High-frequency Microsatellite Instability Research Articles

Microsatellite instability screening should be done for right-sided colon cancer patients less than 60 years of age

Microsatellite analysis is a screening tool used for the identification of Lynch syndrome. We evaluated the occurrence of high-frequency microsatellite instability (MSI-H) in 160 patients with colorectal cancer < or =60 years old to determine if these individuals should be routinely tested for microsatellite instability. From January 2004 and December 2006, we tested specimens of colorectal cancer from 160 patients under 60 years of age for microsatellite instability. The relationships between clinicopathological parameters and MSI-H status were analyzed. MSI-H occurred in 11.3% (18/160) of the tumors assayed, and colorectal tumors with MSI-H status were located predominantly to the right side (56%, P < 0.001) and had a lower pathological stage (72%, P = 0.011). Of the 18 MSI-H tumors, six displayed characteristic MSI histology. Furthermore, of the 18 MSI-H tumors, instability in BAT-26 was 100%, BAT-25 was 94%, D17S250 was 72%, D2S123 was 68%, and D5S346 was 68%. Of the patients with MSI-H tumors, 55.6% were more than 50 years of age, and about 70% of MSI-H tumors did not display characteristic MSI histology. Importantly, up to 40% of the MSI-H patients in this study would have been overlooked using the revised Bethesda guidelines. The revised Bethesda guidelines, broadened to include patients with right-sided colon cancer, could have identified 94% of the MSI-H tumors in this study. Colorectal cancers with MSI-H were predominantly located on the right side and had an early pathological stage. The results of this study suggest that microsatellite instability test should be used for all patients under 60 years of age with right-sided colon cancer.

Increased microsatellite instability and epigenetic inactivation of the hMLH1 gene in head and neck squamous cell carcinoma

Objective The study is designed to elucidate the relationship between epigenetic silencing of the hMLH1 (human MutL homologue 1) gene and microsatellite instability (MSI) and the prognostic values of hMLH1 promoter methylation and MSI in head and neck squamous cell carcinoma (HNSCC). Study Design Cross-sectional study. Setting Tertiary referral center. Subjects and Methods A total of 120 cases of HNSCC were analyzed for hMLH1 promoter hypermethylation, protein expression, and MSI by using methylation-specific polymerase chain reaction, immunohistochemical staining, and polymerase chain reaction amplification with the use of 16 fluorescent-labeled microsatellite markers, followed by fragment analysis. Results Of 120 HNSCCs, hMLH1 promoter hypermethylation and decreased hMLH1 protein expression were shown in 39 (32.5%) and 22 (18.3%), respectively. hMLH1 promoter hypermethylation was detected in 13 of 52 (25%) normal-appearing squamous mucosa adjacent to invasive carcinoma. MSI was detected in 21 (17.5%) tumors at two or more markers and in 99 (82.5%) tumors with no evidence of MSI or at only one marker. Hypermethylation of the hMLH1 gene is significantly associated with decreased hMLH1 protein expression ( P < 0.001). High-frequency MSI was significantly associated with promoter hypermethylation ( P = 0.01) but not with decreased protein expression ( P = 0.069) of hMLH1 gene. hMLH1 promoter hypermethylation is significantly associated with decreased cause-specific survival for HNSCC patients ( P = 0.03). Conclusions Promoter hypermethylation of the hMLH1 gene could be detected early in head and neck squamous carcinogenesis and may be associated with increased MSI and poor survival in HNSCC.

12LBA A Plasma-based colorectal cancer (CRC) screening assay using DNA methylation markers - first results of multicenter studies

Background & Aims: Methylation of the hMLH1 promoter region has been suggested to cause microsatellite instability (MSI) in sporadic colorectal carcinoma (CRC). We studied the methylation profile in a wide region of the hMLH1 promoter and compared with the hMLH1 protein expression and MSI status in 88 cases of sporadic CRC. Methods: Na-bisulfite treatment and polymerase chain reaction single-strand conformation polymorphism analysis was performed using 5 sets of polymerase chain reaction primers spanning the promoter region of the hMLH1 to examine methylation status. Results were compared with immunostaining using anti-hMLH1 monoclonal antibody and MSI status of the tumor samples. Results: Methylation status was classified as full or partial methylation. Full methylation indicates the methylation of all CpG sites in the examined regions. Methylation of the hMLH1 promoter was observed in 88.9% (16 of 18) of CRCs showing high frequency MSI (MSI-H), among which 89% (14 of 16) had full methylation with reduced hMLH1 protein expression. All cases showing full methylation were proximal colon tumors with MSI-H. In cases with partial methylation, only the upstream region of the hMLH1 promoter was methylated. Partial methylation was also shown in 33.3% (6 of 18) of the normal mucosa of MSI-H cases. Frequencies of methylation were significantly correlated with female gender (P = 0.0009) and aging (P = 0.007). Conclusions: Full methylation of the hMLH1 promoter region and subsequent gene inactivation may play a crucial role in the carcinogenesis of MSI-H CRCs in the proximal colon. Methylation upstream of the hMLH1 promoter appears to be an early event in the carcinogenesis of MSI-H tumors.GASTROENTEROLOGY 2001;121:1300-1309

Chemosensitivity and Survival in Gastric Cancer Patients with Microsatellite Instability

Conflicting data exist regarding the relevance of high-frequency microsatellite instability (MSI-H) for predicting the prognosis and benefits of 5-fluorouracil (5-FU)-based chemotherapy. This study investigated the usefulness of MSI as either a prognostic indicator or predictor of distinct clinical attributes regarding the use of adjuvant chemotherapy with 5-FU and its analogues in gastric cancer. Data and tumor specimens were collected from 240 gastric cancer patients from 1993 to 2002. Five microsatellite loci were analyzed using a high-intensity microsatellite analysis reported previously. A Cox proportional hazard model was used to compare the clinical data and survival as well as any associations between MSI and 5-FU treatment status of patients with MSI or microsatellite stability (MSS) gastric cancers. A 3-(4,5-dimethyl-2-thiazolyl) -2,5-diphenyl-2H-tetrazolium bromide (MTT) assay was conducted in 168 cases to investigate chemosensitivity to 5-FU. This analysis identified 22 MSI-H (9.4%), 25 MSI-L (10.7%), and 193 MSS (79.9%) tumors. Gastric cancer with MSI-H tended to have increased likelihood to show higher age, antral location of the tumor, and lymph vessel involvement (P < 0.05). Univariate analyses failed to show any difference between the MSI-H and MSS/MSI-L groups with respect to overall survival. Furthermore, survival after the administration of 5-FU did not correlate with MSI status, and MSI was not associated with 5-FU sensitivity by MTT assay. The results of this study indicate that MSI status has no clear influence on overall survival or response to 5-FU in gastric cancer.

Efficient molecular screening of Lynch syndrome by specific 3' promoter methylation of the MLH1 or BRAF mutation in colorectal cancer with high-frequency microsatellite instability

It is sometimes difficult to diagnose Lynch syndrome by the simple but strict clinical criteria, or even by the definitive genetic testing for causative germline mutation of mismatch repair genes. Thus, some practical and efficient screening strategy to select highly possible Lynch syndrome patients is exceedingly desirable. We performed a comprehensive study to evaluate the methylation status of whole MLH1 promoter region by direct bisulfite sequencing of the entire MLH1 promoter regions on Lynch and non-Lynch colorectal cancers (CRCs). Then, we established a convenient assay to detect methylation in key CpG islands responsible for the silencing of MLH1 expression. We studied the methylation status of MLH1 as well as the CpG island methylator phenotype (CIMP) and immunohistochemical analysis of mismatch repair proteins on 16 cases of Lynch CRC and 19 cases of sporadic CRCs with high-frequency microsatellite instability (MSI-H). Sensitivity to detect Lynch syndrome by MLH1 (CCAAT) methylation was 88% and the specificity was 84%. Positive likelihood ratio (PLR) was 5.5 and negative likelihood ratio (NLR) was 0.15. Sensitivity by mutational analysis of BRAF was 100%, specificity was 84%, PLR was 6.3 and NLR was zero. By CIMP analysis; sensitivity was 88%, specificity was 79%, PLR was 4.2, and NLR was 0.16. BRAF mutation or MLH1 methylation analysis combined with MSI testing could be a good alternative to screen Lynch syndrome patients in a cost effective manner. Although the assay for CIMP status also showed acceptable sensitivity and specificity, it may not be practical because of its rather complicated assay.

Molecular Markers for Individualized Therapy in Colorectal Cancer: Progress Towards a Pharmacogenomics Array

Colorectal cancer is the second most common malignancy in the U.S. In the past 15 years we witnessed the development of new anticancer agents for patients with colorectal cancer. A multitude of therapeutic options creates a challenge for a physician to select the most efficacious and least toxic agent for an individual patient. To this end, pharmacogenomic variability in metabolic pathways for fluorouracil, capecitabine, irinotecan and oxaliplatin has been characterized. Pharmacogenomic investigations of dihydropyrimidine dehydrogenase, thymidylate synthase and thymidine phosphorylase identified a panel of clinically relevant polymorphisms for fluoropyrimidine drugs. Polymorphisms in nucleotide excision repair genes such as ERCC1 can modulate oxaliplatin exposure. For irinotecan, a polymorphism of the uridine diphosphate glucuronosyltransferase increases the risk for neutropenia. The pharmacogenomic test for this variation (UGT1A1*28) is approved by the FDA for patients who are candidates for irinotecan therapy. Disposition and activity of targeted agents, such as therapeutic antibodies bevacizumab and cetuximab, are influenced by additional genomic variations. Deficient nucleotide mismatch repair system, a hallmark of hereditary colon cancer syndrome (identified as high frequency microsatellite instability), emerged as a predictive marker for 5-fluorouracil in the adjuvant setting and the KRAS mutation as a determinant of sensitivity to anti-EGFR antibodies. Collectively, these advances establish a firm basis towards future development of an integrated pharmacogenomics array for prime time applications in the clinic to customize pharmacotherapy for colorectal cancer. We also emphasize that individualizing anticancer chemotherapy is an arduous task because drug efficacy and toxicity represent multifactorial complex traits mediated by multiple DNA sequence variants, temporal variations in gene expression, environmental factors and gene-environment interactions. Keywords: Colorectal cancer, drug metabolism, genetic polymorphism, mismatch repair, UGT1A1*28

Prognostic implications of BAX protein expression and microsatellite instability in all non-metastatic stages of primary colon cancer treated by surgery alone

This study examined whether the apoptosis-related protein, BAX, or the microsatellite-instability phenotype provide prognostic information in patients with resected colon cancer. A total of 371 stage I-III patients that previously underwent radical surgery were included (mean follow-up 51.8 months). BAX expression was examined by immunohistochemical staining; high-frequency microsatellite instability (MSI+) was determined by assessing the specific marker, BAT26, using single-strand conformation polymorphism (SSCP)-based analysis. High BAX expression was found in 66.4% of patients. MSI+ tumors were observed in 14.8% of 344 patients. Univariate analysis showed that unlike MSI, low BAX expression was significantly correlated with poor disease-specific overall survival (OS) in stages I-III (p = 0.04). Multivariate subgroup analyses revealed that unlike MSI, low BAX was an independent predictor for OS in stage II (p = 0.009); however, in stages I or III, BAX or MSI were not independent predictors of OS. In stage II colon cancer treated with surgery alone, BAX protein expression may be a predictor for prognosis.

Alternative lengthening of telomeres frequently occurs in mismatch repair system‐deficient gastric carcinoma

Maintenance of telomeric ends by the telomerase ribonucleoprotein complex or the telomerase-independent alternative lengthening of telomeres is necessary for the immortalization of human cells. The significance of alternative lengthening of telomeres has been suggested in DNA mismatch repair system-deficient cells; however, much remains unknown in human malignancies. In this study, we investigated the telomere maintenance mechanism in gastric carcinoma. In formalin-fixed and paraffin-embedded sections of the high frequency of microsatellite instability (MSI-H) and non-MSI-H gastric carcinomas, there was no difference in telomere length monitored by telomere intensity ratio using telomere-fluorescent in situ hybridization. Immunoreactivity of hTERT, the catalytic subunit of telomerase, was detected in 48% of MSI-H gastric carcinomas. The frequency was significantly lower than that in non-MSI-H gastric carcinomas (86%, P = 0.02). Conversely, the number of the alternative lengthening of telomeres-associated promyelocytic leukemia bodies (APBs) detected by combined promyelocytic leukemia immunofluorescence and telomere-fluorescent in situ hybridization was statistically higher (57%) in the MSI-H gastric carcinomas compared to that in non-MSI-H gastric carcinomas (19%, P = 0.026). The cases with hTERT(+)APBs(-) were more frequent in non-MSI-H gastric carcinomas (76%) than in MSI-H gastric carcinomas (24%), and the cases with hTERT(-)APBs(+) were more frequent in MSI-H gastric carcinomas (33%) than in non-MSI-H gastric carcinomas (10%). These results suggest that alternative lengthening of telomeres-mediated telomere maintenance plays an important role for microsatellite instability-mediated stomach carcinogenesis, as well as the telomerase ribonucleoprotein complex, although the incidence of MSI-H is low. Defects of the mismatch repair system may lead to homeologous recombination of telomeric ends for the telomerase-independent telomere maintenance in gastric carcinomas.

Genomic Instability in Colorectal Cancer; from Bench to Bed

Colorectal cancer is a disease developed by the accumulation of genomic alteration. Two genomic instability pathways, chromosomal instability pathway and microsatellite instability pathway, are known as the main pathways of the development of colorectal cancer. These are almost always mutually exclusive and tumors developed through each pathways show distinct clinicopathologic features. For the reason, molecular markers which represent each genomic instability pathways have been a candidate for translational research to find out prognostic or predictive factors. Loss of heterozygosity and aneuploidy are the hallmark of chromosomal instability and regarded as poor prognostic markers, whereas tumors with high frequency of microsatellite instability show better prognosis than microsatellite stable tumor. As a predictive factor of response from chemotherapy, loss of heterozygosity seems to be associated with a survival benefit from 5-FU adjuvant therapy. MSI-H has been reported as a predictive factor for poor response to 5-FU adjuvant chemotherapy. However, these molecular markers are not accepted to use in the clinic yet, since some of this kind of studies reported contradictory results. Further study will be needed to make more concrete evidences for these markers and to identify new molecular markers for routine use in the clinic.

Prognostic significance of macrosatellite instability in patients under 50 years of age suffering from colorectal cancer

Colorectal cancer (CRC) can arise through two distinct mutational pathways: microsatellite instability or chromosomal instability. High-frequency microsatellite instability (MSI) occurs in approximately 15 percent of sporadic cases of CRCs. Many studies have well established that MSI, the hallmark of defective DNA mismatch repair, is associated with prolonged survival of CRC patients compared with tumors that are microsatellite stable. CRCs in patients under 50 years of age are rare and represent about 5% of the total number of tumors. The aim of this study was to analyze the prognostic significance of MSI in CRC patients younger than 50 at the time of diagnosis. 31 patients with CRC under 50 years of age were tested for the presence of MSI, and compared with 35 patients aged 50 or more at the time of diagnosis. CRC-specific survival five-year-follow-up period was analyzed in relation to MSI status. The frequency of MSI among the young patients was 35.48%, which was significantly higher than the rate of 11.43% noted in older patients with CRCs (p<0.042). This study revealed no difference in survival in patients with CRCs aged less than 50 compared with those over 50 years of age. The five-years survival of young CRCs patients with MSI 81.82%, was better than that of the patients with cancers with microsatellite stability, 60%, but there was no significant difference in statistics. In our study there was no statistically detectable significant difference between tumor microsatellite status and survival in young patients, although we confirmed the previous observations that MSI is associated with better prognosis. We found that the pathological stage of CRC was an independent and powerful predictor of the clinical outcome.

Analysis of genomic instability in adult-onset celiac disease patients by microsatellite instability and loss of heterozygosis

Malignant complications of celiac disease (CD) include carcinomas and lymphomas. The genetic basis behind cancer development in CD is not known, but acquisition of genetic abnormalities and genomic instability has been involved. The aim of this study was to explore molecular characteristics of genomic instability in CD patients by analyzing microsatellite instability (MSI) and loss of heterozygosis (LOH) with carefully selected microsatellites. We genotyped small bowel biopsies and peripheral blood samples from 20 untreated CD patients using five microsatellites related to MMR genes (panel A), and five repeats associated with tumor suppressor genes, chromosome instability, inflammation, and cancer (panel B). Genomic instability was found in seven out of 20 (35%) cases at: D5S107, D18S58, GSTP, TP53 or DCC, being TP53 the most frequently affected (five out of seven cases; 71%). Microsatellite alterations were significantly found using panel B markers (P=0.04). No cases with high frequency of MSI and replication error phenotype were detected. Only one case displayed MSI-L alone. Three patients exhibited LOH and three other cases showed LOH with low level of MSI, being classified as having chromosome instability phenotype. Two novel observations were found in this study: first, the finding that non-neoplastic cells from a group of untreated CD patients present genomic instability at nucleotide level; and second, the advantage to use carefully selected microsatellites to identify celiac patients with molecular instability. Our data support the existence of chromosome instability phenotype in CD, suggesting that stable and unstable patients are genomically distinct subtypes that may follow a different evolution.

Clinical significance of signet-ring cells in colorectal mucinous adenocarcinoma

Mucin occasionally accumulates intracellularly in colorectal mucinous adenocarcinomas, resulting in signet-ring cell morphology. In the current practice of pathology, there is no definitive rule on how to report a minor component of signet-ring cells in colorectal mucinous adenocarcinomas. We hypothesized that the absence of signet-ring cell component might have a favorable effect on survival of mucinous adenocarcinoma patients. To assess the biological characteristics of colorectal mucinous adenocarcinoma, we analyzed its clinicopathological features, microsatellite instability status, and survival outcomes and compared them with those of colorectal signet-ring cell carcinoma. A total of 266 consecutive colorectal mucinous adenocarcinoma patients and 65 signet-ring cell carcinoma patients were included. Mucinous adenocarcinomas, by comparison with signet-ring cell carcinomas, were characterized by development at an older age, less frequent vascular invasion and lymph node metastasis, and lower TNM stage at presentation. A total of 21 (22%) of 95 mucinous adenocarcinomas and 12 (19%) of 63 signet-ring cell carcinomas were high-frequency microsatellite instability. Patients with mucinous adenocarcinoma had significantly better survival than those with signet-ring cell carcinoma (P<0.0001) or than those with signet-ring cell carcinoma showing >50% extracellular mucin by volume (P<0.0001). In univariate analysis, absence of signet-ring cell component (P=0.0197), absence of vascular invasion, decreased invasion depth, no lymph node metastasis, and lower TNM stage had a favorable effect on survival of mucinous adenocarcinoma patients. Absence of vascular invasion, no lymph node metastasis, and lower TNM stage had a favorable effect on survival of signet-ring cell carcinoma patients. Multivariate analysis showed that higher TNM stage and T stage 4 were independent predictors of poor outcome in patients with mucinous adenocarcinoma. Our observations strongly suggest that pathologists should report the percentage of signet-ring cell component in colorectal mucinous adenocarcinomas and mucinous adenocarcinoma has different biologic behavior compared with signet-ring cell carcinoma.

Immunohistochemical and Molecular Features of Sporadic and FAP-associated Duodenal Adenomas of the Ampullary and Nonampullary Mucosa

The pathogenesis of duodenal adenomas is not well elucidated. Much of the literature pertains to ampullary adenomas and those associated with familial adenomatous polyposis (FAP). In this study, we evaluated the molecular features of a series of sporadic duodenal adenomas (n=22) that developed distal to the ampulla, and compared them with the features of sporadic ampullary adenomas (n=9) and FAP-related polyps (n=12). Using a combination of immunohistochemical studies [cytokeratins 7 and 20, E-cadherin, beta-catenin, p53, MLH-1, MSH-2, MSH-6, and O6-methylguanine methyltransferase (MGMT)], DNA sequencing [beta-catenin, adenomatous polyposis coli (APC), p53, KRAS, and BRAF], and a polymerase chain reaction-based microsatellite instability assay; we assessed each case for abnormalities in the Wnt signaling and mitogen-activated protein kinase pathways and DNA repair mechanisms. Wnt signaling pathway abnormalities occurred in sporadic, nonampullary (82%), and ampullary (77%) adenomas at comparable rates, usually reflecting nuclear beta-catenin immunostaining (64% and 44%, respectively), and APC rather than beta-catenin, mutations. KRAS mutations were infrequent in sporadic, nonampullary adenomas (18%), and FAP-related adenomas (9%); moderately frequent in ampullary adenomas (44%); and none of the cases harbored BRAF mutations. Only 4 (13%) sporadic adenomas showed nuclear p53 staining, but no p53 mutations were detected in exons 5 to 8. Loss of O-methylguanine methyltransferase immunostaining was identified in 1 sporadic, nonampullary adenoma, and none of the polyps in any group showed loss of MLH-1, MSH-2, or MSH-6 staining, or high-frequency microsatellite instability. We conclude that sporadic and FAP-related adenomas show similar molecular features, regardless of their anatomic location. Similar to colorectal adenomas, they harbor APC and KRAS mutations; but BRAF mutations, p53 alterations, and DNA mismatch repair abnormalities are rare.

Foxp3 and microsatellite stability phenotype in colorectal cancer

Colorectal tumourigenesis is in the majority of cases regarded as a multistep process resulting in chromosomal instability.1 High-frequency microsatellite instability (MSI-H) can be detected in ∼15–20% of all sporadic colorectal...

Immunohistochemical expression of folate receptor α in colorectal carcinoma: patterns and biological significance

Folate receptor alpha (FRalpha) has emerged as a potential cancer therapy target with several folate-linked therapeutic agents currently undergoing clinical trials. In addition, FRalpha expression in tumors may offer prognostic significance. Most studies on FRalpha expression used reverse transcriptase polymerase chain reaction or cytofluorimetric assays. The applicability of such methods to paraffin-embedded tissues is limited. The aims of this study were to assess the feasibility of immunohistochemistry in detecting FRalpha expression and to assess the patterns and clinical significance of FRalpha expression in colorectal tissues. We used tissue microarrays containing 152 normal colorectal mucosa samples, 42 adenomas, 177 primary, and 52 metastatic colorectal carcinomas. Our results showed that staining for FRalpha on colorectal tissues was simple and easy to read. FRalpha positivity was more frequent in carcinomas (33% in primaries and 44% in metastases) than in normal mucosa or adenoma (7% in both) (P < .001). Positive staining in primary carcinomas correlated with younger age (n = 130) (P = .008), presence of distant metastasis (n = 130) (P = .043), and non-high-frequency microsatellite instability status (as detected by the standard polymerase chain reaction method using the 5 National Cancer Institute-recommended markers) (n = 77) (P = .006). Positive staining in primary carcinomas also correlated with a worse 5-year disease-specific survival (P = .04) on univariate but not multivariate analysis. Thus, our data show that there is selective expression of FRalpha in some colorectal cancers, providing a foundation for investigating the use of folate conjugates for imaging and therapy of colorectal tumors. Furthermore, our results suggest that a possible association exists between FRalpha expression and the microsatellite instability status in colorectal carcinoma. The significance of such an association as well as the prognostic value of FRalpha expression deserves further exploration.

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.

Tumor histology helps to identify Lynch syndrome among colorectal cancer patients

To determine the value of histology in identifying Lynch syndrome among those patients with early onset of colorectal cancer (CRC). Demographic, clinical and cancer history data from patients diagnosed with CRC before 60 years of age, and treated at our institution between 1997 and 2005, were collected from medical records and direct interview. Their tumors were assessed to identify histological features suggestive of high frequency microsatellite instability (MSI-H): tumor infiltrating lymphocytes, Crohn's like inflammatory reaction, mucinous, signet ring cells, medullary growth pattern and then, tested for microsatellite instability (MSI) and MLH1/ MSH2 protein expression. Sixty-five patients were included in the study. The mean age at diagnosis was 48 +/- 9.9 years. Overall, 28 (43%) patients, including 13 of 35 diagnosed between ages 50 and 60, had tumor demonstrating one or more histological features suggestive of MSI-H. These patients were younger (45 vs. 50 years, P = 0.02) and more commonly had family history of Lynch syndrome-related cancers (36 vs. 19%), though the latter feature did not reach statistical significance (P = 0.07). Eleven of 25 tumors with MSI-H histology, but only 1 of 29 tumors without special histological features were found to be MSI-H (P < 0.0001). Histology had a positive predictive value of 44% and a negative predictive value of 97% for identifying MSI-H tumors. Limiting MSI analysis only to those tumors with suggestive histology would have reduced the need for testing by nearly 60% of all tumors from patients that met the revised Bethesda guidelines.

Microsatellite stable genome in an epithelioid hemangioendothelioma: An example of a microsatellite stable tumor

Microsatellite stable genome in an epithelioid hemangioendothelioma: An example of a microsatellite stable tumor

Café‐au‐lait macules and pediatric malignancy caused by biallelic mutations in the DNA mismatch repair (MMR) gene PMS2

A 14-year-old male presented with a T4 sigmoid adenocarcinoma, <10 colonic adenomas and multiple café-au-lait macules. Family history was not suggestive of a dominant hereditary form of colorectal cancer. Evaluation of the tumor revealed abnormal immunohistochemical staining of the PMS2 protein and high frequency microsatellite instability. Germline analysis identified biallelic PMS2 missense mutations. A new cancer syndrome caused by biallelic mutations in the mismatch repair genes, including PMS2, is now emerging and is characterized by café-au-lait macules, colonic polyps and a distinctive tumor spectrum.

Microsatellite Instability in Benign and Malignant Thyroid Neoplasms

Microsatellite instability (MSI) is a form of genomic instability that has recently been implicated in the pathogenesis of thyroid cancer. The purpose of this study was to further define the distribution of MSI in both normal and neoplastic thyroid follicular epithelium. Using laser capture microdissection, cells from both normal and tumor tissue were individually collected. Polymerase chain reaction amplification of the DNA was then performed using six dinucleotide and two mononucleotide microsatellite markers. Forty benign and malignant thyroid tumors were compared with their adjacent normal thyroid follicular tissue and were analyzed for MSI. Nine of 14 papillary thyroid carcinomas and 10/16 of follicular thyroid carcinomas demonstrated MSI at > or =30-40% of loci tested. For benign follicular adenomas, 9/10 demonstrated microsatellite stability or low-frequency MSI. MSI appears to play a role in thyroid pathogenesis as evidenced by the high frequency of MSI in malignant thyroid neoplasms. In addition our study showed a significant difference in MSI frequency between follicular adenomas and follicular carcinomas. More importantly, the technique of laser capture microdissection allows for more accurate selection of benign, malignant, and normal DNA.