Traditional serrated adenoma has two pathways of neoplastic progression that are distinct from the sessile serrated pathway of colorectal carcinogenesis

Host genetics-associated mechanisms in colorectal cancer

Colorectal cancer (CRC) represents the second leading cause of cancer incidence and the third leading cause of cancer deaths worldwide. There is currently a lack of understanding of the onset of CRC, hindering the development of effective prevention strategies, early detection methods and the selection of appropriate therapies. This article outlines the key aspects of host genetics currently known about the origin and development of CRC. The organisation of the colonic crypts is described. It discusses how the transformation of a normal cell to a cancer cell occurs and how that malignant cell can populate an entire colonic crypt, promoting colorectal carcinogenesis. Current knowledge about the cell of origin of CRC is discussed, and the two morphological pathways that can give rise to CRC, the classical and alternative pathways, are presented. Due to the molecular heterogeneity of CRC, each of these pathways has been associated with different molecular mechanisms, including chromosomal and microsatellite genetic instability, as well as the CpG island methylator phenotype. Finally, different CRC classification systems are described based on genetic, epigenetic and transcriptomic alterations, allowing diagnosis and treatment personalisation.

Dysbiosis promotes recurrence of adenomatous polyps in the distal colorectum

BACKGROUND

Colorectal polyps, which are characterized by a high recurrence rate, represent preneoplastic conditions of the intestine. Due to unclear mechanisms of pathogenesis, first-line therapies for non-hereditary recurrent colorectal polyps are limited to endoscopic resection. Although recent studies suggest a mechanistic link between intestinal dysbiosis and polyps, the exact compositions and roles of bacteria in the mucosa around the lesions, rather than feces, remain unsettled.

AIM

To clarify the composition and diversity of bacteria in the mucosa surrounding or 10 cm distal to recurrent intestinal polyps.

METHODS

Mucosal samples were collected from four patients consistently with adenomatous polyps (Ade), seven consistently with non-Ade (Pol), ten with current Pol but previous Ade, and six healthy individuals, and bacterial patterns were evaluated by 16S rDNA sequencing. Linear discriminant analysis and Student's t-tests were used to identify the genus-level bacteria differences between groups with different colorectal polyp phenotypes. Pearson's correlation coefficients were used to evaluate the correlation between intestinal bacteria at the genus level and clinical indicators.

RESULTS

The results confirmed a decreased level of probiotics and an enrichment of pathogenic bacteria in patients with all types of polyps compared to healthy individuals. These changes were not restricted to the mucosa within 0.5 cm adjacent to the polyps, but also existed in histologically normal tissue 10 cm distal from the lesions. Significant differences in bacterial diversity were observed in the mucosa from individuals with normal conditions, Pol, and Ade. Increased abundance of Gram-negative bacteria, including Klebsiella, Plesiomonas, and Cronobacter, was observed in Pol group and Ade group, suggesting that resistance to antibiotics may be one risk factor for bacterium-related harmful environment. Meanwhile, age and gender were linked to bacteria changes, indicating the potential involvement of sex hormones.

CONCLUSION

These preliminary results support intestinal dysbiosis as an important risk factor for recurrent polyps, especially adenoma. Targeting specific pathogenic bacteria may attenuate the recurrence of polyps.

Nonconventional Dysplasia is Frequently Associated With Goblet Cell Deficient and Serrated Variants of Colonic Adenocarcinoma in Inflammatory Bowel Disease

Various subtypes of nonconventional dysplasia have been recently described in inflammatory bowel disease (IBD). We hypothesized that goblet cell deficient dysplasia and serrated dysplasia may be the primary precursor lesions for goblet cell deficient (GCDAC) and serrated (SAC) variants of colonic adenocarcinoma, respectively. Clinicopathologic features of 23 GCDAC and 10 SAC colectomy cases were analyzed. All dysplastic lesions found adjacent to the colorectal cancers (n = 22 for GCDACs and n = 10 for SACs) were subtyped as conventional, nonconventional, or mixed-type dysplasia. As controls, 12 IBD colectomy cases with well to moderately differentiated adenocarcinoma that lacked any mucinous, signet ring cell, low-grade tubuloglandular, or serrated features while retaining goblet cells throughout the tumor (at least 50% of the tumor) were evaluated. The cohort consisted of 19 (58%) men and 14 (42%) women, with a mean age of 53 years and a long history of IBD (mean duration: 18 y). Twenty-seven (82%) patients had ulcerative colitis. GCDACs (57%) were more often flat or invisible than SACs (10%) and controls (25%; P = 0.023). The GCDAC and SAC groups were more likely to show lymphovascular invasion (GCDAC group: 52%, SAC group: 50%, control group: 0%, P = 0.001) and lymph node metastasis (GCDAC group: 39%, SAC group: 50%, control group: 0%, P = 0.009) than the control group. Notably, GCDACs and SACs were more frequently associated with nonconventional dysplasia than controls (GCDAC group: 77%, SAC group: 40%, control group: 0%, P < 0.001). Goblet cell deficient dysplasia (73%) was the most prevalent dysplastic subtype associated with GCDACs ( P = 0.049), whereas dysplasias featuring a serrated component (60%) were most often associated with SACs ( P = 0.001). The GCDAC group (75%) had a higher rate of macroscopically flat or invisible synchronous dysplasia compared with the SAC (20%) and control (33%) groups ( P = 0.045). Synchronous dysplasia demonstrated nonconventional dysplastic features more frequently in the GCDAC (69%) and SAC (40%) groups compared with the control group (0%; P = 0.016). In conclusion, goblet cell deficient dysplasia and dysplasias featuring a serrated component could potentially serve as high-risk markers for GCDACs and SACs, respectively.

Downregulation of SMOC1 is associated with progression of colorectal traditional serrated adenomas

BACKGROUND

Aberrant DNA methylation is prevalent in colorectal serrated lesions. We previously reported that the CpG island of SMOC1 is frequently methylated in traditional serrated adenomas (TSAs) and colorectal cancers (CRCs) but is rarely methylated in sessile serrated lesions (SSLs). In the present study, we aimed to further characterize the expression of SMOC1 in early colorectal lesions.

METHODS

SMOC1 expression was analyzed immunohistochemically in a series of colorectal tumors (n = 199) and adjacent normal colonic tissues (n = 112).

RESULTS

SMOC1 was abundantly expressed in normal colon and SSLs while it was significantly downregulated in TSAs, advanced adenomas and cancers. Mean immunohistochemistry scores were as follows: normal colon, 24.2; hyperplastic polyp (HP), 18.9; SSL, 23.8; SSL with dysplasia (SSLD)/SSL with early invasive cancer (EIC), 15.8; TSA, 5.4; TSA with high grade dysplasia (HGD)/EIC, 4.7; non-advanced adenoma, 21.4; advanced adenoma, 11.9; EIC, 10.9. Higher levels SMOC1 expression correlated positively with proximal colon locations and flat tumoral morphology, reflecting its abundant expression in SSLs. Among TSAs that contained both flat and protruding components, levels of SMOC1 expression were significantly lower in the protruding components.

CONCLUSION

Our results suggest that reduced expression of SMOC1 is associated with progression of TSAs and conventional adenomas and that SMOC1 expression may be a biomarker for diagnosis of serrated lesions and risk prediction in colorectal tumors.

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.

Sessile serrated lesions with dysplasia: is it possible to nip them in the bud?

The serrated neoplasia pathway constitutes an "alternative route" to colorectal cancer (CRC), and sessile serrated lesions with dysplasia (SSLDs) are an intermediate step between sessile serrated lesions (SSLs) and invasive CRC in this pathway. While SSLs show indolent growth before becoming dysplastic (> 10-15 years), SSLDs are considered to rapidly progress to either immunogenic microsatellite instable-high (MSI-H) CRC (presumably 75% of cases) or mesenchymal microsatellite stable (MSS) CRC. Their flat shapes and the relatively short window of this intermediate state make it difficult to detect and diagnose SSLDs; thus, these lesions are potent precursors of post-colonoscopy/interval cancers. Confusing terminology and the lack of longitudinal observation data of serrated polyps have hampered the accumulation of knowledge about SSLDs; however, a growing body of evidence has started to clarify their characteristics and biology. Together with recent efforts to incorporate terminology, histological studies of SSLDs have identified distinct dysplastic patterns and revealed alterations in the tumor microenvironment (TME). Molecular studies at the single-cell level have identified distinct gene alterations in both the epithelium and the TME. Mouse serrated tumor models have demonstrated the importance of TME in disease progression. Advances in colonoscopy provide clues to distinguish pre-malignant from non-malignant-SSLs. Recent progress in all aspects of the field has enhanced our understanding of the biology of SSLDs. The aim of this review article was to assess the current knowledge of SSLDs and highlight their clinical implications.

Serrated polyps in patients with ulcerative colitis: Unique clinicopathological and biological characteristics

BACKGROUND

Serrated polyps have recently been reported in patients with ulcerative colitis (UC); however, their prevalence and detailed characteristics remain unclear.

METHODS

The prevalence and clinicopathological and biological characteristics of serrated polyps in patients with UC were retrospectively examined in a single tertiary inflammatory bowel disease center in Japan from 2000 to 2020.

RESULTS

Among 2035 patients with UC who underwent total colonoscopy, 252 neoplasms, including 36 serrated polyps (26 in colitis-affected segments, 10 in colitis-unaffected segments), were identified in 187 patients with UC. The proportion of serrated polyps was 1.8% (36/2035). Serrated polyps in colitis-affected segments were common with extensive colitis (88%), history of persistent active colitis (58%), and long UC duration (12.1 years). Serrated polyps in colitis-affected segments were more common in men (88%). Of the 26 serrated polyps in colitis-affected segments, 15, 6, and 5 were categorized as sessile serrated lesion-like dysplasia, traditional serrated adenoma-like dysplasia, and serrated dysplasia not otherwise specified, respectively. Sessile serrated lesion-like dysplasia was common in the proximal colon (67%) and with BRAF mutation (62%), whereas traditional serrated adenoma-like dysplasia and serrated dysplasia not otherwise specified were common in the distal colon (100% and 80%, respectively) and with KRAS mutations (100% and 75%, respectively).

CONCLUSIONS

Serrated polyps comprised 14% of the neoplasias in patients with UC. Serrated polyps in colitis-affected segments were common in men with extensive and longstanding colitis, suggesting chronic inflammation in the development of serrated polyps in patients with UC.

Novel prognostic implications of complement activation in the tumour microenvironment for de novo metastatic BRAF V600E mutant colorectal cancer

BACKGROUND

Prognosis of metastatic BRAF V600E mutant colorectal cancer (CRC) is poor, and the prognostic implications of immune contextures in the tumour microenvironment (TME) for CRC remain elusive.

METHODS

We collected the primary tumour specimens and clinicopathological characteristics of patients with de novo metastatic microsatellite-stable BRAF V600E mutant CRC from two medical centres. Gene expression analysis was performed using the nCounterⓇ PanCancer Immune Profiling Panel. The Cox proportional hazards regression model was used for analysing survival outcomes in association with immune gene expression and immune cells. Our complement score was defined on the basis of the average gene expression in the selected co-expression module.

RESULTS

High expression of classical and regulatory complement genes was significantly associated with poor prognosis (N = 54). A high complement score (defined as a score above the median value) indicated significantly shorter survival. The overall survival (OS) impact of the high score remained significant in multivariate analyses. Additionally, our complement score was strongly correlated with C4d expression in immunohistochemical staining and tumour-associated macrophage (TAM) M2 signatures.

CONCLUSIONS

Complement activation in the TME was significantly associated with poor OS and was correlated with TAM M2 in patients with de novo metastatic BRAF V600E mutant CRC.

Traditional Serrated Adenoma of the Urinary Bladder: The First Report

A 71-year-old woman was hospitalized with hematuria and underwent cystourethroscopy. Cystourethroscopy revealed a polypoid bladder tumor. Histopathologic examination showed complex villiform growth pattern, slit-like serrations, and ectopic crypts lined by epithelium with eosinophilic cytoplasm, pseudostratified elongated nuclei, consistent with traditional serrated adenoma. Nephrogenic and intestinal metaplasia with severe inflammation were present in adjacent bladder mucosa. Molecular study of the polyp revealed mutation (p.G12V) in codon 12 of exon 2 of the KRAS gene. Traditional serrated adenoma is a rare type of colonic serrated polyp, making up less than 1% of the colonic polyps with a predilection to distal colon. In the literature, there is no traditional serrated adenoma reported outside the gastrointestinal tract. Here in we report the first extra-gastrointestinal traditional serrated adenoma within the bladder and bladder diverticulum, arising from intestinal metaplasia. The present study reports an additional information on molecular background of this unusual bladder polyp.

Clinical, Pathologic, Genetics and Intratumoral Immune Milieu of Serrated Adenocarcinoma of the Colon

BACKGROUND

Serrated adenocarcinoma (SAC), a recognized WHO variant of colonic adenocarcinoma, is the purported end-product of serrated neoplasia. Yet, the diagnosis of SAC is infrequently rendered, and little is known about its prognosis, immune microenvironment, and molecular alterations.

MATERIALS AND METHODS

We assessed 903 consecutive colon carcinomas and recognized tumors with ≥5% (n=77) serrated pattern, and ≥50% serrated pattern (n=13). We assessed precursor polyps and synchronous polyps. We recorded demographic/clinical parameters, histological features, and MMR status. We performed immunohistochemistry and quantification on tissue microarray for HLA class I/II proteins, beta-2-microglobulin (B2MG), CD8, CD163, LAG3, PD-L1, FoxP3, PD-L1and BRAF V600E.

RESULTS

We identified ≥ 5% epithelial serration prevalence in 8.5% of cases, and ≥50% epithelial serration prevalence in 1.4% of cases. Precursor lesions were present in 21.4% of cases; these were mostly tubular adenomas with two traditional serrated adenoma identified. SAC with ≥ 5% serrations exhibited lower numbers of CD8 positive lymphocytes (p=0.002) and lower B2MG expression (p=0.048), although neither value was significant at ≥50% serration threshold. There was no difference in HLA class I/II, or PD-L1 expression on tumor cells and no difference in PD-L1, LAG3, FOXP3 and CD163 expression on immune cells. There was no association with MMR status, or BRAFV600E relative to conventional adenocarcinoma. There was improved disease-specific survival on univariate (but not multivariate) analysis between carcinomas with serrated pattern and non-mucinous conventional colonic carcinomas at ≥5% epithelial serrations (p=0.04).

CONCLUSION

SAC category shows a limited impact on survival, and this phenotype may harbor a unique immunologic milieu.

Serrated Colorectal Lesions: An Up-to-Date Review from Histological Pattern to Molecular Pathogenesis

Until 2010, colorectal serrated lesions were generally considered as harmless lesions and reported as hyperplastic polyps (HPs) by pathologists and gastroenterologists. However, recent evidence showed that they may bear the potential to develop into colorectal carcinoma (CRC). Therefore, the World Health Organization (WHO) classification has identified four categories of serrated lesions: hyperplastic polyps (HPs), sessile serrated lesions (SSLs), traditional serrated adenoma (TSAs) and unclassified serrated adenomas. SSLs with dysplasia and TSAs are the most common precursors of CRC. CRCs arising from serrated lesions originate via two different molecular pathways, namely sporadic microsatellite instability (MSI) and the CpG island methylator phenotype (CIMP), the latter being considered as the major mechanism that drives the serrated pathway towards CRC. Unlike CRCs arising through the adenoma-carcinoma pathway, APC-inactivating mutations are rarely shown in the serrated neoplasia pathway.

Sessile Serrated Adenoma With Dysplasia of the Colon

OBJECTIVES

Sessile serrated adenomas with dysplasia (SSADs) of the colon are transitional lesions between sessile serrated adenomas (SSAs) and a subset of colorectal adenocarcinomas. We wished to gain insight into the relative percentages and significance of SSAD subtypes.

METHODS

Retrospective (2007-2012) clinicopathologic review of colorectal polyps initially regarded as having mixed serrated and dysplastic elements. SSADs were subdivided into those with cap-like adenomatous dysplasia (ad1), non-cap-like adenomatous dysplasia (ad2), serrated dysplasia (ser), minimal dysplasia (min), and dysplasia not otherwise specified (nos). MLH1 immunostaining was performed on many.

RESULTS

SSADser (7.7%) had a greater propensity for right colon, women, and MLH1 loss vs the entire cohort. SSAad1 (11.6%) had the least female preponderance, was least likely to have MLH1 loss, and was most likely to affect the left colorectum. SSAD with MLH1 loss was associated with an increased burden of SSAs in the background colon (P = .0003) but not tubular adenomas or hyperplastic polyps. Most SSADs (ad2 and nos groups, 80% combined) showed difficult-to-classify dysplasia, intermediate MLH1 loss rates, and intermediate clinical features.

CONCLUSIONS

While some trends exist, morphologically subclassifying SSADs is probably not justified in routine clinical practice. MLH1 loss portends a greater burden of SSAs in the background colon.

Serrated neoplasia in the colorectum: gut microbiota and molecular pathways

Colorectal cancer (CRC) is a heterogeneous disease with different gene expression patterns. There are two major colorectal carcinogenesis pathways: conventional adenoma-carcinoma pathway and alternative serrated neoplasia pathway. Apart from the conventional pathway that is typically initiated by characteristic APC mutation and chromosomal instability, the serrated neoplasia pathway is mainly characterized by mutations of BRAF or KRAS, microsatellite instability (MSI), and CpG island methylator phenotype (CIMP). Despite the malignant potential of serrated lesions, they can be easily overlooked during endoscopy screening and even in pathological assessment due to its anatomical location, morphology, and histological features. It has been shown that environmental factors especially the gut microbial composition play a key role in CRC pathogenesis. Thus, the preferential localization of serrated lesions in specific intestine areas suggest that niche-specific microbiota composition might intertwined with host genetic perturbations during the development of serrated lesions. Although serrated lesions and conventional adenomas are biologically different, most studies have focused on conventional adenomas, while the pathophysiology and role of microorganisms in the development of serrated lesions remain elusive. In this review, we discuss on the role of gut microbiota in the serrated neoplasia pathway of colorectal carcinogenesis and its specific clinical and molecular features, and summarize the potential mechanisms involved.

Familial Adenomatous Polyposis-associated Traditional Serrated Adenoma of the Small Intestine: A Clinicopathologic and Molecular Analysis

Familial adenomatous polyposis (FAP) is an inherited cancer predisposition syndrome associated with numerous gastrointestinal tract adenomatous polyps, as well as gastric fundic gland polyps and pyloric gland adenomas in the upper gastrointestinal tract. While colonic FAP-associated traditional serrated adenomas (TSAs) have been reported in a few studies, small bowel FAP-associated adenomas with TSA morphology have not been characterized. This study describes the clinicopathologic and molecular findings of this type of adenoma in the small bowel of patients with FAP. We reviewed small bowel adenomas in 45 consecutive FAP patients to identify adenomas with zones showing slit-like serrations, cells with eosinophilic cytoplasm, ectopic crypt formation, and vesicular nuclei. Sporadic small bowel adenomas from 51 consecutive patients were also reviewed for adenomas with the same features. Of the 177 polyps from 45 FAP patients and 60 polyps from 51 nonsyndromic patients, 18 TSAs from 9 FAP patients (20%) and 10 TSAs from the sporadic group (19.6%) were identified. FAP patients presented at a younger age than nonsyndromic patients (median: 43 vs. 66; P=0.0048). FAP-associated TSAs were asymptomatic and smaller than sporadic TSAs (median size: 0.6 vs. 2.5 cm; P=0.00006). Immunostaining for β-catenin and testing for BRAF and KRAS mutations were performed in a subset of the cohort. Nuclear β-catenin was seen in 1 FAP-associated TSA and 3 nonsyndromic TSAs. All TSAs (FAP-associated and nonsyndromic) showed wild-type BRAF, while KRAS mutations were identified only in the nonsyndromic setting. In summary, small bowel FAP-associated and sporadic TSAs share a similar morphology, and the BRAF-serrated pathway does not contribute to their pathogenesis.

Patient, Physician, and Procedure Characteristics Are Independently Predictive of Polyp Detection Rates in Clinical Practice

BACKGROUND

Variability in colon polyp detection impacts patient outcomes. However, the relative influence of physician, patient, and procedure-specific factors on polyp detection is unclear. Therefore, determining how these factors contribute to adenoma and sessile serrated polyp (SSP) detection is important to contextualize measures of colonoscopy quality such as adenoma detection rate and patient outcomes.

AIMS

To determine the relative contribution of physician, patient, and procedure-specific factors in total polyp, adenoma, and SSP detection rates.

METHODS

We performed a retrospective study of patients undergoing screening colonoscopy and used a two-level generalized linear mixed regression model to identify factors associated with polyp detection.

RESULTS

7799 average risk screening colonoscopies were performed between July 2016 and October 2017. The patient factor most strongly associated with increased risk of adenoma and sessile serrated polyp detection was white race (OR 1.21, 95% CI 1.05-1.39 and OR 3.17, 95% CI 2.34-4.30, respectively). Adenomatous (OR 1.92, 95% CI 1.04-3.57) and sessile serrated polyps (OR 5.56, 95% CI 1.37-20.0) were more likely to be found during procedures performed with anesthesia care as compared to those with moderate sedation. Physician with a luminal gastrointestinal focus had increased odds of adenoma detection (OR 1.61, 95% CI 1.02-2.50).

CONCLUSIONS

In a multi-level model accounting for clustering effects, we identified patient, provider and procedural factors independently influence adenoma and sessile serrated polyp detection. Our findings suggest that to compare polyp detection rates between endoscopists, even at the same institution, risk adjustment by characteristics of the patient population and practice is necessary.

Applying Precision to the Management of BRAF-Mutant Metastatic Colorectal Cancer

Identifying the presence or absence of a BRAFV600E mutation is paramount for the management of patients with metastatic colorectal cancer (mCRC) as there are distinct predictive and prognostic implications, as well as unique therapeutic approaches for this molecular subtype. Traditional cytotoxic doublet chemotherapy has historically been ineffective for this poor prognostic group, thereby highlighting the critical need for novel targeted therapies to drive management. Unlike the early success achieved with BRAF-inhibitor monotherapy for patients with BRAFV600E-mutated metastatic melanoma, response rates were found to only be 5% in early-phase clinical trials for patients with BRAFV600E mCRC. A deeper understanding of predominant resistance mechanisms in BRAFV600E mCRC after exposure to BRAF inhibition has resulted in innovative combinatorial approaches targeting the mitogen-activated protein kinase (MAPK) pathway, revitalizing the treatment portfolio for these patients. Of note, in recent years non-V600 BRAF mutations have been appreciated as a distinct molecular subset in mCRC, representing 2-4% of patients with a unique clinical presentation and complex signaling biology. These mutations, referred to as "atypical" BRAF mutations, warrant individual clinical investigation and demand innovative drug development that leverages known signaling class biology. Here, we summarize the current molecular and clinicopathologic understanding of BRAFV600E mCRC, as well as the landmark clinical trials that have led to successful targeted therapy for this historically aggressive subtype of colorectal cancer. Additionally, we briefly describe the current understanding of patients with atypical BRAF mutations, highlighting the importance of continued research efforts to appropriately treat this evolving subset of BRAF mutations.

Macroscopic and microscopic morphology and molecular profiling to distinguish heterogeneous traditional serrated adenomas of the colorectum

OBJECTIVES

Serrated lesions of the colorectum often have complex histological morphology, and some groups include subtypes with different molecular biology. This study aimed to characterize serrated lesions with heterogeneous histology that was dominated by a traditional serrated adenoma (TSA) component.

METHODS

Representative lesions were selected based on both endoscopic and histological features. If a lesion had more than one component, each of the different structural parts was considered as a separate sample. DNA was extracted from 177 samples of 60 lesions and amplified to screen for BRAF and K/NRAS mutations.

RESULTS

Heterogeneous TSA samples were classified into four categories: sessile serrated lesion with TSA (SA-1); TSAs with microvesicular hyperplastic polyp (SA-2); TSAs with unclassified adenoma, characterized by tubulo-serrated histology (SA-3); and TSAs with conventional adenomas (SA-4). On endoscopy, SA-1 lesions had sessile-elevated morphology with the small reddish elevations; SA-2 lesions had a pedunculated appearance with a whitish mucosal component at the stalk; SA-3 lesions had a sessile-elevated component surrounded by flat spreading margins; and SA-4 lesions had mixed adenomatous morphology. Eighteen of the 19 category SA-1 and -2 lesions (95%) had BRAF mutations, and all of the SA-3 and -4 lesions had K/NRAS mutations.

CONCLUSIONS

Traditional serrated adenomas were classified into two phenotypes according to their molecular characteristics: microvesicular serrated subtypes with BRAF mutations (SA-1 and -2 lesions) and subtypes containing tubulo-serrated/conventional adenoma with K/NRAS mutations (SA-3 and -4 lesions). Each subtype had characteristic macroscopic and microscopic morphologies and was distinct on endoscopy.

Gastric and small intestinal traditional serrated adenomas: a detailed morphologic and immunohistochemical analysis

BACKGROUND/AIMS

Traditional serrated adenomas (TSAs), despite their low incidence in colorectum, may originate in other parts of the gastrointestinal (GI) tract, including stomach and small intestine. Malignant transformation for upper GI TSAs has recently been reported in the literature. Here, we present a series of gastric and small intestinal TSAs with the aim to characterize their morphologic and immunophenotypic features as well as their neoplastic potential in a compartmental manner using digitalized images.

MATERIALS AND METHODS

The study comprised 12 GI polyps with TSA features-5 gastric and 7 small intestinal. The extent of the characteristic features of TSA, including eosinophilic cells, ectopic crypt foci (ECF), slit-like serration, foveolar epithelium, goblet cells, together with dysplastic-carcinomatous foci were assessed on digitalized H-E images and were used as reference for immunohistochemical analysis.

RESULTS

All polyps in the cohort contained eosinophilic cells as the most extensive morphologic feature followed by ECF and slit-like serration in decreasing order. Serrated dysplasia was more common in gastric polyps, which more frequently showed neoplastic progression compared with the intestinal ones. CK20 was the most widely expressed marker with a preference to eosinophilic cells while ECFs were mostly negative. Ki67 showed the opposite pattern of CK20. MUC6 and MUC2 were selectively expressed in the basal zone and goblet cells, respectively.

CONCLUSION

Our results showed that the presence of eosinophilic cells with pencillate nuclei commonly accompanied by ECF and slit-like serration are the defining features of gastric and small intestinal TSAs. They frequently harbor neoplastic foci, particularly in gastric location where serrated dysplasia seems to be more common.

Evolving pathologic concepts of serrated lesions of the colorectum

Here, we provide an up-to-date review of the histopathology and molecular pathology of serrated colorectal lesions. First, we introduce the updated contents of the 2019 World Health Organization classification for serrated lesions. The sessile serrated lesion (SSL) is a new diagnostic terminology that replaces sessile serrated adenoma and sessile serrated polyp. The diagnostic criteria for SSL were revised to require only one unequivocal distorted serrated crypt, which is sufficient for diagnosis. Unclassified serrated adenomas have been included as a new category of serrated lesions. Second, we review ongoing issues concerning the morphology of serrated lesions. Minor morphologic variants with distinct molecular features were recently defined, including serrated tubulovillous adenoma, mucin-rich variant of traditional serrated adenoma (TSA), and superficially serrated adenoma. In addition to intestinal dysplasia and serrated dysplasia, minimal deviation dysplasia and not otherwise specified dysplasia were newly suggested as dysplasia subtypes of SSLs. Third, we summarize the molecular features of serrated lesions. The critical determinant of CpG island methylation development in SSLs is patient age. Interestingly, there may be ethnic differences in BRAF/KRAS mutation frequencies in SSLs. The molecular pathogenesis of TSAs is divided into KRAS and BRAF mutation pathways. SSLs with MLH1 methylation can progress into favorable prognostic microsatellite instability-positive (MSI+)/CpG island methylator phenotype-positive (CIMP+) carcinomas, whereas MLH1-unmethylated SSLs and BRAF-mutated TSAs can be precursors of poor-prognostic MSI-/CIMP+ carcinomas. Finally, based on our recent data, we propose an algorithm for stratifying risk subgroups of non-dysplastic SSLs.

Correlations of morphology and molecular alterations in traditional serrated adenoma

Traditional serrated adenoma was first reported by Longacre and Fenoglio-Presier in 1990. Their initial study described main features of this lesion, but the consensus diagnostic criteria were not widely adopted until recently. Traditional serrated adenoma presents with grossly protuberant configuration and pinecone-like appearance upon endoscopy. Histologically, it is characterized by ectopic crypt formation, slit-like serration, eosinophilic cytoplasm and pencillate nuclei. Although much is now known about the morphology and molecular changes, the mechanisms underlying the morphological alterations are still not fully understood. Furthermore, the origin of traditional serrated adenoma is not completely known. We review recent studies of the traditional serrated adenoma and provide an overview on current understanding of this rare entity.

Nonconventional dysplasia in patients with inflammatory bowel disease and colorectal carcinoma: a multicenter clinicopathologic study

Several types of nonconventional dysplasia have been recently described in inflammatory bowel disease (IBD). However, strict morphologic criteria are lacking, and their clinicopathologic features (including potential association with conventional dysplasia and/or colorectal cancer [CRC]) are poorly understood. A total of 106 dysplastic or serrated lesions in 58 IBD patients with CRC were retrospectively identified from five institutions. Thirty-six cases of nonconventional dysplasia were identified in 26 (45%) of the 58 patients and occurred with similar frequency in men and women (58% and 42%, respectively), with a mean age of 54 years (range: 24-73) and a long history of IBD (mean: 17 years, range: 2-43). Six morphologic patterns were recognized. Hypermucinous dysplasia (n = 15; 42%) presented as either a 'pure type' (n = 5; 14%) or a 'mixed type' with either conventional or another nonconventional subtype (n = 10; 28%). Serrated lesions, as a group, were equally common (n = 15; 42%) and included three variants: traditional serrated adenoma-like (n = 10; 28%), sessile serrated lesion-like (n = 1; 3%), and serrated lesion, not otherwise specified (n = 4; 11%). Dysplastic lesions with increased Paneth cell differentiation (n = 4; 11%) and goblet cell deficient dysplasia (n = 2; 6%) were rare. Twelve (46%) of the 26 patients had only nonconventional dysplasia, whereas the remaining 14 patients (54%) had both nonconventional and conventional dysplasias. Nonconventional dysplasia was most often graded as low-grade dysplasia (81%), which was less common in conventional dysplasia (37%) (p = 0.003). When present alone, nonconventional dysplasia was predominantly found in the left colon (81%, p = 0.006) as a polypoid or raised lesion (75%, p < 0.001) compared with when it occurred simultaneously with conventional dysplasia (35% and 50%, respectively). When both nonconventional and conventional dysplasias occurred simultaneously, they were found in the same colonic segment in all but 3 patients (79%). Nonconventional dysplasia was also commonly detected in the same colonic segment as CRC or immediately adjacent to the CRC at a rate (85%) similar to conventional dysplasia (96%). CRC occurring in patients with only nonconventional dysplasia was more likely to be high-grade (poorly differentiated; 36%) than CRC that occurred in association with conventional dysplasia (10%) (p = 0.026). In conclusion, nonconventional dysplasia is common in IBD patients with CRC. It appears to develop in the same field of carcinomatous development, and it is not uncommonly associated with conventional dysplasia.

Clinicopathological and molecular correlations in traditional serrated adenoma

BACKGROUND

Traditional serrated adenoma (TSA) is the least common type of colorectal serrated polyp, which exhibits considerable morphological and molecular diversity.

METHODS

We examined the spectra of alterations in MAPK and WNT pathway genes and their relationship with clinicopathological features in 128 TSAs.

RESULTS

Sequencing analyses identified BRAF V600E, BRAF non-V600E, KRAS, and NRAS mutations in 77, 3, 45, and 1 lesion, respectively. Collectively, 124 lesions (97%) had mutations in MAPK pathway genes. Alterations in WNT pathway genes were identified in 107 lesions (84%), including RSPO fusions/overexpression, RNF43 mutations, ZNRF3 mutations, APC mutations, and CTNNB1 mutations in 47, 45, 2, 13, and 2 lesions, respectively. Ten lesions (8%) harbored GNAS mutations. There was significant interdependence between the altered MAPK and WNT pathway genes. RSPO fusions/overexpression was significantly associated with KRAS mutations (31/47, 66%), whereas most RNF43 mutations coexisted with the BRAF V600E mutation (40/45, 89%). Histologically, extensive slit-like serration was more common in lesions with the BRAF V600E mutation (71%) and those with RNF43 mutations (87%). Prominent ectopic crypt formation was more prevalent in lesions with RSPO fusions/overexpression (58%) and those with GNAS mutations (100%).

CONCLUSIONS

Our observations indicate that TSAs mostly harbor various combinations of concurrent WNT and MAPK gene alterations. The associations between genetic and morphological features suggest that the histological diversity of TSA reflects the underlying molecular heterogeneity.

Traditional Serrated Pathway-associated Colorectal Carcinoma: Morphologic Reappraisal of Serrated Morphology, Tumor Budding, and Identification of Frequent PTEN Alterations

The phenotypic characteristics of traditional serrated adenoma (TSA)-associated malignancies remain obscure. This study was a morphologic reappraisal of 27 colorectal carcinomas arising from TSA (TSA-CRCs) and 53 BRAF-mutated/microsatellite-stable colorectal carcinomas (BRAF-mut/MSS CRCs). Makinen's criteria for serrated adenocarcinoma were applied to assess the morphologic similarity of the 2 entities. Tumor budding, another histologic feature of serrated adenocarcinoma, was also evaluated. Phosphatase and tensin homologue deleted on chromosome 10 (PTEN), a commonly mutated gene in the serrated pathway, was assessed with immunohistochemistry. Tumors with aberrant PTEN expression were subjected to molecular analysis using quantitative methylation assay, exon sequencing, and fluorescence in situ hybridization. Most cases (>90%) of TSA-CRCs and BRAF-mut/MSS CRCs exhibited a constellation of serrated morphology, including epithelial serrations, abundant eosinophilic cytoplasm, and discernible/vesicular nuclei. A majority (65%) of them qualified for the diagnosis of serrated adenocarcinoma. High-grade tumor budding was closely associated with serrated morphology and was a significant independent factor for poor patient survival in multivariate analysis (P=0.008). Aberrant PTEN expression was detected in nearly half of the cases of both entities (P=0.501). Among the 44 samples with aberrant PTEN expression, 8 harbored PTEN somatic mutations, which were characterized by random distribution without hotspot clustering, 12 had promoter hypermethylation, and 14 had deleted alleles. These findings support a unique model of colorectal carcinogenesis that is similar between TSA-CRCs and BRAF-mut/MSS CRCs. Both entities exhibited common histologic patterns and similar molecular alterations and may well constitute the TSA pathway.

Significance of gene mutations in the Wnt signaling pathway in traditional serrated adenomas of the colon and rectum

Recent studies have shown that colorectal serrated lesions, which include sessile serrated adenomas (SSAs) and traditional serrated adenomas (TSAs), are precursors of colorectal cancer. However, the molecular mechanisms underlying the carcinogenesis, particularly in TSAs, remain largely uncharacterized. To clarify their molecular and clinicopathological characteristics, we performed mutation and methylation analyses of cancer-associated genes in 78 serrated lesions, including TSAs, SSAs and microvesicular hyperplastic polyps. Target exon sequence analysis was performed with 39 genes, including genes known to be frequently mutated in colorectal cancers and/or serrated lesions. We also used bisulfite pyrosequencing to assess the methylation status of various cancer-associated genes and marker genes of the CpG island methylator phenotype (CIMP). The prevalence of mutations in genes associated with Wnt signaling was significantly higher in TSAs than SSAs (65% vs. 28%, p < 0.01). Among those, RNF43 mutations were observed in 38% of TSAs and 17% of SSAs. In immunohistochemical studies of 39 serrated lesions, the prevalence of abnormal nuclear β-catenin accumulation was significantly higher in TSAs (57%) than SSAs (8%) (P = 0.01). SMOC1 methylation was detected in 54% of TSAs but in no SSAs (p < 0.01). Additionally, SMOC1 methylation was more prevalent among TSAs with KRAS mutation (82%) than with BRAF mutation (38%, p = 0.03). Lesions with CIMP-high or RNF43 mutations were detected only in TSAs with BRAF mutation, suggesting two distinct carcinogenic pathways in TSAs. Mutations in genes associated with Wnt signaling play a greater role in the carcinogenesis of TSAs than SSAs.

Traditional serrated adenoma-like lesions in patients with inflammatory bowel disease

Patients with inflammatory bowel disease (IBD) have an increased risk of colorectal carcinoma. The significance of serrated lesions resembling traditional serrated adenoma (TSA) in IBD patients is unclear. In this retrospective study, we analyzed 52 TSA-like lesions arising in 30 IBD patients and diagnosed in colectomy or endoscopic specimens. The 27 colectomy lesions presented predominantly as ill-defined areas with granular appearance, with a median size of 15 mm, located throughout the large bowel and associated with synchronous advanced colorectal lesions in 58%. Low-grade serrated dysplasia was present in 56%, high-grade serrated dysplasia in 37%, and TSA-type cytology in 7%. Increased Ki-67 immunostaining and abnormal p53 expression were identified in 96% and 48%, respectively; 74% had a KRAS mutation, and 4% had a BRAF mutation. Endoscopically resectable TSA-like lesions were all discrete polypoid lesions, smaller in size (median 9 mm), predominantly in the distal large bowel, with an adjacent precursor polyp in 24%, and associated with synchronous and metachronous advanced colorectal lesions in 6%. Most (92%) show TSA-type cytology. p53 overexpression was present in 4%, KRAS mutation in 41%, and BRAF mutation in 32%. None of the 52 TSA-like lesions demonstrated loss of MLH1 or SATB2 expression by immunohistochemistry. On follow-up, 4 patients were diagnosed with colorectal carcinoma or high-grade adenomatous IBD-associated dysplasia. None of the patients with lesions showing TSA-type cytology only developed an advanced lesion. Our findings suggest that some TSA-like lesions, essentially from colectomy, may represent a form of IBD-associated dysplasia associated with an increased risk of advanced neoplasia.

Proteome analysis of formalin-fixed paraffin-embedded colorectal adenomas reveals the heterogeneous nature of traditional serrated adenomas compared to other colorectal adenomas

Traditional serrated adenoma (TSA) remains the least understood of all the colorectal adenomas, although these lesions have been associated with a significant cancer risk, twice that of the conventional adenoma (CAD) and of the sessile serrated adenoma (SSA/P). This study was performed to investigate the proteomic profiles of the different colorectal adenomas to better understand the pathogenesis of TSA. We performed a global quantitative proteome analysis using the label-free quantification (LFQ) method on 44 colorectal adenoma (12 TSAs, 15 CADs, and 17 SSA/Ps) and 17 normal colonic mucosa samples, archived as formalin-fixed paraffin-embedded blocks. Unsupervised consensus hierarchical clustering applied to the whole proteomic profile of the 44 colorectal adenomas identified four subtypes: C1 and C2 were well-individualized clusters composed of all the CADs (15/15) and most of the SSA/Ps (13/17), respectively. This is consistent with the fact that CADs and SSA/Ps are homogeneous and distinct colorectal adenoma entities. In contrast, TSAs were subdivided into C3 and C4 clusters, consistent with the more heterogeneous entity of TSA at the morphologic and molecular levels. Comparison of the proteome expression profile between the adenoma subtypes and normal colonic mucosa further confirmed the heterogeneous nature of TSAs, which overlapped either on CADs or SSA/Ps, whereas CADs and SSAs formed homogeneous and distinct entities. Furthermore, we identified LEFTY1 a new potential marker for TSAs that may be relevant for the pathogenesis of TSA. LEFTY1 is an inhibitor of the Nodal/TGFβ pathway, which we found to be one of the most overexpressed proteins specifically in TSAs. This finding was confirmed by immunohistochemistry. Our study confirms that CADs and SSA/Ps form homogeneous and distinct colorectal adenoma entities, whereas TSAs are a heterogeneous entity and may arise from either SSA/Ps or from normal mucosa evolving through a process related to the CAD pathway. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Acquisition of WNT Pathway Gene Alterations Coincides With the Transition From Precursor Polyps to Traditional Serrated Adenomas

Colorectal traditional serrated adenomas (TSAs) are often associated with precursor polyps, including hyperplastic polyps and sessile serrated adenoma/polyps. To elucidate the molecular mechanisms involved in the progression from precursor polyps to TSAs, the present study analyzed 15 precursor polyp-associated TSAs harboring WNT pathway gene mutations. Laser microdissection-based sequencing analysis showed that BRAF or KRAS mutations were shared between TSA and precursor polyps in all lesions. In contrast, the statuses of WNT pathway gene mutations were different between the 2 components. In 8 lesions, RNF43, APC, or CTNNB1 mutations, were exclusively present in TSA. RNF43 mutations were shared between the TSA and precursor components in 3 lesions; however, they were heterozygous in the precursor polyps whereas homozygous in the TSA. In 4 lesions with PTPRK-RSPO3 fusions, RNA in situ hybridization demonstrated that overexpression of RSPO3, reflecting PTPRK-RSPO3 fusion transcripts, was restricted to TSA components. Consistent with the results of the genetic and in situ hybridization analyses, nuclear β-catenin accumulation and MYC overexpression were restricted to the TSA component in 13 and 12 lesions, respectively. These findings indicate that the WNT pathway gene alterations are acquired during the progression from the precursor polyps to TSAs and that the activation of the WNT pathway plays a critical role in the development of TSA rather than their progression to high-grade lesions.

An update on the morphology and molecular pathology of serrated colorectal polyps and associated carcinomas

Our understanding of serrated colorectal polyps has increased dramatically over the past two decades and has led to a modern classification scheme for these lesions. Sessile serrated polyps with dysplasia represent the most clinically significant serrated polyp; however, the morphologic heterogeneity of dysplasia in sessile serrated polyps has only recently been recognized and correlated with MLH1 immunohistochemistry. Detailed morphologic analysis of traditional serrated adenomas has led to the recognition of flat and early forms of this polyp. Robust data on the risk of metachronous lesions in patients with serrated polyps are also beginning to emerge. This review will summarize our current understanding of serrated polyps and associated carcinomas with a focus on diagnostic criteria, morphologic heterogeneity, molecular findings, and natural history. Controversial issues in the diagnosis and classification of these polyps are also discussed.

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.

The Molecular Hallmarks of the Serrated Pathway in Colorectal Cancer

Colorectal cancer (CRC) is a leading cause of cancer death worldwide. It includes different subtypes that differ in their clinical and prognostic features. In the past decade, in addition to the conventional adenoma-carcinoma model, an alternative multistep mechanism of carcinogenesis, namely the “serrated pathway”, has been described. Approximately, 15 to 30% of all CRCs arise from neoplastic serrated polyps, a heterogeneous group of lesions that are histologically classified into three morphologic categories: hyperplastic polyps, sessile serrated adenomas/polyps, and the traditional serrated adenomas/polyps. Serrated polyps are characterized by genetic (BRAF or KRAS mutations) and epigenetic (CpG island methylator phenotype (CIMP)) alterations that cooperate to initiate and drive malignant transformation from normal colon mucosa to polyps, and then to CRC. The high heterogeneity of the serrated lesions renders their diagnostic and pathological interpretation difficult. Hence, novel genetic and epigenetic biomarkers are required for better classification and management of CRCs. To date, several molecular alterations have been associated with the serrated polyp-CRC sequence. In addition, the gut microbiota is emerging as a contributor to/modulator of the serrated pathway. This review summarizes the state of the art of the genetic, epigenetic and microbiota signatures associated with serrated CRCs, together with their clinical implications.

Colorectal Serrated Neoplasia: An Institutional 12-Year Review Highlights the Impact of a Screening Programme

Background

As the malignant potential of sessile serrated lesions/polyps (SSL/Ps) and traditional serrated adenomas (TSAs) has been clearly demonstrated, it is important that serrated polyps are identified and correctly classified histologically.

Aim

Our aim was to characterize the clinicopathological features of a series of SSL/Ps & TSAs, to assess the accuracy of the pathological diagnosis, the incidence, and the rate of dysplasia in SSL/Ps & TSAs.

Methods

We identified all colorectal serrated polyps between 01/01/2004 and 31/05/2016, by searching the laboratory information system for all cases assigned a “serrated adenoma” SNOMED code. All available and suitable slides were reviewed by one pathologist, who was blinded to the original diagnosis and the site of the polyp. Subsequently discordant cases, SSL/Ps with dysplasia, and all TSAs were reviewed by a second pathologist.

Results

Over a 149-month period, 759 “serrated adenoma” polyps were identified, with 664 (from 523 patients) available for review. 41.1% were reviewed by both pathologists; 15.1% (100/664) were reclassified, with the majority being changed from SSL/P to hyperplastic polyp (HYP) (66/664; 9.9%). 80.3% of these HYPs were located in the left colon, and the majority exhibited prolapse effect. There were 520 SSL/Ps (92.2%) & 40 TSAs (7.1%). The majority of SSL/Ps were in the right colon (86.7%) and were small (64.5% <1 cm), while most TSAs were in the left colon (85.7%) and were large (73.1%≥1 cm). 6.7% of SSL/Ps exhibited dysplasia, the majority of which were large (66.7%≥1 cm). Following consensus review, 13/520 (2.5%) SSL/Ps were downgraded from SSL/P with dysplasia to SSL/P without dysplasia. Detection of SSL/Ps peaked in the most recent years reviewed (87.5% reported between 2013 and 2016, inclusive), coinciding with the introduction of “BowelScreen” (the Irish FIT-based colorectal cancer screening programme).

Conclusions

Awareness of, and adherence to, diagnostic criteria is essential for accurate classification of colorectal polyps.

How the BRAF V600E Mutation Defines a Distinct Subgroup of Colorectal Cancer: Molecular and Clinical Implications

The BRAF oncogene is an integral component of the MAP kinase pathway, and an activating V600E mutation occurs in 15% of sporadic colorectal cancer. This is an early event in serrated pathway tumourigenesis, and the BRAF V600E has been commonly associated with the CpG island methylator phenotype, microsatellite instability (MSI), and a consistent clinical presentation including a proximal location and predilection for elderly females. A proportion of the BRAF mutant lesions remain as microsatellite stable (MSS), and in contrast to the MSI cancers, they have an aggressive phenotype and correlate with poor patient outcomes. Recent studies have found that they have clinical and molecular features of both the BRAF mutant/MSI and the conventional BRAF wild-type cancers and comprise a distinct colorectal cancer subgroup. This review highlights the importance of the BRAF mutation occurring in colorectal cancer stratified for molecular background and discusses its prognostic and clinical significance.

A morphological and molecular study of proposed early forms of traditional serrated adenoma

AIMS

Traditional serrated adenoma (TSA) is the least common subtype of serrated colorectal polyp. Large protuberant lesions are easily recognised; however, the origins of TSAs are not known, and early forms have not been described. Some large TSAs present with a flat 'shoulder' component surrounding the central protuberant component. We hypothesised that small polyps with the same histology as these shoulder regions may represent early TSAs. Thus the primary aim of the study is to describe the histology of these presumptive early TSAs.

METHODS AND RESULTS

We collected 70 small (<10 mm) polyps that may represent early TSAs on the basis of typical TSA cytology covering the luminal surface. We also identified 12 large TSAs with a shoulder component resembling these small polyps. The study polyp patients had a mean age of 58 years, and 54% were female; the polyps had a mean diameter of 4.1 mm and were predominantly distal (71%). Morphologically, slit-like serrations were present in 81%, ectopic crypt formations were present in 67%, and a villous component was present in 47%. These histological features were similar to those of the 12 shoulder lesions. Immunohistochemical stains showed an absence of β-catenin nuclear expression in 96% of the small polyps, retained expression of MLH1 in 100%, and Ki67 positivity restricted to the crypt bases and ectopic crypt formations. BRAF and KRAS mutations were identified in 47% and 31% of the polyps, respectively. BRAF-mutated polyps were more likely than KRAS-mutated polyps to arise in a precursor polyp (82% versus 18%, P < 0.001), and were more likely to have slit-like serrations (100% versus 73%, P = 0.003).

CONCLUSIONS

These morphological, immunohistochemical and molecular findings are similar to what has been reported in large TSAs, and support the hypothesis that these polyps represent early forms of TSA.

Superficially serrated adenoma: a proposal for a novel subtype of colorectal serrated lesion

We describe a series of colorectal polyps characterized by mixed adenomatous and serrated features, herein referred to as superficially serrated adenomas. Twenty superficially serrated adenomas were obtained from 11 female and 9 male patients aged 62-87 years. Most lesions endoscopically appeared as small sessile polyps, but larger lesions were plaque-like (2-20 mm; median, 5 mm). Eighteen lesions (90%) were located in the sigmoid colon or rectum. They consisted primarily of straight, adenomatous glands but showed serration confined to the superficial layer. Immunohistochemistry revealed CK20 expression in the upper layer. Proliferating cells, determined by their expression of Ki-67, were localized to the middle to bottom layers. Genetic analyses identified KRAS mutations in 19 lesions and a BRAF mutation in one lesion. Furthermore, RSPO fusions and/or overexpression were observed in 18 lesions and truncating APC mutations were observed in the two remaining lesions. Consistent with the presence of WNT pathway gene alterations, all superficially serrated adenomas showed focal or diffuse nuclear β-catenin accumulation. Since concurrent KRAS mutations and RSPO fusions are reportedly common in traditional serrated adenomas, we reviewed 129 traditional serrated adenomas and found 15 lesions (12%) that were associated with superficially serrated adenoma components. Remarkably, all but one superficially serrated adenoma-associated traditional serrated adenoma exhibited concurrent KRAS mutations and RSPO fusions/overexpression. The present study suggests that superficially serrated adenoma is a morphologically and molecularly distinct type of colorectal serrated polyp that is histogenetically related to traditional serrated adenoma.

Colorectal cancer: genetic abnormalities, tumor progression, tumor heterogeneity, clonal evolution and tumor-initiating cells

Colon cancer is the third most common cancer worldwide. Most colorectal cancer occurrences are sporadic, not related to genetic predisposition or family history; however, 20-30% of patients with colorectal cancer have a family history of colorectal cancer and 5% of these tumors arise in the setting of a Mendelian inheritance syndrome. In many patients, the development of a colorectal cancer is preceded by a benign neoplastic lesion: either an adenomatous polyp or a serrated polyp. Studies carried out in the last years have characterized the main molecular alterations occurring in colorectal cancers, showing that the tumor of each patient displays from two to eight driver mutations. The ensemble of molecular studies, including gene expression studies, has led to two proposed classifications of colorectal cancers, with the identification of four/five non-overlapping groups. The homeostasis of the rapidly renewing intestinal epithelium is ensured by few stem cells present at the level of the base of intestinal crypts. Various experimental evidence suggests that colorectal cancers may derive from the malignant transformation of intestinal stem cells or of intestinal cells that acquire stem cell properties following malignant transformation. Colon cancer stem cells seem to be involved in tumor chemoresistance, radioresistance and relapse.

Assessment of epigenetic alterations in early colorectal lesions containing BRAF mutations

To clarify the molecular and clinicopathological characteristics of colorectal serrated lesions, we assessed the DNA methylation of cancer-associated genes in a cohort of BRAF-mutant precancerous lesions from 94 individuals. We then compared those results with the lesions' clinicopathological features, especially colorectal subsites. The lesions included hyperplastic polyps (n = 16), traditional serrated adenomas (TSAs) (n = 15), TSAs with sessile serrated adenomas (SSAs) (n = 6), SSAs (n = 49) and SSAs with dysplasia (n = 16). The prevalence of lesions exhibiting the CpG island methylator phenotype (CIMP) was lower in the sigmoid colon and rectum than in other bowel subsites, including the cecum, ascending, transverse and descending colon. In addition, several cancer-associated genes showed higher methylation levels within lesions in the proximal to sigmoid colon than in the sigmoid colon and rectum. These results indicate that the methylation status of lesions with BRAF mutation is strongly associated with their location, histological findings and neoplastic pathways. By contrast, no difference in aberrant DNA methylation was observed in normal-appearing background colonic mucosa along the bowel subsites, which may indicate the absence of an epigenetic field defect.

Distinct features between MLH1-methylated and unmethylated colorectal carcinomas with the CpG island methylator phenotype: implications in the serrated neoplasia pathway

The presence or absence of MLH1 methylation may critically affect the heterogeneity of colorectal carcinoma (CRC) with the CpG island methylator phenotype (CIMP). Here, we investigated the differential characteristics of CIMP-high (CIMP-H) CRCs according to MLH1 methylation status. To further confirm the MLH1-dependent features in CIMP-H CRC, an independent analysis was performed using data from The Cancer Genome Atlas (TCGA). In our CIMP-H CRC samples, MLH1-methylated tumors were characterized by older patient age, proximal colonic location, mucinous histology, intense lymphoid reactions, RUNX3/SOCS1 promoter methylation, BRAF mutations, and microsatellite instability-high (MSI-H) status. By contrast, MLH1-unmethylated tumors were associated with earlier age of onset, increased distal colorectal localization, adverse pathologic features, and KRAS mutations. In the TCGA dataset, the MLH1-silenced CIMP-H CRC demonstrated proximal location, MSI-H status, hypermutated phenotype, and frequent BRAF mutations, but the MLH1-non-silenced CIMP-H CRC was significantly associated with high frequencies of KRAS and APC mutations. In conclusion, the differential nature of CIMP-H CRCs depends primarily on the MLH1 methylation status. Based on the current knowledge, the sessile serrated adenoma/polyp may be the major precursor of MLH1-methylated CIMP-H CRCs, whereas MLH1-unmethylated CIMP-H CRCs may develop predominantly from KRAS-mutated traditional serrated adenomas and less commonly from BRAF-mutated traditional serrated adenomas and/or sessile serrated adenomas/polyps.

The Serrated Polyp Pathway: Is It Time to Alter Surveillance Guidelines?

PURPOSE OF REVIEW

In this manuscript, we review current surveillance guidelines for serrated polyps (SPs) and discuss how recent studies inform the selection of appropriate surveillance intervals for patients with SPs.

RECENT FINDINGS

Large and/or proximal SPs, particularly sessile serrated polyps (SSPs), are associated with increased risk of both synchronous and metachronous neoplasia, including advanced adenomas and colorectal cancer (CRC). Persons harboring multiple SSPs or dysplastic SSPs are at the highest risk. Moreover, a high percentage of large and/or proximal SPs are reclassified as SSPs when read by trained gastrointestinal pathologists, even if they were originally reported as hyperplastic polyps. These findings support the adoption of surveillance guidelines that prescribe closer surveillance of large and/or proximal SPs, regardless of subtype. SSPs remain a challenge to reliably identify, resect, and diagnose via histology. The increased risk of future neoplasia in patients with SSPs is likely driven by a combination of underdetection, inadequate removal, misclassification, and biology. Until further evidence emerges, we support guidelines that recommend close surveillance of patients with a history of large and/or proximal SPs and SSPs specifically in order to mitigate the threat of interval CRC.

What influences preneoplastic colorectal lesion recurrence?

The hypothesis of the local recurrence of preneoplastic lesions was first put forward in the 1950s. Disease recurrence may result from an inherent imbalance in cell proliferation that promotes carcinogenesis in apparently normal mucosa. Our review sheds light on how early preneoplastic lesions could be used to diagnose relapsed preneoplastic and, developing neoplastic lesions. We focus in detail on the clinical-pathological and molecular features of adenoma subtypes and their role in relapsed adenoma and their development into colorectal carcinoma. Moreover, we include the data available on microbiota and its metabolites and their role in recurrence. We strongly believe that a significant improvement could be achieved in colorectal screening by introducing personalized endoscopic surveillance for polyp-bearing patients on the basis of the presence of molecular markers that are predictive of recurrence.

Mapping clinicopathological entities within colorectal mucinous adenocarcinomas: a hierarchical clustering approach

The aim of this study was to interrogate the heterogeneity of colorectal mucinous adenocarcinomas. This study is based on hierarchical clustering approach combining clinicopathological and molecular patterns known to be relevant to oncogenesis and therapeutic management of patients with colorectal carcinoma, ie, microsatellite instability, O6-methylguanine-DNA methyltransferase (MGMT) status, KRAS, and BRAF mutations and wnt signaling pathway activation. Comparison of the study group of 60 mucinous adenocarcinomas defined according to World Health Organization classification with control group of 136 colorectal adenocarcinomas successively removed shows higher frequency of BRAF and KRAS mutations and microsatellite instability-high status and lower frequency of wnt signaling pathway activation in mucinous adenocarcinomas. Hierarchical clustering isolated three relevant clusters: (i) cluster of microsatellite stable mucinous adenocarcinomas (54%) with KRAS mutation, and frequent MGMT changes, more frequently located in the left colon, often associated with contiguous precursor adenoma; (ii) cluster of BRAF-mutated mucinous adenocarcinomas (28%) with either microsatellite instability-high or microsatellite stable status, occurring in elderly female patients, nearly all located in the right colon, having the signature of serrated pathway of carcinomas; and (iii) a heterogeneous cluster of microsatellite instability-high mucinous carcinomas (18%), including inherited colorectal carcinomas, displaying a high-grade histological pattern. Age, TNM stage, and BRAF mutation had prognostic value. Hierarchical clustering analysis led to the identification of several clinicopathological entities of colorectal mucinous adenocarcinomas with epidemiologic, prognostic, and therapy relevance. Both KRAS and BRAF mutations appear as drivers in the alternate oncogenetic pathways governing the development of sporadic colorectal mucinous adenocarcinomas.

Detection rate of serrated polyps and serrated polyposis syndrome in colorectal cancer screening cohorts: a European overview

OBJECTIVE

The role of serrated polyps (SPs) as colorectal cancer precursor is increasingly recognised. However, the true prevalence SPs is largely unknown. We aimed to evaluate the detection rate of SPs subtypes as well as serrated polyposis syndrome (SPS) among European screening cohorts.

METHODS

Prospectively collected screening cohorts of ≥1000 individuals were eligible for inclusion. Colonoscopies performed before 2009 and/or in individuals aged below 50 were excluded. Rate of SPs was assessed, categorised for histology, location and size. Age-sex-standardised number needed to screen (NNS) to detect SPs were calculated. Rate of SPS was assessed in cohorts with known colonoscopy follow-up data. Clinically relevant SPs (regarded as a separate entity) were defined as SPs ≥10 mm and/or SPs >5 mm in the proximal colon.

RESULTS

Three faecal occult blood test (FOBT) screening cohorts and two primary colonoscopy screening cohorts (range 1.426-205.949 individuals) were included. Rate of SPs ranged between 15.1% and 27.2% (median 19.5%), of sessile serrated polyps between 2.2% and 4.8% (median 3.3%) and of clinically relevant SPs between 2.1% and 7.8% (median 4.6%). Rate of SPs was similar in FOBT-based cohorts as in colonoscopy screening cohorts. No apparent association between the rate of SP and gender or age was shown. Rate of SPS ranged from 0% to 0.5%, which increased to 0.4% to 0.8% after follow-up colonoscopy.

CONCLUSIONS

The detection rate of SPs is variable among screening cohorts, and standards for reporting, detection and histopathological assessment should be established. The median rate, as found in this study, may contribute to define uniform minimum standards for males and females between 50 and 75 years of age.

Distinct clinical outcomes of two CIMP-positive colorectal cancer subtypes based on a revised CIMP classification system

Background:

Colorectal cancer (CRC) is a heterogeneous disease in terms of molecular carcinogenic pathways. Based on recent findings regarding the multiple serrated neoplasia pathway, we revised an eight-marker panel for a new CIMP classification system.

Methods:

1370 patients who received surgical resection for CRCs were classified into three CIMP subtypes (CIMP-N: 0–4 methylated markers, CIMP-P1: 5–6 methylated markers and CIMP-P2: 7–8 methylated markers). Our findings were validated in a separate set of high-risk stage II or stage III CRCs receiving adjuvant fluoropyrimidine plus oxaliplatin (n=950).

Results:

A total of 1287/62/21 CRCs cases were classified as CIMP-N/CIMP-P1/CIMP-P2, respectively. CIMP-N showed male predominance, distal location, lower T, N category and devoid of BRAF mutation, microsatellite instability (MSI) and MLH1 methylation. CIMP-P1 showed female predominance, proximal location, advanced TNM stage, mild decrease of CK20 and CDX2 expression, mild increase of CK7 expression, BRAF mutation, MSI and MLH1 methylation. CIMP-P2 showed older age, female predominance, proximal location, advanced T category, markedly reduced CK20 and CDX2 expression, rare KRAS mutation, high frequency of CK7 expression, BRAF mutation, MSI and MLH1 methylation. CIMP-N showed better 5-year cancer-specific survival (CSS; HR=0.47; 95% CI: 0.28–0.78) in discovery set and better 5-year relapse-free survival (RFS; HR=0.50; 95% CI: 0.29–0.88) in validation set compared with CIMP-P1. CIMP-P2 showed marginally better 5-year CSS (HR=0.28, 95% CI: 0.07–1.22) in discovery set and marginally better 5-year RFS (HR=0.21, 95% CI: 0.05–0.92) in validation set compared with CIMP-P1.

Conclusions:

CIMP subtypes classified using our revised system showed different clinical outcomes, demonstrating the heterogeneity of multiple serrated precursors of CIMP-positive CRCs.

The clinical impact of serrated colorectal polyps

Serrated polyps (SPs) of the colorectum pose a novel challenge to practicing gastroenterologists. Previously thought benign and unimportant, there is now compelling evidence that SPs are responsible for a significant percentage of incident colorectal cancer worldwide. In contrast to conventional adenomas, which tend to be slow growing and polypoid, SPs have unique features that undermine current screening and surveillance practices. For example, sessile serrated polyps (SSPs) are flat, predominately right-sided, and thought to have the potential for rapid growth. Moreover, SSPs are subject to wide variations in endoscopic detection and pathologic interpretation. Unfortunately, little is known about the natural history of SPs, and current guidelines are based largely on expert opinion. In this review, we outline the current taxonomy, epidemiology, and management of SPs with an emphasis on the clinical and public health impact of these lesions.

From traditional serrated adenoma to tubulovillous adenoma and beyond

It is well established that colorectal cancer develops from a series of precursor epithelial polyps, including tubular adenomas, villous/tubulovillous adenomas (VA/TVA), sessile serrated adenomas (SSA) and traditional serrated adenomas (TSA). Of these, TSAs are least common and account for only 5% of all serrated polyps. TSAs are characterised by the presence of a “pinecone-like” architecture, granular eosinophilic cytoplasm, luminal serrations, ectopic crypt foci (ECF) and elongated, pencillate nuclei. However, the distinct slit-like luminal serrations, reminiscent of small bowel mucosa, appear to be the most unique and reproducible feature to distinguish TSAs from other polyps. There is a contention that TSAs are not inherently dysplastic and that the majority do not show cytological atypia. Two types of dysplasia are associated with TSA. Serrated dysplasia is less well recognised and less commonly encountered than adenomatous dysplasia. In addition, it is now becoming increasingly evident that TSAs can be admixed with HP, SSA and VA/TVA. At a genetic level, polyps may switch phenotype as they accumulate genetic changes, evolving from a serrated pathway to a more conventional one, which could be the basis for a spectrum theory starting out with a TSA with serration and ECF evolving into a TSA with conventional dysplasia and, eventually, to a well-developed conventional adenoma. Nevertheless, there is an exigency for future studies to provide further illumination and bridge the gaps in our present understanding.

BRAF mutation may have different prognostic implications in early- and late-stage colorectal cancer

The prognostic implication of BRAF mutant colorectal cancer remains paradoxical. Records of BRAF mutant and wild-type colorectal cancer patients at all stages were reviewed. Clinicopathologic features, including microsatellite instability, CpG islands methylator phenotype, and overall survival, of these patients were analyzed. Between 2005 and 2013, 428 colorectal cancer patients were enrolled in this study. The overall survival between BRAF mutant and wild-type patients with early-stage (stages I and II) colorectal cancer differed nonsignificantly (P = 0.99). By contrast, in late-stage (stages III and IV) patients, the median overall survival of BRAF mutant patients (N = 25) was significantly poorer than that of BRAF wild-type (N = 207) patients (BRAF mutant: 21.3 months (95% confidence interval [CI] 7.1-35.5); BRAF wild-type: 53.5 months (95% CI 37.5-69.5), P < 0.0001). In early-stage patients, we found that BRAF mutation was significantly associated with CpG island methylator phenotype-positive (P < 0.001), and microsatellite instability-high status (P = 0.0013). Conversely, in late-stage patients, BRAF mutation was significantly associated with CpG island methylator phenotype-positive (P = 0.0015) and the right-side colon (P = 0.014). BRAF mutation may have different prognostic implications in early- and late-stage colorectal cancer.