MLH1 and MSH2 protein immunohistochemistry is useful for detection of hereditary non-polyposis colorectal cancer in young patients

A comparative analysis of MMR immunohistochemistry panels: Evaluating the utility of four-protein versus two-protein panels in endometrial cancer patients

AIMS

This study aimed to assess the accuracy of a two-protein panel for mismatch repair (MMR) immunohistochemistry (IHC) compared to a four-protein panel in a cohort of endometrial cancer patients.

METHODS

The study included patients diagnosed with endometrial cancer between January 2018 and December 2023 with patients underwent MMR IHC staining for the four-protein panel (MSH2, MSH6, MLH1, and PMS2) serving as the reference standard. Various combinations of two proteins were examined and evaluated for their accuracy against the four-protein panel. Sensitivity, negative predictive value (NPV), and negative likelihood ratio were calculated for each combination. McNemar's test was performed to assess discordance, and receiver operating characteristic (ROC) curves were generated to evaluate diagnostic accuracy.

RESULTS

Of 593 patients, MMR deficiency defined as at least one protein loss was observed in 146 patients (24.62%). When compared with four-protein panel, the highest sensitivity was observed with the MSH6/PMS2 combination (99.32%), followed sequentially by MSH6/MLH1 (97.26%), MSH2/PMS2 (93.15%), MSH2/MLH1 (91.10%), MLH1/PMS2 (79.45%), and MSH2/MSH6 (21.92%). The MSH6/PMS2 combination also demonstrated the best NPV of 99.78% and negative likelihood ratio of 0.01, while MSH6/MLH1 showed satisfactory NPV of 99.11% and negative likelihood ratio of 0.03. McNemar's test revealed no statistical difference between the four-protein panel and the MSH6/PMS2 panel (p = 1.000), and the MSH6/MLH1 panel (p = 0.125).

CONCLUSIONS

The two-protein panel, particularly MSH6/PMS2, offers high sensitivity and negative predictive value, suggesting its potential as a cost-effective alternative to the four-protein panel in MMR testing for endometrial cancer patients.

The Prognostic Implications of Tumor Infiltrating Lymphocytes in Colorectal Cancer: A Systematic Review and Meta-Analysis

Tumor-infiltrating lymphocytes (TILs) are an important histopathologic feature of colorectal cancer that confer prognostic information. Previous clinical and epidemiologic studies have found that the presence and quantification of tumor-infiltrating lymphocytes are significantly associated with disease-specific and overall survival in colorectal cancer. We performed a systematic review and meta-analysis, establishing pooled estimates for survival outcomes based on the presence of TILs in colon cancer. PubMed (Medline), Embase, Cochrane Library, Web of Science, and ClinicalTrials.gov were searched from inception to April 2017. Studies were included, in which the prognostic significance of intratumoral tumor infiltrating lymphocytes, as well as subsets of CD3, CD8, FOXP3, CD45R0 lymphocytes, were determined within the solid tumor center, the invasive margin, and tumor stroma. Random-effects models were calculated to estimated summary effects using hazard ratios. Forty-three relevant studies describing 21,015 patients were included in our meta-analysis. The results demonstrate that high levels of generalized TILS as compared to low levels had an improved overall survival (OS) with a HR of 0.65 (p = <0.01). In addition, histologically localized CD3+ T-cells at the tumor center were significantly associated with better disease-free survival (HR = 0.46, 95% CI 0.36–0.61, p = 0.05), and CD3 + cells at the invasive margin were associated with improved disease-free survival (HR = 0.57, 95% CI 0.38–0.86, p = 0.05). CD8+ T-cells at the tumor center had statistically significant prognostic value on cancer-specific survival and overall survival with HRs of 0.65 (p = 0.02) and 0.71 (p < 0.01), respectively. Lastly, FOXP3+ T-cells at the tumor center were associated with improved prognosis for cancer-specific survival (HR = 0.65, p < 0.01) and overall survival (HR = 0.70, p < 0.01). These findings suggest that TILs and specific TIL subsets serve as prognostic biomarkers for colorectal cancer.

Differences of protein expression profiles, KRAS and BRAF mutation, and prognosis in right-sided colon, left-sided colon and rectal cancer

To compare protein expression levels, gene mutation and survival among Right-Sided Colon Cancer (RSCC), Left-Sided Colon Cancer (LSCC) and rectal cancer patients, 57 cases of RSCC, 87 LSCC and 145 rectal cancer patients were included retrospectively. Our results demonstrated significant differences existed among RSCC, LSCC and rectal cancer regarding tumor diameter, differentiation, invasion depth and TNM stage. No significant difference was identified in expression levels of MLH1, MSH2, MSH6, PMS2, β-Tubulin III, P53, Ki67 and TOPIIα, and gene mutation of KRAS and BRAF among three groups. Progression Free Survival (PFS) of RSCC was significantly lower than that of LRCC and rectal cancer. In univariate analyses, RSCC, preoperative chemoradiotherapy, poor differentiation, advanced TNM stage, elevated serum CEA and CA19-9 level, tumor deposit, perineural and vascular invasion were found to be predictive factors of shorter PFS. In multivariate analyses, only differentiation and TNM stages were found to be independent predictors of PFS. In conclusion, compared with LSCC and rectal cancer, RSCC has larger tumor size, poor differentiation, advanced TNM stage and shorter survival. The shorter survival in RSCC might be attributed to the advanced tumor stage caused by its inherent position feature of proximal colon rather than genetic difference.

Reflex test reminders in required cancer synoptic templates decrease order entry error: An analysis of mismatch repair immunohistochemical orders to screen for Lynch syndrome

Background:

Endometrial carcinoma (EC) is the most common extracolonic malignant neoplasm associated with Lynch syndrome (LS). LS is caused by autosomal dominant germline mutations in DNA mismatch repair (MMR) genes. Screening for LS in EC is often evaluated by loss of immunohistochemical (IHC) expression of DNA MMR enzymes MLH1, MSH2, MSH6, and PMS2 (MMR IHC). In July 2013, our clinicians asked that we screen all EC in patients ≤60 for loss of MMR IHC expression. Despite this policy, several cases were not screened or screening was delayed. We implemented an informatics-based approach to ensure that all women who met criteria would have timely screening.

Subjects and Methods:

Reports are created in PowerPath (Sunquest Information Systems, Tucson, AZ) with custom synoptic templates. We implemented an algorithm on March 6, 2014 requiring pathologists to address MMR IHC in patients ≤60 with EC before sign out (S/O). Pathologists must answer these questions: is patient ≤60 (yes/no), if yes, follow-up questions (IHC done previously, ordered with addendum to follow, results included in report, N/A, or not ordered), if not ordered, one must explain. We analyzed cases from July 18, 2013 to August 31, 2016 preimplementation (PreImp) and postimplementation (PostImp) that met criteria. Data analysis was performed using the standard data package included with GraphPad Prism^® 7.00 (GraphPad Software, Inc., La Jolla, CA, USA).

Results:

There were 147 patients who met criteria (29 PreImp and 118 PostImp). IHC was ordered in a more complete and timely fashion PostImp than PreImp. PreImp, 4/29 (13.8%) cases did not get any IHC, but PostImp, only 4/118 (3.39%) were missed (P = 0.0448). Of cases with IHC ordered, 60.0% (15/25) were ordered before or at S/O PreImp versus 91.2% (104/114) PostImp (P = 0.0004). Relative to day of S/O, the mean days of order delay were longer and more variable PreImp versus PostImp (12.9 ± 40.7 vs. -0.660 ± 1.15; P = 0.0227), with the average being before S/O PostImp.

Conclusion:

This algorithm ensures MMR IHC ordering in women ≤60 with EC and can be applied to similar scenarios. Ancillary tests for management are increasing, especially genetic and molecular-based methods. The burden of managing orders and results remains with the pathologist and relying on human intervention alone is ineffective. Ordering IHC before or at S/O prevents oversight and the additional work of retrospective ordering and reporting.

Expression of p27, COX-2, MLH1, and MSH2 in young patients with colon carcinoma and correlation with morphologic findings

Despite an overall decrease in colorectal carcinoma incidence, rates of colorectal carcinoma have increased substantially in patients aged less than 40 years. Several authors have characterized morphologic features of colorectal carcinoma in young patients, with variable results. To date, there has been 1 detailed molecular and immunohistochemical study in young patients with colorectal carcinoma. We sought to expand the data regarding young patients with colorectal carcinoma by a detailed assessment of morphologic features and by assaying expression of p27, COX-2, MLH1, and MSH2, markers with prognostic or therapeutic implications in colorectal carcinoma. We searched our pathology database from 1985 to 2009 and, after exclusion of cases with insufficient data or neoadjuvant therapy, identified a study population of 23 patients aged 40 or younger, 35 patients between 41 and 49 years of age, and a control group of 83 colorectal carcinoma patients aged 50 or older. Younger patients had higher tumor grade (P = .0085), with a trend toward mucinous differentiation and lymphovascular and perineural invasion. Loss of MSH2 was more prominent in younger patients (P = .02). Loss of p27 expression was not associated with age, but was associated with higher tumor stage (P = .0278), mucinous/signet ring differentiation (P = .0185), loss of either MLH1 or MSH2 (P = .0035), and larger tumor size (P = .0019). There was a trend toward lower COX-2 expression in younger patients, with less COX-2 expression relative to previously published data. Our findings support some prior reports regarding morphologic features in colorectal carcinoma in young patients and provide novel data on expression of several markers in this population.

Molecular signaling mechanisms of apoptosis in hereditary non-polyposis colorectal cancer

Colorectal cancer is the second most leading cause of cancer related deaths in the western countries. One of the forms of colorectal cancer is hereditary non-polyposis colorectal cancer (HNPCC), also known as “Lynch syndrome”. It is the most common hereditary form of cancer accounting for 5%-10% of all colon cancers. HNPCC is a dominant autosomal genetic disorder caused by germ line mutations in mismatch repair genes. Human mismatch repair genes play a crucial role in genetic stability of DNA, the inactivation of which results in an increased rate of mutation and often a loss of mismatch repair function. Recent studies have shown that certain mismatch repair genes are involved in the regulation of key cellular processes including apoptosis. Thus, differential expression of mismatch repair genes particularly the contributions of MLH1 and MSH2 play important roles in therapeutic resistance to certain cytotoxic drugs such as cisplatin that is used normally as chemoprevention. An understanding of the role of mismatch repair genes in molecular signaling mechanism of apoptosis and its involvement in HNPCC needs attention for further work into this important area of cancer research, and this review article is intended to accomplish that goal of linkage of apoptosis with HNPCC. The current review was not intended to provide a comprehensive enumeration of the entire body of literature in the area of HNPCC or mismatch repair system or apoptosis; it is rather intended to focus primarily on the current state of knowledge of the role of mismatch repair proteins in molecular signaling mechanism of apoptosis as it relates to understanding of HNPCC.

hMLH1 immunoexpression is related to the degree of epithelial dysplasia in oral leukoplakia

BACKGROUND

hMLH1 is a protein of the mammalian mismatch repair system responsible for genomic stability during repeated duplication. Relation between its altered expression linked to microsatellite instability has also been observed in oral leukoplakias (OL) and squamous cell carcinomas pointing to a possible role of hMLH1 in oral carcinogenesis. To our knowledge, this is the first study evaluating the immunoexpression of hMLH1 in OLs regarding their different degrees of epithelial dysplasia.

METHODS

Sixty-two specimens of OL were classified in four groups: 17 without dysplasia, 19 with mild dysplasia, 16 with moderate dysplasia, and 10 with severe dysplasia. Immunohistochemistry for hMLH1 was performed, and percentage of positive cells was assessed. In the statistical analysis, P values <0.005 were considered significant.

RESULTS

hMLH1 immunoexpression showed decreasing indexes from lesions with lower degrees of dysplasia to lesions with more severe dysplasia. Statistical difference was found mainly between suprabasal layers and total indexes.

CONCLUSIONS

hMLH1 immunoexpression was inversely related to the OL degree of dysplasia. The total epithelial hMLH1 index seems to be of more clinical relevance than the evaluation stratified by layers. Our findings also suggest a role of such alterations in this pathway of DNA repair as an early event in oral carcinogenesis.

Hereditary non-polyposis colorectal cancer: identification of mutation carriers and assessing pathogenicity of mutations

Hereditary non-polyposis colorectal cancer (HNPCC), also referred to as Lynch syndrome, is an autosomal dominantly inherited disorder that is characterized by susceptibility to colorectal cancer and extracolonic malignancies, in particular endometrial cancer. HNPCC is caused by pathogenic mutations in the mismatch repair (MMR) genes, which play an important role in maintaining genomic stability during DNA replication. Identification of MMR gene mutation carriers is important as this enables them to enrol in surveillance programmes, thus reducing their risk of cancer and increasing survival. Clinical criteria as well as non-clinical criteria have been formulated to select patients for mutation analysis. In this paper we review the approaches used to select patients for mutation analysis. Mutation analysis in the MMR genes may yield mutations of which the pathogenic nature is unclear. Criteria to determine the pathogenicity of such variants are discussed, as well as differences in design of functional assays to assess pathogenicity.

[How and when to search for microsatellite instability in colorectal cancer in 2008?]

Hereditary non polyposis colorectal cancer or Lynch syndrome is due to germline mutation of one the DNA mismatch repair genes. This mutation is associated with an unstable phenotype in tumor DNA characterized by new microsatellite alleles that are absent in matching normal DNA. Besides the Bethesda reference panel, a new panel of 5 mononucleotide microsatellites (BAT25, BAT26, NR21, NR24, NR27) has been proposed, which is more sensitive and faster to use in a multiplex PCR assay. In tumor cells, immunohistochemistry detects the loss of expression of either MLH1, MSH2, MSH6 or PMS2 protein, corresponding to the mutated gene. Immunohistochemistry guides germline analysis, except for MLH1 extinction which may correspond to either MLH1 germline mutation or methylation of MLH1 promoter resulting in inactivation. The latter is mostly due to aging and is often associated to the V600E BRAF gene mutation in tumor DNA. Combination of these 3 somatic analyses should reduce indications of germline mutation analysis in Lynch syndrome.

Immunohistochemical Mismatch Repair Proteins Expression in Colorectal Cancer

Immunohistochemical (IHC) assessment of the mismatch repair proteins has been proposed as an alternative strategy to molecular biology for evaluating the unstable phenotype of tumors. With the aim of introducing IHC analysis as a routine diagnostic test, the authors compared the expression of MLH1 and MSH2 proteins with a PCR-based microsatellite assay. The concordance rate between the two methods was 90% after IHC evaluation of two different areas of each tumor. These results show that IHC may be as efficient as PCR in detecting unstable phenotype by using only one surgical or biopsy sample.

Value of microsatellite instability typing in detecting hereditary non-polyposis colorectal cancer

AIM OF THE STUDY

To detect hereditary non-polyposis colorectal cancer (HNPCC) patients with a strategy combining clinical selection (patient age at onset of cancer less than 50 years or family history of HNPCC tumors) and microsatellite instability typing plus immunohistochemistry, leading to mismatch repair (MMR) germline mutation analysis.

METHODS

Tumors were screened for microsatellite instability (MSI) and for hmlh1 and hmsh2 immunohistochemical expression. Germline mutation analysis was performed to search for MLH1 and MSH2 mutations in patients with MSI-High and MSI-Low tumors.

RESULTS

197 adenocarcinomas were studied: 164 patients were< or =50 years old, 33 were older than 50 years but had a family history of HNPCC tumors. Fifty tumors (25.4%) were MSI-High, 10 were MSI-Low (5.1%), and 130 were MS-Stable (66%). MSI typing was inconclusive in 7 (3.5%). Immunohistochemistry screening was performed on 165 tumors: sensitivity was 63.6%, specificity was 99%. Germline mutation analysis was performed in 33/60 MSI-High or Low tumors: 23 mutations were noted (70% of the tested patients).

CONCLUSION

This proposed strategy of determining microsatellite instability in young colorectal cancer patients or in patients with a family history of HNPCC tumors led to an increased frequency in the detection of MMR germline mutations.

Challenges and pitfalls in HNPCC screening by microsatellite analysis and immunohistochemistry

Hereditary non-polyposis colorectal cancer (HNPCC) accounts for approximately 2 to 4% of the total colorectal cancer burden. For economic reasons a diagnostic "stepladder" is recommended. After evaluation of the family history, diagnostic microsatellite instability (MSI) analysis has found its place as a valuable screening tool for HNPCC. Immunohistochemical analysis can help to pinpoint the affected gene. The detection of a mutation in one of the responsible mismatch repair gene confirmed the diagnosis HNPCC. Here we demonstrate our experience of some important pitfalls that will be discussed in this study. In MSI testing, one potential source for false-negative results is intralesional heterogeneity. We demonstrate examples of a flat adenoma and a carcinoma, which required laser microdissection to correctly determine the microsatellite status. In these lesions manual microdissection, the most frequently applied method, was not sufficient. However, the number of cells obtained by using laser microdisssection can fall below a necessary minimum, which can also cause false-negative results of MSI analysis, as shown here in a mucinous carcinoma. In addition, evaluation of immunohistochemically stained tissue slides requires experience to avoid false-positive or false-negative interpretation. A case with two synchronous colorectal cancers revealed loss of MSH2 expression in one carcinoma, whereas the second carcinoma stained positively leading to a false-negative interpretation. In some cases, false-positive results can be obtained, if a perinuclear-staining pattern is interpreted as positive. In summary, there are several potential pitfalls in the molecular screening for HNPCC. Therefore the importance of correct interpretation of clinical data, immunohistochemistry, and microsatellite analysis in combination, performed by a pathologist with experience in molecular genetics is essential. In addition, laser microdissection of tumor areas that have been chosen by a pathologist is highly recommended in cases that cannot be resolved with manual microdissection.

Value of immunohistochemical detection of DNA mismatch repair proteins in predicting germline mutation in hereditary colorectal neoplasms

The utility of immunohistochemistry (IHC) as a screening method for the identification of persons with mutations in the DNA mismatch repair (MMR) genes in hereditary nonpolyposis colorectal cancer (HNPCC) remains to be defined. In this study, we analyzed the value of IHC versus that of microsatellite instability (MSI) testing in predicting mutation status of the MLH1, MSH2, and MSH6 genes in colorectal carcinomas and adenomas, and explored the frequency and significance of immunohistochemical staining variability. The study samples included 83 carcinomas and 29 adenomas derived from 110 patients who had strong family histories of colorectal cancer. Our results showed that IHC correctly predicted MSI status in 76% of the cases with a specificity of 100%. The overall sensitivity of IHC in predicting a germline mutation was 79% (30 of 38) with a specificity of 89% (48 of 54), whereas that of MSI testing was 97% (30 of 31) with a specificity of 83% (35 of 42). Six of 31 analyzable cases that had a disease-causing mutation and exhibited MSI showed normal IHC. The lower sensitivity of IHC was caused mainly by its low sensitivity in detecting MLH1 gene mutation (4 of 9). Coexisting adenomas and carcinomas observed in the same slide (n=12) showed a similar or identical staining pattern for all three proteins. No significant difference was detected in the sensitivity of IHC or MSI in detecting a germline mutation between isolated adenomas and carcinomas. In IHC-positive cases, heterogeneous staining was noted in 30% to 40% of the cases with the three different antibodies, and cytoplasmic staining in 5% to 13%. Weak IHC (defined as positive staining in <10% of the tumor with weak intensity) was noted in 14 tumors: 5 for the MLH1 antibody, 1 for MSH2, and 8 for MSH6. One of the 5 MLH1 cases exhibited MSI and had an MLH1 germline mutation. Five of the 8 MSH6 cases exhibited MSI and had MSH2 germline mutations. In conclusion, our study shows that 1) IHC identifies a significant portion of colorectal tumors derived from MMR gene germline mutation carriers and can be used as an adjunct measure in the identification of HNPCC families, but IHC cannot replace MSI testing; 2) adenomas have similar MMR protein expression patterns as carcinomas and may serve as an adequate sample for screening purposes in the identification of patients with MMR mutations; 3) not all IHC-positive cases show uniform positivity throughout the tumor; and 4) weak and focal staining of an MMR protein may be associated with MSI or gene mutation or both, suggesting the need to incorporate staining intensity in further IHC studies.

What is the best way to assess microsatellite instability status in colorectal cancer? Study on a population base of 462 colorectal cancers

The assessment of the microsatellite instability (MSI) status in colorectal cancers is presently warranted for three reasons: 1) as a screening tool for hereditary nonpolyposis colorectal cancer, 2) as a prognostic marker, and 3) as a potential predictive factor of chemotherapy response. The aim of this study was to evaluate, on a large scale with tissue samples coming from a number of different sources, the difficulties met with routine use of immunohistochemistry (IHC) and to determine if it really does offer an accurate alternative to PCR genotyping. Colorectal carcinomas from 462 consecutive patients resected in public or private hospitals were assessed for MSI status by two methods: MSI testing (with BAT-26 microsatellite) and IHC detection of hMLH1, hMSH2, and hMSH6 proteins. Of the 398 cancers tested, immunohistochemistry was noncontributory in 42 (10.5%), focal in 9 (2.3%), and discordant with the PCR results in 36 (9%). For these 87 cases, complementary analyses were performed to explain discrepancy. After additional IHC assay with modified processing protocols, 8 cases remained noncontributory, 2 focal, and 28 discordant: 18 microsatellite stability IHC/MSI PCR and 10 MSI IHC/microsatellite stability PCR. For these discordant cases, we performed a multiplex PCR assay on DNA extracted from the frozen sample and BAT-26 was amplified from DNA extracted from the paraffin blocks used for IHC. Four discordant cases were reclassified after PCR multiplex assay (3 as MSI and 1 as microsatellite stability). Five other cases displayed intratumoral heterogeneity and 19 remained discordant. The discrepancy could be partly explained by variable technical protocols of fixation in the different laboratories, leading to variations in staining quality and difficulties in IHC interpretation. This population-based study is the first one to show that IHC is not sensitive and specific enough to be used routinely. Immunohistochemistry analysis of MMR proteins must be performed in standardized conditions and interpreted by confirmed pathologists. It cannot replace PCR as long as protocols are not optimized and harmonized.

Expression of the hMLH1 and hMSH2 proteins in normal tissues: relationship to cancer predisposition in hereditary non-polyposis colon cancer

The majority of tumours in patients with hereditary non-polyposis colon cancer (HNPCC) occur in large intestine and endometrium; also, other tissues are at increased risk. We studied expression of hMLH1 and hMSH2 proteins in 148 normal samples of various tissues from non-HNPCC patients and in 14 normal colon tissues from HNPCC patients. Immunohistochemical technique was used. Intensity of nuclear staining, percentage of stained cells and H-scores were calculated. Tissues were divided into groups. Groups A, B and C included tissues with increased risk of cancer in HNPCC A) stomach, small and large bowel; (B) endometrium; (C) ovary, ureter, urinary bladder, kidney and liver. Group D tissues were without increased risk. Expression of the proteins was significantly higher in groups A, B and C compared with group D (P<0.0001, P=0.0004 for hMSH2 in C versus D). The expression was highest in testis. In colons of HNPCC patients, expression of the mutated gene product was significantly lower than in non-HNPCC patients. In conclusion, hMLH1/hMSH2 protein expression is constitutively higher in certain cell types of certain tissues, including the majority of tissues that are at increased risk of cancer in HNPCC. However, association of strong hMLH1/hMSH2 expression with cancer risk is not strictly valid.

HNPCC and sporadic MSI-H colorectal cancer: a review of the morphological similarities and differences

Morphological features may serve as diagnostically useful markers of colorectal cancer (CRC) with the microsatellite instability-high (MSI-H) phenotype. The most important of these are lymphocytic infiltration, mucin secretion and poor differentiation. These features are apparent in both sporadic MSI-H CRC and CRC occurring in the context of hereditary non-polyposis colorectal cancer (HNPCC). There is now strong evidence that that the two principal subtypes of MSI-H CRC evolve through different pathways. Sporadic MSI-H CRC orginate within serrated polyps with BRAF mutation and DNA methylation while CRC in HNPCC arise within conventional adenomas in which there is frequent mutation of APC or beta -catenin and/or K- ras. These early differences in pathogenesis translate into multiple morphological distinctions in the cancers developing through the two pathways. Lymphocytic infiltration, tumour budding (de-differentiation), and co-existing adenomas are more evident in HNPCC while mucin secretion, poor differentiation, tumour heterogeneity and glandular serration, and co-existing serrated polyps are more evident in sporadic MSI-H CRC. Sporadic MSI-H CRC are also characterized by cytoplasmic eosinophilia and nuclei that are large, round, vesicular and contain a prominent nucleolus while in HNPCC the cytological features recapitulate the basophilia and nuclear characteristics of conventional adenomas. In practice, lymphocytic infiltration is the most sensitive marker of MSI-H status in both sporadic CRC and HNPCC. The crucial distinction between HNPCC and sporadic MSI-H CRC should be achieved by means of all available data including family history, age at onset of malignancy and molecular features. There is increasing evidence that genetic factors may predispose to DNA methylation. This can result in familial clustering of MSI-H CRC in which the underlying mechanism is methylation of hMLH1 rather than germline mutation. Morphological features can assist is distinguishing such families from bona fide HNPCC families which they closely mimic.

Microsatellite instability, immunohistochemistry, and additional PMS2 staining in suspected hereditary nonpolyposis colorectal cancer

PURPOSE

Immunohistochemistry (IHC) and microsatellite instability (MSI) analysis can be used to identify patients with a possible DNA mismatch repair defect [hereditary nonpolyposis colorectal carcinoma (HNPCC)]. The Bethesda criteria have been proposed to select families for determination of MSI. The aims of this study were to assess the yield of MSI analysis in families suspected for HNPCC, to compare the results of immunohistochemical staining and MSI analysis, and to assess the additional value of PMS2 staining.

EXPERIMENTAL DESIGN

Clinical data and tumors were collected from 725 individuals from 631 families with suspected HNPCC. MSI analysis was performed using eight markers including the 5 National Cancer Institute markers. Four immunohistochemical staining antibodies were used (MLH1, MSH2, MSH6 and PMS2).

RESULTS

A MSI-H (tumors with instability for >30% of the markers) phenotype in colorectal cancers (CRCs) was observed in 21-49% of families that met the various Bethesda criteria. In families with three cases of CRC diagnosed at age > 50 years, families with a solitary case of CRC diagnosed between ages 45 and 50 years, and families with one CRC case and a first-degree relative with a HNPCC-related cancer, one diagnosed between ages 45 and 50 years (all Bethesda-negative families), the yield of MSI-H was 10-26%. Immunohistochemical staining confirmed the MSI results in 93% of the cases. With IHC, adding PMS2 staining led to the identification of an additional 23% of subjects with an hMLH1 germ-line mutation (35 carriers were tested).

CONCLUSIONS

The Bethesda guidelines for MSI analysis should include families with three or more cases of CRC diagnosed at age > 50 years. The age at diagnosis of CRC in the original guidelines should be raised to 50 years. Routine IHC diagnostics for HNPCC should include PMS2 staining.

[Molecular pathology in hereditary colorectal cancer. Recommendations of the Collaborative German Study Group on hereditary colorectal cancer funded by the German Cancer Aid (Deutsche Krebshilfe)]

Although twin studies indicate that inherited genetic factors contribute to about 35% of colorectal cancers (CRC), the exact genetic background has currently been elucidated in only 5-10% of cases. These comprise several hereditary cancer predisposition syndromes that present with a high number of syn- or metachronous neoplasms within an affected person and/or family. Many of these tumors exhibit typical histopathological changes. In general, one should discriminate between cancer syndromes associated with adenomatous and non-adenomatous (i.e., hamartomatous) polyps, the latter being quite rare. The patient's age often serves as a substantial hint to hereditary cancer. The next step of diagnostic work-up includes analysis of microsatellite instability (MSI) together with immunohistochemical detection of a loss of expression in one of the most frequently affected mismatch repair genes (MSH2, MSH6; MLH1, PMS2). Finally, the molecular demonstration of a gene mutation in the blood or germline is the most expensive and tedious procedure. This requires a signed informed consent from the patient after appropriate genetic counseling.

Clinical and molecular biologic characteristics of early-onset versus late-onset colorectal carcinoma in Filipinos

A case-control study of Filipino patients who underwent surgical resection for colorectal cancer (CRC) during a 1-year period was undertaken. Thirty-five patients under age 40 years were identified. Paraffin blocks of these and 35 randomly selected patients over age 40 underwent histologic and immunohistochemical evaluation. Markers chosen for evaluation included the apoptosis-associated gene products (p53 and bcl-2), a tumor proliferation activity-related factor (Ki-67), and the markers (MLH1 and MSH2) of DNA microsatellite instability (MSI). Results were correlated with age and the stage and location of the tumor. The average age of the early-onset group was 30.7 years compared to the late-onset group at 67.0 years; and the male/female ratio was equivalent. The younger patients had a significantly higher Dukes' stage, the tumors were more poorly differentiated, and they were more frequently of the mucinous and signet ring cell histopathologic type. Expression of p53 was higher in the younger patients ( p < 0.001) and was independent of the degree of differentiation or the stage of the tumor. No differences of expression were noted for the other markers measured. The increased frequency of CRC in Filipino patients less than 40 years of age offers a unique opportunity to gain a better understanding of carcinogenesis, which might be exploited during diagnosis and management. The differences noted between the early- and late-onset CRC are provocative and provide an impetus for increased screening in Filipinos.

Microsatellite instability analysis and/or immunostaining for the diagnosis of hereditary nonpolyposis colorectal cancer?

Hereditary nonpolyposis colorectal cancer (HNPCC) represents 2-4% of colorectal cancers and is caused by a constitutional defect in a mismatch repair (MMR) gene, most commonly affecting the genes MLH1, MSH2, and MSH6. The MMR defect results in an increased cancer risk with the greatest lifetime risks for colorectal cancer and endometrial cancer. The HNPCC-associated tumor phenotype is generally characterized by microsatellite instability (MSI) and immunohistochemical loss of expression of the affected MMR protein. We have evaluated the information obtained from MSI analysis and immunostaining for MLH1, MSH2, and MSH6 in a series of 128 tumors from patients suspected of having HNPCC. A MSI-high pattern was present in 59 of 128 (46%) tumors. Loss of immunohistochemical expression for at least one of these MMR proteins was found in 54 of 59 (92%) evaluable MSI tumors. This loss affected MLH1 in 28, MSH2 in 22, and MSH6 in 21 tumors (with MSH6 as the only loss in 4 tumors). Five (8%) MSI-high tumors showed normal MMR protein expression. All 69 microsatellite stable or MSI-low tumors showed normal immunostaining for all three proteins. In 28 patients, all with MSI-H tumors, germ-line mutations of MLH1, MSH2, or MSH6 had been identified, and a corresponding immunohistochemical loss of MMR protein expression was identified in all these cases. In summary, immunostaining for the MMR proteins MLH1, MSH2, and MSH6 had a sensitivity of 92% and a specificity of 100% for detecting MMR-deficient tumors. MMR protein immunostaining facilitates mutation analysis in suspected HNPCC patients, since it pinpoints the mutated gene, but until the genetic background to the MSI tumors with retained MMR protein expression has been clarified, we suggest that MSI and MMR protein immunostaining should optimally be combined in clinical HNPCC analysis.

Histopathology and mismatch repair status of 458 consecutive colorectal carcinomas

Defects in the mismatch repair (MMR) genes hMLH1 and hMSH2 have been found in 10% to 20% of sporadic colorectal carcinomas and also many cases of hereditary nonpolyposis colorectal cancer syndrome. Patients with these tumors have an improved prognosis and may show greater sensitivity to chemotherapy. We examined 458 resected colorectal carcinomas from 430 consecutive patients and used immunohistochemistry to determine which tumors lacked expression of these genes (MMR-d). We correlated the status of MMR-d or "intact" expression with stage, site, and histology. Eighty-nine of 458 tumors (19.4%) were MMR-d, including 80 hMLH1 and 9 hMSH2 tumors. A total of 6% of patients had synchronous tumors, and 37.7% of these were MMR-d (P=0.0008). A high proportion of patients with previous breast cancer (4 of 6 patients) had hMLH1-defective colorectal carcinomas. MMR-d tumors presented at an earlier stage than intact tumors, and the node-positive MMR-d tumors were less likely than intact tumors to have pericolonic extranodal tumor deposits (18.2% vs. 44%). The proportion of tumors at each site that were MMR-d increased progressively from cecum (32%) to ascending (35%) to transverse colon, where 41% of all tumors were defective. The proportions then rapidly decreased, reaching the lowest rate (4.7%) in the rectum. Both types of MMR-d tumors more often had expansive borders, intraepithelial lymphocytosis, peritumoral lymphoid, and Crohn's-like lymphoid responses than the intact tumors; the frequencies of these features diminished with advancing stage. Tumor budding was less common in stage II and III MMR-d tumors than in intact tumors. Keloid and myxoid type stromas correlated with stage and vascular invasion and were not related to mismatch repair status. Significant differences existed between the hMLH1 and hMSH2 tumors. The reported right-sided preponderance of MMR-d tumors is due to most hMLH1, but not hMSH2, tumors being found there (87.5% vs. 44.4%). hMSH2 tumors were most common in the rectum (55.6%). Mucinous tumors were common in hMLH1 tumors (36.3%) but not in hMSH2 tumors (11.1%). hMLH1 tumors were most likely to be poorly differentiated (70%), which was uncommon with hMSH2 tumors (22.2%). hMSH2 tumors were more likely to be confined to the wall (66.7%) than hMLH1 (20%) or intact tumors (23%). We conclude that hMLH1 and hMSH2-defective tumors have distinctly differing histologic features from each other.

Microsatellite instability in colorectal carcinoma. The comparison of immunohistochemistry and molecular biology suggests a role for hMSH6 [correction of hMLH6] immunostaining

CONTEXT

Microsatellite instability (MSI) due to defective mismatch repair (MMR) genes has been reported in the majority of colorectal tumors from patients with hereditary nonpolyposis colorectal cancer syndrome and in 10% to 15% of sporadic colorectal cancers. The identification of cancers associated with MSI requires classical molecular testing as the gold standard.

OBJECTIVE

The aim of this study was to evaluate the role of immunohistochemistry with antibodies directed against 4 MMR proteins as a screening tool for carcinomas with MSI.

METHODS

In this study, 204 formalin-fixed, paraffin-embedded colorectal carcinomas were examined for MMR protein expression (hMLH1, hMSH2, hMSH6, and hPMS2) and analyzed for MSI (MSI-H indicates at least 2 of 6 markers affected). These results were correlated with histopathologic parameters.

RESULTS

Immunohistochemical analysis revealed that loss of expression of at least 1 protein was present in 17% of cases. One hundred percent of carcinomas that showed high instability (MSI-H) showed loss of expression of hMLH1, hMSH2, or hMSH6. Loss of expression of 2 proteins was present in 59.4% of MSI-H cases, with only 2 combinations, namely, hMLH1/hPMS2 and hMSH2/hMSH6. Isolated loss of hMSH6 expression was present in 2 MSI-H cases.

CONCLUSIONS

These findings confirm that examination of MMR protein expression by immunohistochemistry is a simple method to diagnose colorectal cancer with MSI. Our data suggest that the study of hMSH6 may be useful, in addition to hMLH1 and hMSH2. Moreover, immunohistochemistry could represent a screening method with which to direct research on the mutations of MMR genes observed in hereditary nonpolyposis colorectal cancer syndrome.

Conventional and tissue microarray immunohistochemical expression analysis of mismatch repair in hereditary colorectal tumors

Immunohistochemistry (IHC) of mismatch repair (MMR) proteins in colorectal tumors together with microsatellite analysis (MSI) can be helpful in identifying families eligible for mutation analysis. The aims were to determine sensitivity of IHC for MLH1, MSH2, and MSH6 and MSI analysis in tumors from known MMR gene mutation carriers; and to evaluate the use of tissue microarrays for IHC (IHC-TMA) of colon tumors in its ability to identify potential carriers of MMR gene mutations, and compare it with IHC on whole slides. IHC on whole slides was performed in colorectal tumors from 45 carriers of a germline mutation in one of the MMR genes. The TMA cohort consisted of 129 colon tumors from (suspected) hereditary nonpolyposis colorectal cancer (HNPCC) patients. Whole slide IHC analysis had a sensitivity of 89% in detecting MMR deficiency in carriers of a pathogenic MMR mutation. Sensitivity by MSI analysis was 93%. IHC can also be used to predict which gene is expected to harbor the mutation: for MLH1, MSH2, and MSH6, IHC on whole slides would have correctly predicted the mutation in 48%, 92%, and 75% of the cases, respectively. We propose a scheme for the diagnostic approach of families with (suspected) HNPCC. Comparison of the IHC results based on whole slides versus TMA, showed a concordance of 85%, 95%, and 75% for MLH, MSH2, and MSH6, respectively. This study therefore shows that IHC-TMA can be reliably used to simultaneously screen a large number of tumors from (suspected) HNPCC patients, at first in a research setting.