Diagnosis, Oral Subsite and Aneuploidy in OPMDs/OSCCs

Oral potentially malignant disorders (OPMDs) characterized by the presence of dysplasia and DNA copy number aberrations (CNAs), may reflect chromosomal instability (CIN) and predispose to oral squamous cell carcinoma (OSCC). Early detection of OPMDs with such characteristics may play a crucial role in OSCC prevention. The aim of this study was to explore the relationship between CNAs, histological diagnosis, oral subsite and aneuploidy in OPMDs/OSCCs. Samples from OPMDs and OSCCs were processed by high-resolution DNA flow cytometry (hr DNA-FCM) to determine the relative nuclear DNA content. Additionally, CNAs were obtained for a subset of these samples by genome-wide array comparative genomic hybridization (aCGH) using DNA extracted from either diploid or aneuploid nuclei suspension sorted by FCM. Our study shows that: i) aneuploidy, global genomic imbalance (measured as the total number of CNAs) and specific focal CNAs occur early in the development of oral cancer and become more frequent at later stages; ii) OPMDs limited to tongue (TNG) mucosa display a higher frequency of aneuploidy compared to OPMDs confined to buccal mucosa (BM) as measured by DNA-FCM; iii) TNG OPMDs/OSCCs show peculiar features of CIN compared to BM OPMDs/OSCCs given the preferential association with total broad and specific focal CNA gains. Follow-up studies are warranted to establish whether the presence of DNA aneuploidy and specific focal or broad CNAs may predict cancer development in non-dysplastic OPMDs.

Correlation between histological grading and ploidy status in potentially malignant disorders of the oral mucosa: A flow cytometric analysis

Background:

Histopathological grading of oral dysplastic lesions is the method of choice for evaluating malignant and potentially malignant disorders. Owing to inter- and intra-observer variability, determination of the DNA ploidy status of lesions may serve as an adjunct in the prediction of malignant transformation.

Aim:

To correlate histopathological grading and ploidy status in potentially malignant and malignant disorders of the oral mucosa.

Settings and Design:

A pilot study was done with 30 patients (10 patients with oral potentially malignant disorders predominantly leukoplakia, 10 patients with oral malignant lesions and 10 patients with normal mucosa).

Materials and Methods:

Incisional biopsy was done after isolating the biopsy site with 1% Toluidine blue staining. Two sections of the tissue were removed and sent for histopathological and Flow-cytometric analysis respectively. Histopathological diagnosis was obtained and compared with Flow-cytometric results which were graded as diploid and aneuploid. Further, the S – phase fraction, DNA index were also calculated to evaluate the severity of malignant transformation or malignancy.

Statistical Analysis:

The results were analyzed using Pearson Chi-Square Test.

Results:

There exists a significant correlation between histopathology and ploidy status in both potentially malignant and malignant group. (P = 0.002).

Conclusion:

The data from this study has shown that DNA Ploidy analysis can be used as a valuable tool in assessing the carcinomatous progression of potentially malignant and malignant lesions.

Chromosomal instability, aneuploidy and routine high-resolution DNA content analysis in oral cancer risk evaluation

Carcinogen exposure of the oral cavity is thought to create an extensive 'field cancerization'. According to this model, a very early precursor of oral cancer is a patch of normal-appearing mucosa in which stem cells share genetic/genomic aberrations. These precancerous fields then become clinically visible as white and red lesions (leuko- and erythro-plakias), which represent the vast majority of the oral potentially malignant disorders. This review focuses on aneuploidy (where it is from) and on biomarkers associated with DNA aneuploidy in oral mucosa and oral potentially malignant disorders, as detected by DNA image and flow cytometry. Data from the literature strongly support the association of DNA ploidy with dysplasia. However, work is still needed to prove the clinical value of DNA ploidy in large-scale prospective studies. Using high-resolution DNA flow cytometry with fresh/frozen material and the degree of DNA aneuploidy (DNA Index) might improve the prediction of risk of oral cancer development.

Urban legends series: oral leukoplakia

To date, the term oral leukoplakia (OL) should be used to recognize 'predominantly white plaques of questionable risk, having excluded (other) known diseases or disorders that carry no increased risk of cancer'. In this review, we addressed four controversial topics regarding oral leukoplakias (OLs): (i) Do tobacco and alcohol cause OLs?, (ii) What percentage of OLs transform into oral squamous cell carcinoma (OSCC)?, (iii) Can we distinguish between premalignant and innocent OLs?, and (iv) Is proliferative verrucous leukoplakia (PVL) a specific entity or just a form of multifocal leukoplakia? Results of extensive literature search suggest that (i) no definitive evidence for direct causal relationship between smoked tobacco and alcohol as causative factors of OLs, (ii and iii) the vast majority of OLs follow a benign course and do not progress into a cancer, and no widely accepted and/or validated clinical and/or biological factors can predict malignant transformation, and (iv) the distinction between multifocal/multiple leukoplakias and PVL in their early presentation is impossible; the temporal clinical progression and the high rate of recurrences and development of cancer of PVL are the most reliable features for diagnosis.

Genetics/epigenetics of oral premalignancy: current status and future research

Squamous cell carcinoma (SCC) of the oral and oropharyngeal region is the sixth most common malignancy in the world today. Despite numerous advances in treatment, long-term survival from this disease remains poor. Early detection can decrease both morbidity and mortality associated with this neoplasm. However, screening for potentially malignant disease is typically confounded by difficulty in discriminating between reactive/inflammatory lesions vs those lesions that are premalignant in nature. Furthermore, the histologic diagnosis of dysplasia can be subjective and is thus prone to a considerable range of interpretation. Similarly, no definitive, validated criteria exist for predicting which dysplastic lesions are most likely to progress to cancer over time. Given this state of science, the presence of dysplasia can only be used to indicate that an oral lesion may have an increased risk of malignant transformation. Molecular biomarkers capable of identifying the subset of lesions likely to progress to cancer are required to eliminate this clinical diagnostic dilemma. The purpose of this review is to assess the current state of knowledge regarding genetic/epigenetic alterations observed in oral mucosal premalignancy. In addition, recommendations for future research studies directed at defining the predictive capacity of specific biomarkers in this modeling are presented.

DNA aneuploidy and dysplasia in oral potentially malignant disorders: association with cigarette smoking and site

To date there are still no reliable biomarkers for oral potentially malignant disorders (PMDs) to predict the risk of progression to squamous cell carcinoma (SCC). Within a prospective clinical trial of patients with PMDs, DNA content flow cytometry (DNA FCM) was evaluated for 60 PMDs using fresh samples obtained by a dermatological curette. There were 6/42 PMDs without dysplasia, but with DNA aneuploidy, versus 8/18 with both dysplasia and aneuploidy (p=0.02). When the tongue and the buccal mucosa, the two most common sites in the present series of cases were compared, dysplastic PMDs were mainly located on the tongue (p=0.01). Tobacco smokers, who preferentially developed PMDs in the buccal mucosa at a younger age than non-smokers (p=0.002), had fewer dysplastic PMDs than did non-smokers (p=0.01). Dysplasia was significantly linked to DNA aneuploidy (p=0.03) in smokers. The present data suggest that aneuploidy is an early event in oral carcinogenesis and that the influence of tobacco varies according to subsite and patient age. When DNA FCM of PMD samples are obtained by curette scraping, extensive areas can be covered with a minimally invasive, rapid, inexpensive procedure. Moreover DNA FCM of these samples appears easy amenable to routine analysis. Further research on larger numbers of PMDs should be carried out to determine whether DNA FCM plays a role in the prediction of risk of PMD transformation.

Natural history of potentially malignant oral lesions and conditions: an overview of the literature

At a workshop coordinated by the WHO Collaborating Centre for Oral Cancer and Pre-cancer in the UK issues related to potentially malignant disorders of the oral cavity were discussed by an expert group. The consensus views of the Working Group are presented in a series of papers. In this report we review the literature on the epidemiology and natural history of potentially malignant disorders (PMD), detailing those characteristics of the patients and lesions thought to be associated with future development of oral squamous cell carcinoma (OSCC). Older patients, particularly females are more at risk than younger patients; the duration of PMD may be important. Those who have never used tobacco seem at greater risk than smokers. OSCC is more likely with PMD on the lateral and ventral tongue, floor of mouth and retromolar/soft palate complex than with those elsewhere. The vast majority of PMD in which OSCC develop are non-homogenous although 5% of homogenous PMD will develop carcinoma. Large lesions covering several intraoral subsites also appear more at risk.

Detection of non-diploid cells in premalignant and malignant oral lesions using combined morphological and FISH analysis - a new method for early detection of suspicious oral lesions

Alteration in DNA content is an early event in oral carcinogenesis. We have examined oral brush samples to detect non-diploid cells (NDC) using simultaneous morphological and cytogenetic analysis. The study included 8 oral squamous cell carcinomas (OSCC), 22 premalignant lesions (OPLs), and 25 control individuals. Slides stained with Giemsa followed by FISH using chromosome 2 centromeric DNA probe, were scanned and fluorescent signals were simultaneously analyzed in parallel with the morphology. The proportion of NDC increased with the severity of the diagnosis. In two control subjects, 1-1.5% of the examined cells were NDC. Over 2% NDC were present in all OSCC cases and in 11 of the OPLs, of which, in 8 the histologic diagnosis was either epithelial hyperplasia or mild dysplasia. A significant number of NDC had normal morphology when cytomorphology and FISH were compared. Two patients with OPLs developed OSCC these patients had a significant proportion of NDC. We suggest that the combined morphological and cytogenetic analysis of cells collected by a non-invasive brush sampling can enhance early detection of potentially malignant cells.

Management of oral epithelial dysplasia: a review

One of the goals of the fourth meeting of The World Workshop on Oral Medicine (WWOM IV) included a review of the pathophysiology and future directions for the clinical management of patients with oral epithelial dysplasia, excluding the lips and oropharynx. In the pathophysiology review of dysplasia since WWOM III (1998-2006), a wide range of molecular changes associated with progression of dysplasia to squamous cell carcinoma were found. These include loss of heterozygosity, dysregulation of apoptosis, aberrant DNA expression, and altered expression of numerous tissue markers. Based on the literature search, no single molecular pathway has been identified as the primary factor in progression of dysplasia to squamous cell carcinoma. A systematic review of medical (i.e., nonsurgical) management strategies for the treatment of dysplastic lesions has shown promising results in short-term resolution of dysplasia in the small number of studies that met eligibility criteria for review. However, because of the limited periods of follow-up reported in these studies, it remains unclear as whether resolution of dysplasia would actually be a long-term benefit of these interventions. This question is particularly germane when it is considered in the context of prevention of future development of squamous cell carcinoma. Because of the lack of randomized controlled trials that have shown effectiveness in the prevention of malignant transformation, no recommendations can be provided for specific surgical interventions of dysplastic oral lesions either.

Ploidy analysis of field cancerization and cancer development in the hamster cheek pouch carcinogenesis model

BACKGROUND

The hamster cheek-pouch carcinogenesis model is a well-known animal system that closely mimics the development of premalignant and malignant lesions in human oral cancer. Our aim was to numerically characterize the premalignant and malignant lesions and expressions of field cancerization in this model using ploidy as the end-point.

METHODS

To study the DNA content and proliferation status of the cells in this model we assessed the Feulgen reaction and the immunohistochemical reaction for 5-bromo-2-deoxiuridine (BrdU) in different histological areas of serial tissue sections of the cheek pouches of animals injected with BrdU.

RESULTS

Ploidy values were higher in cancerized epithelia with no unusual microscopic features (NUMF), in preneoplastic and tumor areas than in control epithelia. The aneuploidy index was higher in NUMF areas than in control and differed significantly from control in preneoplastic areas and carcinoma.

CONCLUSIONS

The unexpected alteration in DNA content observed in NUMF epithelia is of great relevance as a biomarker of field cancerized areas.

Prognosis of oral pre-malignant lesions: significance of clinical, histopathological, and molecular biological characteristics

The concept of a two-step process of cancer development in the oral mucosa, i.e., the initial presence of a precursor subsequently developing into cancer, is well-established. Oral leukoplakia is the best-known precursor lesion. The evidence that oral leukoplakias are pre-malignant is mainly derived from follow-up studies showing that between < 1 and 18% of oral pre-malignant lesions will develop into oral cancer; it has been shown that certain clinical sub-types of leukoplakia are at a higher risk for malignant transformation than others. The presence of epithelial dysplasia may be even more important in predicting malignant development than the clinical characteristics. Three major problems, however, are attached to the importance of epithelial dysplasia in predicting malignant development: (1) The diagnosis is essentially subjective, (2) it seems that not all lesions exhibiting dysplasia will eventually become malignant and some may even regress, and (3) carcinoma can develop from lesions in which epithelial dysplasia was not diagnosed in previous biopsies. There is, therefore, a substantial need to improve the histologic assessment of epithelial dysplasia or, since epithelial dysplasia does not seem to be invariably associated with or even a necessary prerequisite for malignant development, it may be necessary to develop other methods for predicting the malignant potential of pre-malignant lesions. As a consequence of these problems, numerous attempts have been made to relate biological characteristics to the malignant potential of leukoplakias. Molecular biological markers have been suggested to be of value in the diagnosis and prognostic evaluation of leukoplakias. Markers of epithelial differentiation and, more recently, genomic markers could potentially be good candidates for improving the prognostic evaluation of precursors of oral cancer. As yet, one or a panel of molecular markers has not been determined that allows for a prognostic prediction of oral pre-cancer which is any more reliable than dysplasia recording. However, these new markers could be considered complementary to conventional prognostic evaluation.

Sanguinaria-associated oral leukoplakia: comparison with other benign and dysplastic leukoplakic lesions

OBJECTIVE

This study was undertaken to compare and contrast biomarkers and ploidy data from maxillary gingiva leukoplakias associated with dentifrices and mouthrinses containing the herbal compound sanguinaria with other forms of oral benign and premalignant mucosal keratosis.

STUDY DESIGN

Representative archived specimens of benign keratosis, sanguinaria-associated keratosis, and keratosis with dysplasia were used for computerized image analysis and biomarker immunohistochemical assays to assess ploidy, DNA content, and p53 and proliferating cell nuclear antigen immunoreactivity of nuclei.

RESULTS

DNA content was significantly higher and higher numbers of cell populations with hyperploid nuclei were encountered in the dysplastic group than in the other two groups (P <.001). Sanguinaria-associated keratosis did not harbor significant numbers of p53-expressing nuclei, yet it showed a significant elevation in proliferating cell nuclear antigen-labeled nuclei in total, in the basal layer, and in the spinous layer in comparison with benign keratoses (P <.001). In addition, 1.5% of the sanguinaria-associated leukoplakia epithelial cell population was characterized by nuclei with a greater than 4-fold increase in DNA content.

CONCLUSIONS

Sanguinaria-associated keratoses show some marker and image analysis profiles similar to those of non-sanguinaria dysplastic lesions of the lip and mucosa. Preparations containing sanguinaria should be avoided until the risk for malignant transformation is determined.

Characterization of epithelial cell activity in patients with oral cancer

Accurate, predictive assessment of the clinical behaviour and progression of individual oral cancers and premalignant lesions requires reproducible and quantitative analyses of diseased tissue. In this paper we describe the use of in vitro double labelling (sequential tritiated thymidine and bromodeoxyuridine staining of proliferating epithelial cells) to calculate S phase labelling indices (LIs), estimation of S phase duration (tS), and measurement of variables of flux to and from S for excised specimens of oral squamous cell carcinoma, premalignant lesions, and clinically normal mucosa from patients with oral cancer. There was a significant increase in mean LIs in buccal mucosa leukoplakias (14.5%) compared with normal mucosa (10.3%); P = 0.03. LIs were also increased in patients with cancers of the floor of mouth and ventral tongue but neither these changes nor alterations in flux parameters or S Phase durations were significant. Twenty-one kinetic profiles of dysplastic and malignant tissue were compared with conventional histopathological results, however, and these showed a 2.2% increase in LIs with each increase in grade of dysplasia (P = 0.004) and a 12% increase in LIs with each reduction in tumour differentiation (P = 0.02).

Flow cytometric analysis of cell cycle fractions in oral leukoplakia

Flow cytometric analysis of cell cycle fractions and DNA ploidy was performed on 39 biopsy specimens of oral leukoplakia. The aneuploidy rate of these leukoplakias was 9/39 (23.1%) and the mean DNA index of the aneuploid lesions was 1.34. The aneuploidy rate was significantly higher in severely dysplastic lesions (8/17) than in mildly dysplastic (1/15, P<0.02) and nondysplastic (0/7, P<0.05) lesions. No significant differences in the percentages of each cell cycle fraction were seen between the diploid and the aneuploid leukoplakias. However, the S-phase fraction of the severely dysplastic lesions (23.0%) among the diploid leukoplakias was higher than those of the mildly dysplastic (12.4%) and nondysplastic (15.5%) lesions, and the difference between the severely dysplastic and the mildly dysplastic lesions was statistically significant (P<0.001). These results suggest that flow cytometric analysis of cell cycle fractions and DNA ploidy might offer additional information for assessing the malignant potential of oral leukoplakias.

Oral leukoplakia: a clinicopathological review

Leukoplakia is the most common premalignant or potentially malignant lesion of the oral mucosa. It seems preferable to use the term leukoplakia as a clinical term only. When a biopsy is taken, the term leukoplakia should be replaced by the diagnosis obtained histologically. The annual percentage of malignant transformation varies in different parts of the world, probably as a result of differences in tobacco and dietary habits. Although epithelial dysplasia is an important predictive factor of malignant transformation, it should be realized that not all dysplastic lesions will become malignant. On the other hand non-dysplastic lesions may become malignant as well. In some parts of the world the tongue and the floor of the mouth can be considered to be high-risk sites with regard to malignant transformation of leukoplakia, while this does not have to be the case in other parts of the world. The cessation of tobacco habits, being the most common known aetiological factor of oral leukoplakia, has been shown to be an effective measure with regard to the incidence of leukoplakia and, thereby, the incidence of oral cancer as well. Screening for oral precancer may be indicated in individuals at risk.