Serrated tubulovillous adenoma of the large intestine

The histologic features, molecular features, detection and management of serrated polyps: a review

The serrated pathway to colorectal cancers (CRCs) is a significant pathway encompassing five distinct types of lesions, namely hyperplastic polyps (HPs), sessile serrated lesions (SSLs), sessile serrated lesions with dysplasia (SSL-Ds), traditional serrated adenomas (TSAs), and serrated adenoma unclassified. In contrast to the conventional adenoma-carcinoma pathway, the serrated pathway primarily involves two mechanisms: BRAF/KRAS mutations and CpG island methylator phenotype (CIMP). HPs are the most prevalent non-malignant lesions, while SSLs play a crucial role as precursors to CRCs, On the other hand, traditional serrated adenomas (TSAs) are the least frequently encountered subtype, also serving as precursors to CRCs. It is crucial to differentiate these lesions based on their unique morphological characteristics observed in histology and colonoscopy, as the identification and management of these serrated lesions significantly impact colorectal cancer screening programs. The management of these lesions necessitates the crucial steps of removing premalignant lesions and implementing regular surveillance. This article provides a comprehensive summary of the epidemiology, histologic features, molecular features, and detection methods for various serrated polyps, along with recommendations for their management and surveillance.

Comprehensive proteogenomic characterization of early duodenal cancer reveals the carcinogenesis tracks of different subtypes

The subtypes of duodenal cancer (DC) are complicated and the carcinogenesis process is not well characterized. We present comprehensive characterization of 438 samples from 156 DC patients, covering 2 major and 5 rare subtypes. Proteogenomics reveals LYN amplification at the chromosome 8q gain functioned in the transmit from intraepithelial neoplasia phase to infiltration tumor phase via MAPK signaling, and illustrates the DST mutation improves mTOR signaling in the duodenal adenocarcinoma stage. Proteome-based analysis elucidates stage-specific molecular characterizations and carcinogenesis tracks, and defines the cancer-driving waves of the adenocarcinoma and Brunner's gland subtypes. The drug-targetable alanyl-tRNA synthetase (AARS1) in the high tumor mutation burden/immune infiltration is significantly enhanced in DC progression, and catalyzes the lysine-alanylation of poly-ADP-ribose polymerases (PARP1), which decreases the apoptosis of cancer cells, eventually promoting cell proliferation and tumorigenesis. We assess the proteogenomic landscape of early DC, and provide insights into the molecular features corresponding therapeutic targets.

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.

The histomorphological and molecular landscape of colorectal adenomas and serrated lesions

The 2019 WHO classification of digestive system tumors significantly reformed the classificatory definition of serrated lesions of the colorectal mucosa and added new essential diagnostic criteria for both conventional adenomas and hereditary gastrointestinal polyposis syndromes. Histopathological examination of colorectal adenocarcinoma precursors lesions represents an important segment of daily clinical practice in a pathology department and is essential for the implementation of current colorectal adenocarcinoma secondary prevention strategies. This overview will focus on a schematic histopathological and molecular classification of precursor lesions arising within colorectal mucosa.

The spectrum of serrated colorectal lesions-new entities and unanswered questions

Hyperplastic polyps (HPs) of the colon and rectum were historically thought not to be associated with an increased risk of development of colorectal cancer (CRC). The recognition of variants of serrated colorectal lesions that possessed relatively subtle but significant morphological differences from those of HPs and that could be associated with epithelial dysplasia and CRC led to the characterisation of sessile serrated lesions (SSLs) and traditional serrated adenomas (TSAs). These links were supported by the identification of genetic alterations that are commonly found in HPs, SSLs, TSAs, and CRC, e.g. BRAF and KRAS mutations. The 'serrated pathway' to CRC may progress faster than the traditional 'adenoma-carcinoma sequence', underlining the importance of identifying these lesions. The diagnostic histological criteria for SSLs have since been more clearly defined, in parallel with a drive to increase the recognition of these lesions at endoscopy. The existence of lesions showing overlapping morphological and molecular features with those of HPs, SSLs and TSAs has most recently been highlighted-including mucin-rich TSA, serrated tubulovillous adenoma, and those showing mixed histological features, e.g. comprising differing combinations of HP, SSL, and TSA. Morphological and molecular studies of this range of lesions are providing insights into the relationships of serrated colorectal lesions with each other and with CRC. This article provides an overview of the current understanding of serrated colorectal lesions, including a discussion of those with overlapping and mixed features.

The 2019 World Health Organization Classification of appendiceal, colorectal and anal canal tumours: an update and critical assessment

The recently published 5th edition 2019 World Health Organization (WHO) Classification of Tumours of the Digestive System brings significant changes from the 2010 4th edition. An emphasis on uniformity in nomenclature and grading for tumours across all organ systems is a particular feature of the 5th edition blue book series that is reflected in the gastrointestinal tract (GIT) classification. For example, simplified two tiered grading is reinforced for preinvasive lesions throughout the GIT, with dysplasia at all sites now being considered either low or high grade. Similarly, a uniform approach to classification and grading of GIT neuroendocrine neoplasms has been consolidated, with an emphasis on distinguishing grade 3 neuroendocrine tumours from neuroendocrine carcinomas. In this review, we discuss and critically assess the important and sometimes controversial changes made to the classification of tumours of the lower GIT, comprising the colorectum, vermiform appendix and anal canal. The particularly controversial decision to endorse the term 'sessile serrated lesion' for lesions previously termed 'sessile serrated polyp/adenoma' is explored. The morphological, molecular, and clinical insights behind the substitution of the term 'goblet cell adenocarcinoma' for 'goblet cell carcinoid' are assessed. The evolution of the classification of appendiceal mucinous neoplasms is considered. Inflammatory bowel disease related dysplasia and its evolving subtypes, with major implications for pathologists in routine practice, is explained.

Serrated Lesions in Inflammatory Bowel Disease: Genotype-Phenotype Correlation

BACKGROUND

Patients with inflammatory bowel disease (IBD) and hyperplastic/serrated polyposis have an increased risk of colorectal cancer. The aim of our study was to elucidate the nature of serrated lesions in IBD patients.

MATERIALS AND METHODS

Sixty-five lesions with serrated morphology were analyzed in 39 adult IBD patients. Lesions were classified according to the WHO 2019 criteria or regarded as reactive, and molecular analysis was performed.

RESULTS

82.1% of patients had ulcerative colitis, 17.9% had Crohn's disease; 51.3% were female, and the mean age was 54.5 years. The duration of IBD varied significantly (16.7 ± 11.4 years). Endoscopy showed polypoid lesions in 80.3%; the size ranged from 2 to 20 mm. A total of 21.6% of the lesions were located in the right colon. Five lesions were classified as inflammatory pseudopolyps, 28 as hyperplastic polyp, 21 and 2 as sessile serrated lesion without and with dysplasia, respectively, and 9 as traditional serrated adenoma with low-grade dysplasia. Analysis of all true serrated lesions revealed 31 mutations in KRAS and 32 in BRAF gene. No mutations were identified in inflammatory pseudopolyps. In the right colon BRAF mutations were more frequent than KRAS (16 vs 3), while KRAS mutations prevailed on the left side (28 vs 16, P < .001). One patient with traditional serrated adenomas progressed to an adenocarcinoma after 61 months.

CONCLUSION

The molecular analysis could help discriminate true serrated lesions (IBD-associated or not) from reactive pseudopolyps with serrated/hyperplastic epithelial change. These should help in more accurate classification of serrated lesions.

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.

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.

Correlation of molecular and morphological features of appendiceal epithelial neoplasms

AIMS

The aims of this study were to identify the genetic features of appendiceal epithelial neoplasms and correlate the genetic features with morphology.

METHODS AND RESULTS

We analysed the genetic features of a series of 47 appendiceal epithelial neoplasms of various morphologies by using targeted next-generation sequencing of 11 genes commonly mutated in gastrointestinal neoplasms. Seven of nine serrated polyps harboured BRAF mutations, which are rare in other types of appendiceal tumours. Most cases of low-grade appendiceal mucinous neoplasms (LAMNs) exhibited GNAS and KRAS mutations. LAMNs with a coexisting serrated polyp were all KRAS mutated. Four LAMNs with mutations in the Wnt/β-catenin pathway, either through inactivating mutations in APC or RNF43 or activating mutations in CTNNB1, had focal proliferation of mucin-poor low-grade tumour cells, reminiscent of colorectal adenomas. Mutations in the Wnt/β-catenin pathway were also identified in high-grade appendiceal mucinous neoplasms, suggesting that Wnt/β-catenin pathway activation is the driving force for the progression of LAMN to a higher-grade lesion. Adenomatous polyps of the appendix frequently had APC, KRAS and TP53 mutations and were morphologically and molecularly similar to adenomatous polyps of the colorectum.

CONCLUSIONS

Our results indicate a close association between morphology and genetic events in appendiceal neoplasms and suggest a phylogenetic relationship between different entities.

Correlation analysis of IL-4, IL-10 and APN levels with postoperative infection of colorectal cancer

Changes in expression levels of serum interleukin-4 (IL-4), IL-10 and adiponectin (APN) in patients with postoperative infection of colorectal cancer were studied. The clinical data of 159 patients receiving radical surgery for colorectal cancer in Xiangyang No. 1 People's Hospital, Hubei University of Medicine from January 2014 to December 2017, were retrospectively analyzed. A total of 67 patients with postoperative infection were enrolled into the infection group, while the remaining 92 patients without infection were enrolled into the non-infection group. The expression levels of serum IL-4, IL-10 and APN of patients were detected via enzyme-linked immunosorbent assay. The correlation of IL-4, IL-10 and APN levels with stage of colorectal cancer were explored by the Spearmans correlation analysis. The expression levels of IL-4 and IL-10 in the infection group were significantly higher than those in the non-infection group at day 3 after surgery (P<0.05). The expression level of APN in the infection group was lower than that in the non-infection group at day 3 after surgery (P<0.05). The serum IL-4 and IL-10 levels in pulmonary infection was higher and the serum IL-10 level in pulmonary infection was higher than those in incision infection and abdominal infection (P<0.05). The IL-4 and IL-10 levels in patients with colorectal cancer in the infection group at day 3 after surgery had a significant positive correlation with the stage of colorectal cancer (r=0.9357, P<0.001; r=0.9717, P<0.001), and the APN level in patients with colorectal cancer in the infection group at day 3 after surgery had a significant negative correlation with the stage of colorectal cancer (r=-0.9736, P<0.001). The serum IL-4 and IL-10 levels in patients with postoperative infection of colorectal cancer are positively correlated with the stage of cancer, while the serum APN level was negatively correlated with the stage of cancer.

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.

Factors Associated With Classification of Hyperplastic Polyps as Sessile Serrated Adenomas/Polyps on Morphologic Review

BACKGROUND

Distinguishing sessile serrated adenomas/polyp (SSA/P), a subset of serrated polyps, from hyperplastic polyps (HPs) remains a challenge and has surveillance implications. Our goal was to identify clinical and pathologic factors associated with serrated polyps originally read as HPs being reassessed as SSA/Ps versus confirmed as HPs.

METHODS

Data were collected from consecutive patients with a right-sided HP and a corresponding comparison group with conventional adenomas between 1993 and 2003. Two experienced gastrointestinal pathologists, blinded to polyp and clinical factors, reinterpreted the HPs using current SSA/P classification criteria. These HPs were classified as SSA/P when diagnostic histologic feature(s) were present in at least 3 crypts. Analyses, conducted on a per polyp basis, examined the factors associated with risk of individual HPs being reassessed as SSA/Ps as opposed to being confirmed as HPs.

RESULTS

Of the 702 HPs (355 adults), 188 (26.8%) were reclassified as SSA/Ps. Predictors of HPs being reinterpreted as SSA/Ps included: size ≥5 mm [odds ratio (OR), 2.09; 95% confidence interval (CI), 1.34-3.26], proximal location (OR, 2.83; 95% CI, 1.69-4.74), synchronous adenomas with advanced pathology (OR, 2.61; 95% CI, 1.22-5.55) and ≥1 synchronous HPs (other than HP being reassessed) reclassified as SSA/Ps (OR, 11.76; 95% CI, 6.75-20.49).

CONCLUSIONS

Because HP versus SSP is not very reproducible the predictors of SSA/P that we identified, including size, location, and synchronous lesions, can offer some additional help to endoscopists when determining surveillance intervals in patients with serrated polyps. In addition, observed association between SSA/P with advanced conventional neoplasia (but not low-grade adenomas) suggests 2 distinct groups of patient predisposition, one with both advanced conventional and important serrated precursors (SSA/P) and the other largely restricted to nonadvanced conventional adenomas and HPs only. Whether the association reported here has to do with SSA/P diagnosis per se or generally larger size of SSA/P remains to be determined in future studies.

The role of APC in WNT pathway activation in serrated neoplasia

Conventional adenomas are initiated by APC gene mutation that activates the WNT signal. Serrated neoplasia is commonly initiated by BRAF or KRAS mutation. WNT pathway activation may also occur, however, to what extent this is owing to APC mutation is unknown. We examined aberrant nuclear β-catenin immunolocalization as a surrogate for WNT pathway activation and analyzed the entire APC gene coding sequence in serrated and conventional pathway polyps and cancers. WNT pathway activation was a common event in conventional pathway lesions with aberrant nuclear immunolocalization of β-catenin and truncating APC mutations in 90% and 89% of conventional adenomas and 82% and 70% of BRAF wild-type cancers, respectively. WNT pathway activation was seen to a lesser extent in serrated pathway lesions. It occurred at the transition to dysplasia in serrated polyps with a significant increase in nuclear β-catenin labeling from sessile serrated adenomas (10%) to sessile serrated adenomas with dysplasia (55%) and traditional serrated adenomas (9%) to traditional serrated adenomas with dysplasia (39%) (P=0.0001). However, unlike the conventional pathway, truncating APC mutations were rare in the serrated pathway lesions especially sessile serrated adenomas even when dysplastic (15%) and in the BRAF mutant cancers with microsatellite instability that arise from them (8%). In contrast, APC missense mutations that were rare in conventional pathway adenomas and cancers (3% in BRAF wild-type cancers) were more frequent in BRAF mutant cancers with microsatellite instability (32%). We conclude that increased WNT signaling is important in the transition to malignancy in the serrated pathway but that APC mutation is less common and the spectrum of mutations is different than in conventional colorectal carcinogenesis. Moderate impact APC mutations and non-APC-related causes of increased WNT signaling may have a more important role in serrated neoplasia than the truncating APC mutations common in conventional adenomas.

Epigenetic silencing of SMOC1 in traditional serrated adenoma and colorectal cancer

Colorectal sessile serrated adenoma/polyps (SSA/Ps) are well-known precursors of colorectal cancer (CRC) characterized by BRAF mutation and microsatellite instability. By contrast, the molecular characteristics of traditional serrated adenoma (TSAs) are not fully understood. We analyzed genome-wide DNA methylation in TSAs having both protruding and flat components. We identified 11 genes, including SMOC1, methylation of which progressively increased during the development of TSAs. SMOC1 was prevalently methylated in TSAs, but was rarely methylated in SSA/Ps (p < 0.001). RT-PCR and immunohistochemistry revealed that SMOC1 was expressed in normal colon and SSA/Ps, but its expression was decreased in TSAs. Ectopic expression of SMOC1 suppressed proliferation, colony formation and in vivo tumor formation by CRC cells. Analysis of colorectal lesions (n = 847) revealed that SMOC1 is frequently methylated in TSAs, high-grade adenomas and CRCs. Among these, SMOC1 methylation was strongly associated with KRAS mutation and CpG island methylator phenotype (CIMP)-low. These results demonstrate that epigenetic silencing of SMOC1 is associated with TSA development but is rarely observed in SSA/Ps. SMOC1 expression could thus be a diagnostic marker of serrated lesions, and SMOC1 methylation could play a role in neoplastic pathways in TSAs and conventional adenomas.

Copy number profiles of paired primary and metastatic colorectal cancers

Liver metastasis is the major cause of death following a diagnosis of colorectal cancer (CRC). In this study, we compared the copy number profiles of paired primary and liver metastatic CRC to better understand how the genomic structure of primary CRC differs from the metastasis. Paired primary and metastatic tumors from 16 patients and their adjacent normal tissue samples were analyzed using single nucleotide polymorphism arrays. Genome-wide chromosomal copy number alterations were assessed, with particular attention to 188 genes known to be somatically altered in CRC and 24 genes that are clinically actionable in CRC. These data were analyzed with respect to the timing of primary and metastatic tissue resection and with exposure to chemotherapy. The genomic differences between the tumor and paired metastases revealed an average copy number discordance of 22.0%. The pairs of tumor samples collected prior to treatment revealed significantly higher copy number differences compared to post-therapy liver metastases (P = 0.014). Loss of heterozygosity acquired in liver metastases was significantly higher in previously treated liver metastasis samples compared to treatment naive liver metastasis samples (P = 0.003). Amplification of the clinically actionable genes ERBB2, FGFR1, PIK3CA or CDK8 was observed in the metastatic tissue of 4 patients but not in the paired primary CRC. These examples highlight the intra-patient genomic discrepancies that can occur between metastases and the primary tumors from which they arose. We propose that precision medicine strategies may therefore identify different actionable targets in metastatic tissue, compared to primary tumors, due to substantial genomic differences.

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.

Comprehensive characterization of RSPO fusions in colorectal traditional serrated adenomas

AIMS

Traditional serrated adenoma (TSA) is a rare but distinct type of colorectal polyp. Our previous study showed that PTPRK-RSPO3 fusions are frequent and characteristic genetic alterations in TSAs. This study aimed to characterize comprehensively the prevalence and variability of RSPO fusions in colorectal TSAs.

METHODS AND RESULTS

We examined RSPO expression and explored novel RSPO fusions in 129 TSAs, including 66 lesions analysed previously for WNT pathway gene mutations. Quantitative polymerase chain reaction (qPCR) analyses identified three and 43 TSAs overexpressing RSPO2 and RSPO3, respectively, whereas the expression of RSPO1 and RSPO4 was marginal or undetectable in all cases. RSPO overexpression was always mutually exclusive with other WNT pathway gene mutations. Known PTPRK-RSPO3 fusions were detected in 37 TSAs, all but one of which overexpressed RSPO3. In addition, rapid amplification of cDNA ends revealed three novel RSPO fusion transcripts, an NRIP1-RSPO2 fusion and two PTPRK-RSPO3 fusion isoforms, in six TSAs. Overall, 43 TSAs had RSPO fusions (33%), whereas four TSAs (3%) overexpressed RSPO in the absence of RSPO fusions. TSAs with RSPO fusions showed several clinicopathological features, including distal localization (P = 0.0063), larger size (P = 0.0055), prominent ectopic crypt foci (P = 8.4 × 10^-4 ), association of a high-grade component (P = 1.1 × 10^-4 ), and the presence of KRAS mutations (P = 4.5 × 10^-5 ).

CONCLUSIONS

The present study identified RSPO fusion transcripts, including three novel transcripts, in one-third of colorectal TSAs and showed that PTPRK-RSPO3 fusions were the predominant cause of RSPO overexpression in colorectal TSA.

GNAS mutations are present in colorectal traditional serrated adenomas, serrated tubulovillous adenomas and serrated adenocarcinomas with adverse prognostic features

AIMS

Activating mutations in GNAS are important in the development of a range of neoplasms, including a small proportion of conventional adenomas and colorectal carcinomas (CRCs). However, their contribution to serrated pathway neoplasia is unclear, as mutations have only been examined in small series of sessile serrated adenomas (SSAs) and traditional serrated adenomas (TSAs), and not in serrated tubulovillous adenomas (sTVAs). The aim of this study was to investigate the frequency and significance of GNAS mutations in colorectal adenomas and CRCs.

METHODS AND RESULTS

Using a large, well-characterized series, we identified GNAS mutations in 9.2% (18 of 196) of TSAs, 7.1% (four of 56) of sTVAs and 2.0% (nine of 459) of CRCs. Mutations were absent in SSAs (none of 43), tubular adenomas (none of 50) and conventional tubulovillous adenomas (none of 50). A BRAF or KRAS mutation was seen in 77.4% of GNAS mutant lesions, suggesting a synergistic effect with the mitogen-activated protein kinase pathway. In CRCs, GNAS mutations were associated with mucinous differentiation and serrated morphological features.

CONCLUSIONS

GNAS mutations contribute significantly to the development of a subset of serrated adenomas and CRCs.

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.

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.

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.

Traditional serrated adenoma (TSA): morphological questions, queries and quandaries

AIM

Traditional serrated adenoma (TSA) is an uncommon type of serrated adenoma that can be a precursor to biologically aggressive colorectal cancer that invokes the serrated (accelerated) pathway. The purpose of this review is to address some of the more contentious issues around nomenclature, diagnostic criteria, histological variants, coexistence with other polyp types, the occurrence of dysplasia and the differential diagnosis.

RESULTS

While the vast majority of TSAs are exophytic villiform polyps composed of deeply eosinophilic cells, flat top luminal serrations and numerous ectopic crypt foci, histological variants include flat TSA, filiform TSA and one composed of large numbers of mucin-containing cells. It is unlikely that there is any biological difference between the histological variants. There is a contention that TSAs are not dysplastic ab initio 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. TSA with dysplasia must be separated from TSA with coexisting conventional adenoma.

CONCLUSIONS

TSA is a characteristic polyp that may be extremely exophytic, flat or composed of mucin-rich cells and is typified by numerous ectopic crypt foci. They may coexist with other serrated polyps and conventional adenomas. Approximately 20-25% will be accompanied by adenomatous dysplasia.