Immunohistochemical testing of conventional adenomas for loss of expression of mismatch repair proteins in Lynch syndrome mutation carriers: a case series from the Australasian site of the colon cancer family registry

Pathology of Gastrointestinal Polyposis Disorders

Gastrointestinal polyposis disorders are a group of syndromes defined by clinicopathologic features that include the predominant histologic type of colorectal polyp and specific inherited gene mutations. Adenomatous polyposis syndromes comprise the prototypical familial adenomatous polyposis syndrome and other recently identified genetic conditions inherited in a dominant or recessive manner. Serrated polyposis syndrome is defined by arbitrary clinical criteria. The diagnosis of hamartomatous polyposis syndromes can be suggested from the histologic characteristics of colorectal polyps and the association with various extraintestinal manifestations. Proper identification of affected individuals is important due to an increased risk of gastrointestinal and extragastrointestinal cancers.

Sporadic Polyps of the Colorectum

Colorectal polyps are common, and their diagnosis and classification represent a major component of gastrointestinal pathology practice. The majority of colorectal polyps represent precursors of either the chromosomal instability or serrated neoplasia pathways to colorectal carcinoma. Accurate reporting of these polyps has major implications for surveillance and thus for cancer prevention. In this review, we discuss the key histologic features of the major colorectal polyps with a particular emphasis on diagnostic pitfalls and areas of contention.

Evaluating Multiple Next-Generation Sequencing-Derived Tumor Features to Accurately Predict DNA Mismatch Repair Status

Identifying tumor DNA mismatch repair deficiency (dMMR) is important for precision medicine. Tumor features, individually and in combination, derived from whole-exome sequenced (WES) colorectal cancers (CRCs) and panel-sequenced CRCs, endometrial cancers (ECs), and sebaceous skin tumors (SSTs) were assessed for their accuracy in detecting dMMR. CRCs (n = 300) with WES, where mismatch repair status was determined by immunohistochemistry, were assessed for microsatellite instability (MSMuTect, MANTIS, MSIseq, and MSISensor), Catalogue of Somatic Mutations in Cancer tumor mutational signatures, and somatic mutation counts. A 10-fold cross-validation approach (100 repeats) evaluated the dMMR prediction accuracy for i) individual features, ii) Lasso statistical model, and iii) an additive feature combination approach. Panel-sequenced tumors (29 CRCs, 22 ECs, and 20 SSTs) were assessed for the top performing dMMR predicting features/models using these three approaches. For WES CRCs, 10 features provided >80% dMMR prediction accuracy, with MSMuTect, MSIseq, and MANTIS achieving ≥99% accuracy. The Lasso model achieved 98.3% accuracy. The additive feature approach, with three or more of six of MSMuTect, MANTIS, MSIseq, MSISensor, insertion-deletion count, or tumor mutational signature small insertion/deletion 2 + small insertion/deletion 7 achieved 99.7% accuracy. For the panel-sequenced tumors, the additive feature combination approach of three or more of six achieved accuracies of 100%, 95.5%, and 100% for CRCs, ECs, and SSTs, respectively. The microsatellite instability calling tools performed well in WES CRCs; however, an approach combining tumor features may improve dMMR prediction in both WES and panel-sequenced data across tissue types.

Large Cancer Pedigree Involving Multiple Cancer Genes including Likely Digenic MSH2 and MSH6 Lynch Syndrome (LS) and an Instance of Recombinational Rescue from LS

Lynch syndrome (LS), caused by heterozygous pathogenic variants affecting one of the mismatch repair (MMR) genes (MSH2, MLH1, MSH6, PMS2), confers moderate to high risks for colorectal, endometrial, and other cancers. We describe a four-generation, 13-branched pedigree in which multiple LS branches carry the MSH2 pathogenic variant c.2006G>T (p.Gly669Val), one branch has this and an additional novel MSH6 variant c.3936_4001+8dup (intronic), and other non-LS branches carry variants within other cancer-relevant genes (NBN, MC1R, PTPRJ). Both MSH2 c.2006G>T and MSH6 c.3936_4001+8dup caused aberrant RNA splicing in carriers, including out-of-frame exon-skipping, providing functional evidence of their pathogenicity. MSH2 and MSH6 are co-located on Chr2p21, but the two variants segregated independently (mapped in trans) within the digenic branch, with carriers of either or both variants. Thus, MSH2 c.2006G>T and MSH6 c.3936_4001+8dup independently confer LS with differing cancer risks among family members in the same branch. Carriers of both variants have near 100% risk of transmitting either one to offspring. Nevertheless, a female carrier of both variants did not transmit either to one son, due to a germline recombination within the intervening region. Genetic diagnosis, risk stratification, and counseling for cancer and inheritance were highly individualized in this family. The finding of multiple cancer-associated variants in this pedigree illustrates a need to consider offering multicancer gene panel testing, as opposed to targeted cascade testing, as additional cancer variants may be uncovered in relatives.

Loss of mismatch repair promotes a direct selective advantage in human stem cells

Lynch syndrome (LS) is the most common hereditary form of colon cancer, resulting from a germline mutation in a DNA mismatch repair (MMR) gene. Loss of MMR in cells establishes a mutator phenotype, which may underlie its link to cancer. Acquired downstream mutations that provide the cell a selective advantage would contribute to tumorigenesis. It is unclear, however, whether loss of MMR has other consequences that would directly result in a selective advantage. We found that knockout of the MMR gene MSH2 results in an immediate survival advantage in human stem cells grown under standard cell culture conditions. This advantage results, in part, from an MMR-dependent response to oxidative stress. We also found that loss of MMR gives rise to enhanced formation and growth of human colonic organoids. These results suggest that loss of MMR may affect cells in ways beyond just increasing mutation frequency that could influence tumorigenesis.

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.

From Genetics to Histomolecular Characterization: An Insight into Colorectal Carcinogenesis in Lynch Syndrome

Lynch syndrome is a hereditary cancer-predisposing syndrome caused by germline defects in DNA mismatch repair (MMR) genes such as MLH1, MSH2, MSH6, and PMS2. Carriers of pathogenic mutations in these genes have an increased lifetime risk of developing colorectal cancer (CRC) and other malignancies. Despite intensive surveillance, Lynch patients typically develop CRC after 10 years of follow-up, regardless of the screening interval. Recently, three different molecular models of colorectal carcinogenesis were identified in Lynch patients based on when MMR deficiency is acquired. In the first pathway, adenoma formation occurs in an MMR-proficient background, and carcinogenesis is characterized by APC and/or KRAS mutation and IGF2, NEUROG1, CDK2A, and/or CRABP1 hypermethylation. In the second pathway, deficiency in the MMR pathway is an early event arising in macroscopically normal gut surface before adenoma formation. In the third pathway, which is associated with mutations in CTNNB1 and/or TP53, the adenoma step is skipped, with fast and invasive tumor growth occurring in an MMR-deficient context. Here, we describe the association between molecular and histological features in these three routes of colorectal carcinogenesis in Lynch patients. The findings summarized in this review may guide the use of individualized surveillance guidelines based on a patient’s carcinogenesis subtype.

Prevalence of Mismatch Repair-Deficient Colorectal Adenoma/Polyp in Early-Onset, Advanced Cases: a Cross-Sectional Study Based on Iranian Hereditary Colorectal Cancer Registry

BACKGROUND

Lynch syndrome (LS) increases the risk of many types of cancer, mainly colorectal cancer (CRC). The purpose of this study was to assess the prevalence of mismatch repair (MMR) deficiency in patients under the age of 50 with advanced adenomatous polyps, aiming at an early diagnosis of LS.

METHODS

This retrospective, cross-sectional study included eligible patients with advanced adenomas diagnosed ≤ 50 years of age registered between April 2014 and February 2017 at three pathology centers in Mashhad. Pathological records were reviewed, and colon tissue specimens were analyzed by immunohistochemistry (IHC) staining to identify proteins which serve as markers for LS as they are related to loss of MMR gene (MLH1, MSH2, MSH6, and PMS2) expression.

RESULTS

Of 862 consecutive patients, a total of 50 adenomas (54% males, 46% females of mean age 41.24 ± 6.5) met the eligibility criteria. Of the adenomas examined, 20 (40%) had a tubulovillous component, 34 (68%) had high-grade dysplasia, and 30 (60%) had were larger than 10 mm protrusions. None of the patients had loss of MMR protein expression.

CONCLUSION

No individual with MMR genetic disorder was identified by IHC screening of early-onset advanced colorectal adenomas. This strategy is therefore not an effective strategy for detecting MMR mutation carriers.

Diagnosis of Lynch Syndrome and Strategies to Distinguish Lynch-Related Tumors from Sporadic MSI/dMMR Tumors

Simple Summary

Microsatellite instability (MSI) is a hallmark of Lynch syndrome (LS)-related tumors but is not specific, as most of MSI/mismatch repair-deficient (dMMR) tumors are sporadic. Therefore, the identification of MSI/dMMR requires additional diagnostic tools to identify LS. In this review, we address the hallmarks of LS and present recent advances in diagnostic and screening strategies to identify LS patients. We also discuss the pitfalls associated with current strategies, which should be taken into account in order to improve the diagnosis of LS.

Abstract

Microsatellite instability (MSI) is a hallmark of Lynch syndrome (LS)-related tumors but is not specific to it, as approximately 80% of MSI/mismatch repair-deficient (dMMR) tumors are sporadic. Methods leading to the diagnosis of LS have considerably evolved in recent years and so have tumoral tests for LS screening and for the discrimination of LS-related to MSI-sporadic tumors. In this review, we address the hallmarks of LS, including the clinical, histopathological, and molecular features. We present recent advances in diagnostic and screening strategies to identify LS patients. We also discuss the pitfalls associated with the current strategies, which should be taken into account to improve the diagnosis of LS and avoid inappropriate clinical management.

How Should We Test for Lynch Syndrome? A Review of Current Guidelines and Future Strategies

International guidelines for the diagnosis of Lynch syndrome (LS) recommend molecular screening of colorectal cancers (CRCs) to identify patients for germline mismatch repair (MMR) gene testing. As our understanding of the LS phenotype and diagnostic technologies have advanced, there is a need to review these guidelines and new screening opportunities. We discuss the barriers to implementation of current guidelines, as well as guideline limitations, and highlight new technologies and knowledge that may address these. We also discuss alternative screening strategies to increase the rate of LS diagnoses. In particular, the focus of current guidance on CRCs means that approximately half of Lynch-spectrum tumours occurring in unknown male LS carriers, and only one-third in female LS carriers, will trigger testing for LS. There is increasing pressure to expand guidelines to include molecular screening of endometrial cancers, the most frequent cancer in female LS carriers. Furthermore, we collate the evidence to support MMR deficiency testing of other Lynch-spectrum tumours to screen for LS. However, a reliance on tumour tissue limits preoperative testing and, therefore, diagnosis prior to malignancy. The recent successes of functional assays to detect microsatellite instability or MMR deficiency in non-neoplastic tissues suggest that future diagnostic pipelines could become independent of tumour tissue.

Progress Report: New insights into the prevention of CRC by colonoscopic surveillance in Lynch syndrome

Lynch syndrome is the most frequent hereditary colorectal cancer (CRC) syndrome, affecting approximately 1 in 300 in the Western population. It is caused by pathogenic variants in the mismatch repair (MMR) genes including MLH1, MSH2 (EPCAM), MSH6 and PMS2, and is associated with high risks of CRC, endometrial cancer and other cancers. In view of these risks, carriers of such variants are encouraged to participate in colonoscopic surveillance programs that are known to substantially improve their prognosis. In the last decade several important studies have been published that provide detailed cancer risk estimates and prognoses based on large numbers of patients. These studies also provided new insights regarding the pathways of carcinogenesis in CRC, which appear to differ depending on the specific MMR gene defect. In this report, we will discuss the implications of these new findings for the development of new surveillance protocols.

Complete Loss of EPCAM Immunoexpression Identifies EPCAM Deletion Carriers in MSH2-Negative Colorectal Neoplasia

Simple Summary

Colorectal carcinomas from patients with Lynch syndrome (LS) due to EPCAM deletions show loss of MSH2 expression. The aim of our study was to evaluate the usefulness of EPCAM expression in identifying carriers of EPCAM deletion among patients with MSH2-negative lesions. MSH2 and EPCAM immunohistochemistry was performed in a large series of lesions (190) composed of malignant and benign neoplasms as well as precursor lesions of different organs from 71 patients with suspected LS due to MSH2 alterations. Germ-line analysis confirmed LS in 68 patients due to MSH2 mutations (53) and EPCAM deletions (15). Among colorectal lesions with lack of MSH2 expression, only 17 were EPCAM-negative and belonged to patients with EPCAM deletions. We confirm that loss of EPCAM expression identifies EPCAM deletion carriers with 100% specificity and we recommend adding EPCAM IHC to the algorithm of MSH2-negative colorectal neoplasia.

Abstract

The use of epithelial cell adhesion molecule (EPCAM) immunohistochemistry (IHC) is not included in the colorectal cancer (CRC) screening algorithm to detect Lynch syndrome (LS) patients. The aim of the present study was to demonstrate that EPCAM IHC is a useful tool to guide the LS germ-line analysis when a loss of MSH2 expression was present. We retrospectively studied MSH2 and EPCAM IHC in a large series of 190 lesions composed of malignant neoplasms (102), precursor lesions of gastrointestinal (71) and extra-gastrointestinal origin (9), and benign neoplasms (8) from different organs of 71 patients suspicious of being LS due to MSH2 alterations. LS was confirmed in 68 patients, 53 with MSH2 mutations and 15 with EPCAM 3′-end deletions. Tissue microarrays were constructed with human normal tissues and their malignant counterparts to assist in the evaluation of EPCAM staining. Among 154 MSH2-negative lesions, 17 were EPCAM-negative, including 10 CRC and 7 colorectal polyps, and 5 of them showed only isolated negative glands. All lesions showing a lack of EPCAM expression belonged to patients with EPCAM 3′-end deletions. EPCAM IHC is a useful screening tool, with 100% specificity to identify LS patients due to EPCAM 3′-end deletions in MSH2-negative CRC and MSH2-negative colorectal polyps.

Diet quality and colorectal tumor risk in persons with Lynch syndrome

BACKGROUND

Persons with Lynch syndrome (LS) have an increased risk of developing colorectal tumors (CRTs). Adherence to diet quality indices associated with colorectal cancer (CRC) risk in the general population has not been studied before in LS.

METHODS

Dietary habits of 490 participants with LS from a prospective cohort study was collected using a food frequency questionnaire. The Dutch Healthy Diet index 2015 (DHD15-index) and Dietary Approaches to Stop Hypertension (DASH) were used to score food-based diet quality. Diet quality scores were divided into tertiles where a higher tertile reflects a higher diet quality. Multivariable Cox proportional hazard regression models were used to estimate the association between the DHD15-index, DASH score and CRT risk.

RESULTS

During a median follow-up time of 53.4 months, 210 participants (42.9%) developed CRTs. The DHD-index and DASH score were not associated with CRT risk; hazard ratios for highest vs. lowest tertile were 1.00 (95% Confidence Interval (CI): 0.67-1.48) and 1.11 (95% CI: 0.74-1.69), respectively. No linear trends across the DHD-index and DASH score tertiles were observed (P-trend = 0.97 and 0.83 respectively).

CONCLUSION

In contrast to observations in the general population, no evidence for an association between the food-based DHD15-index or DASH score and CRT risk was observed in persons with LS. Further studies are needed investigating the association between diet quality and mechanisms leading to the development of LS-associated tumors.

Frequent loss of mutation-specific mismatch repair protein expression in nonneoplastic endometrium of Lynch syndrome patients

Lynch syndrome is most often caused by a germline mutation in one of four DNA mismatch repair (MMR) genes (MLH1, PMS2, MSH2, or MSH6) or EPCAM and is associated with a significantly increased risk of endometrial cancer in affected women. Although universal screening of endometrial cancer for Lynch syndrome is becoming increasingly common by various algorithms using MMR immunohistochemistry and/or microsatellite instability testing by PCR, establishing the diagnosis of Lynch syndrome can be still challenging. MMR-deficient nonneoplastic colonic crypts have been recently described in Lynch syndrome patients with colorectal carcinoma, and have been proposed to be a novel indicator of Lynch syndrome. Presence of MMR-deficient nonneoplastic endometrial glands have not yet been systematically evaluated in Lynch syndrome patients. We performed MMR protein immunohistochemistry in prophylactic hysterectomies and endometrial curettings/biopsies from 27 patients with known Lynch syndrome confirmed by germline mutation analysis. A total of 56 control benign endometrial tissues were also analyzed, and included benign endometrium adjacent to MMR-deficient sporadic (MLH1 promoter hypermethylated) endometrial carcinoma (n = 9), adjacent to MMR-intact sporadic endometrial carcinoma (n = 27), and normal endometrium from hysterectomies performed for benign disease (n = 20). MMR protein deficient nonneoplastic endometrial glands were identified in 70% (19 of 27) of Lynch syndrome patients. In all 19 cases the MMR protein loss was specific for the patients' known germline mutation. None of the control cases showed loss of MMR protein expression in nonneoplastic endometrium. Our findings suggest that MMR-deficient nonneoplastic endometrial glands may be a unique, specific marker of Lynch syndrome, and may provide an important insight into the pathogenesis of Lynch syndrome-associated endometrial cancer. Evaluation of MMR protein expression of benign background endometrium in endometrial cancer patients may be further explored as a possible useful addition to the Lynch syndrome screening algorithm.

Associations of Pathogenic Variants in MLH1, MSH2, and MSH6 With Risk of Colorectal Adenomas and Tumors and With Somatic Mutations in Patients With Lynch Syndrome

BACKGROUND & AIMS

Lynch syndrome is caused by variants in DNA mismatch repair (MMR) genes and associated with an increased risk of colorectal cancer (CRC). In patients with Lynch syndrome, CRCs can develop via different pathways. We studied associations between Lynch syndrome-associated variants in MMR genes and risks of adenoma and CRC and somatic mutations in APC and CTNNB1 in tumors in an international cohort of patients.

METHODS

We combined clinical and molecular data from 3 studies. We obtained clinical data from 2747 patients with Lynch syndrome associated with variants in MLH1, MSH2, or MSH6 from Germany, the Netherlands, and Finland who received at least 2 surveillance colonoscopies and were followed for a median time of 7.8 years for development of adenomas or CRC. We performed DNA sequence analyses of 48 colorectal tumors (from 16 patients with mutations in MLH1, 29 patients with mutations in MSH2, and 3 with mutations in MSH6) for somatic mutations in APC and CTNNB1.

RESULTS

Risk of advanced adenoma in 10 years was 17.8% in patients with pathogenic variants in MSH2 vs 7.7% in MLH1 (P < .001). Higher proportions of patients with pathogenic variants in MLH1 or MSH2 developed CRC in 10 years (11.3% and 11.4%) than patients with pathogenic variants in MSH6 (4.7%) (P = .001 and P = .003 for MLH1 and MSH2 vs MSH6, respectively). Somatic mutations in APC were found in 75% of tumors from patients with pathogenic variants in MSH2 vs 11% in MLH1 (P = .015). Somatic mutations in CTNNB1 were found in 50% of tumors from patients with pathogenic variants in MLH1 vs 7% in MSH2 (P = .002). None of the 3 tumors with pathogenic variants in MSH6 had a mutation in CTNNB1, but all had mutations in APC.

CONCLUSIONS

In an analysis of clinical and DNA sequence data from patients with Lynch syndrome from 3 countries, we associated pathogenic variants in MMR genes with risk of adenoma and CRC, and somatic mutations in APC and CTNNB1 in colorectal tumors. If these findings are confirmed, surveillance guidelines might be adjusted based on MMR gene variants.

Microsatellite instability screening in colorectal adenomas to detect Lynch syndrome patients? A systematic review and meta-analysis

The colorectal cancer spectrum has changed due to population screening programs, with a shift toward adenomas and early cancers. Whether it would be a feasible option to test these adenomas for detection of Lynch syndrome (LS) patients is unclear. Through meta-analysis and systematic review, risk factors for DNA mismatch repair deficiency (dMMR) and microsatellite instability (MSI) in adenomas were identified in LS and unselected patient cohorts. Data were extracted for patient age and MMR variant together with adenoma type, grade, size, and location. A total of 41 studies were included, and contained more than 519 LS patients and 1698 unselected patients with 1142 and 2213 adenomas respectively. dMMR/MSI was present in 69.5% of conventional adenomas in LS patients, compared with 2.8% in unselected patients. In the LS cohort, dMMR/MSI was more frequently present in patients older than 60 years (82% versus 54%). dMMR/MSI was also more common in villous adenomas (84%), adenomas over 1 cm (81%), and adenomas with high grade dysplasia (88%). No significant differences were observed for dMMR/MSI in relation to MMR variants and location of adenomas. In the context of screening, we conclude that detection of dMMR/MSI in conventional adenomas of unselected patients is uncommon and might be considered as indication for LS testing. Within the LS cohort, 69.5% of LS patients could have been detected through dMMR/MSI screening of their conventional adenomas.

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.

Microsatellite Instability assessment in Black South African Colorectal Cancer patients reveal an increased incidence of suspected Lynch syndrome

Microsatellite Instability (MSI) is a hallmark of colorectal cancer (CRC) and occurs in 15–16% of CRC. Molecular biological information of CRC in South Africa (SA) is largely unrecorded. This study was undertaken to determine the frequency of MSI, with particular reference to Lynch syndrome (LS) with a view to improve surveillance and prevention strategies. This was a retrospective study on CRC samples diagnosed between 2011–2015 at Charlotte Maxeke Johannesburg Academic Hospital (CMJAH). Samples diagnosed between 2011–2012 were screened for MSI by PCR and mismatch repair (MMR) immunohistochemistry (IHC), and additional BRAFV600E mutational analysis performed. T-tests, Fischer’s exact and Chi square statistical tests were applied. Twelve percent of patients displayed MSI, with increased frequency in black (15%) versus other ethnic group (OEG) (8%) patients. MSI patients were significantly younger than microsatellite stable (MSS) patients, however when stratified by ethnicity, black patients were predominantly younger (median age: 47), with increased MSH2/6 loss, and no BRAF mutations. These findings suggest a large proportion of young black SA CRC patients develop via the LS pathway due to earlier age onset and predominant MSH2/6 protein loss. SA patients of other ethnicities appear to follow the more well established sporadic MSI pathway.

Traditional serrated adenoma: an overview of pathology and emphasis on molecular pathogenesis

Objective

To provide an overview of the pathology and molecular pathogenesis of traditional serrated adenomas (TSA).

Design

Describe the morphology and molecules that play a role in their pathogenesis.

Results

These exuberant polypoid lesions are typified by tall cells with deeply eosinophilic cytoplasm, elongated nuclei bearing delicate chromatin, ectopic crypt foci, deep clefting of the lining mucosa and an overall resemblance to small bowel mucosa.

Broadly, TSAs arise via three mechanisms. They may be BRAF mutated and CpG island methylator phenotype (CIMP)-high: right sided, mediated through a microvesicular hyperplastic polyp or a sessile serrated adenoma, may also have RNF43 mutations and result in microsatellite stable (MSS) colorectal cancers (CRC). The second pathway that is mutually exclusive of the first is mediated through KRAS mutation with CIMP-low TSAs. These are left-sided TSAs, are not associated with another serrated polyp and result in MSS CRC. These TSAs also have RSPO3, RNF43 and p53 mutations together with aberrant nuclear localisation of β-catenin. Third, there is a smaller group of TSAs that are BRAF and KRAS wild type and arise by as yet unknown molecular events. All TSAs show retention of mismatch repair proteins.

Conclusion

These are characteristic unusual polyps with a complex molecular landscape.

Utility of immunohistochemistry for mismatch repair proteins on colorectal polyps in the familial cancer clinic

BACKGROUND

Immunohistochemistry for loss of expression of one or more of the mismatch repair proteins is performed on colorectal cancer tissue as a screening test for Lynch syndrome; however, its role in pre-malignant polyps remains controversial.

AIM

To determine the effectiveness of mismatch repair immunohistochemistry performed on pre-malignant colorectal polyps in identifying Lynch syndrome, focusing on clinical utility and value.

METHODS

A retrospective audit was conducted of mismatch repair immunohistochemistry performed on non-malignant polyps in patients who attended the Family Cancer Clinic at the Royal Melbourne Hospital. Two hundred and six patient records over a 10-year period (2006-2016) were reviewed. Personal and family history data were collected, including genetic testing results.

RESULTS

Of the 57 patients who underwent polyp testing, the family histories comprised Amsterdam II Criteria (12.3%), Lynch syndrome-associated malignancies (42.1%), Lynch syndrome-associated malignancies and polyps (35.1%) and polyps only (8.8%); 10.5% of patients had no significant family history. Normal expression of the mismatch repair proteins was observed in 94.7% of patients; loss of expression was observed in three individuals with concordant germline variants in two patients (one PMS2 variant of unknown significance and one MSH6 mutation). Additional genetic testing in 21 patients with normal immunohistochemistry did not identify any additional Lynch syndrome cases.

CONCLUSION

The clinical utility of mismatch repair immunohistochemistry on polyp tissue was low. No additional cases of Lynch syndrome were identified, and a large proportion of patients proceeded to germline testing despite normal polyp immunohistochemistry. We suggest there is no value in this approach.

The mismatch repair-dependent DNA damage response: Mechanisms and implications

An important role for the DNA mismatch repair (MMR) pathway in maintaining genomic stability is embodied in its conservation through evolution and the link between loss of MMR function and tumorigenesis. The latter is evident as inheritance of mutations within the major MMR genes give rise to the cancer predisposition condition, Lynch syndrome. Nonetheless, how MMR loss contributes to tumorigenesis is not completely understood. In addition to preventing the accumulation of mutations, MMR also directs cellular responses, such as cell cycle checkpoint or apoptosis activation, to different forms of DNA damage. Understanding this MMR-dependent DNA damage response may provide insight into the full tumor suppressing capabilities of the MMR pathway. Here, we delve into the proposed mechanisms for the MMR-dependent response to DNA damaging agents. We discuss how these pre-clinical findings extend to the clinical treatment of cancers, emphasizing MMR status as a crucial variable in selection of chemotherapeutic regimens. Also, we discuss how loss of the MMR-dependent damage response could promote tumorigenesis via the establishment of a survival advantage to endogenous levels of stress in MMR-deficient cells.

Single-center study of Lynch syndrome screening in colorectal polyps

Background

Lynch syndrome is the most common hereditary colorectal cancer syndrome, and adenoma is one of the important premalignant lesions to colorectal cancer in Lynch syndrome. The first objective of this study was to calculate the detection rate of Lynch syndrome in colorectal polyps by using mismatch repair immunohistochemistry as the initial screening strategy. The second objective of this study was to optimize screening strategies for adenoma associated with Lynch syndrome by integrating polyp and/or patient characteristics such as polyp size, location, dysplasia, age of onset and/or family history of cancer.

Methods

From June 2014 to May 2016, immunohistochemistry was performed for mismatch repair proteins (MLH1, MSH2, MSH6, and PMS2) using endoscopically resected specimens obtained from newly diagnosed colorectal adenomas. Gene analysis was performed in patients with missing expression of mismatched repair protein.

Results

Five hundred and ten patients underwent colorectal polyp resection, with a total of 718 polyps. Five hundred and eight resected adenomas underwent mismatch repair protein immunohistochemical testing. Loss of mismatch repair protein expression was observed in six adenomas, accounting for 1.18% of all adenomas. Five patients then underwent genetic tests to identify two pathogenic mutations from different individuals, while another patient was suspected to have a pathogenic mutation. Three patients were younger than 50 years old. Two patients had advanced histology (high-grade dysplasia and malignant components) and one patient had a family history of cancer.

Conclusion

Immunohistochemical detection of colorectal polyp mismatch repair protein as Lynch syndrome screening efficiency is low. Effective screening strategies may be improved by optimizing patient/polyp selection, such as focusing on young adenoma patients with a family history of cancer, or patients who present with high-risk features (large size, villous, high-grade dysplasia and malignant components).

MSI/MMR-deficient tumor diagnosis: Which standard for screening and for diagnosis? Diagnostic modalities for the colon and other sites: Differences between tumors

Microsatellite instability (MSI), which is caused by deficiency of the DNA mismatch repair (MMR) system, is the molecular abnormality observed in tumors associated with Lynch syndrome. Lynch syndrome represents one of the most frequent conditions of cancer predisposition in human, thus requiring specific care and genetic counseling. Moreover, research has recently focused increasingly on MMR deficiency due to its positive predictive value for the efficacy of immune checkpoints inhibitors (ICKi) in metastatic tumors, regardless of their primary origin. MSI has also been demonstrated to constitute an independent prognostic factor in several tumor types, being also associated with alternative response to chemotherapy. These observations have led many professional medical organizations to recommend universal screening of all newly diagnosed colorectal cancers for dMMR/MSI status and increasing evidence support the evaluation of MSI in all human tumors regardless of the cancer tissue of origin. Currently, two standard reference methods, namely immunohistochemistry and polymerase chain reaction, are recommended for the detection of dMMR/MSI status. These methods are equally valid as the initial screening test for dMMR/MSI in colorectal cancer. To date, there is no recommendation for the detection of dMMR/MSI in other primary tumors. In this review, we will present a comprehensive overview of the methods used for evaluation of tumor dMMR/MSI status in colorectal cancer, as well as in other tumor sites. We will see that the evaluation of this status remains challenging in some clinical settings, with the need to improve the above methods in these specific contexts.

A practical guide to biomarkers for the evaluation of colorectal cancer

Evaluation of microsatellite instability (MSI) of every colorectal cancer (CRC) is important for prognostic and therapeutic purposes, while molecular testing helps identify actionable targeted therapy for patients with metastatic disease. This review will discuss the biomarkers commonly encountered in the clinical evaluation of CRC, and practical issues regarding MSI screening, reporting, interpretation, molecular test indication, and specimen requirements.

Two-stain immunohistochemical screening for Lynch syndrome in colorectal cancer may fail to detect mismatch repair deficiency

Universal screening for Lynch syndrome in colorectal cancer is recommended, and immunohistochemistry for the mismatch repair proteins is commonly used. To reduce cost, some screen using only MSH6 and PMS2, with reflex to the partner stain if either are absent (two-stain method). An expression pattern revealing absent MSH2 and intact MSH6 is not expected, but could result in failed Lynch syndrome detection. We analyzed tumors with absent MSH2 but any degree of MSH6 expression to determine if the two-stain method could miss MSH2 mutations. One-thousand seven-hundred thirty colorectal cancer patients from the Ohio Colorectal Cancer Prevention Initiative underwent tumor screening using microsatellite instability and immunohistochemistry. The two-stain method was used for 1235 cases; staining for all four proteins was completed for 495 cases. The proportion of positive cells and staining intensity were reviewed for MSH6, as well as MSH2 when available. Patients with mismatch repair deficiency underwent next-generation sequencing of germline DNA for mismatch repair genes. If negative, tumor next-generation sequencing was performed to assess for somatic mutations. Overall, thirty-three (1.9%, 33/1730) MSH2-absent cases were identified. Of those, fourteen had no MSH6 expression but eight (0.5%, 8/1730) had ambiguous and eleven (0.6%, 11/1730) had convincing MSH6 expression that could have been interpreted as intact. Germline next-generation sequencing identified MSH2 mutations in 11/14 cases with absence of both stains, 7/8 cases with ambiguous MSH6 expression, and 9/11 cases with convincing MSH6 expression. All remaining cases, except one, had double somatic mutations. The two-stain method fails to detect some patients with Lynch syndrome: (1) significant staining weaker than the control may be incorrectly interpreted as intact MSH6, or (2) Weak or focal/patchy MSH6 can be retained with the absence of MSH2. Accordingly, we recommend the four-stain method be used for optimal Lynch syndrome screening detection.

Routine Molecular Analysis for Lynch Syndrome Among Adenomas or Colorectal Cancer Within a National Screening Program

BACKGROUND & AIMS

It is important to identify individuals with Lynch syndrome because surveillance programs can reduce their morbidity and mortality from colorectal cancer (CRC). We assessed the diagnostic yield of immunohistochemistry to detect Lynch syndrome in patients with advanced and multiple adenomas within our national CRC screening program.

METHODS

We performed a prospective study of all participants (n = 1101; 55% male; median age, 66 years; interquartile range, 61-70 years) referred to the Erasmus MC in The Netherlands after a positive result from a fecal immunohistochemical test, from December 2013 to December 2016. Colon tissues were collected from patients with advanced adenomas, ≥4 nonadvanced adenomas, or CRC, and analyzed by immunohistochemistry to identify patients with loss of mismatch repair (MMR) proteins (MLH1, MSH2, MSH6, or PMS2): a marker of Lynch syndrome. Specimens from patients with loss of MLH1 were analyzed for MLH1 promoter hypermethylation. Patients with an MMR-deficient tumor or adenoma without MLH1 promoter hypermethylation were referred for genetic analysis.

RESULTS

At colonoscopy, 456 patients (41%) (65% male; mean age, 67 years; interquartile range, 63-71 years) were found to have CRC and/or an adenoma eligible for analysis by immunohistochemistry. Of 56 CRCs, 7 (13%) had lost an MMR protein and 5 had hypermethylation of the MLH1 promoter. Analyses of tumor DNA revealed that 2 patients without MLH1 promoter hypermethylation had developed sporadic tumors. In total, 400 patients with adenomas were analyzed. Of the examined adenomas, 208 (52%) had a villous component and/or high-grade dysplasia: 186 (47%) had a villous component and 41 (10%) had high-grade dysplasia. Only 1 adenoma had lost an MMR protein. This adenoma was found to have 2 somatic mutations in MSH6.

CONCLUSIONS

In a CRC screening program in The Netherlands for individuals aged 55 to 75 years, routine screening for Lynch syndrome by immunohistochemistry analysis of colon tissues from patients with advanced and multiple adenomas identified no individuals with this genetic disorder.

Somatic mutations of the coding microsatellites within the beta-2-microglobulin gene in mismatch repair-deficient colorectal cancers and adenomas

In colorectal cancers (CRCs) with tumour mismatch repair (MMR) deficiency, genes involved in the host immune response that contain microsatellites in their coding regions, including beta-2-microglobulin (B2M), can acquire mutations that may alter the immune response, tumour progression and prognosis. We screened the coding microsatellites within B2M for somatic mutations in MMR-deficient CRCs and adenomas to determine associations with tumour subtypes, clinicopathological features and survival. Incident MMR-deficient CRCs from Australasian Colorectal Cancer Family Registry (ACCFR) and the Melbourne Collaborative Cohort Study participants (n = 144) and 63 adenomas from 41 MMR gene mutation carriers from the ACCFR were screened for somatic mutations within five coding microsatellites of B2M. Hazard ratios (HR) and 95% confidence intervals (CI) for overall survival by B2M mutation status were estimated using Cox regression, adjusting for age at CRC diagnosis, sex, AJCC stage and grade. B2M mutations occurred in 30 (20.8%) of the 144 MMR-deficient CRCs (29% of the MLH1-methylated, 17% of the Lynch syndrome and 9% of the suspected Lynch CRCs). No B2M mutations were identified in the 63 adenomas tested. B2M mutations differed by site, stage, grade and lymphocytic infiltration although none reached statistical significance (p > 0.05). The HR for overall survival for B2M mutated CRC was 0.65 (95% CI 0.29-1.48) compared with B2M wild-type. We observed differences in B2M mutation status in MMR-deficient CRC by tumour subtypes, site, stage, grade, immune infiltrate and for overall survival that warrant further investigation in larger studies before B2M mutation status can be considered to have clinical utility.

Gynaecological neoplasms in common familial syndromes (Lynch and HBOC)

Recognising hereditary predisposition in a cancer patient has implications both for the patient and the patient's kindred. For the latter, cascade germline testing can reassure those not-at-risk family members while carriers can be enrolled in cancer screening and prevention programs that are medically effective and economically sustainable for health care systems. Furthermore, in many of these syndromes, ramifications of molecular phenotypes are increasing, and it is now emerging that, in addition, they convey prognostic and predictive information. Although cancer predisposition syndromes are rare, these molecular phenotypes also occur as somatic events in sporadic cancer settings. The information obtained from these molecular phenotypes, regardless of germline or somatic origin, is being incorporated into clinical management in view of their manifold significance. Thus, increasingly, bespoke management of cancer patients involves testing for both germline and somatic mutations in tumours. Lynch syndrome and BRCA-1 and BRCA-2-associated hereditary breast and ovarian cancer are hereditary cancer syndromes frequently involving the gynaecological tract but tumours associated with similar molecular alterations may also occur sporadically. Thus, the molecular phenotype of mismatch repair deficiency, microsatellite instability or hypermutator phenotype may be attributable to germline or somatic events. Similarly, homologous recombination deficiency or 'BRCAness' in ovarian cancers may be syndromic or sporadic. While hereditary syndromes are well recognised, the prognostic and predictive implications of these molecular phenotypes have only recently been elucidated and these aspects will finally ensure that molecular screening may become standard of care. Thus, nowadays pathologists are asked to designate the molecular phenotype of these cancers and then determine whether it is due to hereditary or sporadic causes.

Immunohistochemical Pitfalls: Common Mistakes in the Evaluation of Lynch Syndrome

At least 15% of colorectal cancers diagnosed in the United States are deficient in mismatch repair mechanisms. Most of these are sporadic, but approximately 3% of colorectal cancers result from germline alterations in mismatch repair genes and represent Lynch syndrome. It is critical to identify patients with Lynch syndrome to institute appropriate screening and surveillance for patients and their families. Exclusion of Lynch syndrome in sporadic cases is equally important because it reduces anxiety for patients and prevents excessive spending on unnecessary surveillance. Immunohistochemistry is one of the most widely used screening tools for identifying patients with Lynch syndrome.

The identification of Lynch syndrome in Congolese colorectal cancer patients

BACKGROUND

We aimed to investigate the prevalence of Lynch syndrome as one of hereditary causes of colorectal cancer (CRC) among young Congolese individuals affected by the CRC, and to define methods for diagnosis in Congo Brazzaville.

METHODS

We conducted a transversal cohort study of 34 patients having a CRC with a family history for a period of eight years. They were selected among 89 CRCs of any type from the Bethesda guidelines criteria combined with pedigrees. Mismatch repair (MMR) genes alterations were researched by immunohistochemistry (IHC).

RESULTS

We identified with the Bethesda criteria a total of 38.2% (34/89) patients having familial CRC with a confidence interval (CI) of 95%=[0.34-0.41]. Only 14.7% (5/34) 95% CI=[0.34-2.32] patients showed MMR immunodeficiency involving firstly MLH1 protein then MSH2 protein. These data account for 5.6% (5/89) 95% CI=[0.15-0.33] of patients affected by Lynch syndrome with an earlier median age of 35 years (range 20 to 47 years).

CONCLUSION

The prevalence of Lynch syndrome found in Brazzaville is comparable to that is found in northern countries. The combined Bethesda guidelines, pedigree and IHC is an accessible and good alternative method for the positive diagnosis of Lynch syndrome in current practice in Congo.

Mismatch repair deficiency commonly precedes adenoma formation in Lynch Syndrome-Associated colorectal tumorigenesis

Lynch syndrome is a cancer predisposition syndrome caused by germline mutations in mismatch repair (MMR) genes. MMR deficiency is a ubiquitous feature of Lynch syndrome-associated colorectal adenocarcinomas; however, it remains unclear when the MMR-deficient phenotype is acquired during tumorigenesis. To probe this issue, the present study examined genetic alterations and MMR statuses in Lynch syndrome-associated colorectal adenomas and adenocarcinomas, in comparison with sporadic adenomas. Among the Lynch syndrome-associated colorectal tumors, 68 of 86 adenomas (79%) and all adenocarcinomas were MMR-deficient, whereas all the sporadic adenomas were MMR-proficient, as determined by microsatellite instability testing and immunohistochemistry for MMR proteins. Sequencing analyses identified APC or CTNNB1 mutations in the majority of sporadic adenomas (58/84, 69%) and MMR-proficient Lynch syndrome-associated adenomas (13/18, 72%). However, MMR-deficient Lynch syndrome-associated adenomas had less APC or CTNNB1 mutations (25/68, 37%) and frequent frameshift RNF43 mutations involving mononucleotide repeats (45/68, 66%). Furthermore, frameshift mutations affecting repeat sequences constituted 14 of 26 APC mutations (54%) in MMR-deficient adenomas whereas these frameshift mutations were rare in MMR-proficient adenomas in patients with Lynch syndrome (1/12, 8%) and in sporadic adenomas (3/52, 6%). Lynch syndrome-associated adenocarcinomas exhibited mutation profiles similar to those of MMR-deficient adenomas. Considering that WNT pathway activation sufficiently drives colorectal adenoma formation, the distinct mutation profiles of WNT pathway genes in Lynch syndrome-associated adenomas suggest that MMR deficiency commonly precedes adenoma formation.

Molecular genetics of microsatellite-unstable colorectal cancer for pathologists

Background

Microsatellite-unstable colorectal cancers (CRC) that are due to deficient DNA mismatch repair (dMMR) represent approximately 15% of all CRCs in the United States. These microsatellite-unstable CRCs represent a heterogenous group of diseases with distinct oncogenesis pathways. There are overlapping clinicopathologic features between some of these groups, but many important differences are present. Therefore, determination of the etiology for the dMMR is vital for proper patient management and follow-up.

Main body

Epigenetic inactivation of MLH1 MMR gene (sporadic microsatellite-unstable CRC) and germline mutation in an MMR gene (Lynch syndrome, LS) are the two most common mechanisms in the pathogenesis of microsatellite instability in CRC. However, in a subset of dMMR CRC cases that are identified by screening tests, no known LS-associated genetic alterations are appreciated by current genetic analysis. When the etiology for dMMR is unclear, it leads to patient anxiety and creates challenges for clinical management.

Conclusion

It is critical to distinguish LS patients from other patients with tumors due to dMMR, so that the proper screening protocol can be employed for the patients and their families, with the goal to save lives while avoiding unnecessary anxiety and costs. This review summarizes the major pathogenesis pathways of dMMR CRCs, their clinicopathologic features, and practical screening suggestions. In addition, we include frequently asked questions for MMR immunohistochemistry interpretation.

Molecular Subtypes of Colorectal Cancer and Their Clinicopathologic Features, With an Emphasis on the Serrated Neoplasia Pathway

CONTEXT

-Colorectal cancer is a heterogeneous disease entity with 3 molecular carcinogenesis pathways and 2 morphologic multistep pathways. Right-sided colon cancers and left-sided colon and rectal cancers exhibit differences in their incidence rates according to geographic region, age, and sex. A linear tendency toward increasing frequencies of microsatellite instability-high or CpG island methylator phenotype-high cancers in subsites along the bowel from the rectum to the cecum or the ascending colon accounts for the differences in tumor phenotypes associated with these subsites. The molecular subtypes of colorectal cancers exhibit different responses to adjuvant therapy, which might be responsible for differences in subtype-specific survival.

OBJECTIVES

-To review the clinicopathologic and molecular features of the molecular subtypes of colorectal cancer generated by combined CpG island methylator phenotype and microsatellite statuses, to integrate these features with the most recent findings in the context of the prognostic implications of molecular subtypes, and to emphasize the necessity of developing molecular markers that enable the identification of adenocarcinomas involving the serrated neoplasia pathway.

DATA SOURCES

-Based on the authors' own experimental data and a review of the pertinent literature.

CONCLUSIONS

-Because colorectal cancers arise from 2 different morphologic multistep carcinogenesis pathways with varying contributions from 3 different molecular carcinogenesis pathways, colorectal cancer is a heterogeneous and complex disease. Thus, molecular subtyping of colorectal cancers is an important approach to characterizing their heterogeneity with respect to not only prognosis and therapeutic response but also biology and natural history.

[Prevalence of altered mismatch repair protein nuclear expression detected by immunohistochemistry on adenomas with high-grade dysplasia and features associated with this risk in a population-based study]

INTRODUCTION

Alteration of mismatch repair system protein expression detected by immunohistochemistry (IHQ) in tumoural tissue is a useful technique for Lynch Syndrome (LS) screening. A recent review proposes LS screening through immunohistochemical study not only in all diagnosed cases of colorectal cancer (CRC) but also in advanced adenomas, especially in young patients.

OBJECTIVE

To assess the prevalence of altered IHQ carried out in all adenomas with high-grade dysplasia (HGD) diagnosed in our community in 2011, as well as the variables associated with this alteration.

METHODS

We included all the cases of adenomatous polyps with HGD diagnosed in the three public pathology laboratories of Navarre during 2011 and performed a statistical study to assess the association between different patient and lesion characteristics and altered IHQ results.

RESULTS

A total of 213 colonic adenomas with HGD were diagnosed, and 26 (12.2%) cases were excluded from the final analysis (2 known LS, 22 without IHQ study and 2 with inconclusive IHQ studies). The final number of adenomas included was 187. Pathologic results were found in 10 cases (5.35%)-6 cases in MLH1 and PMS2, 2 cases in PMS2, 1 case in MSH6 and 1 case in MSH2 and MSH6. The factors showing a statistically significant association with the presence of abnormal proteins were the synchronous presence of CRC, the presence of only one advanced adenoma, proximal location of HGD and age <50 years.

CONCLUSIONS

The percentage of pathologic nuclear expression found in IHQ is high. Consequently, screening of all diagnosed HGD could be indicated, especially in young patients, with a single AA and proximal HGD.

Mismatch repair deficient-crypts in non-neoplastic colonic mucosa in Lynch syndrome: insights from an illustrative case

Mono-allelic germline mutations in DNA mismatch repair (MMR) genes lead to Lynch syndrome (LS). Questions remain as to the timing of the inactivation of the wild-type allele in LS-associated tumorigenesis. Speculation exists that it happens after the neoplasia has been initiated. However, a recent study reported the presence of MMR-deficiency in non-neoplastic colonic crypts in LS; thus the possibility can be raised that these crypts may be tumor precursors, and as such, biallelic loss of MMR may occur prior to neoplasia. Here we report a unique case that showed findings supporting both of the two seemingly conflicting notions. The patient was a 40-year-old female with LS, MSH2 type, who underwent a segmental colectomy for an adenocarcinoma. By immunohistochemistry, the carcinoma lost MSH2/MSH6. Interestingly, there was also complete loss of MSH2/MSH6 in a distinct focus of 20 colonic crypts that were morphologically non-neoplastic, thus supporting the possibility of biallelic loss of MMR before initiation of neoplasia. However, in a separate adenoma, MMR was preserved in neoplastic glands with low grade dysplasia and lost only in glands with high grade dysplasia, i.e., MMR loss after tumor initiation. These are relevant findings with regard to the timing of MMR deficiency in LS tumorigenesis, and bring forth the possibility that varied tumorigenic pathways may exist. Additionally, we observed that the MMR-deficient non-neoplastic crypts harbored increased intraepithelial CD8-positive T-lymphocytes similar to the patient's carcinoma, providing a potential new venue for the study of the natural antitumor immune responses in LS individuals.

Improved Detection of Microsatellite Instability in Early Colorectal Lesions

Microsatellite instability (MSI) occurs in over 90% of Lynch syndrome cancers and is considered a hallmark of the disease. MSI is an early event in colon tumor development, but screening polyps for MSI remains controversial because of reduced sensitivity compared to more advanced neoplasms. To increase sensitivity, we investigated the use of a novel type of marker consisting of long mononucleotide repeat (LMR) tracts. Adenomas from 160 patients, ranging in age from 29–55 years old, were screened for MSI using the new markers and compared with current marker panels and immunohistochemistry standards. Overall, 15 tumors were scored as MSI-High using the LMRs compared to 9 for the NCI panel and 8 for the MSI Analysis System (Promega). This difference represents at least a 1.7-fold increase in detection of MSI-High lesions over currently available markers. Moreover, the number of MSI-positive markers per sample and the size of allelic changes were significantly greater with the LMRs (p = 0.001), which increased confidence in MSI classification. The overall sensitivity and specificity of the LMR panel for detection of mismatch repair deficient lesions were 100% and 96%, respectively. In comparison, the sensitivity and specificity of the MSI Analysis System were 67% and 100%; and for the NCI panel, 75% and 97%. The difference in sensitivity between the LMR panel and the other panels was statistically significant (p<0.001). The increased sensitivity for detection of MSI-High phenotype in early colorectal lesions with the new LMR markers indicates that MSI screening for the early detection of Lynch syndrome might be feasible.

Clinicopathological comparison of colorectal and endometrial carcinomas in patients with Lynch-like syndrome versus patients with Lynch syndrome

Screening for DNA mismatch repair (MMR) deficiency in colorectal and endometrial carcinomas identifies patients at risk for Lynch syndrome. Some patients with MMR-deficient tumors have no evidence of a germline mutation and have been described as having Lynch-like syndrome. We compared the clinicopathological features of colorectal and endometrial carcinomas in patients with Lynch-like syndrome and Lynch syndrome. Universal screening identified 356 (10.6%) of 3352 patients with colorectal carcinoma and 72 (33%) of 215 patients with endometrial carcinoma with deficient DNA MMR. Sixty-six patients underwent germline mutation analysis with 45 patients (68%) having evidence of a germline MMR gene mutation confirming Lynch syndrome and 21 patients (32%) having Lynch-like syndrome with no evidence of a germline mutation. Most patients with Lynch-like syndrome had carcinoma involving the right colon compared to patients with Lynch syndrome (93% versus 45%; P < .002). All patients with colorectal carcinomas demonstrating isolated loss of MSH6 expression had Lynch syndrome confirmed by germline mutation analysis. Synchronous or metachronous Lynch syndrome-associated carcinoma was more frequently identified in patients with Lynch syndrome compared to Lynch-like syndrome (38% versus 7%; P = .04). There were no significant differences in clinicopathological variables between patients with Lynch-like syndrome and Lynch syndrome with endometrial carcinoma. In summary, 32% of patients with MMR deficiency concerning Lynch syndrome will have Lynch-like syndrome. Our results demonstrate that patients with Lynch-like syndrome are more likely to have right-sided colorectal carcinoma, less likely to have synchronous or metachronous Lynch syndrome-associated carcinoma, and less likely to demonstrate isolated loss of MSH6 expression within their tumor.

Practical opportunities to improve early detection and prevention of colorectal cancer (CRC) in members of high-risk families

Colorectal cancer (CRC) incidence and mortality are steadily declining and CRC screening rates are increasing in the United States. Although this a very good news, several definable groups still have very low screening rates including younger (under age 50) members of high-risk CRC families. This opinion piece describes five strategies that could be incorporated into routine practice to improve identification and guideline-based screening in members of high-risk families. Routine incorporation of a simple family history screening tool and outreach to high-risk family members could substantially improve guideline-based screening in this population. Identification of CRCs and advanced adenomas in the endoscopy suite defines another group of high-risk families for similar outreach. Lynch syndrome families can be identified by testing CRCs and selected adenomas for microsatellite instability or loss of DNA repair protein expression. Finally, selective addition of aspirin to surveillance endoscopy can decrease the risk of new adenomas and CRCs. The rationale for these strategies as well as mechanisms for their implementation and evaluation in clinical practice is described.

Evaluation of colorectal cancers for Lynch syndrome: practical molecular diagnostics for surgical pathologists

Lynch syndrome is the most common inherited colorectal cancer syndrome, accounting for 2-4% of all colorectal cancer cases. This review focuses on the tissue workup of Lynch syndrome, including methods to determine whether or not a tumor is mismatch repair deficient, and whether a mismatch repair-deficient tumor is sporadic or Lynch syndrome-associated. Strategies for determining which tumors to test and how best to implement a Lynch syndrome screening program are also discussed, as well as potential developments in the future.

Advanced colorectal adenomas in patients under 45 years of age are mostly sporadic

BACKGROUND

The presence of advanced adenomas in younger individuals is a criterion for Lynch syndrome (LS). However, the utility of screening advanced adenomas for loss of mismatch repair (MMR) protein expression to identify suspected LS remains unclear.

AIMS

Determine the prevalence of MMR defects to understand whether these patients harbor a defined genetic risk for CRC.

METHODS

The study cohort included adult patients ≤45 years of age with advanced adenomas (villous histology, ≥1 cm in diameter, ≥3 polyps of any size) endoscopically removed between 2001 and 2011. Clinical records were reviewed along with detailed pathological review and immunohistochemical MMR analysis.

RESULTS

A total of 76 (40.1 % male, age 40.6 ± 5.4 years) patients met inclusion and exclusion criteria. Indications for colonoscopy were gastrointestinal (GI) bleeding 39 (51.3 %), CRC in a first-degree relative 17 (22.4 %) and somatic GI symptoms 20 (26.3 %). Index colonoscopy revealed a median of 1 adenoma (range 1-4), mean diameter of 12.9 ± 7.1 mm, 40 (52.6 %) with villous histology. The mean follow-up duration was 3.3 ± 2 years. Recurrent adenomas developed in 24 (31.6 %), of which 8 (10.5 %) were advanced adenomas; none of these patients developed CRC. One of 66 (1.5 %) adenomas available for immunohistochemical (IHC) testing revealed loss of MLH1 and PMS2.

CONCLUSIONS

IHC screening of advanced adenomas from patients younger than 45 years of age identified potential LS in one of 64 patients. The low yield of IHC screening in this population suggests that universal IHC screening of advanced adenomas from patients younger than 45 years of age for MMR defects is not an efficient strategy for identifying LS subjects.

Lynch syndrome-associated neoplasms: a discussion on histopathology and immunohistochemistry

It was a century ago that Warthin, a pathologist, first described the clinical condition now known as Lynch syndrome. One hundred years later, our understanding of this syndrome has advanced significantly. Much of the progress took place over the last 25 years and was marked by a series of interacting developments from the disciplines of clinical oncology, pathology, and molecular genetics, with each development serving to guide or enhance the next. The advancement of our understanding about the pathology of Lynch syndrome associated tumors exemplifies such intimate interplay among disciplines. Today, accumulative knowledge has enabled surgical pathologists to detect tumors that are likely to be associated with Lynch syndrome, and the pathologist is playing an increasingly more important role in the care of these patients. The pathologist's ability is afforded primarily by information gained from tumor histopathology and by DNA mismatch repair protein immunohistochemistry. It is therefore pertinent both for the pathologists to accurately ascertain this morphologic information, and for all that are involved in the care of these patients to thoroughly understand the implications of such information. This article provides an overview of the development of histopathology and immunohistochemistry in Lynch syndrome-associated tumors, particularly in colorectal and endometrial cancers, and outlines the issues and current status of these specific pathologic aspects in not only the major tumors but also those less commonly seen or only newly reported in Lynch syndrome patients.

Colorectal dysplasia in inflammatory bowel disease: a clinicopathologic perspective

Surveillance for neoplasia in colitis is the most challenging diagnostic colonoscopic procedure. The detection and treatment of colorectal dysplasia in inflammatory bowel disease remain problematic to the point that unsuspected colorectal cancers (CRCs) are still identified. Excellent bowel preparation and use of high-resolution colonoscopes with chromoendoscopy facilitate the detection and characterization of subtle neoplasia. This approach is superior to taking random biopsy specimens and should be the standard of care for surveillance but requires adequate training. Suspicious lesions should be assessed carefully and described using objective terminology. The terms dysplasia-associated lesions/masses and flat dysplasia are best avoided because they may be open to misinterpretation. Most suspicious lesions detected during surveillance can be removed endoscopically, precluding the need for surgery. Nevertheless, endotherapy in colitis can be difficult as a result of underlying inflammation and scarring. Lesions that are not endoscopically resectable need to be removed surgically, although the possibility that some lesions might be amenable to local resection (including lymphadenectomy) rather than subtotal colectomy may need to be re-evaluated. Despite surveillance programs, patients still present clinically with CRC. This may occur because lesions are missed (possibly because of the failure to use optimal techniques), lesions are not adequately removed, patients fail to return for colonoscopy, or CRCs arise rapidly in mucosa that is minimally dysplastic and the CRCs are not recognized as being potentially invasive even on biopsy. Future advances in, for example, stool DNA assays, use of confocal endomicroscopy, or use of endoscopic ultrasound, may help in the identification of high-risk patients and the assessment of dysplastic lesions.