Testing for defective DNA mismatch repair in colorectal carcinoma: a practical guide

Microsatellite instability is a biomarker for immune checkpoint inhibitors in endometrial cancer

In recent years, it has become evident that tumor cells have immune escape mechanisms, and immune checkpoint inhibitor therapy (anti-PD-1/PD-L1 antibody) has shown benefit in various cancers. In endometrial tumors with microsatellite-instability (MSI), somatic mutations have the potential to encode ''non-self'' immunogenic antigens, and lymphocytes have been shown to infiltrate the tumor. Therefore, immune checkpoint inhibitor therapy might be effective in endometrial cancers with MSI. Expression of mismatch repair (MMR) proteins (MLH1, PMS2, MSH2, and MSH6), the presence of tumor-infiltrating lymphocytes (CD8+), and PD-1/PD-L1 expression were assessed by immunohistochemistry in 149 patients with endometrial cancer. We examined whether tumors with MSI had an enhanced immune microenvironment and whether MSI could be a predictor of the therapeutic effect of PD-1/PD-L1 immunotherapy in endometrial cancer. Loss of MMR protein expression was identified in 42 (28.2%) of 149 patients (MSI group) with endometrial cancer. There was no significant relationship between MSI status and age (p = 0.193), histological grade (p = 0.097), FIGO stage (p = 0.508), pelvic lymph node metastasis (p = 0.139), or depth of myometrial invasion (p = 0.494). However, the presence of tumor-infiltrating lymphocytes (CD8+) and PD-L1/PD-1 expression were significantly higher in the MSI group compared to the microsatellite-stable group (p = 0.002, p = 0.001, and p = 0.008, respectively). These results suggest that immune checkpoint inhibitors (anti-PD-1/PD-L1 antibody) could be effective in endometrial cancers with MSI. The presence of MSI may be a biomarker for good response to PD-1/PD-L1 immunotherapy in endometrial cancer.

New classification of endometrial cancers: the development and potential applications of genomic-based classification in research and clinical care

Endometrial carcinoma (EC) is the fourth most common cancer in women in the developed world. Classification of ECs by histomorphologic criteria has limited reproducibility and better tools are needed to distinguish these tumors and enable a subtype-specific approach to research and clinical care. Based on the Cancer Genome Atlas, two research teams have developed pragmatic molecular classifiers that identify four prognostically distinct molecular subgroups. These methods can be applied to diagnostic specimens (e.g., endometrial biopsy) with the potential to completely change the current risk stratification systems and enable earlier informed decision making. The evolution of genomic classification in ECs is shared herein, as well as potential applications and discussion of the essential research still needed in order to optimally integrate molecular classification in to current standard of care.

Hereditary cancer syndromes as model systems for chemopreventive agent development

Research in chemoprevention has undergone a shift in emphasis for pragmatic reasons from large, phase III randomized studies to earlier phase studies focused on safety, mechanisms, and utilization of surrogate endpoints such as biomarkers instead of cancer incidence. This transition permits trials to be conducted in smaller populations and at substantially reduced costs while still yielding valuable information. This article will summarize some of the current chemoprevention challenges and the justification for the use of animal models to facilitate identification and testing of chemopreventive agents as illustrated though four inherited cancer syndromes. Preclinical models of inherited cancer syndromes serve as prototypical systems in which chemopreventive agents can be developed for ultimate application to both the sporadic and inherited cancer settings.

Clinical significance of mismatch repair genes immunohistochemical expression of complex endometrial hyperplasia

Objective

Women with Lynch syndrome have an increased risk of developing colorectal and gynecologic malignancies such as endometrial cancer. Complex hyperplasia has about a 30% risk of developing into endometrial cancer. The aim of this study was to determine the genetic risk for developing endometrial cancer by immunohistochemical staining of premalignant lesions for mutL homolog 1, mutS homolog 2, mutS homolog 6, and postmeiotic segregation increased 2.

Methods

Twenty cases (n=20) were selected from among patients with available sample blocks for analysis. Clinical information was obtained from medical chart review. Immunohistochemical staining was performed for all of the tumor blocks. Staining was scored based on the intensity (intensity score 0-3) .

Results

Among the 20 cases of complex endometrial hyperplasia, 11 (55%) patients showed loss of expression of at least one of the following proteins: mutL homolog 1, mutS homolog 2, mutS homolog 6, or postmeiotic segregation increased 2. Seven (35%) patients were negative for the expression of two or more proteins, and one patient (5%) was negative for the expression of all four proteins.

Conclusion

More than half of the patients showed loss of expression of at least one mismatch repair protein in our study population. Genetic risk counseling and further tests are recommended for these patients.

Ovarian and endometrial endometrioid adenocarcinomas have distinct profiles of microsatellite instability, PTEN expression, and ARID1A expression

AIMS

To understand the role of and differences in molecular alterations between endometrial and ovarian endometrioid adenocarcinomas.

METHODS AND RESULTS

We investigated the microsatellite status of 26 ovarian endometrioid adenocarcinomas (OVEMs), 42 endometrial endometrioid adenocarcinomas (EMCAs), and 19 concurrent (endometrial and ovarian) endometrioid adenocarcinomas. We evaluated the expression of the mismatch repair proteins, PTEN and ARID1A, and mutations of PTEN, KRAS, CTNNB1, and PIK3CA. High levels of microsatellite instability (MSI-H) were present in one of 26 OVEMs, 12 of 42 EMCAs, and four of 19 concurrent endometrioid adenocarcinomas. Only four of 19 concurrent endometrioid adenocarcinomas showed identical molecular alterations in their endometrial and ovarian components. Loss of ARID1A or loss of PTEN expression, and MSI-H, were more common in EMCAs than OVEMs (P = 0.044, P = 0.004, and P = 0.012, respectively). MSI-H in endometrial endometrioid adenocarcinomas was also related to loss of ARID1A expression (P < 0.001). In the cohort of MSI-H endometrioid adenocarcinomas involving the endometrium (n = 16), MSH6-deficient cases showed higher frequencies of CTNNB1 and PIK3CA mutations (P = 0.008 and P = 0.036, respectively), but lower frequencies of KRAS mutation (P = 0.011), than PMS2-deficient cases.

CONCLUSIONS

The different frequencies of molecular genetic alterations between endometrial endometrioid adenocarcinomas and ovarian endometrioid adenocarcinomas imply that distinct processes may be involved in their tumorigenesis or tumour progression.

Hereditary risk evaluation for borderline ovarian tumors based on immunohistochemistry

Objectives

Borderline ovarian tumors (BOT) are premalignant lesions. Approximately 10% of all epithelial ovarian cancers are known to be hereditary with hereditary breast and ovarian cancer (HBOC) accounting for approximately 90% of cases; the remaining 10% are attributable to Lynch syndrome, also known as hereditary nonpolyposis colorectal cancer (HNPCC). The aim of our study is to estimate this risk based on screening immunohistochemistry (IHC).

Methods

Thirty-four patients diagnosed with BOT were identified. Family history, clinical characteristics, and IHC data (breast cancer 1, early onset [BRCA1], breast cancer 2, early onset [BRCA2], mutS homolog 2 [MSH2], mutL homolog 1 [MLH1]) were collected for all cases from the patients' medical charts. Nuclear staining of the tumor was scored as negative and positive.

Results

Among 32 patients, 14 (44%) had serous type and 18 (56%) had mucinous type. The mean patient age was 44 years (range 19-86).The number of patients with weak IHC staining for MSH2 and BRCA2 was 1 (3%) and 6 (19%) respectively. The median follow up was 21.8 months.

Conclusion

According to the results, we discovered that 3% and 19% of patients with BOT had a risk of hereditary cancer based on IHC analysis respectively. This pilot study may help clinician to counsel effectively for confirmative tests.

Molecular characteristics of mismatch repair genes in sporadic colorectal tumors in Czech patients

BACKGROUND

Mismatch repair (MMR) genes are known to be frequently altered in colorectal cancer (CRC). Both genetics and epigenetics modifications seems to be relevant in this phenomenon, however it is still not clear how these two aspects are interconnected. The present study aimed at characterizing of epigenetic and gene expression profiles of MMR genes in sporadic CRC patients from the Czech Republic, a country with one of the highest incidences of this cancer all over Europe.

METHODS

Expression levels and CpG promoter methylation status of all MMR genes were evaluated in DNA from tumor and adjacent mucosal samples of 53 incident CRC patients.

RESULTS

We have found significantly increased transcription levels in EXO1 gene in tumor tissues (P = 0.05) and significant over-expression of MSH3 gene in colon tumors when compared to adjacent mucosal tissues (P = 0.02). Interestingly, almost all MMR genes were differently expressed when localization of tumors was compared. In particular, colon tumors showed an up-regulation of EXO1, MSH2, MSH3, MSH6, and PMS2 genes in comparison to rectal tumors (P = 0.02). Expression levels of all MMR genes positively correlated between each other. The promoter methylation of MLH1 gene was observed in 9% of CRC tissues only.

CONCLUSIONS

In our study, we have observed different pattern of MMR genes expression according to tumor localization. However, a lack of association between methylation in MMR genes and their corresponding expressions was noticed in this study, the relationship between these two aspects is worthy to be analyzed in larger population studies and in pre-malignant stages.

An alternative pathway in colorectal carcinogenesis based on the mismatch repair system and p53 expression in Korean patients with sporadic colorectal cancer

PURPOSE

Microsatellite instability (MSI) and chromosomal instability are main mechanisms underlying colorectal carcinogenesis. We determined the features and prognosis of colorectal cancer based on MSI including mismatch repair genes and expression of p53.

METHODS

Between 1999 and 2008, a total of 2,649 colorectal cancer patients were analyzed using a prospective database. A mismatch repair defect (MMR-D) was defined as a loss of expression of more than one MMR protein and/or MSI-high. MMR-proficiency (MMR-P) was defined as expression of all MMR proteins and microsatellite stable (MSS)/MSI-low. Groups 1 (G1), 2 (G2), 3 (G3), and 4 (G4) were defined as MMR-D and p53-positive expression, MMR-D and p53-negative expression, MMR-P and p53-positive expression, MMR-P and p53-negative expression, respectively.

RESULTS

Eighty-two (3.0%), 181 (6.8%), 1,368 (51.7%), and 1,018 (38.5%) patients were classified into groups 1-4, respectively. Comparison between G1 and G2 showed differences in location (p < 0.001), size (p = 0.030), node metastasis (p = 0.027), distant metastasis (p = 0.009), and stage (p = 0.040). Comparison between G3 and G4 showed differences in location (p < 0.001) and histology (p < 0.001). Comparison between G1 and G3 showed differences in location (p < 0.001) and histology (p < 0.001). Comparison between G2 and G4 showed differences in age (p < 0.001), location (p < 0.001), size (p = 0.006), histology (p < 0.001), node metastasis (p < 0.001), distant metastasis (p < 0.001), and stage (p < 0.001). On multivariate analysis, stage (p = 0.007) and histology (p < 0.001) were associated with improved overall survival, and stage (p < 0.001) was associated with disease-free survival.

CONCLUSIONS

According to the MSI and p53 subsets, colorectal cancers showed different clinicopathologic features, but these subsets had no prognostic impact on overall and disease-free survival rate.

Synchronous gynecologic malignancy and preliminary results of Lynch syndrome

Objective

Lynch syndrome is a hereditary cancer syndrome that increases the risks of colorectal and gynecologic malignancies such as endometrial and ovarian cancer. Studies have shown that mutations in mismatch repair genes (MSH2, MSH6, and MLH1) are associated with Lynch syndrome. The aim of our study was to estimate the value of MSH2, MSH6, and MLH1 immunohistochemistry based on family history in a Korean sample.

Methods

Thirty six women with synchronous gynecologic tumors of endometrial and ovarian cancer were identified among patients being treated at our institution. Among them, 32 patients had tumor blocks (total 62 slides) available for analysis. According to a diagnostic algorithm, we performed immunohistochemistry analyses. Staining was scored based on intensity and proportion (negative or 0: intensity undetectable or minimal, proportion <5%; weak or 1+: intensity mild, proportion 5-30%; strong or 2+: intensity moderate to marked, proportion 30-99%).

Results

Among 32 eligible patients, 9 (28%) had a family history of cancer. Six patients (19%) were negative for MLH1; among them, four (4/6) were negative at both sites. Nine patients (28%) were negative for MSH2 or MSH6 at both sites or negative for both MSH2 and MSH6. Among these three patients showed negative staining for both sites. The three patients showing negative staining for MLH1, MSH2, and MSH6 at both sites with family history were considered to be the screening positive groups of Lynch syndrome.

Conclusion

In this study, the frequency of Lynch syndrome associated immunohistochemical staining (MLH1, MSH2, and MSH6) group was estimated as 9% (3/32) among Korean women with synchronous gynecologic tumors.

Aberrant methylation of different DNA repair genes demonstrates distinct prognostic value for esophageal cancer

BACKGROUND

DNA mismatch repair (MMR) deficiency results in a strong mutator phenotype and high-frequency microsatellite instability (MSI-H), which are the hallmarks of many tumors.

AIM

The objective of this study is to investigate the promoter CpG island methylation status of mismatch repair genes human mutL homolog 1 (hMLH1), human mutS homolog 2 (hMSH2), and O(6)-methylguanine-DNA methyltransferase (MGMT) in esophageal squamous cell carcinoma (ESCC) and its roles in alkylating agents chemotherapy.

METHODS

Real-time methylation-specific polymerase chain reaction (PCR) (real-time MSP) was employed to detect promoter CpG island methylation of the hMLH1, hMSH2, as well as MGMT genes in 235 surgical tumor tissue samples from ESCC patients and their corresponding normal tissue samples.

RESULTS

Promoter CpG island methylation of hMLH1, hMSH2, and MGMT were detectable in 43.4, 28.9, and 40.4% of ESCC tumor DNA, respectively, and the loss rates of hMLH1, hMSH2, and MGMT protein expression were 48.6, 34.5, and 40.9% in tumor tissues, respectively. For the entire population of 235 ESCC patients who were enrolled in operating treatment combined with radiotherapy and chemotherapy with alkylating agents, there was a significant difference in the overall survival between patients with methylated MGMT promoter and those with an unmethylated MGMT promoter (P < 0.05).

CONCLUSION

Promoter CpG island methylation may be a frequent event in ESCC carcinogenesis. Detection of the methylated sequences of hMLH1, hMSH2, and MGMT appears to be promising as a predictive factor in primary ESCC.

Analysis of DNA mismatch repair proteins expression and BRAF V600E mutation in a subset of early- and late-onset colorectal carcinoma patients in Mexico

BACKGROUND AND AIMS

A third of colorectal carcinomas (CRC) affect patients <50 years of age. Fifteen percent of CRC cases with microsatellite instability are due to inherited germ-line mutations in DNA mismatch repair genes. The rest have an epigenetic hypermethylation of the MLH1 promoter in whom the BRAF V600E mutation is a common hallmark. Immunohistochemistry helps to classify colorectal cancers with 100% specificity and 92% sensitivity. We undertook this study to determine if age is a risk factor for defective MMR protein expression and BRAF mutations in our population and to compare these results with the histopathological tumor features.

METHODS

Immunohistochemistry for MLH1 and MSH2 and RT-PCR BRAF V600E mutation was performed on tissue specimens from 57 patients <50 years of age. Data on age, gender, tumor location, histology, depth of infiltration, and the presence of metastatic lymph nodes were collected. Forty eight patients >50 years of age were used as a control group. A statistical analysis using ANOVA, χ(2), and Spearman's rho test were performed.

RESULTS

Absent MMR protein expression was more prevalent in patients <50 years of age. No BRAF V600E mutations were detected in either group. Medullary and mucinous types were more prevalent among young patients, whereas intestinal type was more frequent in older patients (p = 0.0008). No differences were found regarding clinicopathological stages between groups.

CONCLUSIONS

We found an association between young age and defective MMR expression. No V600E BRAF mutations were detected in either group.

A two-antibody mismatch repair protein immunohistochemistry screening approach for colorectal carcinomas, skin sebaceous tumors, and gynecologic tract carcinomas

Mismatch repair protein immunohistochemistry is a widely used method for detecting patients at risk for Lynch syndrome. Recent data suggest that a two-antibody panel approach using PMS2 and MSH6 is an effective screening protocol for colorectal carcinoma, but there are limited data concerning this approach for extraintestinal tumors. The purpose of this study was to review the utility of a two-antibody panel approach in colorectal carcinoma and extraintestinal tumors. We evaluated mismatch repair protein expression in two cohorts: (1) a retrospective analysis of intestinal and extraintestinal tumors (n=334) tested for mismatch repair protein immunohistochemistry and (2) a prospectively accrued series of intestinal, gynecologic tract, and skin sebaceous neoplasms (n=98). A total of 432 cases were analyzed, including 323 colorectal, 50 gynecologic tract, 49 skin sebaceous, and 10 other neoplasms. Overall, 102/432 tumors (24%) demonstrated loss of at least one mismatch repair protein. Concurrent loss of MLH1 and PMS2 was the most common pattern of abnormal expression (50/432, 12%) followed by concurrent loss of MSH2 and MSH6 (33/432, 8%). Of 55 cases with abnormal PMS2 expression, 5 (9%) demonstrated isolated loss of PMS2 expression. Of 47 cases with abnormal MSH6 expression, 14 (30%) demonstrated isolated loss of MSH6 expression. Isolated loss of MLH1 or MSH2 was not observed. Colorectal carcinomas more frequently demonstrated abnormal expression of PMS2 (39/59, 66%). Skin sebaceous neoplasms more frequently demonstrated abnormal expression of MSH6 (18/24, 75%, respectively). A total of 65 tumors with abnormal mismatch repair protein expression were tested for microsatellite instability (MSI): 47 (72%) MSI high, 9 (14%) MSI low, and 9 (14%) microsatellite stable (MSS). Abnormal MSH6 expression accounted for 14/18 (78%) cases that were MSS or MSI low. Our findings confirm the utility of a two-antibody approach using PMS2 and MSH6 in colorectal carcinoma and indicate that this approach is effective in extraintestinal neoplasms associated with Lynch syndrome.

Identification of patients at-risk for Lynch syndrome in a hospital-based colorectal surgery clinic

AIM: To determine the prevalence of a family history suggestive of Lynch syndrome (LS) among patients with colorectal cancer (CRC) followed in a coloproctology outpatient clinic in Southern Brazil.

METHODS: A consecutive sample of patients with CRC were interviewed regarding personal and family histories of cancer. Clinical data and pathology features of the tumor were obtained from chart review.

RESULTS: Of the 212 CRC patients recruited, 61 (29%) reported a family history of CRC, 45 (21.2%) were diagnosed under age 50 years and 11 (5.2%) had more than one primary CRC. Family histories consistent with Amsterdam and revised Bethesda criteria for LS were identified in 22 (10.4%) and 100 (47.2%) patients, respectively. Twenty percent of the colorectal tumors had features of the high microsatellite instability phenotype, which was associated with younger age at CRC diagnosis and with Bethesda criteria (P < 0.001). Only 5.3% of the patients above age 50 years had been previously submitted for CRC screening and only 4% of patients with suspected LS were referred for genetic risk assessment.

CONCLUSION: A significant proportion of patients with CRC were at high risk for LS. Education and training of health care professionals are essential to ensure proper management.

The revised Bethesda guidelines: extent of utilization in a university hospital medical center with a cancer genetics program

BACKGROUND

In 1996, the National Cancer Institute hosted an international workshop to develop criteria to identify patients with colorectal cancer who should be offered microsatellite instability (MSI) testing due to an increased risk for Hereditary Nonpolyposis Colorectal Cancer (HNPCC). These criteria were further modified in 2004 and became known as the revised Bethesda Guidelines. Our study aimed to retrospectively evaluate the percentage of patients diagnosed with HNPCC tumors in 2004 who met revised Bethesda criteria for MSI testing, who were referred for genetic counseling within our institution.

METHODS

All HNPCC tumors diagnosed in 2004 were identified by accessing CoPath, an internal database. Both the Tumor Registry and patients' electronic medical records were accessed to collect all relevant family history information. The list of patients who met at least one of the revised Bethesda criteria, who were candidates for MSI testing, was then cross-referenced with the database of patients referred for genetic counseling within our institution.

RESULTS

A total of 380 HNPCC-associated tumors were diagnosed at our institution during 2004 of which 41 (10.7%) met at least one of the revised Bethesda criteria. Eight (19.5%) of these patients were referred for cancer genetic counseling of which 2 (25%) were seen by a genetics professional. Ultimately, only 4.9% of patients eligible for MSI testing in 2004 were seen for genetic counseling.

CONCLUSION

This retrospective study identified a number of barriers, both internal and external, which hindered the identification of individuals with HNPCC, thus limiting the ability to appropriately manage these high risk families.

Maximizing the value of the endoscopist-pathologist partnership in the management of colorectal polyps and carcinoma

Good communication between clinician and pathologist is essential for optimal patient care and management of colorectal polyps and carcinoma. General principles of communication include making sure that the pathologist and endoscopist have all the information needed to make an accurate diagnosis and that the pathologist communicates the diagnosis back to the endoscopist in a clear and timely fashion. The increasing complexity of classification of colorectal polyps and carcinomas has added to the need for clear communication pathways. The first part of this article is devoted to an outline of general communication issues; the second is a discussion of current concepts in colorectal polyps and carcinomas.

Selection of patients with germline MLH1 mutated Lynch syndrome by determination of MLH1 methylation and BRAF mutation

Lynch syndrome is one of the most common hereditary colorectal cancer (CRC) syndrome and is caused by germline mutations of MLH1, MSH2 and more rarely MSH6, PMS2, MLH3 genes. Whereas the absence of MSH2 protein is predictive of Lynch syndrome, it is not the case for the absence of MLH1 protein. The purpose of this study was to develop a sensitive and cost effective algorithm to select Lynch syndrome cases among patients with MLH1 immunohistochemical silencing. Eleven sporadic CRC and 16 Lynch syndrome cases with MLH1 protein abnormalities were selected. The BRAF c.1799T> A mutation (p.Val600Glu) was analyzed by direct sequencing after PCR amplification of exon 15. Methylation of MLH1 promoter was determined by Methylation-Sensitive Single-Strand Conformation Analysis. In patients with Lynch syndrome, there was no BRAF mutation and only one case showed MLH1 methylation (6%). In sporadic CRC, all cases were MLH1 methylated (100%) and 8 out of 11 cases carried the above BRAF mutation (73%) whereas only 3 cases were BRAF wild type (27%). We propose the following algorithm: (1) no further molecular analysis should be performed for CRC exhibiting MLH1 methylation and BRAF mutation, and these cases should be considered as sporadic CRC; (2) CRC with unmethylated MLH1 and negative for BRAF mutation should be considered as Lynch syndrome; and (3) only a small fraction of CRC with MLH1 promoter methylation but negative for BRAF mutation should be true Lynch syndrome patients. These potentially Lynch syndrome patients should be offered genetic counselling before searching for MLH1 gene mutations.

Location-related differences in sporadic microsatellite unstable colorectal cancer

BACKGROUND

Microsatellite unstable CRC is associated with female gender, large tumours, and poor differentiation. However, there are few reports about the characteristics and differences of sporadic microsatellite unstable CRC based on tumour location.

AIMS

Site-specific heterogeneity of sporadic microsatellite unstable colorectal cancer (CRC) based on location was elucidated.

METHODS

We enrolled 164 CRC patients with high-frequency microsatellite instability (MSI-H) from the prospective database of 2686 consecutive CRC patients who underwent surgical resection. We analysed microsatellite instability (MSI) and expression of mismatch repair (MMR) proteins (MLH1, MSH2, and MSH6).

RESULTS

Among the 164 MSI-H CRC, 105 (64.0%) were located in the proximal colon and 59 (36.0%) were located in the distal colon. The proximal MSI-H CRC was predominantly in female (p=0.014), had a more aggressive differentiation (p=0.001), was of advanced stage (p=0.035), and had a frequent loss of MLH1 expression (p=0.005) compared to the distal MSI-H CRC.

CONCLUSION

There were different clinicopathologic characteristics and MMR protein expression between proximal and distal MSI-H CRC. These findings suggest that the underlying carcinogenic pathway or molecular background differs according to location, despite being microsatellite unstable CRC.

Molecular Testing in Colorectal Carcinoma

An estimated 150,000 individuals are diagnosed with colorectal carcinoma (CRC) each year, and approximately 50,000 will die from this disease, making CRC the third leading cause of cancer deaths in the United States. For this reason, an enormous amount of effort has been spent to understand the molecular pathogenesis of this disease and to develop screening tests and prognostic markers. In the last 10 years, there has been a revolution in the understanding of CRC due to the identification of multiple distinct molecular pathways. With the introduction of biologic agents that target particular subtypes of CRC, molecular analysis of CRC is becoming standard of care in surgical pathology. In this context, the authors first describe the multiple molecular pathways leading to CRC and then discuss the role of molecular testing in the diagnosis of Lynch syndrome (formerly hereditary nonpolyposis colorectal carcinoma), prognosis, and therapy.

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.

Four novel germline mutations in the MLH1 and PMS2 mismatch repair genes in patients with hereditary nonpolyposis colorectal cancer

BACKGROUND

Hereditary nonpolyposis colorectal cancer (HNPCC) is the most common cause of early onset hereditary colorectal cancer. In the majority of HNPCC families, microsatellite instability (MSI) and germline mutation in one of the DNA mismatch repair (MMR) genes are found.

MATERIALS AND METHODS

The entire coding sequence of MMR genes (MLH1, MLH2, MLH6, and PMS2) was analyzed using direct sequencing. Also, tumor tests were done as MSI and immunohistochemistry testing.

RESULTS

We were able to find three novel MLH1 and one novel PMS2 germline mutations in three Iranian HNPCC patients. The first was a transversion mutation c.346A>C (T116P) and happened in the highly conserved HATPase-c region of MLH1 protein. The second was a transversion mutation c.736A>T (I246L), which caused an amino acid change of isoleucine to leucine. The third mutation (c.2145,6 delTG) was frameshift and resulted in an immature stop codon in five codons downstream. All of these three mutations were detected in the MLH1 gene. The other mutation was a transition mutation, c.676G>A (G207E), which has been found in exon six of the PMS2 gene and caused an amino acid change of glycine to glutamic acid. MSI assay revealed high instability in microsatellite for two patients and microsatellite stable for one patient.

CONCLUSION

In all patients, an abnormal expression of the MMR proteins in HNPCC was related to the above novel mutations.

Hereditary colorectal cancer syndromes: familial adenomatous polyposis and lynch syndrome

Familial colorectal cancer (CRC) accounts for 10% to 20% of all cases of CRC. Two major autosomal dominant forms of heritable CRC are familial adenomatous polyposis (FAP) and Lynch syndrome (also known as hereditary nonpolyposis colorectal cancer). Along with the risk for CRC, both syndromes are associated with elevated risk for other tumors. Improved understanding of the genetic basis of these diseases has not only facilitated the identification and screening of at-risk individuals and the development of prophylactic or early-stage intervention strategies but also provided better insight into sporadic CRC. This article reviews the clinical and genetic characteristics of FAP and Lynch syndrome, recommended screening and surveillance practices, and appropriate surgical and nonsurgical interventions.

Molecular diagnostic testing in malignant gliomas: a practical update on predictive markers

Advances in understanding the molecular underpinnings of cancer and in molecular diagnostic technologies have changed the clinical practice of oncologic pathology. The development of targeted therapies against specific molecular alterations in cancer further portends changes in the role of the pathology laboratory to guide such custom therapies. To reconcile the flood of scientific discoveries in this area, the promises of highly touted novel therapeutics, and the practicality of applying this knowledge to the day-to-day practice of clinical neuropathology, the present review highlights the operative differences between diagnostic, predictive, and prognostic markers, and discusses issues surrounding the transition of prospective biomarkers to routine laboratory implementation. This review focuses on 3 predictive molecular markers that are either in clinical use or are contemplated for use in the evaluation of malignant gliomas: assessment of 1p/19q loss in oligodendroglial tumors, examination of O6-methylguanine DNA methyltransferase promoter methylation status in glioblastomas, and molecular dissection of the epidermal growth factor receptor-phosphatidylinositol 3-kinase pathway in glioblastomas. Implementation of such predictive markers is not straightforward and requires critical review of the available literature and attention to practical laboratory, compliance, financial, and clinical management issues.

Further evidence for heritability of an epimutation in one of 12 cases with MLH1 promoter methylation in blood cells clinically displaying HNPCC

Germline mutations in mismatch repair (MMR) genes, tumours with high microsatellite instability (MSI-H) and loss of MMR protein expression are the hallmarks of HNPCC (Lynch syndrome). While somatic MLH1 promoter hypermethylation is generally accepted in the tumorigenesis of sporadic tumours, abnormal MLH1 promoter methylation in normal body cells is controversially discussed as a mechanism predisposing patients to HNPCC. In all 94 patients suspected of HNPCC-syndrome with a mean age of onset of 45.5 years, MLH1-deficiency in their tumours but no germline mutation, underwent methylation-specific PCR-screening for MLH1 promoter methylation. In peripheral blood cells of 12 patients an MLH1 promoter methylation, in seven informative cases allele-specific, was found. Normal colonic tissue, buccal mucosa, and tumour tissue available from three patients also presented abnormal methylation in the MLH1 promoter. The heredity of aberrant methylation is questionable. Pro: MLH1 promoter methylation was found in a patient and his mother giving evidence for a familial predisposition for an epimutation in MLH1. Contra: a de novo set-up of methylation in one patient, a mosaic or incomplete methylation pattern in six patients, and no evidence for inheritance of MLH1 promoter methylation in the remaining families. Our findings provide strong evidence that MLH1 promoter methylation in normal body cells mimics HNPCC and constitutes a pathogenic pre-lesion in MLH1. The identification of hypermethylation as an epigenetic defect has important implications for surveillance recommendations, as these patients should be treated like Lynch syndrome patients, whereas the heritability of methylation is still under investigation.

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.

Incorporation of somatic BRAF mutation testing into an algorithm for the investigation of hereditary non-polyposis colorectal cancer

Patients suspected on clinical grounds to have hereditary non-polyposis colorectal cancer (HNPCC) may be offered laboratory testing in order to confirm the diagnosis and to facilitate screening of pre-symptomatic family members. Tumours from an affected family member are usually pre-screened for microsatellite instability (MSI) and/or loss of immunohistochemical expression of mismatch repair (MMR) genes prior to germline MMR gene mutation testing. The efficiency of this triage process is compromised by the more frequent occurrence of sporadic colorectal cancer (CRC) showing high levels of MSI (MSI-H) due to epigenetic loss of MLH1 expression. Somatic BRAF mutations, most frequently V600E, have been described in a significant proportion of sporadic MSI-H CRC but not in HNPCC-associated cancers. BRAF mutation testing has therefore been proposed as a means to more definitively identify and exclude sporadic MSI-H CRC cases from germline MMR gene testing. However, the clinical validity and utility of this approach have not been previously evaluated in a familial cancer clinic setting. Testing for the V600E mutation was performed on MSI-H CRC samples from 68 individuals referred for laboratory investigation of suspected HNPCC. The V600E mutation was identified in 17 of 40 (42%) tumours showing loss of MLH1 protein expression by immunohistochemistry but in none of the 28 tumours that exhibited loss of MSH2 expression (P < 0.001). The assay was negative in all patients with an identified germline MMR gene mutation. Although biased by the fact that germline testing was not pursued beyond direct sequencing in many cases lacking a high clinical index of suspicion of HNPCC, BRAF V600E detection was therefore considered to be 100% specific and 48% sensitive in detecting sporadic MSI-H CRC amongst those cases showing loss of MLH1 protein expression, in a population of patients with MSI-H CRC and clinical features suggestive of HNPCC. Accordingly, we recommend the incorporation of BRAF V600E mutation testing into the laboratory algorithm for pre-screening patients with suspected HNPCC, whose CRCs show loss of expression of MLH1. In such tumours, the presence of a BRAF V600E mutation indicates the tumour is not related to HNPCC and that germline testing of MLH1 in that individual is not warranted. We also recommend that in families where the clinical suspicion of HNPCC is high, germline testing should not be performed on an individual whose CRC harbours a somatic BRAF mutation, as this may compromise identification of the familial mutation.

Structure and function of the components of the human DNA mismatch repair system

DNA mismatch repair (MMR) is one of the several enzyme systems involved in DNA homeostasis. DNA MMR is involved in the repair of specific types of errors that occur during new DNA synthesis; loss of this system leads to an accelerated accumulation of potential mutations, and predisposes to certain types of cancers. Germline mutations in some of the DNA MMR genes cause the hereditary cancer predisposition, Lynch syndrome. This review addresses advances in the biochemistry of DNA MMR and its relationship to carcinogenesis.