Genetic progression and divergence in superficial esophageal squamous cell carcinoma by loss of heterozygosity analysis

Esophageal squamous cell carcinoma (SCC) is one of the most common fatal carcinomas worldwide and has some of the most malignant characteristics among gastrointestinal tumors. Although a high frequency of loss of heterozygosity (LOH) for various genes has been observed in esophageal SCCs, these findings do not provide any information regarding the genetic pathways that may underlie the development and progression of this type of tumor. To clarify the temporal and topographic pathways in the genetic evolution of esophageal SCC, we microdissected multiple foci from superficial mucosal invasive foci of tumors. We then carried out LOH analyses of the microdissected neoplastic foci. Sixteen superficial esophageal SCCs were examined. Three to six carcinoma foci from each superficial esophageal SCC were individually microdissected. We used 12 oligonucleotide primer pairs specific for the microsatellite markers for which frequent LOH in esophageal SCC has been reported. All tumors exhibited LOH of at least three microsatellite loci. A frequent homogeneous LOH pattern was detected for TP53 (60%), D16S518 (43%) and D3S1234 (29%), suggesting that the loss of these alleles is an early event in the development of esophageal SCC. A heterogeneous LOH pattern was detected for D13S325 (87%), D10S559 (73%), D3S1568 (58%), D3S1234 (57%) and D3S1621 (56%), suggesting that the loss of these alleles is a late event in the development of esophageal SCC. All tumors showed the LOH pattern of single clonal neoplasms with genetic progression and divergence. In conclusion, by extensive sampling of SCC lesions with microdissection and LOH analysis of multiple chromosomal loci, we successfully demonstrated dynamic and successive accumulation of genetic alterations in early SCC.     

Genetic pathways of multiple esophageal squamous cell carcinomas

Whether multiple esophageal squamous cell carcinomas (SCCs) in a patient develop through an identical genetic pathway is still unclear. We examined multiple esophageal SCCs for alterations of p53, p16, IRF and mitochondrial DNA (mtDNA) and microsatellite instability (MSI). Thirty patients with multiple superficial esophageal SCCs, 23 with double lesions and 7 with triple lesions, were enrolled. Loss of heterozygosity (LOH) of p53 (TP53), p16 (D9S171), IRF (IRF) and other microsatellite loci including D1S191, D17S858, D18S58 and D18S61 of the tumors was examined by microsatellite assay. Mutations of p16 and mtDNA were examined with PCR single-strand conformation polymorphism (SSCP) analysis. LOH of p53, p16 and IRF were detected in 16 of 50 (32%), 5 of 38 (13%) and 5 of 48 (10%) tumors, respectively. Mutations of p16 were detected in 4 of 67 (6%) tumors. Six of 67 (9%) tumors had mtDNA alterations and none of the tumors showed high-frequency MSI. All 30 patients showed one or more gene alterations in one or more genetic loci. Discordant genetic patterns among individual lesions within a patient were observed in 28 of the 30 (93%) patients. The most discordant locus was TP53, present in 11 of 29 (38%) informative cases, followed by D18S61, present in 11 of 30 (37%) informative cases. These results suggest that the genetic pathways of multiple esophageal SCCs may differ even within the same patient.     

Allelic loss on the short arm of chromosome 8 in oral squamous cell carcinoma.

Allelic deletions on the short arm of chromosome 8 (8p) are frequent events in many different types of malignant tumors, including head and neck tumors and oropharyngeal cancers. These regions are thought to harbor tumor suppressor genes. However, there has been no detailed analysis of loss of heterozygosity (LOH) on the chromosome arm 8p in oral squamous cell carcinoma (SCC). In order to estimate details of 8p loci involved in oral SCC, 32 patients with oral SCCs were examined for the LOH state 8p by PCR-LOH assay using 14 microsatellite markers. Based on our results a detailed deletion map of 8p showed LOH in at least one of the loci tested in 62.5% (20 of 32) of patients; and microsatellite instability (MI) was observed in 50% (16 of 32). The frequent LOH on this chromosome arm was identified at D8S87 and D8S258, mapped on 8p12 and 8p22, respectively. Fisher's exact test revealed no significant statistical correlation between the incidence of LOH or MI and clinicopathological features. Our observations indicate that the short arm of chromosome 8 may play a role in the pathogenesis of oral SCC; and that the two loci identified in this study may be tumor suppressor gene loci on 8p.     

p53 Gene mutation and genetic instability in superficial multifocal esophageal squamous cell carcinoma

Tumor multicentricity is occasionally observed in esophageal squamous cell carcinoma (SCC). We studied five surgically resected superficial multifocal esophageal SCCs for p53 gene mutation and genetic instability, using DNA extracted from microdissected areas. A total of 38 target areas (TAs) were analyzed in SCC, dysplasia, basal cell hyperplasia (BCH) and normal squamous epithelium. Analysis of the replication error (RER) at 10 microsatellite loci showed microsatellite instability in all TAs, as well as in normal squamous epithelium. p53 gene mutation was identified in 28.9% (11/38 TAs). All cases showed a common missense mutation in exon 8 at codon 273 (CGT-->CAT, Arg-->His), which was DNA contact mutation in the S10 beta strand. In association with microsatellite alterations, 7 of 9 TAs with p53 mutation in exon 8 at codon 273 also showed loss of heterozygosity (LOH) of p53 gene. LOH of p53 gene was detected in 83.8% (31/37 TAs). LOH at D2S123 on 2p16 near MSH2 gene and at D3S1611 on 3p22 near MLH1 gene was detected in 65.4% (17/26) and 71.4% (10/14) TAs, respectively. Frequencies of LOH at p53 and D2S123 were similar in non-cancerous areas and SCCs. LOH of p53 and D2S123 were found in 50% (5/10 TAs) of non-cancerous areas and 60% (9/15 TAs) of SCCs. Our results suggest that genetic instability induces esophageal tumor multicentricity, and that p53 gene contact mutation together with LOH are early events of the multistage carcinogenesis of multifocal primary esophageal SCC.     

Genome-wide allelotype analysis of sporadic primary nasopharyngeal carcinoma from southern China

Nasopharyngeal carcinoma (NPC) is one of the most common malignant tumors in Southern China, especially in the Guangdong area. To demonstrate a comprehensive profile of loss of heterozygosity (LOH) in NPC, we applied a large panel of 382 microsatellite polymorphism markers covering all the 22 autosomes in 98 cases of sporadic primary NPC. Of the 335 informative markers, 83 loci showed high level of LOH (presence in equal to or more than 30% cases) and most of the high frequent loci were clustered to chromosome 1p36 and 1p34, 3p14-p21, 3p24-p26, 3q25-q26 and 3q27, 4q31 and 4q35, 5q15-21 and 5q32-q33, 8p22-p23, 9p21-p23 and 9q33-q34, 11p12-p14, 13q14-q13 and 13q31-q32, 14q13-q11, 14q24-q23 and 14q32. High frequency of LOH was found in chromosomes 3, 5, 9 and 11 (>/=50%), while medium frequency of LOH was found in chromosomes 1, 4, 6, 14, 17 and 19 (40-49%). Several new regions showing high frequency of LOH were found in chromosome 1p36, 3q25-q26, 3q27, 5q15-q21, 8p22-p23 and 11p12-14. The relationship between LOH and TNM stage of NPC was evaluated. Regions 6p23 (D6S289), 8p23.1 (D8S549) and 9q34.2 (D9S1826) showed higher frequency of LOH in later stages (III and IV) than in earlier stages (I and II) (P<0.05). Thus, our study provides a global view on allelic loss in the development of NPC and should shed light on the way for localization of putative tumor suppressor genes associated with the pathogenesis of NPC.     

Allele loss on chromosome-3 in squamous-cell carcinoma of the head and neck correlates with poor clinical prognostic indicators

Cytogenetic studies in squamous cell carcinoma of the head and neck (SCCHN) have identified a clustering of breakpoints in a number of chromosomes, including chromosome 3. We have undertaken a loss of heterozygosity analysis (LOH) of 36 SCCHN and six solid tumours which were not squamous cell, and their respective normal specimens, using a bank of microsatellite markers, with the aim of identifying specific sites of frequent loss on chromosome 3. The analysis was undertaken with 12 microsatellite markers, 10 of which are on the p arm of chromosome 3. Allelic loss greater than 10% was seen at four sites; D3S1269 (13%), D3S1079 (23%), D3S659 (23%) and D3S1293 (31%). None of this series of tumours showed loss of the whole chromosome, however 47% of the tumours analysed had LOH at one or more loci. The highest incidence of LOH was found at D3S1293 in the 3p24-p25 region. The second highest region with LOH was found at D3S1079 and D3S659 at 3p13. The remaining markers telomeric and centromeric to these two regions were found to have a LOH of less than 10%. Furthermore, we found a strong association between loss of one marker on chromosome 3 in these SCCHN and poor clinical prognostic indicators; such as site, pathological differentiation, positive nodes at pathology (p<0.05) and TNM status (p<0.05). This study has identified two regions in SCCHN that are most likely to be important in the development of squamous cell carcinoma of the head and neck at 3p24-p25 and 3p13 and may indicate sites of novel tumour suppressor genes in this disease.     

Distinct regions of frequent loss of heterozygosity of chromosome 5p and 5q in human esophageal cancer

Loss of heterozygosity (LOH) studies reported thus far suggest that tumor suppressor loci on chromosome 5q are important in esophageal cancer (EC) while little is known about the involvement of chromosome 5p. To investigate the potential existence of tumor suppressor gene(s) on chromosome 5 contributing to the development of EC, we performed LOH studies using a total of 24 polymorphic markers spanning the entire chromosome 5. Seventy primary esophageal cancers were microdissected and allelic deletions were detected by polymerase chain reaction (PCR)-single strand conformation polymorphism or by microsatellite analysis. LOH was observed in at least 1 of the loci in 47 of 70 (67%) esophageal tumors. Initially, 40 tumors [24 squamous cell carcinomas (SCC) and 16 adenocarcinomas (ADC)], each with matched histologically normal esophageal mucosa, were analyzed at 15 marker loci on 5p and 5q. A novel locus, D5S667 on 5p15.2, exhibited the highest frequency of LOH (44%) in these tumors along with another previously reported region of frequent deletion, irf-1 (5q31.1). In a series of 30 additional EC tumors (11 SCC and 19 ADC), a detailed LOH analysis of chromosome 5p15.2 region was conducted using 10 additional polymorphic markers, which mapped the frequently deleted region within 1 cM. Overall, LOH at the D5S667 locus was observed more frequently in SCC than in ADC (62% vs. 23%, p = 0.01). This significant rate of LOH of a distinct region of chromosome 5p implicates the existence of a putative tumor suppressor gene locus involved in EC. Int. J. Cancer 78:600–605, 1998. © 1998 Wiley-Liss, Inc.     

Frequent loss of heterozygosity on chromosome 9 in Chinese esophageal squamous cell carcinomas

Multiple and extensive alterations in chromosome 9 were detected in thirty-four esophageal squamous cell carcinoma patients, using seventeen polymorphic markers localized to chromosome 9 to detect the loss of heterozygosity (LOH) by polymerase chain reaction techniques. The LOH rates detected in this study range from 42.9 to 80.0%. Three commonly deleted regions mapping to 9p23-p22, 9q13-q22.3, and 9q34 were observed. D9S1812 LOH at 9q22.1 was significantly associated with well- and moderately-differentiated tumors; LOH at D9S768, mapping to 9q13-21.3, indicated that drinking habits are not a significant risk factor for Chinese esophagus cancer. Interestingly, no case of microsatellite instability was observed.     

The presence of candidate tumor suppressor gene loci at chromosome 3p for oral squamous cell carcinomas

We investigated the short arm of chromosome 3 (3p) for allelic imbalances, including loss of heterozygosity (LOH) and microsatellite instability (MSI) in 40 primary oral squamous cell carcinomas (SCCs) using 10 microsatellite markers and constructed a deletion map for this chromosome arm. We examined 40 primary tumor tissues, 40 corresponding normal tissues, and seven lymph node metastatic tissues. LOH at one or more loci was found in 24/40 (60%) of tumors. Deletion mapping of these tumors revealed at least three discrete, commonly deleted regions on the chromosome arm. Furthermore, we detected MSI in six of those tested cases (15%). We compared our results with the clinicopathologic features. A number of sites displaying LOH at 3p could be detected in early stage lesions, and the frequencies of LOH tended to be higher in later clinical stages. Thus, the frequent LOH was observed from early stage in pTNM classification. An unknown tumor suppressor gene in the genesis of oral squamous cell carcinoma may exist in 3p.     

Loss of heterozygosity analysis on chromosome 5p defines 5p13-12 as the critical region involved in tumor progression of bladder carcinomas

We have previously observed loss of heterozygosity (LOH) at a single locus (del-27) on human chromosome 5p13-12 to correlate with bladder tumor progression. In this study, we examined 33 bladder tumors for their pattern of allelic loss on chromosome 5p using 7 microsatellite markers. In 14 of 15 bladder tumors with LOH at locus del-27, allelic loss was confined to chromosomal region 5p13-12. This region included the microsatellite marker D5S2025 that showed LOH in 5 of 11 (45%) informative cases with LOH at del-27. This suggests that D5S2025 and del-27 are located within a single critical region of LOH on 5p13-12 harboring a tumor suppressor gene involved in bladder tumor progression. Recurrent LOH at other loci was observed at microsatellite markers located at 5p15. However, these losses appeared to be independent of LOH at 5p13-12 and occurred predominantly in poorly differentiated (G3) and advanced (T3-T4) tumors.     

Frequent loss of heterozygosity on chromosome 10p15, a putative telomerase repressor/senescence gene locus,in gastric cancer

Previous studies suggest that a telomerase repressor/senescence gene, which acts as a tumor suppressor gene, may be located on chromosome 10p15. However, there are no studies on alterations on chromosome 10p15 in gastric cancers. We, therefore, examined loss of heterozygosity (LOH) on the 10p15 in gastric cancers by microsatellite assay. Two microsatellite loci, D10S501 and D10S602, were used. Fifty-seven gastric cancers, including 36 intestinal type and 21 diffuse type, were selected. LOH at D10S602 and D10S501 was detected in 6 of 18 (33%) and 5 of 27 (19%) gastric cancers, respectively. There was no significant correlation between LOH at these loci and clinicopathologic features, including patient age, sex, tumor location, histologic subtype, depth of invasion, and lymph node metastasis. These data suggest that a putative telomerase repressor/senescence gene may be located on chromosome 10p15, especially at the D10S602, in gastric carcinogenesis, and that the putative gene malfunction may be involved in the early stages of gastric carcinogenesis.     

Human bladder cancers and normal bladder mucosa present the same hot spot of heterozygous chromosome-9 deletion

Loss of heterozygosity (LOH) on chromosome 9 is the most frequent genetic alteration in bladder cancer identified to date, suggesting the presence of key gene(s) for this pathology. In this study, we examined 44 bladder tumors and 21 normal bladder samples for LOH on both arms of chromosome 9. Sixteen microsatellite markers, 12 on the short arm (encompassing 9p21-22) and 4 on the long arm (encompassing 9q33-34), were chosen for their highly frequent alterations in bladder cancer. LOH for at least one marker was identified in 42 tumor samples (95.5%), and 14 tumors (32%) displayed LOH for all informative tested markers. Detailed analysis showed that 2 markers on chromosome 9p (D9S157 and D9S156) had the highest frequencies of allelic loss (about 70%), independent of tumor grade and stage. The same study was performed on the 21 normal bladder mucosa samples: 50% of informative cases presented a single specific LOH at the D9S156 locus. Normal samples showing LOH at this locus were therefore screened with 3 novel microsatellite markers in the 810-kb region incorporating D9S156. Using this marker, we found no further heterozygous loss in this region. This result allows different interpretations of the D9S156 loss in normal bladder mucosa, and suggests that D9S156 may be more an indicator of bladder epithelium impairment than a tumor-initiation marker. Similarly, this unexpected result calls in question the interpretation of LOH studies. Int. J. Cancer 77:821–824, 1998.© 1998 Wiley-Liss, Inc.     

Allelic loss on chromosome 1 is associated with tumor progression of cervical carcinoma.

BACKGROUND: Alterations in chromosome 1 are common in human malignancies. The frequency of loss of heterozygosity (LOH) on chromosome 1 in cervical carcinoma and its clinical significance are not clearly understood. METHODS: LOH on chromosome 1 was studied in 100 cervical carcinomas by the polymerase chain reaction (PCR) using 29 highly polymorphic microsatellite markers spaced approximately 10 centimorgans apart. Loci with high frequencies of LOH were identified and the findings were correlated with clinicopathologic characteristics. RESULTS: LOH on chromosome 1 at 1 or more loci was detected in 93% of tumors. The frequencies of LOH at locus D1S2829 (1p31), D1S2663 (1p36.3), and D1S2725 (1q25) exceeded 30%, and 12 other loci exhibited frequencies of LOH of 20-30%. Advanced stage tumors had a significantly higher percentage of informative microsatellite markers with LOH than early stage tumors. Of the 29 microsatellite markers studied, 4 loci had a significantly higher frequency of LOH in Stage III and IV tumors than in earlier stage tumors. CONCLUSIONS: Frequent aberrations on chromosome 1 in cervical carcinoma suggest that inactivation of tumor suppressor genes is important in cervical tumorigenesis. Higher frequencies of LOH in Stage III and IV tumors suggest that chromosome 1 changes are late events in cervical carcinoma. The findings of this study are consistent with earlier reports that suggest that tumor suppressor genes are present at 1p36.3 and 1p31. To the authors' knowledge, the high frequency of LOH mapped to 1q25 has not been reported previously. Its significance awaits further clarification.     

Characterization of genetic alteration patterns in human esophageal squamous cell carcinoma using selected microsatellite markers spanning multiple loci

In order to identify representative genetic alterations in esophageal squamous cell carcinomas (ESCC) and useful markers for future early detection, 34 ESCC samples with neighboring normal epithelia and 30 esophageal biopsy samples from Linzhou, P.R. China, were studied. Of the 38 microsatellite markers selected, half were linked with tumor suppressors. More than 40% of the tumor samples showed loss of heterozygosity (LOH) in at least one of the eight markers, D3S1067 and D3S1561 (both linked to hMLH1 locus), FABP2, D4S1613, D9S171 (p14ARF, p15INK4b, p16INK4a loci), Rb1 (intron), p53-2 (intron), and NM23-H1. Most of the 38 microsatellite markers did not display microsatellite instability (MSI) in more than 30% of the tumor samples, except D9S942 (p14ARF, p15INK4b, p16INK4a loci) and Bat26, which showed frequency at 32 and 41%, respectively. Of all the ESCC samples examined, 20 samples exhibited LOH in 25% or more of the informative markers. Three samples displayed MSI in more than 30% of the markers, indicating that MSI might be an important event in these subset ESCC cases. Statistically significant correlations were found between LOH of the hMLH1 locus and the general LOH status of the sample, and between the LOH of the hMLH1 locus and p53 mutations. In addition, correlation was found between MSI in D3S1067/D3S1561 and the general MSI status in the samples. However, MSI in the introns of hMLH1 and hMSH2 were not correlated with the general MSI status of the tumors. LOH analysis was also performed in 30 esophageal biopsy samples containing precancerous lesions with matching blood samples using nine microsatellite markers selected from the above studies. LOH frequence ranged from 0 to 33% in informative cases, mostly in the 9p21 and p53 gene regions, suggesting these regions are possible targets of genomic instability in early stage ESCC carcinogenesis. The results demonstrate the degree of genetic alterations at different loci of the chromosomes. Some of the microsatellite markers may be useful for the early detection of ESCC.     

10号染色体可能含有多个与胶质母细胞瘤相关的肿瘤抑制基因

目的 寻找胶质母细胞瘤（GBM）10号染色体上可能存在肿瘤抑制基因的杂合性丢失（LOH）区域,为发现和定位肿瘤抑制基因（TSG）提供线索和依据。方法 应用聚合酶链反应（PCR）方法,采用荧光标记的引物和先进的377型DNA序列自动分析仪,分析了21例GBM10号染色体上20个微卫星多态性标记的LOH。结果 在85．7％（18／21例）GBM的10号染色体上观察到LOH,在57．7％（162／281）可提供信息位点上存在LOH。10q的LOH率高于10p,分别是81．0％（17／21）、66．7％（14／21）。在下列位点或区域检测到较高的LOH率（＞60％）：10q22.3-23.3上的D10s185-D10s192间区域,10p14-15.1上的D10s591-D10s249间区域,10q24.2-26.3上的D10s1693-D10s212间区域,10p12.2-14上的D10s547位点,10q21.3上的D10537位点。结论 10号染色体可能在GBM的分子水平发病机制中发挥着重要作用,它上面的多个染色体区域可能存在与GBM相关的多个TSG。     

Allelic loss in esophageal squamous cell carcinoma patients with and without family history of upper gastrointestinal tract cancer.

Chromosomal regions with frequent allelic loss may point to major susceptibility genes that will assist in understanding molecular events involved in esophageal carcinogenesis. Esophageal squamous cell carcinoma samples and blood from 46 patients, including 23 patients with and 23 patients without a family history of upper gastrointestinal cancer, were screened using laser microdissected DNA and tested for loss of heterozygosity (LOH) at 18 marker loci representing 14 chromosomal regions (on 2q, 3p, 4p, 4p, 5q, 6q, 8p, 9p, 9q, 11p, 13q, 14q, 15q, and 17p) identified in an earlier genome-wide scan to have frequent LOH. Clinical/pathological and lifestyle risk factor data were also collected. For all 46 tumors combined, the lowest frequency LOH for any of the 18 markers was 37%, and 8 markers showed LOH in > or =75% of informative tumors. One marker (D13S894 on 13q) showed greater LOH in patients with a positive family history (93% versus 50%; P = 0.04), whereas two markers (D6S1027 on 6q and D9S910 on 9q) had significantly more LOH in patients with metastasis, and one marker (D4S2361 on 4p) showed significantly higher LOH in patients with a lower pathological tumor grade. No relation was seen between LOH and lifestyle risk factors. This study confirms the previously observed high frequency LOH for these 14 chromosomal regions, including a locus on 13q where LOH is more common in patients with a family history of upper gastrointestinal cancer than in those without such history, suggesting that a gene in this area may be involved in genetic susceptibility to esophageal cancer.     

Genetic mapping of allelic loss on chromosome 6q within heterogeneous prostate carcinoma

A number of genetic events have been reported in prostate carcinogenesis, including frequent loss of heterozygosity (LOH) on chromosomes 8q, 10q, 16q and 18q, In samples of heterogeneous, multifocal prostate carcinomas, we focused on chromosome 6q using PCR-based techniques with 15 microsatellite markers to identify the specific 6q deletion within tumors. LOH of one or more polymorphic markers was detected in 10 of 21 tumors (48%). Two of these 10 tumors demonstrated LOH in all cancerous foci at specific loci and 4 tumors showed deletion in one focus. Different deletion patterns were found in 3 tumors when different polymorphic markers were used. In 90% of tumors showing LOH in one or more foci, however, two common regions of LOH were identified; one at 1.81 cM on 6q15–16.3 between markers D6S1631 and D6S1056, and the other at 5.11 cM on 6q16–21 between markers D6S424 and D6S283. By RT-PCR analysis, the TAK1 gene located at these loci did not correlate with LOH status, indicating that TAK1 is not a target gene in prostate carcinoma. The 6q deletion occurs heterogeneously and LOH was more frequent in tumors of higher pathological stages, implying that this alteration is a late event in prostate carcinogenesis. Because prostate carcinomas are genetically multicentric and of multifocal origin, it remains unclear whether the foci containing 6q deletions specifically expand within tumors or to what extent they contribute to the histological heterogeneity characteristic of the disease.     

A novel region of deletion on 13q33-q34 in esophageal squamous cell carcinoma

Chromosome 13 presents frequent allelic loss in esophageal squamous cell carcinomas (ESCC). However, no ESCC suppressor gene has been identified from this chromosome. To define common deletion regions that possibly contain the ESCC suppressor gene(s), we performed a mapping of allelic loss in 50 esophageal squamous cell carcinomas using a panel of 25 microsatellite markers on chromosome 13q21-qter, which has rarely been studied for allelic loss. Loss of heterozygosity (LOH) with high frequencies (> or = 50%) was observed at markers D13S1494, D13S1323, D13S248, D13S1315, D13S285, and D13S1295, in which the peak LOH (69.2%) was at locus D13S248. Seven cases presented LOH at three consecutive markers D13S248, D13S1315 and D13S285, 4 of which also displayed LOH at another adjacent marker D13S1295. This overlapping region of deletion covers an interval of 6.36 Mb at 13q33.1-q34, whose deletion has not previously been reported in ESCC. Tumors of grade II showed significantly more frequent LOH at D13S248 than those of grade I. A significantly higher frequency of allelic loss at D13S152 was also found in tumors with lymph node metastasis compared to those without lymph node metastasis. The present study defined a novel region of allelic loss in 13q33-q34. LOH at D13S248 and D13S152 are associated with higher tumor grade and metastasis, respectively.     

Investigation of allelic imbalances on chromosome 3p in nasopharyngeal carcinoma in Tunisia: high frequency of microsatellite instability in patients with early-onset of the disease

Tunisia is one of the world's intermediate risk areas for nasopharyngeal carcinoma (NPC). Loss of heterozygosity (LOH) on the short arm of chromosome 3 (3p) is the most frequent genetic change reported in NPC from endemic areas. In the present study, we investigate the incidence of LOH and microsatellite instability (MSI) on chromosome 3p in 49 microdissected primary NPC specimens and corresponding non-cancerous tissues from Tunisian patients using six microsatellite polymorphic markers. LOH at one or more markers was observed in 40 out of 48 informative cases (83.3%). The markers D3S1038 at 3p25.2-26.1 and D3S1076 at 3p21.1-21.2 have showed the highest frequency of LOH (51.3%), followed by D3S1067 at 3p14.3-21.1 (48.7%), D3S1568 at 3p21.3 (47.4%), D3S659 at 3p13 (15.3%), and D3S1228 at 3p14.1-14.2 (11%). Interestingly, MSI at one or more microsatellite markers was observed in 15 cases (31.2%). The highest frequency of MSI was presented by D3S1568 (18.4%), D3S1067 (17.9%), and D3S1038 (12.8%). With regard to clinicopathological features, LOH was found to be less common in young patients (under 25 years) than in adults (p=0.04), whereas MSI was found to be more frequent in patients under 45 years than in older patients (p=0.006). No significant correlation was found between LOH or MSI and the other clinicopathological features investigated including, gender, tumor size, lymph node metastasis, UICC clinical stage, and histological subtype. This study revealed different patterns of allelic imbalance on chromosome 3P in NPC between age groups in Tunisia, and suggests an alteration in the DNA mismatch repair machinery that may be, in part, responsible of the early age onset form of this disease in North African populations. More attention should be given to the mismatch repair system in the juvenile form of this disease in future studies.