Intermediate serrated polyp as an intermediate lesion of hyperplastic polyp and sessile serrated polyp/adenoma in terms of morphological and molecular features

From Mixed Hyperplastic/Adenomatous Polyp to Sessile Serrated Lesion: A Long and Winding Road for Long and Winding Crypts

CONTEXT.—

During the past 3 decades, numerous articles in the literature have offered terminology, diagnostic criteria, and consensus recommendations regarding the entity currently referred to by the World Health Organization as sessile serrated lesion. Given the many names and various, variably reproducible diagnostic criteria ascribed to sessile serrated lesion, confusion persists for many pathologists and gastroenterologists regarding the diagnosis. This distinction is important, as sessile serrated lesion can progress to malignancy, unlike its main differential diagnosis, hyperplastic polyp. Research studies have shed light on the characteristic architecture and morphology, immunohistochemical patterns, and molecular alterations of sessile serrated lesion, and multiple consensus meetings around the globe have developed their criteria and nomenclature, often clashing or mixing terms.

OBJECTIVE.—

To provide a narrative review from the entity's early description to our current understanding.

DATA SOURCES.—

The existing scientific and clinical literature, published texts, medical society recommendations, and specialty consensus guidelines.

CONCLUSIONS.—

The current World Health Organization criteria are a distillation of this scientific process, but terminology is still a point of contention worldwide.

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.

Clinicopathological factors associated with BRAF-V600E mutation in colorectal serrated adenomas

Serrated adenomas are genetically heterogeneous, and the histological classification into sessile serrated (SSA) adenoma and traditional serrated adenoma (TSA) does not reflect the molecular landscape. The objective of this study was to assess clinical or pathological factors associated with BRAF-V600E mutation in serrated adenomas. Systematic review and meta-analysis was performed by searching electronic databases from January 2011 to January 2019 for studies assessing the association of BRAF-V600E mutation with clinical or pathological features of serrated adenomas. Odds ratio (OR) was calculated for each factor; a P-value <0.05 was considered significant. Forty studies assessing 3511 serrated adenomas (2375 SSAs and 1136 TSAs) were included. BRAF-V600E mutation was significantly associated with proximal localisation (OR = 2.71; P < 0.00001) and CIMP-H status (OR = 4.81; P < 0.0001) in both SSA and TSA, with polyp size <10 mm (OR = 0.41; P = 0.02) in TSA, and with endoscopic pit pattern II-O (OR = 13.11; P < 0.00001) and expression of MUC5A5 (OR = 4.43; P = 0.003) and MUC6 (OR = 2.28; P < 0.05) in SSA. Conversely, BRAF mutation was not associated with age <70 years (OR = 1.63; P = 0.34), age <60 years (OR = 0.86; P = 0.79), female sex (OR = 0.77; P = 0.12), flat morphology (OR = 1.52; P = 0.16), presence of any dysplasia (OR = 1.01; P = 0.59), serrated dysplasia (OR = 1.23; P = 0.72) and invasive cancer (OR = 0.67; P = 0.32), nuclear β-catenin expression (OR = 0.73; P = 0.21) and p53 overexpression (OR = 1.24; P = 0.82). In conclusion, BRAF-V600E mutation is associated with proximal localisation and CIMP-H status in both SSA and TSA, with size <10 mm only in TSA, and with expression of MUC5A5 and MUC6 and endoscopic pit pattern II-O at least in SSA. In serrated adenomas, BRAF-V600E mutation does not seem to be associated with age and sex, with the prevalence of dysplasia and cancer and with the morphology of the dysplastic component.

Exome sequencing characterizes the somatic mutation spectrum of early serrated lesions in a patient with serrated polyposis syndrome (SPS)

Background

Serrated or Hyperplastic Polyposis Syndrome (SPS, HPS) is a yet poorly defined colorectal cancer (CRC) predisposition characterised by the occurrence of multiple and/or large serrated polyps throughout the colon. A serrated polyp-CRC sequence (serrated pathway) of CRC formation has been postulated, however, to date only few molecular signatures of serrated neoplasia (BRAF, KRAS, RNF43 mutations, CpG Island Methylation, MSI) have been described in a subset of SPS patients and neither the etiology of the syndrome nor the distinct genetic alterations during tumorigenesis have been identified.

Methods

To identify somatic point mutations in potential novel candidate genes of SPS-associated lesions and the involved pathways we performed exome sequencing of eleven early serrated polyps obtained from a 41 year-old female patient with clinically confirmed SPS. For data filtering and analysis, standard pipelines were used. Somatic mutations were identified by comparison with leukocyte DNA and were validated by Sanger sequencing.

Results

The BRAF p.V600E or KRAS p.G12D mutation was identified in six polyps (~50%) and not found in polyps from the distal colon. In addition, we found seven unique rare somatic alterations of seven different genes in four serrated tumours, all of which are missense variants. The variant in ABI3BP and CATSPERB are predicted to be deleterious. No established cancer gene or candidate genes related to serrated tumorigenesis were affected.

Conclusions

Somatic mutations seem to be rare events in early hyperplastic and serrated lesions of SPS patients. Neither frequently affected genes nor enrichment of specific pathways were observed. Thus, other alterations such as non-coding variants or epigenetic changes might be the major driving force of tumour progression in SPS.

Electronic supplementary material

The online version of this article (10.1186/s13053-017-0082-9) contains supplementary material, which is available to authorized users.

Inflammatory response in serrated precursor lesions of the colon classified according to WHO entities, clinical parameters and phenotype-genotype correlation

Studies on traditional serrated adenoma (TSA) and sessile serrated adenoma with dysplasia (SSA‐D) are rare due to the low frequency of these lesions, which are well defined by the latest WHO classification. However, introducing new morphological criteria such as intra‐epithelial lymphocytes (IELs) might facilitate colorectal polyp diagnoses. Additionally, the phenotype–genotype correlation needs to be updated as the terminology has repeatedly changed. This study analysed 516 polyps, consisting of 118 classical adenomas (CAD), 116 hyperplastic polyps (HPP), 179 SSAs, 41 SSA‐Ds, and 62 TSAs. The lesions were analysed in relation to the patients’ clinical parameters including gender, age, localisation, and size. The inflammatory background of the polyps was quantified and BRAF and KRAS mutations as well as MLH1 and CDKN2A promoter methylation were assessed. In multivariate analyses, an increase in IELs was an independent and robust new criterion for the diagnosis of SSA‐D (p < 0.001). Superficial erosions and acute neutrophil granulocytes led to reactive changes potentially resembling dysplasia. KRAS and BRAF mutations were associated with CAD/TSA and HPP/SSA, respectively. However, almost half of TSAs had a BRAF mutation and were KRAS wild type. CDKN2A seems to precede MLH1 hyper‐methylation within the serrated carcinogenesis model. The genotyping of WHO‐based entities – and especially SSA – has sharpened in comparison to previously published data. TSAs can be sub‐grouped according to their mutation status. Of note, the higher number of IELs in SSA‐D reflects their close relationship to colorectal cancers with micro‐satellite instability. Therefore, IELs might represent a new diagnostic tool for SSA‐D.

The serrated neoplasia pathway of colorectal tumors: Identification of MUC5AC hypomethylation as an early marker of polyps with malignant potential

The serrated neoplasia pathway accounts for 20-30% of colorectal cancers (CRC), which are characterized by extensive methylation (CpG island methylation phenotype, CIMP), frequent BRAF mutation and high microsatellite instability (MSI). We recently identified MUC5AC mucin gene hypomethylation as a specific marker of MSI CRC. The early identification of preneoplastic lesions among serrated polyps is currently challenging. Here, we performed a detailed pathological and molecular analysis of a large series of colorectal serrated polyps and evaluated the usefulness of mucin genes MUC2 and MUC5AC to differentiate serrated polyps and to identify lesions with malignant potential. A series of 330 colorectal polyps including 218 serrated polyps [42 goblet cell-rich hyperplastic polyps (GCHP), 68 microvesicular hyperplastic polyps (MVHP), 100 sessile serrated adenoma (SSA) and eight traditional serrated adenoma (TSA)] and 112 conventional adenomas was analyzed for BRAF/KRAS mutations, MSI, CIMP, MLH1 and MGMT methylation, and MUC2 and MUC5AC expression and methylation. We show that MUC5AC hypomethylation is an early event in the serrated neoplasia pathway, and specifically detects MVHP and SSA, arguing for a filiation between MVHP, SSA and CIMP-H/MSI CRC, whereas GCHP and TSA arise from a distinct pathway. Moreover, MUC5AC hypomethylation specifically identified serrated lesions with BRAF mutation, CIMP-H or MSI, suggesting that it may be useful to identify serrated neoplasia pathway-related precursor lesions. Our data suggest that MVHP should be recognized among HP and require particular attention.

Are clinicopathological features of colorectal cancers with methylation in half of CpG island methylator phenotype panel markers different from those of CpG island methylator phenotype-high colorectal cancers?

CpG island methylator phenotype (CIMP)-high (CIMP-H) colorectal cancer (CRC) is defined when a tumor shows methylation at greater than or equal to 60% of CIMP panel markers. Although CRCs with methylation at 50% of panel markers are classified as CIMP-low/CIMP-0 tumors, little is known regarding the clinicopathological and molecular features of CRCs with methylation at 4/8 panel markers (4/8 methylated markers) and whether they are akin to CIMP-H or CIMP-low/CIMP-0 CRCs in terms of their clinicopathological or molecular features. A total of 1164 cases of surgically resected CRC were analyzed for their methylation status in 8 CIMP panel markers, and the frequencies of various clinicopathological and molecular features were compared between CRCs with 0/8, 1/8 to 3/8, 4/8, and 5/8 to 8/8 methylated markers. CRCs with 4/8 methylated markers were closer to CRCs with 5/8 to 8/8 methylated markers in terms of sex distribution, mucin production, serration, nodal metastasis, CK7 expression, CK20 loss, and CDX2 loss frequencies and overall survival rate. CRCs with methylation at 4/8 markers were closer to CRCs with 1/8 to 3/8 methylated markers in terms of less frequent right colon location and poor differentiation. CRCs with 4/8 methylated markers showed the shortest overall survival time compared with CRCs with 0/8, 1/8 to 3/8, 4/8, or 5/8 to 8/8 methylated markers. In terms of clinicopathological and molecular features, CRCs with 4/8 methylated markers appeared to be closer to CIMP-H than to CIMP-low/CIMP-0 and would thus be better classified as CIMP-H if the CRCs require classification into either CIMP-H or CIMP-low/CIMP-0.

A morphologic reappraisal of endoscopically but not histologically apparent polyps and the emergence of the overlooked goblet cell--rich hyperplastic polyp

Goblet cell--rich hyperplastic polyps (GCRHP) are morphologically subtle compared to microvesicular hyperplastic polyps (MVHP) and are believed to be the most commonly unrecognized serrated polyp, though this has not been systematically studied. We hypothesize that a gastrointestinal pathologist's review of endoscopically but not histologically apparent polyps will identify previously missed GCRHPs, a finding that may be clinically significant if the addition of this subtype of serrated polyp contributes to sufficient numeric criteria for a clinical diagnosis of serrated polyposis syndrome (SPS). Two blinded reviews were performed on 160 endoscopically but not histologically apparent polyps by a gastrointestinal pathologist, separated by a 6 month "washout period." A final review diagnosis of GCRHP was applied to all polyps with complete agreement on both reviews. Patient records were then searched to determine if the addition of a GCRHP resulted in sufficient numeric criteria for a clinical diagnosis of SPS. Fourteen (9%) polyps were reclassified as GCRHPs. The majority (n = 12, 86%) were originally called "colonic mucosa with surface hyperplastic change (CMWSHC)." Two polyps (1%) were re-classified as MVHPs. No other serrated or adenomatous polyps were identified. For each patient, the addition of a hyperplastic polyp did not result in a clinical diagnosis of SPS, though one patient fell short of this diagnosis by only one polyp. GCRHPs are the most commonly underdiagnosed serrated polyp and are often called CMWSHC. The addition of previously missed GCRHPs is unlikely to contribute to a diagnosis of SPS in an individual patient.

Cyclooxygenase-2 immunohistochemical expression in serrated polyps of the colon

Aim of the study

Cyclooxygenase-2 (COX-2) expression has been observed in a substantial percentage of classical adenomas of the large bowel. The aim of the study was to assess and compare the expression of COX-2 in serrated polyps of the colon.

Material and methods

One hundred and nineteen serrated polyps were analyzed. There were 83 hyperplastic polyps (HP), 19 sessile serrated polyps (SSP) and 17 traditional serrated adenomas (TSA). COX-2 expression was assessed semi-quantitatively (0–2) and each lesion was fully characterized in terms of anatomical location, size, histology, age and sex of the patient. The general estimating equation (GEE) model with logit link was used in the statistical analysis.

Results

Epithelial expression of COX-2 was found in 85/119 serrated polyps (71.43%): 57/83 (68.67%) HP, 16/19 (84.21%) SSP, and 12/17 (70.59%) TSA. In HP and SSP it was predominantly of weak (49/83 HP, 12/19 SSP), whereas in TSA it was mainly of medium/strong intensity (8/17). The TSA category was associated with more frequent COX-2 expression (OR = 7.00, 95% CI: 1.49–32.88, p = 0.014) than HP, but such relation was not found for SSP vs. HP (p > 0.1). No associations between COX-2 expression and clinical parameters were found.

Conclusions

Immunohistochemical COX-2 expression cannot serve as a diagnostic adjunct to differentiate HP and SSP.