Isolated loss of PMS2 expression in colorectal cancers: frequency, patient age, and familial aggregation

Diabetes mellitus impacts on expression of DNA mismatch repair protein PMS2 and tumor microenvironment in pancreatic ductal adenocarcinoma

AIMS/INTRODUCTION

The mismatch repair (MMR) protein recognizes DNA replication errors and plays an important role in tumorigenesis, including pancreatic ductal adenocarcinoma (PDAC). Although PMS2, a MMR protein, is degraded under oxidative stress, the effects of diabetes are still unclear. Herein, we focused on whether diabetes affected MMR protein expression in PDAC.

MATERIALS AND METHODS

Tissues from 61 surgically resected PDAC subjects were clinicopathologically analyzed. Immunohistochemical analysis was performed for MMR protein expression, oxidative stress, and immune cell infiltration. The change of MMR protein expression was assessed in PDAC cell lines under stimulation with 25 mM glucose and 500 μM palmitic acid. Survival curves were analyzed by the Kaplan-Meier method with the log-rank test.

RESULTS

Diabetes complicated with dyslipidemia significantly decreased the expression of PMS2 in PDAC tissues with an inverse correlation with the degree of oxidative stress. Palmitic acid combined with high glucose induced degradation of PMS2 protein, enhancing oxidative stress in vitro. CD8⁺ T-cell infiltration was associated with a short duration of type 2 diabetes (≤4 years) and a low expression of PMS2 in PDAC tissues, while CD163⁺ tumor-associated macrophage infiltration was increased with a long duration of diabetes (>4 years). A short duration of diabetes exhibited a better prognosis than nondiabetic subjects with PDAC (P < 0.05), while a long duration of diabetes had a worse prognosis (P < 0.05).

CONCLUSIONS

The different phases of diabetes have a major impact on PDAC by altering PMS2 expression and the tumor immune microenvironment, which can be targeted by an immune checkpoint inhibitor.

Biallelic PMS2 Mutations in a Family with Uncommon Clinical and Molecular Features

We describe a patient with constitutional mismatch repair-deficiency (CMMR-D) in whom the syndrome started at age 10 with the development of multiple adenomas in the large bowel. In the successive 25 years, four malignancies developed in different organs (rectum, ileum, duodenum, and lymphoid tissue). The patient had biallelic constitutional pathogenic variants in the PMS2 gene. We speculate that besides the PMS2 genotype, alterations of other genes might have contributed to the development of the complex phenotype. In the nuclear family, both parents carried different PMS2 germline mutations. They appeared in good clinical condition and did not develop polyps or cancer. The index case had a brother who died at age three of lymphoblastic leukemia, and a sister who was affected by sarcoidosis. Tumor tissue showed diffuse DNA microsatellite instability. A complete absence of immunoreactivity was observed for the PMS2 protein both in the tumors and normal tissues. Next-generation sequencing and multiple ligation-dependent probe amplification analyses revealed biallelic PMS2 germline pathogenic variants in the proband (genotype c.[137G>T];[(2174+1_2175-1)_(*160_?)del]), and one of the two variants was present in both parents—c.137G>T in the father and c.(2174+1-2175-1)_(*160_?)del in the mother—as well as c.137G>T in the sister. Moreover, Class 3 variants of MSH2 (c.1787A>G), APC (c.1589T>C), and CHEK2 (c.331G>T) genes were also detected in the proband. In conclusion, the recognition of CMMR-D may sometimes be difficult; however, the possible role of constitutional alterations of other genes in the development of the full-blown phenotype should be investigated in more detail.

An unusual phenotype occurs in 15% of mismatch repair-deficient tumors and is associated with non-colorectal cancers and genetic syndromes

Immunohistochemistry (IHC) and/or MSI-PCR (microsatellite instability-polymerase chain reaction) tests are performed routinely to detect mismatch repair deficiency (MMR-D). Classical MMR-D tumors present a loss of MLH1/PMS2 or MSH2/MSH6 with MSI-High. Other profiles of MMR-D tumors have been described but have been rarely studied. In this study, we established a classification of unusual MMR-D tumors and determined their frequency and clinical impact. All MMR-D tumors identified between 2007 and 2017 were selected. Any profile besides the classical MMR-D phenotype was defined as unusual. For patients with unusual MMR-D tumors, IHC, and PCR data were reviewed, the tumor mutation burden (TMB) was evaluated and clinical and genetic features were collected. Of the 4948 cases of MMR testing, 3800 had both the available IHC and MSI-PCR results and 585 of these had MMR-D. After reviewing the IHC and PCR, 21% of the cases initially identified as unusual MMR-D were reclassified, which resulted in a final identification of 89 unusual MMR-D tumors (15%). Unusual MMR-D tumors were more often associated with non-CRC than classical MMR-D tumors. Unusual MMR-D tumors were classified into four sub-groups: i) isolated loss of PMS2 or MSH6, ii) classical loss of MLH1/PMS2 or MSH2/MSH6 without MSI, iii) four MMR proteins retained with MSI and, iv) complex loss of MMR proteins, with clinical characteristics for each sub-group. TMB-high or -intermediate was shown in 96% of the cancers studied (24/25), which confirmed MMR deficiency. Genetic syndromes were identified in 44.9% (40/89) and 21.4% (106/496) of patients with unusual and classical MMR-D tumors, respectively (P < 0.001). Five patients treated with an immune checkpoint inhibitor (ICI) had a prolonged clinical benefit. Our classification of unusual MMR-D phenotype helps to identify MMR deficiency. Unusual MMR-D phenotype occurs in 15% of MMR-D tumors. A high frequency of genetic syndromes was noted in these patients who could benefit from ICI.

Characteristics of colorectal carcinoma patients with PMS2 defects detected by immunohistochemistry

Lynch syndrome is the most prevalent form of familial colorectal cancer (CRC) and is caused by pathogenic germline mismatch repair (MMR) gene mutations. MLH1, MSH2 and MSH6 mutations have been well studied, but the rate and characteristics of PMS2 mutations are rare, especially in China. This study enrolled 1706 unselected patients with CRC who underwent colorectal resection from June 2016 to November 2018, the MMR status and clinicopathological features were analysed. A total of 11.8% of patients with CRC had defects in at least one MMR-related protein. Among them, 8.3% were identified with PMS2 defects, and 3.1% of patients had isolated PMS2 defects. Compared with MMR-proficient CRC, PMS2-defect CRC occurred more frequently in the right colon and less frequently in the rectum, had more poorly differentiated and mucinous carcinoma cases, and had fewer perineural invasions and a lower pN stage but a more advanced pT stage and a larger tumour size. In the cases with PMS2 defect, there were fewer tumours in the right colon, fewer poorly differentiated cases and smaller tumour sizes than in the cases with both MLH1 and PMS2 defects. In addition, in cases with isolated PMS2 defects, there were more tumours in the right colon and, more mucinous carcinoma cases than in cases with MMR-proficient CRCs, but had a similar cancer onset age. This study identified the rate, clinicopathological and age characteristics of PMS2 defects in CRCs in China and highlighted the importance of universal screening and germline detection of PMS2 in CRC.

A Novel Germline MLH1 In-Frame Deletion in a Slovenian Lynch Syndrome Family Associated with Uncommon Isolated PMS2 Loss in Tumor Tissue

The diagnostics of Lynch syndrome (LS) is focused on the detection of DNA mismatch repair (MMR) system deficiency. MMR deficiency can be detected on tumor tissue by microsatellite instability (MSI) using molecular genetic test or by loss of expression of one of the four proteins (MLH1, MSH2, MSH6, and PMS2) involved in the MMR system using immunohistochemistry (IHC) staining. According to the National Comprehensive Cancer Network (NCCN) guidelines, definitive diagnosis of LS requires the identification of the germline pathogenic variant in one of the MMR genes. In the report, we are presenting interesting novel MLH1 in-frame deletion LRG_216t1:c.2236_2247delCTGCCTGATCTA p.(Leu746_Leu749del) associated with LS. The variant appears to be associated with uncommon isolated loss of PMS2 immunohistochemistry protein staining (expression) in tumor tissue instead of MLH1 and PMS2 protein loss, which is commonly seen with pathogenic variants in MLH1. The variant was classified as likely pathogenic, based on segregation analysis and molecular characterization of blood and tumor samples. According to the American College of Medical Genetics (ACMG) guidelines, the following evidence categories of PM1, PM2, PM4, and PP1 moderate have been used for classification of the novel variant. By detecting and classifying the novel MLH1 variant as likely pathogenic, we confirmed the LS in this family.

MMR deficiency in urothelial carcinoma of the bladder presents with temporal and spatial homogeneity throughout the tumor mass

BACKGROUND

Microsatellite instability (MSI), a hypermutator phenotype described in many cancers, has emerged as a predictive biomarker for immune checkpoint inhibitor therapy. Cancer heterogeneity represents a potential obstacle for the analysis of predicitive biomarkers. MSI has been reported in bladder cancer, but data on the possible extent of intratumoral heterogeneity are lacking.

METHODS

To study MSI heterogeneity in bladder cancer, a tissue microarray (TMA) comprising 598 muscle-invasive urothelial carcinomas of the bladder was utilized to screen for MSI by immunhistochemistry with antibodies for MLH1, PMS2, MSH2, and MSH6.

RESULTS

In 9 cases suspicious for MSI, MMR status was further evaluated by large section examination and polymerase chain reaction (PCR)-based analysis of microsatellites ("Bethesda panel") resulting in the identification of 5 validated MSI cases from 448 interpretable cancers (prevalence 1.1%). MMR deficiency always involved PMS2 loss, in 3 cases with additional loss or reduction of MLH1 expression. Four cancers were MSI-high and 1 was MSI-low in the PCR analysis. Parallel sequencing revealed an inactivating MLH1 mutation in 1 tumor but no further known pathogenic MMR gene mutations were found. Immunostaining of all available 72 cancer-containing tissue blocks of the 5 confirmed bladder cancer with MSI including prior and subsequent biopsies showed complete homogeneity of the MMR protein defects and the status of the 4 MMR proteins did not markedly change in sequential resections. In all 4 cases with noninvasive precursor lesions, MSI was also detectable.

CONCLUSION

These data suggest that MSI occurs early in invasive bladder cancer and immunohistochemical MMR analysis on limited biopsy material is sufficient to estimate MMR status of the entire cancer mass.

Unique MLH1 mutations in colonic adenomas in an obligate germline Lynch syndrome carrier

BACKGROUND

An obligate germline Lynch syndrome carrier had four colonic adenomas removed.

MATERIALS AND METHODS

The adenomas were evaluated for grade of dysplasia, MLH1, PMS2, MSH2 and MSH6 protein expression, microsatellite instability (MSI), BRAF, methylation status and a next-generation sequencing (NGS) panel of 52 cancer genes.

RESULTS

There were four tubular or tubulovillous adenomas from the hepatic flexure, rectosigmoid and rectum; one with low-grade and high-grade dysplasia, one with high-grade dysplasia only and two with low-grade dysplasia. All four adenomas showed retention of MLH1, MHS2 and MSH6 but complete loss of PMS2 in both low-grade and high-grade dysplasia areas.Two of the four adenomas were MSI-high, BRAF V600E wild type and were not MLH1 methylated. NGS identified an MLH1 germline variant: NM_000249.3: c.1558+1 G>A, p.(?) in all tissue (adenomas and normal), which likely explains the pathophysiology of Lynch syndrome in this patient. Other variants were also detected in MLH1 and MSH6 in all four adenomas tested; these being reported previously in somatic colorectal cancers.

CONCLUSION

We highlight an MLH1 variant in the colonic adenomas in an obligate Lynch syndrome carrier that resulted in PMS2 protein loss in the absence of mutations of the PMS2 gene.

An alternative approach to establishing unbiased colorectal cancer risk estimation in Lynch syndrome

PURPOSE

Biallelic pathogenic variants in the mismatch repair (MMR) genes cause a recessive childhood cancer predisposition syndrome known as constitutional mismatch repair deficiency (CMMRD). Family members with a heterozygous MMR variant have Lynch syndrome. We aimed at estimating cancer risk in these heterozygous carriers as a novel approach to avoid complicated statistical methods to correct for ascertainment bias.

METHODS

Cumulative colorectal cancer incidence was estimated in a cohort of PMS2- and MSH6-associated families, ascertained by the CMMRD phenotype of the index, by using mutation probabilities based on kinship coefficients as analytical weights in a proportional hazard regression on the cause-specific hazards. Confidence intervals (CIs) were obtained by bootstrapping at the family level.

RESULTS

The estimated cumulative colorectal cancer risk at age 70 years for heterozygous PMS2 variant carriers was 8.7% (95% CI 4.3-12.7%) for both sexes combined, and 9.9% (95% CI 4.9-15.3%) for men and 5.9% (95% CI 1.6-11.1%) for women separately. For heterozygous MSH6 variant carriers these estimates are 11.8% (95% CI 4.5-22.7%) for both sexes combined, 10.0% (95% CI 1.83-24.5%) for men and 11.7% (95% CI 2.10-26.5%) for women.

CONCLUSION

Our findings are consistent with previous reports that used more complex statistical methods to correct for ascertainment bias. These results underline the need for MMR gene-specific surveillance protocols for Lynch syndrome.

Circulating Lymphocytes, PD-L1 Expression on Tumor-infiltrating Lymphocytes, and Survival of Colorectal Cancer Patients with Different Mismatch Repair Gene Status

Clinical outcomes of checkpoint blockade immunotherapy on colorectal cancer (CRC) are influenced by mismatch repair (MMR) gene status, which is associated with distinct tumor immune infiltrates and systemic inflammatory response status. However, the prognostic value of PD-L1 expression and the systemic inflammatory response for patients with MMR deficiency has not been fully investigated. In this study, we examined the association of systemic inflammatory markers, PD-1/PD-L1 pathway expression, microsatellite instability (MSI) status, and clinicopathological characteristics of CRC with patient survival between MMR-deficient (dMMR) group (N=168) and MMR-proficient (pMMR) group (N=169). We found a large proportion of dMMR CRC patients displayed increased level of systemic inflammatory markers such as C-reactive protein, Neutrophil/Lymphocyte Ratio (NLR), Glasgow Prognostic Score (GPS), and low expression of PD-L1 in tumor stroma. Several systemic inflammatory markers were associated with AJCC stage only in dMMR patients. Similarly, Tumor infiltrating lymphocyte (TIL) PD-L1 or stroma PD-L1 expression was associated with AJCC stage only in dMMR patients. Circulating serum lymphocytes and TIL PD-L1 expression are both independent prognosis predictors for CRC patients. Overall, we found that dMMR CRC displayed a comprehensively distinct tumor immune microenvironment and systemic inflammatory response makers. PD-L1 expression at different location has different impacts on CRC patient survival, and the TIL PD-L1 expression might be a potential predictor for dMMR CRC patient response to anti-PD-1 therapy.

Expending Role of Microsatellite Instability in Diagnosis and Treatment of Colorectal Cancers

Background

Colorectal carcinomas with high-frequency microsatellite instability (MSI-H) account for 15% of all colorectal cancers, including 12% of sporadic cases and 3% of cancers associated with Lynch syndrome (also known as hereditary nonpolyposis colorectal cancer syndrome, HNPCC). Lynch syndrome is an autosomal dominant hereditary cancer syndrome, caused by germline mutations in mismatch repair genes, including MLH1, MSH2, MSH6 and PMS2.

Methods

Published articles from peer-reviewed journals were obtained from PubMed, Google Scholar and Clinicaltrials.gov. Based on the recent research data, we provide an update on the MSI testing, along with the evolving role of MSI in diagnosis, prognosis and treatment of colorectal cancers.

Results

Studies have led to significant advances in the molecular pathogenesis and clinicopathological characteristics of MSI-H colorectal cancers. Emerging evidence suggests that colorectal cancers with MSI-H show different outcome and treatment response from those with microsatellite stable (MSS) tumors. Therefore, MSI testing is essential not only in the genetic context, but it may also have important prognostic and predictive value of response to chemotherapy and immunotherapy.

Conclusions

Many experts and professional authorities have recommended a universal MSI testing in all individuals newly diagnosed with colorectal cancers.

Cancer molecular markers: A guide to cancer detection and management

Cancer is generally caused by the molecular alterations which lead to specific mutations. Advances in molecular biology have provided an impetus to the study of cancers with valuable prognostic and predictive significance. Over the hindsight various attempts have been undertaken by scientists worldwide, in the management of cancer; where, we have witnessed a number of molecular markers which allow the early detection of cancers and lead to a decrease in its mortality rate. Recent advances in oncology have led to the discovery of cancer markers that has allowed early detection and targeted therapy of tumors. In this context, current review provides a detail outlook on various molecular markers for diagnosis, prognosis and management of therapeutic response in cancer patients.

Colorectal Carcinomas With Isolated Loss of PMS2 Staining by Immunohistochemistry

Context.—

Isolated loss of PMS2 staining is an uncommon immunophenotype in colorectal carcinomas, accounting for approximately 4% of tumors with microsatellite instability. Limited information regarding these tumors is available in the literature.

Objective.—

To compare the clinicopathologic features of colorectal carcinomas with isolated PMS2 loss by immunohistochemistry to those with other forms of mismatch repair deficiency.

Design.—

Ninety-three colorectal carcinomas with isolated PMS2 loss by immunohistochemistry and 193 with other forms of mismatch repair deficiency were identified. Forty (43%) of the isolated PMS2 loss cases and 35 control cases (18%) had a known germline mutation or a clinical diagnosis of Lynch syndrome.

Results.—

Overall, isolated PMS2-loss tumors occurred in significantly younger patients (P &lt; .001) and in fewer female patients (P = .006). These tumors were significantly less likely to be right-sided (P = .001), high-grade (P = .01), or display histologic features of microsatellite instability (P &lt; .001). The isolated PMS2-loss group also exhibited increased odds of disease-specific death (odds ratio [OR], 3.09; 95% CI, 1.41–6.85; P = .007). When the analysis was restricted to germline mutation/Lynch syndrome cases and controls, no significant differences were detected for age, sex, tumor location, tumor grade, histologic features, or distant metastases, although a trend toward increased odds of disease-specific death in the isolated PMS2-loss group was evident (OR, 3.87; 95% CI, 0.89–27.04; P = .10).

Conclusions.—

Unusual clinicopathologic features observed in colorectal carcinomas with isolated PMS2 loss are likely related to the high proportion of cases caused by germline mutations. Isolated PMS2-loss tumors may demonstrate more aggressive behavior than other tumors with microsatellite instability, but larger studies are needed to investigate that possibility further.

The 116G > A MSH6 and IVS1-1121C > T PMS2 Genes Polymorphisms Modulate the Risk of the Sporadic Colorectal Cancer Development in Polish Population

Colorectal cancer (CRC) is one of the most common cancers worldwide. DNA mismatch repair (MMR) is an evolutionarily conserved process that corrects mismatches generated during DNA replication. MMR defects were found to be associated with hereditary non-polyposis colorectal cancer (HNPCC) and a subset of sporadic colon cancers. The inheritance of common variations in MMR genes may influences individual susceptibility to the development of colorectal cancer. The purpose of the study was to evaluate the association between gene polymorphisms Glu39Gly (c.116G > A) of MSH6 gene and IVS1-1121C > T of PMS2 gene and sporadic colorectal cancer risk, in a case-control study comprising 200 patients and 200 controls origination from polish population. DNA was isolated from peripheral blood lymphocytes of enrolled patients, and gene polymorphisms were analysed by restriction fragment length polymorphism-polymerase chain reaction (RFLP-PCR) for MSH6 and TaqMan for PMS2. G/A variant of Glu39Gly (c.116G > A) genotype was associated with an increased risk of colorectal cancer (OR 1,65 95%CI:1,01-2,69 p = 0.44). Presence of A allele was also significantly higher in patient with CRC (OR 1,57 95% CI: 1,04-2,38 p = 0.032). Prevalence of this genotype was also markedly higher in females and patients above 60 years in CRC group (OR 2.25 95%CI: 1.22-4.14 p = 0.0098 and OR 2.74 95% CI: 1.27-5.93 p = 0.0097 respectively). None of such correlations was observed for genotype variants of IVS1-1121C > T PMS2. In conclusion, our data suggests thatMSH6 Glu39Gly polymorphism is associated with the risk of developing sporadic colorectal cancer in polish population. Linkage to the female gender, onset above 60 years old and further increase of risk when combined with wild-type allele of PMS2 IVS1-1121C > T polymorphism indicates defective mismatch repair system.

Hereditary Syndromes Manifesting as Endometrial Carcinoma: How Can Pathological Features Aid Risk Assessment?

Endometrial carcinoma is the most common gynecological tumor worldwide. It can be the presenting malignancy, acting as the harbinger, of an undiagnosed hereditary syndrome. Up to 50% of females with Lynch syndrome present in this manner. Differentiation between Lynch, Muir-Torre, and Cowden syndromes can at times be challenging due to the overlapping features. Our review emphasizes on the strengths, pitfalls, and limitations of microscopic features as well as immunohistochemical and polymerase chain reaction- (PCR-) based tests used by laboratories to screen for DNA mismatch repair (MMR) and PTEN gene mutations in patients to enable a more targeted and cost effective approach in the use of confirmatory gene mutational analysis tests. This is crucial towards initiating timely and appropriate surveillance measures for the patient and affected family members. We also review the evidence postulating on the possible inclusion of uterine serous carcinoma as part of the spectrum of malignancies seen in hereditary breast and ovarian carcinoma syndrome, driven by mutations in BRCA1/2.

PMS2 monoallelic mutation carriers: the known unknown

Germ-line mutations in MLH1, MSH2, MSH6, and PMS2 have been shown to cause Lynch syndrome. The penetrance of the cancer and tumor spectrum has been repeatedly studied, and multiple professional societies have proposed clinical management guidelines for affected individuals. Several studies have demonstrated a reduced penetrance for monoallelic carriers of PMS2 mutations compared with the other mismatch repair (MMR) genes, but clinical management guidelines have largely proposed the same screening recommendations for all MMR gene carriers. The authors considered whether enough evidence existed to propose new screening guidelines specific to PMS2 mutation carriers with regard to age at onset and frequency of colonic screening. Published reports of PMS2 germ-line mutations were combined with unpublished cases from the authors' research registries and clinical practices, and a discussion of potential modification of cancer screening guidelines was pursued. A total of 234 monoallelic PMS2 mutation carriers from 170 families were included. Approximately 8% of those with colorectal cancer (CRC) were diagnosed before age 30, and each of these tumors presented on the left side of the colon. As it is currently unknown what causes the early onset of CRC in some families with monoallelic PMS2 germline mutations, the authors recommend against reducing cancer surveillance guidelines in families found having monoallelic PMS2 mutations in spite of the reduced penetrance.Genet Med 18 1, 13-19.

Mismatch repair mRNA and protein expression in intestinal adenocarcinoma in sika deer (Cervus nippon) resembling heritable non-polyposis colorectal cancer in man

Intestinal adenocarcinomas seen in an inbred herd of farmed sika deer (Cervus nippon) morphologically resembled human hereditary non-polyposis colorectal cancer (HNPCC). Features common to both included multiple de novo sites of tumourigenesis in the proximal colon, sessile and non-polyposis mucosal changes, the frequent finding of mucinous type adenocarcinoma, lymphocyte infiltration into the neoplastic tubules and Crohn's-like lymphoid follicles at the deep margin of the tumour. HNPCC is defined by a germline mutation of mismatch repair (MMR) genes resulting in their inactivation and loss of expression. To test the hypothesis that similar MMR gene inactivation occurs in the deer tumours, the expression of the four most important MMR genes, MSH2, MLH1, MSH6 and PMS2, was examined at the mRNA level by reverse transcriptase polymerase chain reaction (n = 12) and at the protein level by immunohistochemistry (n = 40) in tumour and control tissues. All four genes were expressed equally in normal and neoplastic tissues, so MMR gene inactivation could not be implicated in the carcinogenesis of this tumour in sika deer.

Involvement of p53 mutation and mismatch repair proteins dysregulation in NNK-induced malignant transformation of human bronchial epithelial cells

Genome integrity is essential for normal cellular functions and cell survival. Its instability can cause genetic aberrations and is considered as a hallmark of most cancers. To investigate the carcinogenesis process induced by tobacco-specific carcinogen NNK, we studied the dynamic changes of two important protectors of genome integrity, p53 and MMR system, in malignant transformation of human bronchial epithelial cells after NNK exposure. Our results showed that the expression of MLH1, one of the important MMR proteins, was decreased early and maintained the downregulation during the transformation in a histone modification involved and DNA methylation-independent manner. Another MMR protein PMS2 also displayed a declined expression while being in a later stage of transformation. Moreover, we conducted p53 mutation analysis and revealed a mutation at codon 273 which led to the replacement of arginine by histidine. With the mutation, DNA damage-induced activation of p53 was significantly impaired. We further reintroduced the wild-type p53 into the transformed cells, and the malignant proliferation can be abrogated by inducing cell cycle arrest and apoptosis. These findings indicate that p53 and MMR system play an important role in the initiation and progression of NNK-induced transformation, and p53 could be a potential therapeutic target for tobacco-related cancers.

Molecular testing for lymph node metastases as a determinant of colon cancer recurrence: results from a retrospective multicenter study

PURPOSE

Recurrence risk assessment to make treatment decisions for early-stage colon cancer patients is a major unmet medical need. The aim of this retrospective multicenter study was to evaluate the clinical utility of guanylyl cyclase C (GCC) mRNA levels in lymph nodes on colon cancer recurrence.

METHODS

The proportion of lymph nodes with GCC-positive mRNA (LNR) was evaluated in 463 untreated T3N0 patients, blinded to clinical outcomes. One site's (n = 97) tissue grossing method precluded appropriate lymph node assessment resulting in post hoc exclusion. Cox regression models tested the relationship between GCC and the primary endpoint of time to recurrence. Assay methods, primary analyses, and cut points were all prespecified.

RESULTS

Final dataset contained 366 patients, 38 (10%) of whom had recurrence. Presence of four or more GCC-positive lymph nodes was significantly associated with risk of recurrence [hazard ratio (HR) = 2.46, 95% confidence interval (CI), 1.07-5.69, P = 0.035], whereas binary GCC LNR risk class (HR = 1.87, 95% CI, 0.99-3.54, P = 0.054) and mismatch repair (MMR) status (HR = 0.77, 95% CI, 0.36-1.62, P = 0.49) were not. In a secondary analysis using a 3-level GCC LNR risk group classification of high (LNR > 0.20), intermediate (0.10 < LNR ≤ 0.20), and low (LNR ≤ 0.10), high-risk patients had a 2.5 times higher recurrence risk compared with low-risk patients (HR = 2.53, 95% CI, 1.24-5.17, P = 0.011).

CONCLUSIONS

GCC status is a promising prognostic factor independent of traditional histopathology risk factors in a contemporary population of patients with stage IIa colon cancer not treated with adjuvant therapy, but GCC determination must be performed with methodology adapted to the tissue procurement and fixation technique.

The Norwegian PMS2 founder mutation c.989-1G > T shows high penetrance of microsatellite instable cancers with normal immunohistochemistry

Background

Using immunohistochemistry (IHC) to select cases for mismatch repair (MMR) genetic testing, we failed to identify a large kindred with the deleterious PMS2 mutation c.989-1G > T. The purpose of the study was to examine the sensitivity of IHC and microsatellite instability-analysis (MSI) to identify carriers of the mutation, and to estimate its penetrance and expressions.

Methods

All carriers and obligate carriers of the mutation were identified. All cancer diagnoses were confirmed. IHC and MSI-analysis were performed on available tumours. Penetrances of cancers included in the Amsterdam and the Bethesda Criteria, for MSI-high tumours and MSI-high and low tumours were calculated by the Kaplan-Meier algorithm.

Results

Probability for co-segregation of the mutation and cancers by chance was 0.000004. Fifty-six carriers or obligate carriers were identified. There was normal staining for PMS2 in 15/18 (83.3%) of tumours included in the AMS1/AMS2/Bethesda criteria. MSI-analysis showed that 15/21 (71.4%) of tumours were MSI-high and 4/21 (19.0%) were MSI-low. Penetrance at 70 years was 30.6% for AMS1 cancers (colorectal cancers), 42.8% for AMS2 cancers, 47.2% for Bethesda cancers, 55.6% for MSI-high and MSI-low cancers and 52.2% for MSI-high cancers.

Conclusions

The mutation met class 5 criteria for pathogenicity. IHC was insensitive in detecting tumours caused by the mutation. Penetrance of cancers that displayed MSI was 56% at 70 years. Besides colorectal cancers, the most frequent expressions were carcinoma of the endometrium and breast in females and stomach and prostate in males.

Discovery of novel non-synonymous SNP variants in 988 candidate genes from 6 centenarians by target capture and next-generation sequencing

Despite evidence of a substantial genetic component, the genetic factors that underlie longevity in humans remain to be identified. Previous genome-wide linkage and association studies have not found strong evidence for the contribution of common variants besides the APOE gene, suggesting the role of rare variants in human longevity. To discover rare variants that might contribute to longevity, we selected 988 candidate genes and performed a pilot study to identify novel non-synonymous variants in 6 Ashkenazi Jewish centenarians older than 105. Our candidate genes act in pathways implicated in aging and longevity, including neurodegeneration, cognitive function, lipid metabolism, DNA repair, and genome maintenance. By implementing custom-designed Agilent SureSelect target capture and next-generation sequencing, we discovered a total of 89 novel non-synonymous SNPs (nsSNPs) and validated 51 nsSNPs by iPLEX MassArray assays. Genotyping analysis of these novel SNPs in 410 Ashkenazi Jewish controls and 390 centenarians showed significant enrichment (5.3 fold, p = 0.02) of the p.Y318C variant in PMS2 and significant depletion (7.5 fold, p = 0.04) of the p.V465A variant in GABRR3 in centenarians compared to controls. Our study presents the potential of targeted next-generation sequencing for discovery of rare but functional genetic variation which may lead to exceptional longevity in humans.

A systems biology approach to the global analysis of transcription factors in colorectal cancer

Background

Biological entities do not perform in isolation, and often, it is the nature and degree of interactions among numerous biological entities which ultimately determines any final outcome. Hence, experimental data on any single biological entity can be of limited value when considered only in isolation. To address this, we propose that augmenting individual entity data with the literature will not only better define the entity’s own significance but also uncover relationships with novel biological entities.

To test this notion, we developed a comprehensive text mining and computational methodology that focused on discovering new targets of one class of molecular entities, transcription factors (TF), within one particular disease, colorectal cancer (CRC).

Methods

We used 39 molecular entities known to be associated with CRC along with six colorectal cancer terms as the bait list, or list of search terms, for mining the biomedical literature to identify CRC-specific genes and proteins. Using the literature-mined data, we constructed a global TF interaction network for CRC. We then developed a multi-level, multi-parametric methodology to identify TFs to CRC.

Results

The small bait list, when augmented with literature-mined data, identified a large number of biological entities associated with CRC. The relative importance of these TF and their associated modules was identified using functional and topological features. Additional validation of these highly-ranked TF using the literature strengthened our findings. Some of the novel TF that we identified were: SLUG, RUNX1, IRF1, HIF1A, ATF-2, ABL1, ELK-1 and GATA-1. Some of these TFs are associated with functional modules in known pathways of CRC, including the Beta-catenin/development, immune response, transcription, and DNA damage pathways.

Conclusions

Our methodology of using text mining data and a multi-level, multi-parameter scoring technique was able to identify both known and novel TF that have roles in CRC. Starting with just one TF (SMAD3) in the bait list, the literature mining process identified an additional 116 CRC-associated TFs. Our network-based analysis showed that these TFs all belonged to any of 13 major functional groups that are known to play important roles in CRC. Among these identified TFs, we obtained a novel six-node module consisting of ATF2-P53-JNK1-ELK1-EPHB2-HIF1A, from which the novel JNK1-ELK1 association could potentially be a significant marker for CRC.

Inherited colorectal cancer syndromes

Colorectal cancer is common in the Western world; ~5% of individuals diagnosed with colorectal cancer have an identifiable inherited genetic predisposition to this malignancy. Genetic testing and rational clinical management recommendations currently exist for the management of individuals with a variety of colorectal cancer syndromes, including hereditary nonpolyposis colorectal cancer (HNPCC, also known as Lynch syndrome), familial adenomatous polyposis (FAP), MYH-associated polyposis (MAP), and the hamartomatous polyposis syndromes (Peutz-Jeghers, juvenile polyposis, and Cowden disease). In addition to colorectal neoplasia, these syndromes frequently predispose carriers to a variety of extracolonic cancers. The elucidation of the genetic basis of several colorectal cancer predisposition syndromes over the past two decades has allowed for better management of individuals who are either affected with, or at-risk for inherited colorectal cancer syndromes. Appropriate multidisciplinary management of these individuals includes genetic counseling, genetic testing, clinical screening, and treatment recommendations.

Frequency of deletions of EPCAM (TACSTD1) in MSH2-associated Lynch syndrome cases

Lynch syndrome is an autosomal dominant cancer predisposition syndrome characterized by loss of function of DNA mismatch repair enzyme MLH1, MSH2, MSH6, or PMS2. Mutations in MLH1 and MSH2 account for ∼80% of the inherited cases. However, in up to 20% of cases suspected of having a germline mutation in MSH2 due to loss of MSH2 expression, a germline mutation is not identified. Recent studies have shown that some Lynch syndrome cases are due to 3' EPCAM/TACSTD1 deletions that subsequently lead to MSH2 promoter hypermethylation. In this study, we examined the frequency of this novel mechanism for MSH2 inactivation in cases recruited through the Colon Cancer Family Registry and from the Mayo Clinic Molecular Diagnostics Laboratory. From the combined cohort, 58 cases were selected in which immunohistochemical staining suggested a mutation in MSH2 or MSH6, but no mutations were identified on follow-up testing. Of these 58 cases, 11 demonstrated a deletion of EPCAM/TACSTD1. Of cases with a deletion, the methylation status of the MSH2 promoter was confirmed in tumor tissue using methylation-sensitive PCR primers. One case showed MSH2 promoter hypermethylation in the absence of a detectable EPCAM/TACSTD1 deletion. These results indicate that approximately 20% to 25% of cases suspected of having a mutation in MSH2 but in which a germline mutation is not detected, can be accounted for by germline deletions in EPCAM/TACSTD1. These data also suggest the presence of other alterations leading to MSH2 promoter hypermethylation.

Development of sporadic microsatellite instability in colorectal tumors involves hypermethylation at methylated-in-tumor loci in adenoma

Microsatellite instability (MSI) and genomic hypermethylation of methylated-in-tumor (MINT) loci are both strong prognostic indicators in a subgroup of patients with sporadic colorectal cancer (CRC). The present study was designed to determine whether the methylation of MINT loci during the progression of adenoma to CRC is related to MSI in CRC cases. Methylation index (MI) was measured by absolute quantitative assessment of methylated alleles at seven MINT loci in primary CRC with contiguous adenomatous and normal tissues of 79 patients. Results were then validated in primary CRC tissues from an independent group of 54 patients. Increased MI of both MINT loci 1 and 31 was significantly associated with MSI in CRC and was specific for adenoma. Total MI and the number of methylated loci were threefold (P=0.02) and fivefold (P=0.004) higher, respectively, in adenomas associated with microsatellite-stable CRC versus microsatellite-unstable CRC. MINT MI was found to be correlated with mismatch repair protein expression, MSI, BRAF (V600E) mutation status, mut-L homologue 1 methylation status, and disease-specific survival in the second independent validation group of patients. MI of specific MINT loci may be prognostic indicators of colorectal adenomas that will develop into sporadic microsatellite-unstable CRCs. Increased MINT locus methylation appears to precede MSI and may have utility in defining clinical pathology in the absence of features of malignant invasive tumors.

Gene signature is associated with early stage rectal cancer recurrence

BACKGROUND

Despite expected excellent outcomes of surgical resection for early stage rectal cancers, 20% of stage I and II rectal cancers recur. Identifying biologic factors that predict the subset prone to recur could allow more directed therapy. This study identifies a tumor gene expression profile that accurately predicts disease recurrence.

STUDY DESIGN

Stage I/II rectal cancer patients treated by surgery alone at a single institution were included and classified as having recurrent or nonrecurrent cancer. Tumor mRNA was isolated from frozen tissue and evaluated for total genome gene expression by microarray analysis. Background-corrected and normalized microarray data were analyzed using BAMarray software. Selected genes were further analyzed using unsupervised clustering and nearest-centroid classification. A balanced K-fold scoring-pair algorithm using 1,000 independent replications was used for gene signature development.

RESULTS

Sixty-nine patients with disease-free survival and 31 patients with recurrent disease were included at a median follow-up of 105 months (interquartile range 114 months) and 32 months (interquartile range 25 months), respectively. Demographics and tumor characteristics between groups were similar. Fifty-two genes from 43,148 probes were differentially expressed, and a 36-gene signature was found to be statistically associated with recurrence using a scoring-pair algorithm. Accuracy to identify recurrence as measured by area under the receiver operating characteristic curve was 0.803.

CONCLUSIONS

Differential gene expression within rectal cancers is associated with recurrence of early stage disease. A 36-gene signature correlates with an increased risk of more or less aggressive tumor behavior. This information obtainable at biopsy may assist in determining treatment decisions.

Stabilization of mismatch repair gene PMS2 by glycogen synthase kinase 3beta is implicated in the treatment of cervical carcinoma

Background

PMS2 expression loss was reported in a variety of human. However, its importance has not been fully understood in cervical carcinoma. The aim of this study was to determine the expression of PMS2 in cervical carcinoma and evaluate the significance of mismatch repair gene PMS2 regulated by glycogen synthase kinase 3β (GSK-3β) in chemosensitivity.

Methods

We examined PMS2 and phosphorylated GSK-3β(s9) expression in cervical carcinoma tissues using immunohistochemical staining. Furthermore, we detected PMS2 expression in HeLa cells and evaluate the interaction with GSK-3β after transfection with GSK-3β by small interference RNA (siRNA), co-immunoprecipitation and immunoblotting. We also evaluated the effect of PMS2 transfection on HeLa cells' chemosensitivity to cisplatin treatment.

Results

We found significant downregulation of PMS2 in cervical carcinoma, which was negatively associated with phosphorylated GSK-3β (s9). Furthermore, we demonstrated GSK-3β transfection was able to interact with PMS2 and enhance PMS2 production in HeLa cells, and increased PMS2 production was responsible for enhanced chemosensitivity.

Conclusions

Our results provide the evidence that stabilization of PMS2 production by GSK-3β was important to improve chemosensitization, indicating the significance of GSK-3β-related PMS2 downregulation in the development of cervical carcinoma and in developing a potential strategy for chemotherapy.

Validation of predictive models for germline mutations in DNA mismatch repair genes in colorectal cancer

Lynch syndrome is defined by the presence of germline mutations in mismatch repair (MMR) genes. Several models have been recently devised that predict mutation carrier status (Myriad Genetics, Wijnen, Barnetson, PREMM and MMRpro models). Families at moderate-high risk for harboring a Lynch-associated mutation, referred to the BC Cancer Agency (BCCA) Hereditary Cancer Program (HCP), underwent mutation analysis, immunohistochemistry and/or microsatellite testing. Seventy-two tested cases were included. Twenty-five patients were mutation positive (34.7%) and 47 were mutation negative (65.3%). Nineteen of 43 patients who were both microsatellite stable and normal on immunohistochemistry for MLH1 and MSH2 were also genotyped for mutations in these genes; all 19 were negative for MMR gene mutations. Model-derived probabilities of harboring a MMR gene mutation in the proband were calculated and compared to observed results. The area under the ROC curves were 0.75 (95%CI; 0.63-0.87), 0.86 (0.7-0.96), 0.89 (0.82-0.97), 0.89 (0.81-0.98) and 0.93 (0.86-0.99) for the Myriad, Barnetson, Wijnen, MMRpro and PREMM models, respectively. The Amsterdam II criteria had a sensitivity and specificity of 0.76 and 0.74, respectively, in this cohort. The PREMM model demonstrated the best performance for predicting carrier status based on the positive likelihood ratios at the >10%, >20% and >30% probability thresholds. In this referred cohort, the PREMM model had the most favorable concordance index and predictive performance for carrier status based on the positive LR. These prediction models (PREMM, MMRPro and Wijnen) may soon replace the Amsterdam II and revised Bethesda criteria as a prescreening tool for Lynch mutations.

Role of MSH6 and PMS2 in the dna mismatch repair process and carcinogenesis

In comparison with the mismatch repair genes MLH1 and MSH2, the genes MSH6 and PMS2 are relatively understudied with respect to cancer risk. However, some recent large studies of data combined from several sources, using analytic methods that appropriately condition on the varying methods of ascertainment, are producing reasonably precise estimates, which can be used for risk estimation in patients. To identify modifiers for risk in such carriers, a goal for epidemiologists to improve the health of carriers, such collaborative studies need to continue and expand to include additional mutation carriers in which lifestyle factors and DNA samples are available for analysis.

Colorectal cancer due to deficiency in DNA mismatch repair function: a review

Lynch syndrome (LS) is an autosomal dominant cancer predisposition syndrome attributable to deleterious germline mutations in mismatch repair (MMR) genes. The syndrome is typified by early-onset, frequently right-sided colorectal cancers (CRCs) with characteristic histologic features and tendency for multiplicity and an increased risk for extracolonic tumors at particular sites; it accounts for 1% to 5% of CRC. Deficient mismatch repair (dMMR) function manifests as immunohistochemically detectable absence of one or more MMR proteins and microsatellite instability (MSI). Approximately 15% of sporadic, noninherited CRC are characterized by high-level MSI, nearly always owing to transcriptional silencing of MLH1; these sporadic and LS cases exhibit considerable phenotypic overlap. Identification of CRC with dMMR is desirable to identify LS and because MSI status is prognostic and potentially predictive. This review will discuss the history of LS, the principles of MMR and MSI, the clinicopathologic features of LS-associated and sporadic high-level MSI CRC, the fundamentals of clinical testing for dMMR CRC, and the results of the Columbus-area Lynch syndrome study. We conclude with our approach to population-based LS screening based on institutional experience with nearly 2000 cases.

Molecular characterization of MSI-H colorectal cancer by MLHI promoter methylation, immunohistochemistry, and mismatch repair germline mutation screening

Microsatellite instability (MSI) occurs in 10% to 20% of colorectal cancers (CRC) and has been attributed to both MLH1 promoter hypermethylation and germline mutation in the mismatch repair (MMR) genes. We present results from a large population- and clinic-based study of MLH1 methylation, immunohistochemistry, and MMR germline mutations that enabled us to (a) estimate the prevalence of MMR germline mutations and MLH1 methylation among MSI-H cases and help us understand if all MSI-H CRC is explained by these mechanisms and (b) estimate the associations between MLH1 methylation and sex, age, and tumor location within the colon. MLH1 methylation was measured in 1,061 population-based and 172 clinic-based cases of CRC. Overall, we observed MLH1 methylation in 60% of population-based MSI-H cases and in 13% of clinic-based MSI-H cases. Within the population-based cases with MMR mutation screening and conclusive immunohistochemistry results, we identified a molecular event in MMR in 91% of MSI-H cases: 54% had MLH1 methylation, 14% had a germline mutation in a MMR gene, and 23% had immunohistochemistry evidence for loss of a MMR protein. We observed a striking age difference, with the prevalence of a MMR germline mutation more than 4-fold lower and the prevalence of MLH1 methylation more than 4-fold higher in cases diagnosed after the age of 50 years than in cases diagnosed before that age. We also determined that female sex is an independent predictor of MLH1 methylation within the MSI-H subgroup. These results reinforce the importance of distinguishing between the underlying causes of MSI in studies of etiology and prognosis.

Prognostic significance of defective mismatch repair and BRAF V600E in patients with colon cancer

PURPOSE

Colon tumors with defective DNA mismatch repair (dMMR) have a well-characterized phenotype and accounts for approximately 15% to 20% of sporadic colon cancer as well as those colon cancer patients with Lynch syndrome. Although the presence of dMMR seems to be a favorable prognostic marker, data suggest that these patients do not respond as well to adjuvant chemotherapy.

EXPERIMENTAL DESIGN

In this study, we examined the prognostic significance of tumor MMR deficiency and the presence of a specific mutation in BRAF (V600E) in a group of patients (n = 533) who participated in a randomized prospective clinical trial through the North Central Cancer Treatment Group.

RESULTS

Tumors with dMMR were found to be associated with higher tumor grade (P = 0.001), proximal location (P < 0.0001), and improved overall and disease-free survival (P = 0.05 and 0.04, respectively). Among all cases examined, evaluation of the BRAF V600E mutation status revealed no statistically significant differences in either disease-free or overall survival. Patients were then grouped into four categories for further analysis: dMMR/BRAF(-), dMMR/BRAF(+), pMMR/BRAF(-), and pMMR/BRAF(+). The dMMR/BRAF(-) group had a significantly improved overall survival (5-year overall survival of 100% versus 73%, P = 0.002) compared with all others. The remaining three groups had very similar survival outcomes. An additional cohort of tumors previously classified as having dMMR were also tested for the BRAF V600E alteration. Results remained significant (P = 0.006) when the two groups were combined for analysis.

CONCLUSIONS

Overall, these data suggest that the underlying molecular etiology of those tumors having dMMR may influence the disease outcome in these patients.

The clinical phenotype of Lynch syndrome due to germ-line PMS2 mutations

BACKGROUND & AIMS

Although the clinical phenotype of Lynch syndrome (also known as hereditary nonpolyposis colorectal cancer) has been well described, little is known about disease in PMS2 mutation carriers. Now that mutation detection methods can discern mutations in PMS2 from mutations in its pseudogenes, more mutation carriers have been identified. Information about the clinical significance of PMS2 mutations is crucial for appropriate counseling. Here, we report the clinical characteristics of a large series of PMS2 mutation carriers.

METHODS

We performed PMS2 mutation analysis using long-range polymerase chain reaction and multiplex ligation-dependent probe amplification for 99 probands diagnosed with Lynch syndrome-associated tumors showing isolated loss of PMS2 by immunohistochemistry. Penetrance was calculated using a modified segregation analysis adjusting for ascertainment.

RESULTS

Germ-line PMS2 mutations were detected in 62% of probands (n = 55 monoallelic; 6 biallelic). Among families with monoallelic PMS2 mutations, 65.5% met revised Bethesda guidelines. Compared with the general population, in mutation carriers, the incidence of colorectal cancer was 5.2-fold higher, and the incidence of endometrial cancer was 7.5-fold higher. In North America, this translates to a cumulative cancer risk to age 70 years of 15%-20% for colorectal cancer, 15% for endometrial cancer, and 25%-32% for any Lynch syndrome-associated cancer. No elevated risk for non-Lynch syndrome-associated cancers was observed.

CONCLUSIONS

PMS2 mutations contribute significantly to Lynch syndrome, but the penetrance for monoallelic mutation carriers appears to be lower than that for the other mismatch repair genes. Modified counseling and cancer surveillance guidelines for PMS2 mutation carriers are proposed.

Mismatch repair protein expression in ovine intestinal adenocarcinomas

Sheep in New Zealand develop small intestinal adenocarcinomas more frequently than sheep elsewhere in the world. This high rate of neoplasm development could be due to a genetic predisposition or due to an environmental carcinogen. Differentiation between a genetic and an environmental factor is important as, if an environmental carcinogen is present, people could be exposed directly or by consuming sheep meat. In humans, germline defects in the mismatch repair (MMR) genes cause hereditary nonpolyposis colorectal cancer (HNPCC). Affected people are predisposed to neoplasm development, most commonly colonic adenocarcinomas. It was hypothesized that MMR defects are common within the New Zealand sheep flock, and these defects predispose New Zealand sheep to intestinal neoplasia. To investigate this, immunohistochemistry was used to evaluate the expression of the MMR proteins MSH2, MSH6, MLH1, and PMS2 within 49 ovine intestinal adenocarcinomas. Neoplastic cells within all sheep tumors expressed MSH2, MSH6, and MLH1. Expression of PMS2 could not be assessed, most likely because of insufficient affinity of the anti-human PMS2 antibody to ovine PMS2. The consistent expression of MSH2, MSH6, and MLH1 within the ovine intestinal adenocarcinomas does not support the hypothesis that defects in the MMR genes are common in New Zealand sheep.

A frame-shift mutation of PMS2 is a widespread cause of Lynch syndrome

BACKGROUND

When compared to the other mismatch repair genes involved in Lynch syndrome, the identification of mutations within PMS2 has been limited (<2% of all identified mutations), yet the immunohistochemical analysis of tumour samples indicates that approximately 5% of Lynch syndrome cases are caused by PMS2. This disparity is primarily due to complications in the study of this gene caused by interference from pseudogene sequences.

METHODS

Using a recently developed method for detecting PMS2 specific mutations, we have screened 99 patients who are likely candidates for PMS2 mutations based on immunohistochemical analysis.

RESULTS

We have identified a frequently occurring frame-shift mutation (c.736_741del6ins11) in 12 ostensibly unrelated Lynch syndrome patients (20% of patients we have identified with a deleterious mutation in PMS2, n = 61). These individuals all display the rare allele (population frequency <0.05) at a single nucleotide polymorphism (SNP) in exon 11, and have been shown to possess a short common haplotype, allowing us to calculate that the mutation arose around 1625 years ago (65 generations; 95% confidence interval 22 to 120).

CONCLUSION

Ancestral analysis indicates that this mutation is enriched in individuals with British and Swedish ancestry. We estimate that there are >10 000 carriers of this mutation in the USA alone. The identification of both the mutation and the common haplotype in one Swedish control sample (n = 225), along with evidence that Lynch syndrome associated cancers are rarer than expected in the probands' families, would suggest that this is a prevalent mutation with reduced penetrance.

Pathology of the hereditary colorectal carcinoma

Positive familial history (first or second degree relative) for colorectal carcinoma (CRC) can be found in approximately 30% of all newly diagnosed cases, but less than 5% will be due to a defined genetic category of hereditary CRC. Pathologic examination of the biopsy or resection specimen can help in identification of unsuspected cases of certain forms of hereditary CRC due to the characteristic morphologic findings. Additional immunohistochemical and molecular studies can then provide a definitive diagnosis. The most common form of hereditary CRC is Lynch syndrome (hereditary non-polyposis colorectal cancer, HNPCC) which is characterized by proximally located tumors frequently showing mucinous and medullary type histologic features. The syndrome results from a germline mutation in genes for mismatch repair (MMR) proteins leading to insufficient DNA repair and development of tumors characterized by high levels of instability in short tandem repeat DNA sequences (microsatellites) or "microsatellite instability-high" (MSI-H). The presence of intra-epithelial lymphocytes is single most helpful morphologic feature in identification of CRC caused by deficiency in MMR proteins, for which MSI-H status is a good marker but morphologic features and MSI-H do not differentiate tumors caused by germline mutations in one of the MMR genes (Lynch syndrome) from sporadic CRC due to inactivation of MLH-1 through promoter methylation. Hereditary CRC may also arise in various familial polyposis syndromes which include familial adenomatous polyposis (FAP), attenuated FAP and other multiple adenomas syndromes as well as various hamartomatous polyposis syndromes. All of these rare conditions have characteristic clinical presentation and histopathologic features of polyps and most of them have defined genetic abnormality. Furthermore, due to the germline nature of mutations in these syndromes, various extracolonic manifestations may be the first sign of the disease and knowledge of such associations can greatly improve the quality of care for these patients. The role of pathologist is to recognize these characteristics and initiate appropriate follow up with clinicians and genetic counselors.

Homozygous PMS2 deletion causes a severe colorectal cancer and multiple adenoma phenotype without extraintestinal cancer

BACKGROUND & AIMS

We report a patient of Indian descent with parental consanguinity, who developed 10 carcinomas and 35 adenomatous polyps at age 23 and duodenal adenocarcinoma at age 25. He also had dysmorphic features, mental retardation, and café-au-lait spots but no brain tumor. We aimed to establish his molecular diagnosis.

METHODS

Germ-line screening for APC and MYH/MUTYH mutations was normal as was immunohistochemistry for MLH1 and MSH2 proteins. Investigation by array-comparative genomic hybridization revealed deletion of a small region on chromosome 7. Using polymerase chain reaction, this region was refined to a 400-kilobase deletion, which included exons 9-15 of the PMS2 gene, and all coding regions of oncomodulin, TRIAD3, and FSCN1.

RESULTS

The deletion was confirmed as homozygous, and both parents were carriers. Immunohistochemistry showed absent PMS2 expression in all tumors and normal tissue. Most tumors showed microsatellite instability, more marked at dinucleotide than mononucleotide repeats. The tumors harbored no somatic mutations in APC, BRAF, AXIN2, or beta-catenin, but KRAS2 and TGFBR2 mutations were found.

CONCLUSIONS

Our patient represents a novel phenotype for homozygous PMS2 mutation and perhaps the most severe colorectal cancer phenotype-in terms of numbers of malignancies at an early age-described to date. PMS2 mutations-and perhaps other homozygous mismatch repair mutations-should be considered in any patient presenting with multiple gastrointestinal tumors, since our patient could not be distinguished clinically from cases with attenuated familial adenomatous polyposis or MUTYH-associated polyposis.

MLH3 Mutation in Endometrial Cancer

MLH3 is a recently described member of the DNA mismatch repair gene family. Based on its interaction with the MutL homologue MLH1, it was postulated that MLH3 might play a role in tumorigenesis. Germ line and somatic mutations in MLH3 have been identified in a small fraction of colorectal cancers, but the role of MLH3 in colorectal cancer tumorigenesis remains controversial. We investigated MLH3's role in endometrial tumorigenesis through analysis of tumor and germ line DNA from 57 endometrial cancer patients who were at increased risk for having inherited cancer susceptibility. Patients with known MSH2 or MSH6 mutations were excluded as well as those who had MLH1-methylated tumors. Sixteen different variants were identified by single-strand conformational variant analysis. Of the 12 missense changes identified, three were somatic mutations. One patient had a germ line missense variant and loss of heterozygosity (LOH) in her tumor specimen. There was no evidence of MLH3 promoter methylation based on combined bisulfite restriction analysis. The identification of inherited missense variants, somatic missense mutations (present in 3 of 57 tumors), and LOH in the tumor from a patient with a germ line missense change suggest a role for MLH3 in endometrial tumorigenesis.

Clinical Implications of Our Advancing Knowledge of Colorectal Cancer Genetics: Inherited Syndromes, Prognosis, Prevention, Screening and Therapeutics

Recent genetic advances in our knowledge of colorectal cancer genetics are beginning to pay translational dividends in the management of this common clinical problem. We are now able to accurately screen and counsel individuals at risk of rare inherited cancer syndromes. We have recently introduced two of what are sure to be numerous biologic-based therapies, and have shown that colorectal neoplasia risk can be modestly reduced by various chemopreventative agents. Finally, our advancing knowledge has led to significant inroads into understanding what genetic alterations define prognosis and predict response to specific chemotherapeutic agents, and we are beginning to explore the utility of this knowledge in mass genetic-based clinical screening efforts. Enthusiasm must be tempered, however, by the extraordinary cost that often accompanies relatively modest gains. Finally, although genetic-based therapy often receives the greatest attention, molecular genetics, will likely have the greatest cost-effective impact in primary prevention and early diagnosis.

The added value of PMS2 immunostaining in the diagnosis of hereditary nonpolyposis colorectal cancer

Identification and characterization of the genetic background in patients with the hereditary nonpolyposis colorectal cancer (HNPCC) syndrome is important since control programmes can in a cost-effective manner prevent cancer development in high-risk individuals. HNPCC is caused by germline mismatch repair (MMR) gene mutations and the genetic analysis of HNPCC therefore includes assessment of microsatellite instability (MSI) and immunohistochemical MMR protein expression in the tumor tissue. MSI is found in >95% of the HNPCC-associated tumors and immunostaining using antibodies against the MMR proteins MLH1, MSH2, and MSH6 has been found to correctly pinpoint the affected gene in about 90% of the cases. The PMS2 antibody was the most recently developed and we have in a clinical material assessed the added value of PMS2 immunostaining in 213 patients with suspected hereditary colorectal cancer. All 119 MSS tumors showed retained expression for all four antibodies and PMS2 did thus not identify any underlying MMR defect in these cases. However, PMS2 immunostaining contributed to the characterization of the MMR defect in a subset of the MSI tumors. Concomitant loss of MLH1 and PMS2, which functionally interact in the MutLalpha complex, was found in 98% of the tumors from patients with germline MLH1 mutations. Among the 12 MSI-high tumors with retained expression of MLH1, MSH2 and MSH6, 8 tumors showed loss of PMS2 staining, and mutations in MLH1 were identified in 2 and mutations in PMS2 in 3 of these individuals. In summary, isolated loss of PMS2 was found in 8% of the MSI-high tumors in our series, including 8/12 previously unexplained MSI-high tumors, in which mutations either in MLH1 or in PMS2 were identified in five cases.