Sessile serrated polyps of the colorectum are rare in patients with Lynch syndrome and in familial colorectal cancer families

Novel insights into tumorigenesis revealed by molecular analysis of Lynch syndrome cases with multiple colorectal tumors

Background

Lynch syndrome (LS) is an autosomal dominant multi-organ cancer syndrome with a high lifetime risk of cancer. The number of cumulative colorectal adenomas in LS does not generally exceed ten, and removal of adenomas via routine screening minimizes the cancer burden. However, abnormal phenotypes may mislead initial diagnosis and subsequently cause suboptimal treatment.

Aim

Currently, there is no standard guide for the care of multiple colorectal adenomas in LS individuals. We aimed to shed insight into the molecular features and reasons for multiplicity of adenomas in LS patients.

Methods

We applied whole exome sequencing on nine adenomas (ten samples) and three assumed primary carcinomas (five samples) of an LS patient developing the tumors during a 21-year follow-up period. We compared the findings to the tumor profiles of two additional LS cases ascertained through colorectal tumor multiplicity, as well as to ten adenomas and 15 carcinomas from 23 unrelated LS patients with no elevated adenoma burden from the same population. As LS associated cancers can arise via several molecular pathways, we also profiled the tumors for CpG Island Methylator Phenotype (CIMP), and LINE-1 methylation.

Results

All tumors were microsatellite unstable (MSI), and MSI was present in several samples derived from normal mucosa as well. Interestingly, frequent frameshift variants in RNF43 were shared among substantial number of the tumors of our primary case and the tumors of LS cases with multiple tumors but almost absent in our control LS cases. The RNF43 variants were completely absent in the normal tissue, indicating tumor-associated mutational hotspots. The RNF43 status correlated with the mutational signature SBS96. Contrary to LS tumors from the reference set with no elevated colorectal tumor burden, the somatic variants occurred significantly more frequently at C>T in the CpG context, irrespective of CIMP or LINE-1 status, potentially indicating other, yet unknown methylation-related mechanisms. There were no signs of somatic mosaicism affecting the MMR genes. Somatic variants in APC and CTNNB1 were unique to each tumor.

Conclusion

Frequent somatic RNF43 hot spot variants combined with SBS96 signature and increased tendency to DNA methylation may contribute to tumor multiplicity in LS.

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.

Novel methylated DNA markers accurately discriminate Lynch syndrome associated colorectal neoplasia

Aim:

Acquired molecular changes in Lynch syndrome (LS) colorectal tumors have been largely unstudied. We identified methylated DNA markers (MDMs) for discrimination of colorectal neoplasia in LS and determined if these MDMs were comparably discriminant in sporadic patients.

Patients & methods:

For LS discovery, we evaluated DNA from 53 colorectal case and control tissues using next generation sequencing. For validation, blinded methylation-specific PCR assays to the selected MDMs were performed on 197 cases and controls.

Results:

OPLAH was the most discriminant MDM with areas under the receiver operating characteristic curve ≥0.97 for colorectal neoplasia in LS and sporadic tissues. ALKBH5, was uniquely hypermethylated in LS neoplasms.

Conclusion:

Highly discriminant MDMs for colorectal neoplasia in LS were identified with potential use in screening and surveillance.

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.

Hereditary or Not? Understanding Serrated Polyposis Syndrome

PURPOSE OF REVIEW

To present the current understanding of the diagnosis, management, and potential genetic causes of serrated polyposis syndrome.

RECENT FINDINGS

The clinical criteria for serrated polyposis syndrome was recently updated and now includes individuals with five or more serrated polyps proximal to the rectum that are 5 mm in size or greater and at least two that are 10 mm in size of greater as well as individuals with 20 or more serrated polyps throughout the colon with at least five proximal to the rectum. There is a significant risk for colon cancer in first-degree relatives of individuals with serrated polyposis syndrome. However, less than 3% of serrated polyposis syndrome cases are explained by identifiable germline mutations, with mutations in RNF43 being the only currently validated genetic cause. Serrated polyposis syndrome is rarely explained by identifiable germline mutations, but there remains an increased risk for colorectal cancer in first-degree relatives. Referral for genetic counseling and testing is recommended for individuals with serrated polyposis syndrome and a personal history of coexisting adenomatous polyposis or with a concerning family history and can be considered for all individuals with serrated polyposis syndrome. Close endoscopic surveillance of those with serrated polyposis syndrome and their first-degree relatives is recommended. Continued efforts at identifying hereditary causes of serrated polyposis are needed.

Serrated Colorectal Cancer: The Road Less Travelled?

Studies of colorectal cancer (CRC) originating through the conventional adenoma-carcinoma sequence have provided insight into the molecular mechanisms controlling its initiation and progression. Less is known about the alternative 'serrated' pathway, which has been associated with BRAF mutation and microsatellite instability. Recent transcriptomics approaches to classify human CRC revealed that mesenchymal and/or desmoplastic features combined with an immunosuppressive microenvironment are key determinants of CRC with the poorest prognosis. Importantly, these aggressive CRCs harbor the characteristics of serrated tumors, suggesting that initiation through this alternative pathway determines how aggressive the CRC becomes. Here, we review recent evidence on how serrated carcinogenesis contributes to the subtype of CRC with the poorest prognosis.

Ionizing radiation, inflammation, and their interactions in colon carcinogenesis in Mlh1-deficient mice

Genetic, physiological and environmental factors are implicated in colorectal carcinogenesis. Mutations in the mutL homolog 1 (MLH1) gene, one of the DNA mismatch repair genes, are a main cause of hereditary colon cancer syndromes such as Lynch syndrome. Long-term chronic inflammation is also a key risk factor, responsible for colitis-associated colorectal cancer; radiation exposure is also known to increase colorectal cancer risk. Here, we studied the effects of radiation exposure on inflammation-induced colon carcinogenesis in DNA mismatch repair-proficient and repair-deficient mice. Male and female Mlh1^−/− and Mlh1^+/+ mice were irradiated with 2 Gy X-rays when aged 2 weeks or 7 weeks and/or were treated with 1% dextran sodium sulfate (DSS) in drinking water for 7 days at 10 weeks old to induce mild inflammatory colitis. No colon tumors developed after X-rays and/or DSS treatment in Mlh1^+/+ mice. Colon tumors developed after DSS treatment alone in Mlh1^−/− mice, and exposure to radiation prior to DSS treatment increased the number of tumors. Histologically, colon tumors in the mice resembled the subtype of well-to-moderately differentiated adenocarcinomas with tumor-infiltrating lymphocytes of human Lynch syndrome. Immunohistochemistry revealed that expression of both p53 and β-catenin and loss of p21 and adenomatosis polyposis coli proteins were observed at the later stages of carcinogenesis, suggesting a course of molecular pathogenesis distinct from typical sporadic or colitis-associated colon cancer in humans. In conclusion, radiation exposure could further increase the risk of colorectal carcinogenesis induced by inflammation under the conditions of Mlh1 deficiency.

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.

Serrated lesions of the colorectum: review and recommendations from an expert panel

Serrated lesions of the colorectum are the precursors of perhaps one-third of colorectal cancers (CRCs). Cancers arising in serrated lesions are usually in the proximal colon, and account for a disproportionate fraction of cancer identified after colonoscopy. We sought to provide guidance for the clinical management of serrated colorectal lesions based on current evidence and expert opinion regarding definitions, classification, and significance of serrated lesions. A consensus conference was held over 2 days reviewing the topic of serrated lesions from the perspectives of histology, molecular biology, epidemiology, clinical aspects, and serrated polyposis. Serrated lesions should be classified pathologically according to the World Health Organization criteria as hyperplastic polyp, sessile serrated adenoma/polyp (SSA/P) with or without cytological dysplasia, or traditional serrated adenoma (TSA). SSA/P and TSA are premalignant lesions, but SSA/P is the principal serrated precursor of CRCs. Serrated lesions have a distinct endoscopic appearance, and several lines of evidence suggest that on average they are more difficult to detect than conventional adenomatous polyps. Effective colonoscopy requires an endoscopist trained in the endoscopic appearance of serrated lesions. We recommend that all serrated lesions proximal to the sigmoid colon and all serrated lesions in the rectosigmoid > 5 mm in size, be completely removed. Recommendations are made for post-polypectomy surveillance of serrated lesions and for surveillance of serrated polyposis patients and their relatives.

Beta-catenin nuclear labeling is a common feature of sessile serrated adenomas and correlates with early neoplastic progression after BRAF activation

Recent observations indicate that some sessile serrated adenomas (SSAs) have aberrant beta-catenin nuclear labeling, implicating the Wnt pathway in the molecular progression of SSAs to colorectal carcinoma. We sought to expand upon this finding by characterizing beta-catenin expression in the full spectrum of serrated colorectal polyps, and correlating these findings with the genetic status of BRAF, KRAS and CTNNB1. Immunolabeling for beta-catenin confirmed the presence of abnormal nuclear accumulation in SSAs, with 35/54 (67%) SSAs showing nuclear labeling compared with 0/12 hyperplastic polyps. Abnormal nuclear labeling was also identified in 4/11 (36%) traditional serrated adenomas (TSAs) (P=0.00001). When SSAs were further analyzed with respect to the presence or absence of conventional epithelial dysplasia, nuclear beta-catenin labeling was seen in 8/27 (29%) SSAs without dysplasia (SSA) but in 27/27 (100%) of SSAs with dysplasia (P=0.000001). Sequencing of genomic DNA extracted from a subset of hyperplastic polyps, SSAs, SSAs with dysplasia, TSAs and tubular adenomas failed to identify any CTNNB1 mutations to account for abnormal beta-catenin nuclear labeling. However, abnormal nuclear labeling always occurred in the setting of a BRAF V600E mutation, indicating aberrant nuclear labeling occurs on a background of BRAF activation. Of interest, all 6 TSAs contained a KRAS mutation confirming that SSAs and TSAs are genetically distinct entities. These findings validate previous reports implicating activation of the Wnt signaling pathway in SSAs, and further indicate that Wnt pathway activation plays a role in the neoplastic progression of SSAs and TSAs to colonic carcinoma by mechanisms independent of CTNNB1 mutation.

Is the phenotype mixed or mistaken? Hereditary nonpolyposis colorectal cancer and hyperplastic polyposis syndrome

PURPOSE

Hereditary nonpolyposis colorectal cancer is a hereditary syndrome defined by personal and family history of colorectal and other cancers. Some patients with this condition have multiple serrated polyps, which are the hallmark of hyperplastic polyposis syndrome, a rare colorectal cancer syndrome characterized by multiple hyperplastic/serrated polyps and an increased risk of colorectal cancer. We hypothesized that this may represent a unique group of patients, and this study investigates a possible association between the two syndromes.

METHODS

A hereditary colorectal cancer registry was reviewed for patients who fit hereditary nonpolyposis colorectal cancer or familial colorectal cancer and hyperplastic polyposis syndrome criteria.

RESULTS

Twelve patients from seven families were identified. Four families had more than one person meeting the criteria. All patients were white, and four were women. Ten of 12 patients fit Amsterdam criteria, and two were designated with familial colorectal cancer. The median cumulative number of hyperplastic polyps resected per patient was 6, half of which were located in the right colon. Seven of the 12 patients developed colorectal cancer. Ten patients had personal or family history of other cancers: prostate, breast, testicular, salivary gland, lung, and Hodgkin's disease.

CONCLUSIONS

Patients meeting criteria for hereditary nonpolyposis colorectal cancer may also carry a diagnosis of hyperplastic polyposis syndrome. Possible explanations include: 1) two hereditary syndromes are present in the same patient, 2) serrated polyps are part of the phenotype of hereditary nonpolyposis colorectal cancer, or 3) hereditary nonpolyposis colorectal cancer is potentially misdiagnosed in some families who do, in fact, have hyperplastic polyposis.

Analysis of families with Lynch syndrome complicated by advanced serrated neoplasia: the importance of pathology review and pedigree analysis

The identification of Lynch syndrome has been greatly assisted by the advent of tumour immunohistochemistry (IHC) for mismatch repair (MMR) proteins, and by the recognition of the role of acquired somatic BRAF mutation in sporadic MMR-deficient colorectal cancer (CRC). However, somatic BRAF mutation may also be present in the tumours in families with a predisposition to develop serrated polyps in the colorectum. In a subgroup of affected members in these families, CRCs emerge which demonstrate clear evidence of MMR deficiency with absent MLH1 staining and high-level microsatellite instability (MSI). This may result in these families being erroneously classified as Lynch syndrome, or conversely, an individual is considered "sporadic" due to the presence of a somatic BRAF mutation in a tumour. In this report, we describe two Lynch syndrome families who demonstrated several such inconsistencies. In one family, IHC deficiency of both MSH2 and MLH1 was demonstrated in tumours from different affected family members, presenting a confusing diagnostic picture. In the second family, MLH1 loss was observed in the lesions of both MLH1 mutation carriers and those who showed normal MLH1 germline sequence. Both families had Lynch syndrome complicated by an independently segregating serrated neoplasia phenotype, suggesting that in families such as these, tumour and germline studies of several key members, rather than of a single proband, are indicated to clarify the spectrum of risk.