Frequent deletion of chromosome 3p in oral squamous cell carcinoma

Repression of hTERT transcription by the introduction of chromosome 3 into human oral squamous cell carcinoma

Telomerase is a ribonucleoprotein enzyme that maintains telomere length. Telomerase activity is primarily attributed to the expression of telomerase reverse transcriptase (TERT). It has been reported that introduction of an intact human chromosome 3 into the human oral squamous cell carcinoma cell line HSC3 suppresses the tumorigenicity of these cells. However, the mechanisms that regulate tumorigenicity have not been elucidated. To determine whether this reduction in tumorigenicity was accompanied by a reduction in telomerase activity, we investigated the transcriptional activation of TERT in HSC3 microcell hybrid clones with an introduced human chromosome 3 (HSC3#3). HSC#3 cells showed inhibition of hTERT transcription compared to that of the parental HSC3 cells. Furthermore, cell fusion experiments showed that hybrids of HSC3 cells and cells of the RCC23 renal carcinoma cell line, which also exhibits suppression of TERT transcription by the introduction of human chromosome 3, also displayed suppressed TERT transcription. These results suggested that human chromosome 3 may carry functionally distinct, additional TERT repressor genes.

Genome-Wide Loss of Heterozygosity and DNA Copy Number Aberration in HPV-Negative Oral Squamous Cell Carcinoma and Their Associations with Disease-Specific Survival

Oral squamous cell cancer of the oral cavity and oropharynx (OSCC) is associated with high case-fatality. For reasons that are largely unknown, patients with the same clinical and pathologic staging have heterogeneous response to treatment and different probability of recurrence and survival, with patients with Human Papillomavirus (HPV)-positive oropharyngeal tumors having the most favorable survival. To gain insight into the complexity of OSCC and to identify potential chromosomal changes that may be associated with OSCC mortality, we used Affymtrix 6.0 SNP arrays to examine paired DNA from peripheral blood and tumor cell populations isolated by laser capture microdissection to assess genome-wide loss of heterozygosity (LOH) and DNA copy number aberration (CNA) and their associations with risk factors, tumor characteristics, and oral cancer-specific mortality among 75 patients with HPV-negative OSCC. We found a highly heterogeneous and complex genomic landscape of HPV-negative tumors, and identified regions in 4q, 8p, 9p and 11q that seem to play an important role in oral cancer biology and survival from this disease. If confirmed, these findings could assist in designing personalized treatment or in the creation of models to predict survival in patients with HPV-negative OSCC.

Molecular profiling of premalignant lesions in lung squamous cell carcinomas identifies mechanisms involved in stepwise carcinogenesis

Lung squamous cell carcinoma (SCC) is thought to arise from premalignant lesions in the airway epithelium; therefore, studying these lesions is critical for understanding lung carcinogenesis. Previous microarray and sequencing studies designed to discover early biomarkers and therapeutic targets for lung SCC had limited success identifying key driver events in lung carcinogenesis, mostly due to the cellular heterogeneity of patient samples examined and the interindividual variability associated with difficult to obtain airway premalignant lesions and appropriate normal control samples within the same patient. We performed RNA sequencing on laser-microdissected representative cell populations along the SCC pathologic continuum of patient-matched normal basal cells, premalignant lesions, and tumor cells. We discovered transcriptomic changes and identified genomic pathways altered with initiation and progression of SCC within individual patients. We used immunofluorescent staining to confirm gene expression changes in premalignant lesions and tumor cells, including increased expression of SLC2A1, CEACAM5, and PTBP3 at the protein level and increased activation of MYC via nuclear translocation. Cytoband enrichment analysis revealed coordinated loss and gain of expression in chromosome 3p and 3q regions, respectively, during carcinogenesis. This is the first gene expression profiling study of airway premalignant lesions with patient-matched SCC tumor samples. Our results provide much needed information about the biology of premalignant lesions and the molecular changes that occur during stepwise carcinogenesis of SCC, and it highlights a novel approach for identifying some of the earliest molecular changes associated with initiation and progression of lung carcinogenesis within individual patients.

Microsatellite instability and loss of heterozygosity in oral squamous cell carcinoma in Malaysian population

Loss of heterozygosity (LOH) and microsatellite instability (MSI) have been documented as important events in oral squamous cell carcinoma (OSCC). Five microsatellite markers D3S192, D3S966, D3S647, D3S1228 and D3S659 were selected on chromosome 3p because of high frequency of alterations reported in head and neck squamous cell carcinoma and the involvement of von Hippel Lindau (VHL) at 3p25-26 and the fragile histidine triad (FHIT) at 3p14.2 genes proven in many tumour types. A total of 50 archival tissue samples of OSCC and corresponding normal samples were analyzed for LOH and MSI status. The overall LOH for the markers selected on 3p was 56 out of 189 informative cases (29.6%). The most frequent LOH was identified for the marker D3S966 which was 18/42 (42.8%) of informative cases suggesting the presence of putative tumour suppressor genes (TSGs) in this loci. In this study, high frequency of microsatellite instability was found in D3S966 which was 28.6% of informative cases; this reveals the possibility of mutations of MMR genes in this region. Frequent microsatellite alterations (MA) were observed in 3 markers D3S966 (71.4%), D3S1228 (56.7%) and D3S192 (41.0%). There was no significant association between LOH with gender, tumour stages and differentiation grades. However, there was a significant association between tumour stage and differentiation grades with MSI status in OSCC in Malaysian population with p values of 0.002 and 0.035, respectively. There was also a significant association between MA and differentiation grades (p=0.041).

Role of microsatellites instability in carcinogenesis of postcricoid carcinoma on top of plummer-vinson syndrome

To develop a molecular pattern that might help in understanding carcinogenesis of postcricoid carcinoma (PCC) on top of Plummer-Vinson syndrome (PVS) in a prospective controlled study. Twenty-four patients with PVS were diagnosed and followed up over a 4 year period, during which eight of them showed malignant change to PCC. Twenty volunteers free of neoplastic diseases were included as a control group. In the two groups, DNA extraction from mononuclear peripheral blood cells, and analysis of loss of heterozygosity (LOH) and microsatellite instability (MSI) using six paired simple tandem repeats (STRs) primers were done. The molecular weight of each STRs locus was scored and statistical correlations were performed. LOH occurred in 55.6 and 72.9% of PVS and PCC cases compared to 25% of control group. At loci D17S695, D9S753 and D9S171, LOH occurred in 54.2, 66.7, and 70.8% of PVS cases; and in 62.5% of PCC cases for each locus compared to 15, 25 and 45% of control cases. D3S1286 and CFS1-R displayed the highest frequency of LOH in PCC (100% for each) while recorded in 58.3 and 33.3% in PVS compared to 30 and 0% in control cases. Certain genetic events tend to occur as early and late events in malignant change of PVS to PCC. Detection of these events may help in understanding carcinogenesis and in early detection of malignancy. CFS1-R is the most informative marker of tumor progression.

Advances in the biology of oral cancer

The incidence of oral cancer remains high and is associated with many deaths in both Western and Asian countries. Several risk factors for the development of oral cancer are now well known, including smoking, drinking and consumption of smokeless tobacco products. Genetic predisposition to oral cancer has been found in certain cases but its components are not yet entirely clear. In accordance with the multi-step theory of carcinogenesis, the natural history of oral cancer seems to gradually evolve through transitional precursor lesions from normal epithelium to a full-blown metastatic phenotype. A number of genomic lesions accompany this transformation and a wealth of related results has appeared in recent literature and is being summarized here. Furthermore, several key genes have been implicated, especially well-known tumor suppressors like the cyclin-dependent kinase inhibitors, TP53 and RB1 and oncogenes like the cyclin family, EGFR and ras. Viral infections, particularly with oncogenic HPV subtypes and EBV, can have a tumorigenic effect on oral epithelia and their role is discussed, along with potential therapeutic interventions. A brief explanatory theoretical model of oral carcinogenesis is provided and potential avenues for further research are highlighted.

Distinct array comparative genomic hybridization profiles in oral squamous cell carcinoma occurring in young patients

BACKGROUND

Oral cancer typically affects smokers older than 50 years of age. Recently, however, a marked increase in the number of patients 40 years old and younger, many with no history of tobacco smoking, has been noted. Studies in this age group have so far been restricted to genomic areas well recognized as abnormal in typical patients with oral cancer. The aim of this study was to assess genomic aberrations in oral cancer, using comparative genomic hybridization (CGH) microarray technology, and to compare the genomic aberration profile of patients older than 40 years old with those 40 years old and younger.

METHODS

Tumor samples from 20 patients with oral cancer (age range, 21-78; 10 smokers and 10 nonsmokers) were laser microdissected, and array CGH was used to identify genomic imbalances in these two cohorts.

RESULTS

The older cohort showed high numbers of gains and losses in contrast to very few copy number changes in the younger nonsmoker cohort. In concurrence with the literature, tumors from the older cohort manifested deletions involving 3p and 9p21 and gains involving 3q, 5q, 7p, 8q, 11q, and 20q. The younger group, particularly the nonsmokers, showed very few changes overall, and the aberrations were not in the sites classically associated with oral cancer. Deletion of CDKN2A (p16) was completely absent in the younger group but was present in 50% of the older cohort.

CONCLUSIONS

We have demonstrated that there is far less genomic instability in young nonsmokers with oral cancer than found in typical patients with oral cancer. These observations indicate that oral cancer presenting at a younger age, particularly in nonsmokers, has a genomic profile different from the classically described oral cancer.

Molecular analysis of paired tumours: Time to start treating the field

Molecular analysis of paired tumours highlights the limitations of the current clinical criteria for identifying second primary tumours. At present the finding of identical novel microsatellite alleles in paired lesions provides a "gold standard" marker for establishing clonal origin. However, these aberrations occur at low frequency and other methods for determining clonality have been proposed. In the present study we have applied 3 molecular tests to establish whether it is possible to combine the results obtained with the different approaches to provide information about the likely origin of a second tumour when novel alleles are not found. Our findings provide substantive molecular evidence that a proportion of second tumours are recurrences of an index lesion and suggest that the finding of concordant allelic imbalance at two or more loci at two different chromosome arms together with concordant p53 mutations might provide a useful surrogate. We briefly review other published reports and emphasis the need to plan treatment to eliminate precursor lesions in the field rather than focusing on the visible primary lesion and the 1-2 cm of surrounding mucosa traditionally considered to be "at risk".

Oral cancer research with an emphasis on genomic analysis

Ablative surgery has been a standard procedure for many years, but during the past few years there has been a significant improvement in our understanding of invasion and metastasis in oral cancer. Each procedure has to be planned individually. Before surgery, every attempt must have been made to arrive at a proper diagnosis, including the exact nature and aggressiveness of the tumor and an analysis of the patient's genetic background. These procedures and the prognosis will be discussed.

Frequent allelic loss/imbalance on the short arm of chromosome 3 in tongue cancer

Frequent allelic imbalances including loss of heterozygosity (LOH) and microsatellite instability (MSI) on the short arm of chromosome 3 (3p) have been found in several types of human cancer. This study was designed to identify the tumor suppressor locus (or loci) on 3p associated with tongue squamous cell carcinoma (SCC). Among 16 patients with tongue SCC tested, 7 (44%) of 16 informative cases showed LOH at one or more loci. Deletion mapping of these 16 tumors revealed two discrete, commonly deleted regions on the chromosome arm. Our data support the notion that tumor suppressor gene(s) contributing to the progression of tongue squamous cell carcinoma reside on 3p24 and 3p25.

A review of inherited cancer syndromes and their relevance to oral squamous cell carcinoma

This paper examines the genetic defects associated with inherited cancer syndromes and their relevance to oral cancer. Tumour suppressor genes are now thought of as either gatekeepers or caretakers according to whether they control cell growth directly by inhibiting cell proliferation and/or promoting cell death (gatekeepers) or whether they maintain the integrity of the genome by DNA repair mechanisms (caretakers). In disorders such as xeroderma pigmentosum, ataxia telangiectasia, Bloom syndrome and Fanconi's anaemia, where there are defective caretaker genes, there is an increased incidence of second primary malignancies, including oral cancer. By contrast, with the exception of Li Fraumeni syndrome, abnormalities of gatekeeper genes do not predispose to oral cancer. Not only do Li Fraumeni patients develop second primary malignancies, but defects of the p53 pathway (p53 mutation, MDM2 over-expression, CDKN2A deletion) appear to be a ubiquitous feature of sporadic oral cancer as it occurs in the West. The findings suggest that genetic instability is of fundamental importance in the pathogenesis of oral cancer.

Distinct chromosomal deleted regions defining different subsets of head and neck tumors

The aim of this work is detecting the loss of heterozygosity (LOH) and its relationship with the development and progression of head and neck cancer. Matched normal and tumor DNA from 81 patients with head and neck cancer were examined for LOH using six microsatellite repeat markers mapped to chromosomal regions 3p13, 6q13, 9p21, 11p15, 17p13.1, and 17q22. LOH frequency at a locus ranged from 21% to 55%. The highest frequencies were at 3p (41%), 9p (48%), and 17p (54%). Thirty-two of 81 tumor samples showed allelic loss at more than one region. Significant associations were found between LOH at 3p and 9p (P = 0.001), 9p and 11p (P = 0.03), and 9p and 17p (P = 0.007). LOH at 11p was frequent in tumors from the oral cavity (5/17), oropharynx (2/7), and hypopharynx (5/10), but absent in tumors from the larynx (0/11) (P = 0.02), and LOH at 17q was observed in tumors from oral cavity (10/30) and hypopharynx (3/9), but not in tumors from the oropharynx (0/10) or larynx (0/13) (P = 0.003). In addition to that, the occurrence of allelic losses at 9p and 17p strongly correlates to tobacco smoking (P = 0.03 and P = 0.006, respectively) and alcohol intake (P = 0.01 and P = 0.005, respectively). These results suggest that tumors from different sites have different LOH patterns and corroborate with epidemiological data implicating tobacco and alcohol in the etiology of head and neck tumors.

The prognostic significance of allelic imbalance at key chromosomal loci in oral cancer

Forty-eight primary oral squamous cell carcinomas (SCC) were screened for allelic imbalance (AI) at 3p24-26, 3p21, 3p13, 8p21-23, 9p21, 9q22 and within the Rb, p53 and DCC tumour suppressor genes. AI was detected at all TNM stages with stage 4 tumours showing significantly more aberrations than stage 1-3. A factional allelic loss (FAL) score was calculated for all tumours and a high score was associated with development of local recurrence (P = 0.033) and reduced survival (P = 0.0006). AI at one or more loci within the 3p24-26, 3p21, 3p13 and 9p21 regions or within the THRB and DCC genes was associated with reduced survival. The hazard ratios for survival analysis revealed that patients with AI at 3p24-26, 3p13 and 9p21 have an approximately 25 times increase in their mortality rate relative to a patient retaining heterozygosity at these loci. AI at specific pairs of loci, D3S686 and D9S171 and involving at least two of D3S1296, DCC and D9S43, was a better predictor of prognosis than the FAL score or TNM stage. These data suggest that it will be possible to develop a molecular staging system which will be a better predict of outcome than conventional clinicopathological features as the molecular events represent fundamental biological characteristics of each tumour.

Loss of heterozygosity at 5q21-22 (adenomatous polyposis coli gene region) in oral squamous cell carcinoma is common and correlated with advanced disease

We determined the frequency of loss of heterozygosity (LOH) at chromosome 5q21-22 (adenomatous polyposis gene region) in oral SCC from 49 patients using PCR-based assays. Of 43 informative (heterozygous) tumors, 41.9% [95% confidence interval (CI)=27.0, 57.9] contained LOH at 5q21-22. LOH at 5q21-22 was strongly associated with stage at diagnosis: 100%, (3/3), 50% (13/26), and 14% (2/14) of tumors from patients with distant metastases, regional spread, and localized disease, respectively, contained this genetic alteration (P=0.01). There were no statistically significant associations between LOH at 5q21-22 and other patient or tumor characteristics, but LOH was more commonly found in the tumors of heavy smokers, infrequent alcohol consumers, and in tumors containing either p53 mutations or HPV-DNA. In univariate analyses, LOH at 5q21-22 was associated with poor prognosis (hazard ratio=1.8, 95%, CI 0.8, 4.5); this relationship did not persist after adjustment for stage of disease (hazard ratio=1.1, 95% CI=0.4, 3.1). These data provide further evidence that inactivation of the APC gene and/or other genes at 5q21-22 is common and may be involved in the development and/or progression of oral SCC. Larger studies are needed to determine whether LOH at 5q21-22 is linked to known oral SCC etiologic factors and/or the prognosis of oral SCC patients, as well as to genetic instability at other loci involved in these malignancies.

Allelic imbalance at chromosomal loci implicated in the pathogenesis of oral precancer, cumulative loss and its relationship with progression to cancer

A microsatellite assay was used to screen 31 potentially malignant oral lesions presenting as leukoplakia and erythroplakia, with histological evidence of dysplasia, for genetic abnormalities at loci which frequently show allelic imbalance when oral squamous cell carcinomas (SCC) are examined. The microsatellite and restriction fragment length polymorphism (RFLP) markers selected were at 3p21, 8p21-23, 9p21 and included sequences within the Rb (13q14.2), p53 (17p13.1) and DCC (18q21.1) tumour suppressor genes. 8 patients subsequently developed an invasive tumour at the same site, or within 2 cm of the premalignant lesion. A further 8 patients developed SCC at a distant site. Seventy-seven per cent (24/31) of these potentially malignant lesions showed allelic imbalance (AI) and 55% (17/31) of cases showed microsatellite instability (msi). The probability of developing SCC was much greater for patients with lesions showing AI at two or more relevant loci (P = 0.008 by the logrank test) than the group with AI at fewer loci. The estimated probability of development of SCC in this group by 5 years was 73% (95% Cl: 50-92%). This suggests that determining the number of genetic abnormalities in a potentially malignant lesion can help identify patients with true precancers who should be followed closely to ensure that they receive chemoprevention and appropriate advice to limit risk factors, and to allow the early detection of invasive lesions.

Field cancerisation of the oral cavity: comparison of the spectrum of molecular alterations in cases presenting with both dysplastic and malignant lesions

Dysplastic lesions and invasive oral squamous cell carcinoma (SCC) from patients with field change were screened by restriction fragment length polymorphism (RFLP) and microsatellite assay. All tumours contained more genetic changes than the matched dysplasia which are likely to represent progression. Four of the 15 dysplastic lesions harboured the same abnormalities detected in the tumour and some paired lesions showed identical novel microsatellite alleles. The finding of identical 'genetic fingerprints' in dysplastic lesions and invasive carcinoma from the same patient provides strong evidence that these dysplasias are precursor lesions and that multiple lesions have probably arisen due to transfer of the progeny of an altered cell. Eight of the 15 dysplastic lesions showed alterations which were not present in the matched cancer, showing that evolution of subclones, or fusion of multiple clones also occurs. A further case showed loss of different alleles in the paired samples. These findings highlight the complexity of the genetic abnormalities present in the mucosa of patients with field change and suggests that the origin of these altered foci may be diverse.

The molecular biology of oral carcinogenesis: toward a tumor progression model

PURPOSE

An understanding of the molecular basis of oral carcinogenesis will alter our clinical approach to oral cancer. The nomenclature and major themes of molecular oral tumor biology are reviewed, beginning with the regulation events governing normal cellular physiology. In carcinogenesis, chromosomal or cytogenetic alterations lead to deregulation of tightly controlled stimulatory and inhibitory pathways, growth-promoting proto-oncogenes are mutated into overactive oncogenes, and growth-suppressing or tumor suppressor genes are inactivated. Recent advances in defining these fundamental mechanisms of tumor biology may allow prevention, diagnosis, and treatment of oral cancer to be approached at the molecular level.

Frequent gene deletions in potentially malignant oral lesions

Some oral cancers are preceded by premalignant lesions which include leucoplakia and erythroplakia. At present there are no reliable markers to identify lesions that may progress to malignancy. We have analysed 30 potentially malignant oral lesions for deletions at chromosomal regions that harbour tumour-suppressor genes for oral cancer. A total of 16 of 30 cases (53%) showed loss of heterozygosity (LOH) or allele imbalance at TP53, DCC, 3p21.3-22.1 or 3p12.1-13. These genetic alterations were detected in dysplastic lesions but not in histologically normal mucosa and may be early events in the carcinogenic process. A total of 64% of dysplastic lesions that recurred during the study showed LOH or allele imbalance in the initial biopsy and the number of genetic abnormalities increased in the tumours that developed. This type of molecular profiling may help to identify patients with lesions that may recur or acquire additional genetic events and progress to malignancy.

LOH at 3p correlates with a poor survival in oral squamous cell carcinoma

We analysed chromosome 3p for loss of heterozygosity (LOH) in 48 primary oral squamous cell carcinomas (SCCs) using 15 markers and constructed a deletion map for this chromosome arm. LOH at one or more loci was found in 34/48 (71%) of tumours. The data support the existence of at least three distinct regions of deletion at 3p24-26, 3p21.3-22.1 and 3p12.1-14.2. A significant correlation was observed between the number of regions showing allele loss at 3p and tumour stage, consistent with the progressive accumulation of genetic errors during the development of oral SCC. There were also significant associations between LOH at 3p and disease-free and overall survival of patients with early stage disease. This study is the first to demonstrate the prognostic significance of LOH at 3p for oral cancer and may help to identify patients who should receive more aggressive treatment.