Distinct CpG island methylation profiles and BRAF mutation status in serrated and adenomatous colorectal polyps

A population-based analysis on the incidence of metachronous colon cancer after endoscopic resection of advanced adenomas with high-grade dysplasia: does location matter?

BACKGROUND

Advanced adenomas (AAs) with high-grade dysplasia (HGD) represent a risk factor for metachronous neoplasia, with guidelines recommending short-interval surveillance. Although the worse prognosis of proximal (vs distal) colon cancers (CCs) is established, there is paucity of evidence on the impact of laterality on the risk of subsequent neoplasia for these AAs.

METHODS

Adults with HGD adenomas undergoing polypectomy were identified in the Surveillance, Epidemiology, and End Results database (2000-2019). Cumulative incidence of malignancy was estimated using the Kaplan-Meier method. Fine-Gray models assessed the effect of patient and disease characteristics on CC incidence.

RESULTS

Of 3199 patients, 26% had proximal AAs. A total of 65 cases of metachronous adenocarcinoma were identified after polypectomy of 35 proximal and 30 distal adenomas with HGD. The 10-year cumulative incidence of CC was 2.3%; when stratified by location, it was 4.8% for proximal vs 1.4% for distal adenomas. Proximal location was significantly associated with increased incidence of metachronous cancer (adjusted hazard ratio, 3.32; 95% CI, 2.05-5.38).

CONCLUSION

Proximal location of AAs with HGD was associated with >3-fold increased incidence of metachronous CC and shorter time to diagnosis. These data suggest laterality should be considered in the treatment and follow-up of these patients.

Prevalence, risk factors, and BRAF mutation of colorectal sessile serrated lesions among Vietnamese patients

BACKGROUND

Sessile serrated lesions (SSLs) are considered precancerous colorectal lesions that should be detected and removed to prevent colorectal cancer. Previous studies in Vietnam mainly investigated the adenoma pathway, with limited data on the serrated pathway.

AIM

To evaluate the prevalence, risk factors, and BRAF mutations of SSLs in the Vietnamese population.

METHODS

This is a cross-sectional study conducted on patients with lower gastrointestinal symptoms who underwent colonoscopy at a tertiary hospital in Vietnam. SSLs were diagnosed on histopathology according to the 2019 World Health Organization classification. BRAF mutation analysis was performed using the Sanger DNA sequencing method. The multivariate logistic regression model was used to determine SSL-associated factors.

RESULTS

There were 2489 patients, with a mean age of 52.1 ± 13.1 and a female-to-male ratio of 1:1.1. The prevalence of SSLs was 4.2% [95% confidence interval (CI): 3.5-5.1]. In the multivariate analysis, factors significantly associated with SSLs were age ≥ 40 [odds ratio (OR): 3.303; 95%CI: 1.607-6.790], male sex (OR: 2.032; 95%CI: 1.204-3.429), diabetes mellitus (OR: 2.721; 95%CI: 1.551-4.772), and hypertension (OR: 1.650, 95%CI: 1.045-2.605). The rate of BRAF mutations in SSLs was 35.5%.

CONCLUSION

The prevalence of SSLs was 4.2%. BRAF mutations were present in one-third of SSLs. Significant risk factors for SSLs included age ≥ 40, male sex, diabetes mellitus, and hypertension.

DNA methylation modulates epigenetic regulation in colorectal cancer diagnosis, prognosis and precision medicine

Colorectal cancer (CRC) is a multifaceted disease influenced by the interplay of genetic and environmental factors. The clinical heterogeneity of CRC cannot be attributed exclusively to genetic diversity and environmental exposures, and epigenetic markers, especially DNA methylation, play a critical role as key molecular markers of cancer. This review compiles a comprehensive body of evidence underscoring the significant involvement of DNA methylation modifications in the pathogenesis of CRC. Moreover, this review explores the potential utility of DNA methylation in cancer diagnosis, prognostics, assessment of disease activity, and prediction of drug responses. Recognizing the impact of DNA methylation will enhance the ability to identify distinct CRC subtypes, paving the way for personalized treatment strategies and advancing precision medicine in the management of CRC.

Smoking and risk of colorectal cancer according to KRAS and BRAF mutation status in a Japanese prospective Study

Although smoking is a major modifiable risk factor for many types of cancer, evidence for colorectal cancer is equivocal in Asian populations. Recent Western studies have proposed that the association between smoking and colorectal cancer is restricted to specific tumor molecular subtypes. However, no studies have evaluated the association according to tumor molecular subtypes in Asian populations. In a Japanese prospective population-based cohort study of 18 773 participants, we collected tumor tissues from incident colorectal cancer cases and evaluated KRAS (Kirsten rat sarcoma viral oncogene homolog) and BRAF (v-raf murine sarcoma viral oncogene homolog B) mutation status using target sequencing. Multivariable-adjusted Cox proportional hazard model was used to estimate the hazard ratios (HRs) and 95% confidence intervals (CIs) for associations of smoking with the risk of overall colorectal cancer and its subtypes defined by KRAS and BRAF mutation status. Among 339 cases, KRAS and BRAF mutations were identified in 164 (48.4%) and 16 (4.7%) cases, respectively. The multivariable-adjusted HR for ever smoking compared with never smoking was 1.24 [95% CI: 0.93-1.66], 1.75 [1.14-2.68], 0.87 [0.59-1.29], 1.24 [0.93-1.67] and 1.22 [0.38-3.93] for overall, KRAS wild-type, KRAS-mutated, BRAF wild-type and BRAF-mutated colorectal cancer, respectively. The statistically significant heterogeneity was indicated between KRAS mutation status (Pheterogeneity = 0.01) but not between BRAF mutation status. This study is the first to demonstrate that smokers have an approximately 2-fold higher risk of KRAS wild-type colorectal cancer than never smokers in an Asian population. Our findings support that smoking is a risk factor for colorectal cancer, especially for its subtype without KRAS mutations, in Asian populations.

Endoscopic polypectomy for malignant polyps: Should tumor location (right versus left side) guide clinical decisions?

BACKGROUND

Current guidelines consider endoscopic resection appropriate treatment for malignant colon polyps with negative margins, low-grade histology, and no lymphovascular invasion. While increasing literature demonstrates a worse prognosis for advanced stage right- versus left-sided colon cancers after curative treatment, there is paucity of data regarding prognostic effect of location in patients undergoing endoscopic resection of T1 polyps. We hypothesized the more aggressive biologic behavior observed in advanced right-sided cancers would be similarly represented in malignant polyps, and this location would be associated with lower overall survival.

METHODS

The National Cancer Database was queried for adults with T1NxMx tumors who underwent endoscopic polypectomy (2004-2017). Patients with positive margins or without follow-up information were excluded.

RESULTS

A total of 2,337 patients met inclusion criteria; 22% had right-sided polyps. Endoscopically excised proximal tumors were more common in elderly, and those with public insurance and more comorbidities (all P < .01). Among patients with complete pathologic data, there were no statistical differences between right- and left-sided polyps with 1 cm median size, >92% without lymphovascular invasion, and 100% without tumor deposits. Univariate analysis showed 73% vs 86% 5-year overall survival for right versus left polyps (P < .01). After adjustment for available confounders, right-sided location remained significantly associated with worse overall survival (hazard ratio 1.49, 95% confidence interval 1.21-1.83).

CONCLUSION

In this national cohort of patients with endoscopically excised malignant polyps, we identified right colon location as an independent prognostic factor associated with increased risk of mortality. Our data suggest polyp location should be taken into consideration when making clinical decisions regarding treatment and/or surveillance.

Sessile serrated lesions: Clinicopathological characteristics, endoscopic diagnosis, and management

The 2019 World Health Organization (WHO) Classification of Tumours of the Digestive System (5th edition) introduced the term "sessile serrated lesion" (SSL) to replace the term "sessile serrated adenoma/polyp" (SSA/P). SSLs are early precursor lesions in the serrated neoplasia pathway that result in colorectal carcinomas with BRAF mutations, methylation for DNA repair genes, a CpG island methylator phenotype, and high levels of microsatellite instability. Some of these lesions can rapidly become dysplastic or invasive carcinomas that exhibit high lymphatic invasion and lymph node metastasis potential. The 2019 WHO classification noted that dysplasia arising in an SSL most likely is an advanced polyp, regardless of the morphologic grade of the dysplasia. Detecting SSLs with or without dysplasia is critical; however, detection of SSLs is challenging, and their identification by endoscopists and pathologists is inconsistent. Furthermore, indications for their endoscopic treatment have not been established. Moreover, SSLs are considered to contribute to the development of post-colonoscopy colorectal cancers. Herein, the clinicopathological and endoscopic characteristics of SSLs, including features determined using white light and image-enhanced endoscopy, therapeutic indications, therapeutic methods, and surveillance are reviewed based on the literature. This information may lead to more intensive research to improve detection, diagnosis, and rates of complete resection of these lesions and reduce post-colonoscopy colorectal cancer rates.

Sessile serrated lesions in patients with adenoma on index colonoscopy do not increase metachronous advanced adenoma risk

OBJECTIVES

Post-polypectomy surveillance intervals should be determined based on index colonoscopy findings. However, the risk of metachronous lesions, resulting from the coexistence of adenoma and sessile serrated lesions (SSLs), has rarely been addressed. We evaluated the impact of synchronous SSL on the risk of metachronous lesions within similar adenoma risk groups.

METHODS

We retrieved individuals with one or more adenomas on index colonoscopy in a single-center retrospective cohort and stratified them into four groups depending on the presence of SSL and low-risk/high-risk adenoma (LRA/HRA). Participants who underwent surveillance colonoscopies at least 12 months apart were included. We compared the risks of metachronous lesions including HRA, advanced adenoma (AA), or SSL within similar adenoma risk groups according to the presence of SSL.

RESULTS

Overall 4493 individuals were included in the analysis. The risk of metachronous HRA/AA was not significantly higher in the adenoma with SSL group compared with the adenoma without SSL group, irrespective of LRA (HRA, 6/86 vs. 231/3297, P = 1.00; AA, 0/86 vs. 52/3297, P = 0.64) or HRA (HRA, 11/64 vs. 240/1046, P = 0.36; AA, 3/64 vs. 51/1046, P = 1.00). However, the risk of metachronous SSL in individuals with synchronous SSL was higher than that in those without SSL for both LRA (15/86 vs. 161/3297, P < 0.001) and HRA groups (11/64 vs. 61/1046, P = 0.002).

CONCLUSION

The presence of synchronous SSL did not increase the risk of metachronous HRA/AA, compared with isolated adenoma, but increased the risk of metachronous SSL.

Risk stratification for colorectal cancer in individuals with subtypes of serrated polyps

OBJECTIVE

The longitudinal risk of colorectal cancer (CRC) associated with subtypes of serrated polyps (SPs) remains incompletely understood.

DESIGN

This community-based, case-control study included 317 178 Kaiser Permanente Northern California members who underwent their first colonoscopy during 2006-2016. Nested within this population, we identified 695 cases of CRC and 3475 CRC-free controls (matched 5:1 to cases for age, sex and year of colonoscopy). Two expert pathologists reviewed the tissue slides of all SPs identified on the first colonoscopy and reclassified them to sessile serrated lesions (SSLs), hyperplastic polyps (HPs) and traditional serrated adenomas. SPs with borderline characteristics of SSLs but insufficient to make a definitive diagnosis were categorised as unspecified SPs. The association with development of CRC was assessed using multivariable logistic regression.

RESULTS

Compared with individuals with no polyp, the adjusted ORs (aORs) for SSL alone or with synchronous adenoma were 2.9 (95% CI: 1.8 to 4.8) and 4.4 (95% CI: 2.7 to 7.2), respectively. The aORs for SSL with dysplasia, large proximal SSL,and small proximal SSL were 10.3 (95% CI: 2.1 to 50.3), 12.8 (95% CI: 3.5 to 46.9) and 1.9 (95% CI: 0.8 to 4.7), respectively. Proximal unspecified SP also conferred an increased risk (aOR: 5.8, 95% CI: 2.2 to 15.2). Women with SSL were associated with higher risk (aOR: 4.4; 95% CI: 2.3 to 8.2) than men (aOR: 1.7; 95% CI: 0.8 to 3.8).

CONCLUSION

Increased risk of CRC was observed in individuals with SSLs, particularly large proximal ones or with dysplasia, supporting close endoscopic surveillance. Proximal unspecified SPs were also associated with increased risk of CRC and should be managed as SSLs.

Association Between Smoking and Molecular Subtypes of Colorectal Cancer

Background

Smoking is associated with colorectal cancer (CRC) risk. Previous studies suggested this association may be restricted to certain molecular subtypes of CRC, but large-scale comprehensive analysis is lacking.

Methods

A total of 9789 CRC cases and 11 231 controls of European ancestry from 11 observational studies were included. We harmonized smoking variables across studies and derived sex study-specific quartiles of pack-years of smoking for analysis. Four somatic colorectal tumor markers were assessed individually and in combination, including BRAF mutation, KRAS mutation, CpG island methylator phenotype (CIMP), and microsatellite instability (MSI) status. A multinomial logistic regression analysis was used to assess the association between smoking and risk of CRC subtypes by molecular characteristics, adjusting for age, sex, and study. All statistical tests were 2-sided and adjusted for Bonferroni correction.

Results

Heavier smoking was associated with higher risk of CRC overall and stratified by individual markers (P trend < .001). The associations differed statistically significantly between all molecular subtypes, which was the most statistically significant for CIMP and BRAF. Compared with never-smokers, smokers in the fourth quartile of pack-years had a 90% higher risk of CIMP-positive CRC (odds ratio = 1.90, 95% confidence interval = 1.60 to 2.26) but only 35% higher risk for CIMP-negative CRC (odds ratio = 1.35, 95% confidence interval = 1.22 to 1.49; P difference = 2.1 x 10-6). The association was also stronger in tumors that were CIMP positive, MSI high, or KRAS wild type when combined (P difference < .001).

Conclusion

Smoking was associated with differential risk of CRC subtypes defined by molecular characteristics. Heavier smokers had particularly higher risk of CRC subtypes that were CIMP positive and MSI high in combination, suggesting that smoking may be involved in the development of colorectal tumors via the serrated pathway.

Genetic testing for inherited colorectal cancer and polyposis, 2021 revision: a technical standard of the American College of Medical Genetics and Genomics (ACMG)

Colorectal cancer (CRC) is the fourth most frequently diagnosed cancer and 30% of all cases of CRC are believed to have a familial component and up to one-third of these (10%) are hereditary. Pathogenic germline variants in multiple genes have been associated with predisposition to hereditary CRC or polyposis. Lynch syndrome (LS) is the most common hereditary CRC syndrome, caused by variants in the mismatch repair (MMR) genes MLH1, MSH2, MSH6, and PMS2 and is inherited in a dominant manner. Heritable conditions associated with colonic polyposis include familial adenomatous polyposis (FAP) associated with APC pathogenic variants, MUTYH-associated polyposis (MAP) caused by biallelic MUTYH pathogenic variants, and polymerase proofreading-associated polyposis (PPAP) caused by POLE or POLD1 pathogenic variants. Given the overlapping phenotypes of the cancer syndromes along with the limited sensitivity of using clinical criteria alone, a multigene panel testing approach to diagnose these conditions using next-generation sequencing (NGS) is effective and efficient. This technical standard is not recommended for use in the clinic for patient evaluation. Please refer to National Comprehensive Cancer Network (NCCN) clinical practice guidelines to determine an appropriate testing strategy and guide medical screening and management. This 2021 edition of the American College of Medical Genetics and Genomics (ACMG) technical standard supersedes the 2013 edition on this topic.

Molecular Features of the Serrated Pathway to Colorectal Cancer: Current Knowledge and Future Directions

Serrated lesions are the precursor lesions of a new model of colorectal carcinogenesis. From a molecular standpoint, the serrated pathway is thought to be responsible for up to 30% of all colorectal cancer cases. The three major processes of this molecular mechanism are alterations in the mitogen-activated protein kinase pathway, production of the CpG island methylation phenotype, and generation of microsatellite instability. Other contributing processes are activation of WNT, alterations in the regulation of tumor suppressor genes, and alterations in microRNAs or in MUC5AC hypomethylation. Although alterations in the serrated pathway also contribute, their precise roles remain obscure because of the various methodologies and definitions used by different research groups. This knowledge gap affects clinical assessment of precursor lesions for their carcinogenic risk. The present review describes the current literature reporting the molecular mechanisms underlying each type of serrated lesion and each phenotype of serrated pathway colorectal cancer, identifying those areas that merit additional research. We also propose a unified serrated carcinogenesis pathway combining molecular alterations and types of serrated lesions, which ends in different serrated pathway colorectal cancer phenotypes depending on the route followed. Finally, we describe some key issues that need to be addressed in order to incorporate the newest technologies in serrated pathway research and to improve overall knowledge for developing specific prevention strategies and new therapeutic targets.

Effects of Somatic Methylation in Colonic Polyps on Risk of Developing Metachronous Advanced Colorectal Lesions

The utility of molecular markers for predicting the risk of metachronous advanced colorectal lesions (MACLs) remains poorly investigated. We examined the relationship between somatic hypermethylation in polyps at baseline and the risk of developing MACL. This retrospective cohort study included 281 consecutive patients with colonic polyps who were enrolled between 2007 and 2009 and followed-up until 2014. MACLs were defined as adenomas of ≥10 mm, high-grade dysplasia, or with a villous component; and serrated lesions of ≥10 mm or with dysplasia. In total, 595 polyps were removed at baseline colonoscopy and analyzed for pathological characteristics and CpG island methylator phenotype (CIMP) using the MS-MLPA (Methylation-Specific -- Multiplex Ligation-dependent Probe Amplification) technique. Forty-five patients (16.0%) showed at least one CIMP+ polyp. MACL risk was higher in patients with CIMP+ polyps (odds ratio (OR), 4.50; 95% CI, 1.78-11.4; p = 0.002). Patients with CIMP+ polyps also exhibited shorter time to MACL development (33.8 months vs. 50.1 months; p < 0.001), even with adjustment for polyp size and number (OR, 2.40; 95% CI, 1.33-4.34). Adding CIMP analysis improved the sensitivity (57.0% to 70.9%), negative predictive value (71.1% to 77.3%), and overall accuracy (49.8% to 52.0%) for MACL risk estimation. These results highlight that CIMP may be a useful marker for endoscopic surveillance.

DNMT3B Expression Might Contribute to Abnormal Methylation of RASSF1A in Lager Colorectal Adenomatous Polyps

Background

It is pretty well known that DNA methyltransferases (DNMTs) are actively involved in abnormal cell growth. The goal of the current study is to explore the correlation between DNMT expression and colorectal adenomatous polyps (CAPs).

Method

Twenty pairs of CAP samples with a diameter ≥ 10 mm and corresponding normal colorectal mucosa (NCM) tissues from patients were used in the present study. The expression levels and activity of DNA methyltransferases (DNMTs) were measured in the CAP tissues. The global methylation and the promoter methylation level of 3 kinds of tumour suppressor gene were detected.

Results

mRNA and protein levels of DNMT3B were found to be elevated in the CAP tissues compared with the control tissue. Additionally, the methylation of long interspersed nuclear elements-1 (LINE-1/L1) was decreased in the CAP tissue. Furthermore, methylation of the promoter of a tumour suppressor gene Ras association domain family 1A (RASSF1A) was increased in the CAP tissues, while the mRNA levels of RASSF1A were decreased.

Conclusions

These results suggest that the overexpression of DNMT3B may contribute to a role in the genesis of CAPs through the hypomethylation of chromosomes in the whole cell and promoter hypermethylation of RASSF1A.

An update on colorectal cancer microenvironment, epigenetic and immunotherapy

Colorectal cancer (CRC) is considered as the second most common cancer worldwide. For the past few years, the role of immunotherapy has been extensively studied and it has been demonstrated that its related approaches, such as programmed death-1 (PD-1) inhibitors, are promising. In addition to identifying molecular characteristics of tumor cells, recent studies are mainly focused on the profiling of tumor microenvironment. Dissecting immune status of a tumor is interesting, since development of a tumor is associated with deficiencies relate to immune defense, immune surveillance and immune hemostasis. In this review, we discuss main obstacles of immunotherapy including immunosuppressive niche and low immunogenicity of CRC as well as reviewing current achievements in immunotherapy.

Usefulness of the Japan narrow-band imaging expert team classification system for the diagnosis of sessile serrated lesion with dysplasia/carcinoma

BACKGROUND

Sessile serrated lesion (SSL) is a colorectal polyp that has malignant potential. However, the dysplastic components within an SSL can be difficult to diagnose with conventional endoscopy, because most SSLs with dysplasia/carcinoma have subtle mucosal features. Many studies have indicated that narrow-band imaging (NBI) observations of colorectal polyps are very useful, accurate predictors of histology. We aimed to verify the usefulness of the Japan NBI Expert Team (JNET) classification system for the diagnosis of SSLs with dysplasia/carcinoma.

METHODS

We examined 709 endoscopically or surgically resected lesions that were pathologically diagnosed as SSL, including 647 with no dysplasia, 37 with low-grade dysplasia, 15 with high-grade dysplasia, and 10 with submucosal invasive carcinoma. We retrospectively evaluated their clinicopathologic characteristics and conventional endoscopic and magnifying NBI endoscopic findings using the JNET system.

RESULTS

Cases in all groups were more frequently located in the proximal colon. Submucosal invasive carcinomas were significantly larger than no dysplasia and low-grade dysplasia lesions. Almost all studied lesions (96.3%) were covered with a mucus cap. Five hundred and eighty (81.8%) lesions exhibited dark spots inside the crypts, which are NBI findings' characteristic of SSL. As for the JNET classification of magnifying NBI endoscopic findings, all 709 lesions showed Type 1. Six hundred and eighteen (95.5%) SSLs with no dysplasia lesions exhibited Type 1 only, whereas 52 (83.9%) SSLs with dysplasia/carcinoma had a combination of Type 1 and Type 2A, 2B, or 3, corresponding to SSL and dysplasia/carcinoma, respectively. The JNET classification had high sensitivity (83.9%), specificity (95.5%), and overall diagnostic accuracy (94.5%) for diagnosing SSLs with dysplasia/carcinoma.

CONCLUSIONS

Use of magnifying NBI endoscopy with the JNET classification might be useful for diagnosing SSLs with dysplasia/carcinoma. This increased awareness may also improve the recognition of SSLs with dysplasia/carcinoma.

Increased Risk of Colorectal Cancer in Individuals With a History of Serrated Polyps

BACKGROUND AND AIMS

Serrated polyp (SPs) are precursors to 20% to 30% of cases of colorectal tumors, but patients' long-term risk after removal of SPs is poorly understood. We investigated the risk of colorectal cancer (CRC) in individuals with a history of SPs.

METHODS

We performed a retrospective cohort study of Kaiser Permanente Northern California members who underwent colonoscopy from 2006 through 2016. Study participants were categorized based on the size and location of SPs. We used Cox proportional hazards modeling to estimate the hazard ratio (HR) and 95% confidence interval (CI) for the association of CRC diagnosed more than 1 year after colonoscopy, with polyp type vs no polyp after adjustment for year of colonoscopy, age, sex, race/ethnicity, and smoking history.

RESULTS

The study included 233,393 individuals, of whom 445 developed incident CRC. At 10 years, the cumulative incidence rates of CRC for individuals with no polyp, proximal small SPs, proximal large SPs, and distal SPs were 4.7 (95% CI, 4.0-5.6), 14.8 (95% CI, 9.0-24.3), 30.2 (95% CI, 13.2-68.4), and 5.9 (95% CI, 3.6-9.5) per 1000 persons, respectively. In patients with SPs, risk of CRC was not increased until 3 years or more after the first colonoscopy (HR for small proximal SPs 2.6; 95% CI, 1.7-3.9 and HR for large proximal SPs 8.0; 95% CI, 3.6-16.1). The presence of synchronous adenomas increased the risk for CRC (HR for proximal SPs with synchronous adenomas 4.0; 95% CI, 3.0-5.5 and HR for distal SPs with synchronous adenomas 2.4; 95% CI, 1.7-3.4).

CONCLUSIONS

In a retrospective analysis of a large cohort of individuals examined by colonoscopy, we found that risk of incident CRC increased in individuals with proximal SPs (large SPs in particular) 3 years or more after the colonoscopy. These findings support guidelines that recommend surveillance colonoscopy for individuals with SPs.

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.

Associations between molecular characteristics of colorectal serrated polyps and subsequent advanced colorectal neoplasia

PURPOSE

BRAF mutation and DNA hypermethylation have linked sessile serrated adenomas/polyps (SSA/Ps) to serrated colorectal cancer (CRC) in cross-sectional studies, but they have not been evaluated in a longitudinal study. We aimed to evaluate the associations between molecular markers of serrated polyps and subsequent advanced colorectal neoplasia.

METHODS

Study subjects included Kaiser Permanente Washington members aged 20-75 years who received an index colonoscopy between 1/1/1998 and 12/31/2007 and had hyperplastic polyps (HPs) or SSA/Ps according to study pathology review. Polyps from index colonoscopies were removed and assayed for BRAF mutation, CpG island methylator phenotype (CIMP), and MLH1 methylation. Pathology reports and biopsies from the subsequent lower gastrointestinal endoscopy through 1/1/2013 were reviewed for advanced colorectal neoplasia. We identified additional incident CRC cases through linkage to the Seattle-Puget Sound Surveillance Epidemiology and End Results registry. We used generalized estimating equations to calculate adjusted odds ratios (OR) and 95% confidence intervals (CI) for subsequent advanced colorectal neoplasia, comparing index serrated polyps with different molecular markers.

RESULTS

We included 553 individuals with index serrated polyps (420 HPs and 133 SSA/Ps) and 795 subsequent endoscopies. The prevalence of BRAF-mutant, CIMP-high, and MLH1-methylated serrated polyps were 51%, 4%, and 2%, respectively. BRAF and CIMP were not associated with subsequent advanced colorectal neoplasia. MLH1-methylated SSP/As were significantly more likely to have subsequent advanced neoplasia (OR = 4.66, 95% CI 1.06-20.51).

CONCLUSION

Our results suggest that BRAF-mutant and CIMP-high serrated polyps are not associated with subsequent advanced colorectal neoplasia. Among SSA/Ps, MLH1 methylation may be an important marker to identify high-risk CRC precursors.

Receptor tyrosine kinase fusions act as a significant alternative driver of the serrated pathway in colorectal cancer development

Serrated polyps are a clinically and molecularly heterogeneous group of lesions that can contribute to the development of colorectal cancers (CRCs). However, the molecular mechanism underlying the development of serrated lesions is still not well understood. Here, we combined multiple approaches to analyze the genetic alterations in 86 colorectal adenomas (including 35 sessile serrated lesions, 15 traditional adenomas, and 36 conventional adenomatous polyps). We also investigated the in vitro and in vivo oncogenic properties of a novel variant of the NCOA4-RET fusion gene. Molecular profiling revealed that sessile serrated lesions and traditional serrated adenomas have distinct clinicopathological and molecular features. Moreover, we identified receptor tyrosine kinase translocations exclusively in sessile serrated lesions (17%), and the observation was validated in a separate cohort of 34 sessile serrated lesions (15%). The kinase fusions as well as the BRAF and KRAS mutations were mutually exclusive to each other. Ectopic expression of a novel variant of the NCOA4-RET fusion gene promoted cell proliferation in vitro and in vivo, and the proliferation was significantly suppressed by RET kinase inhibitors. All of these underscored the importance of mitogen-activated protein kinase (MAPK) pathway activation in the serrated pathway of colorectal tumorigenesis. In addition, we demonstrated that the kinase fusion may occur early in the precursor lesion and subsequent loss of TP53 may drives the transformation to carcinoma during serrated tumorigenesis. In conclusion, we identified kinase fusions as a significant alternative driver of the serrated pathway in colorectal cancer development, and detecting their presence may serve as a biomarker for the diagnosis of sessile serrated lesions. © 2020 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Colorectal Cancer Modeling with Organoids: Discriminating between Oncogenic RAS and BRAF Variants

RAS and BRAF proteins are frequently mutated in colorectal cancer (CRC) and have been associated with therapy resistance in metastatic CRC patients. RAS isoforms are considered to act as redundant entities in physiological and pathological settings. However, there is compelling evidence that mutant variants of RAS and BRAF have different oncogenic potentials and therapeutic outcomes. In this review we describe similarities and differences between various RAS and BRAF oncogenes in CRC development, histology, and therapy resistance. In addition, we discuss the potential of patient-derived tumor organoids for personalized therapy, as well as CRC modeling using genome editing in preclinical model systems to study similarities and discrepancies between the effects of oncogenic MAPK pathway mutations on tumor growth and drug response.

Clinicopathological features, diagnosis, and treatment of sessile serrated adenoma/polyp with dysplasia/carcinoma

Sessile serrated adenoma/polyps (SSA/Ps) are early precursor lesions in the serrated neoplasia pathway, which results in BRAF-mutated colorectal carcinomas with not only high levels of microsatellite instability but also microsatellite stable. SSA/Ps with advanced histology, including cytological dysplasia or minimally invasive carcinomas, are important lesions because SSA/Ps are considered major contributors to "interval cancers" and these lesions can rapidly become dysplastic or invasive carcinomas. Clinicopathologically, SSA/Ps with dysplasia or invasive carcinoma were associated with advanced age, female sex, and proximal colon. Although SSA/Ps with submucosal invasive carcinoma were smaller and invaded less deeply into the submucosal layer than conventional tubular adenomas with submucosal invasive carcinoma, SSA/Ps with submucosal invasive carcinoma frequently had a mucinous component and exhibited a higher potential for lymphatic invasion and lymph node metastasis. In an SSA/P series, endoscopic characteristics, including (semi)pedunculated morphology, double elevation, central depression, and reddishness, may help accurately diagnose SSA/Ps with advanced histology. Removal of SSA/Ps with dysplasia or invasive carcinoma was recommended. Endoscopic treatment such as endoscopic mucosal resection or endoscopic submucosal dissection is useful for those lesions. However, surgical resection with lymph node dissection might be indicated when SSA/Ps with invasive carcinoma are endoscopically suspected, because these have the high risk of lymph node metastasis. Greater awareness may promote further research into improving the detection, recognition, and complete resection rates of SSA/Ps with dysplasia or invasive carcinoma and reduce the interval cancer rates.

Signet ring cell colorectal cancer: genomic insights into a rare subpopulation of colorectal adenocarcinoma

Background

Signet ring cell carcinoma (SRCC) is a rare subtype of colorectal cancer (CRC). The aim of this study was to characterise the genomic alterations and outcomes of SRCC.

Methods

Medical records of metastatic CRC (mCRC) patients whose tumours were evaluated by NGS analysis were reviewed. SC-mCRC were classified into two groups: SRCC (>50% signet ring cells) and adenocarcinoma (AC) with SC component (≤50% signet ring cells).

Results

Six hundred and sixty-five mCRC patients were included. Of the 93 mCRC cases with SC features, 63 had slides for review. Of those 63 cases, 35 were confirmed SRCC, and 28 were AC with SC component. Compared with AC group, KRAS and PIK3CA mutations (mts) were found in only 11% (OR: 0.13) and 3% (OR: 0.15) of SRCC cases, respectively. In contrast to the 44% rate of APC mts in AC group, only 3% of SRCC patients had APC mts (OR = 0.04).

Conclusions

SRCC has distinct molecular features, including low rates of KRAS, PIK3CA and APC mts. Further study to identify activation pathways and potential therapeutic targets are needed.

High Frequency of KRAS Codon 146 and FBXW7 Mutations in Thai Patients with Stage II-III Colon Cancer

Background: KRAS, NRAS, and BRAF gene mutations are the most clinically relevant and frequently reported in colorectal cancer (CRC). Although data on these genes are frequently reported in several counties, data specific to these genes among Thai population are scarce. The aim of this study was to investigate and identify molecular alterations associated with colon cancer in Thai population, and to determine the impact of these genetic aberrations on clinical outcome. Methods: DNA from 108 archived formalin-fixed, paraffin-embedded (FFPE) tissue samples that histologically confirmed adenocarcinoma of stage II-III colon cancer between 2010 and 2012 at Siriraj Hospital (Bangkok, Thailand) were extracted. Gene mutational analysis was performed by next-generation sequencing (NGS) using an Oncomine Solid Tumor DNA kit (Thermo Fisher Scientific, Inc., Waltham, MA, USA). Results: A total of 22 somatic gene mutations were detected. The mutation frequency observed in KRAS, NRAS, BRAF, PIK3CA, and FBXW7 mutations was 47.2%, 1.9%, 1.9%, 12%, and 14.8%, respectively. KRAS mutation codon 12, 13, 59, 61, 117, and 146 mutations were identified in 29.6%, 8.3%, 1.8%, 0.9%, 0.0%, and 8.3%, respectively. KRAS Exon 4 had better DFS compared with Exon 2 and 3. Conclusions: This study is the first to comprehensively report hotspot mutations using NGS in Thai colon cancer patients. The most commonly identified gene mutation frequencies among Thai patients (KRAS, NRAS, BRAF, TP53, and PIK3CA) were similar to the gene mutation frequencies reported in Western population, except for subgroup of KRAS codon 146 and FBXW7 mutations that had a slightly higher frequency.

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 association between colorectal sessile serrated adenomas/polyps and subsequent advanced colorectal neoplasia

PURPOSE

Colorectal cancer (CRC) screening guidelines recommend increased surveillance of individuals with sessile serrated adenomas/polyps (SSA/Ps), but there is uncertainty about the risk associated with SSA/Ps. We aimed to determine the association between SSA/Ps and subsequent advanced colorectal neoplasia.

METHODS

This case-control study included Kaiser Permanente Washington (KPWA) members who received an index colonoscopy between 1/1/1998 and 12/31/2007, and had hyperplastic polyps (HPs) or SSA/Ps but no conventional adenomas according to study pathologist histologic review. Subsequent pathology reports and biopsies through 1/1/2013 were reviewed for advanced colorectal neoplasia. We linked to the Seattle-Puget Sound Surveillance Epidemiology and End Results (SEER) registry to identify additional CRC cases. We used generalized estimating equations with a logit link to estimate adjusted odds ratios (ORs) and 95% confidence intervals (CIs) for advanced colorectal neoplasia, comparing those with SSA/Ps to those with HPs.

RESULTS

There were 161 individuals with index SSA/Ps, 548 with HPs, and 918 subsequent endoscopies included in analyses. Of those with index SSA/Ps, 19 had subsequent advanced colorectal neoplasia; 39 with HPs had subsequent advanced colorectal neoplasia. Compared to those with HPs, those with SSA/Ps were not statistically significantly more likely to have subsequent advanced colorectal neoplasia (adjusted OR 1.79; CI 0.98-3.28). Polyp size ≥ 10 mm, right colon location, and the presence of multiple serrated polyps were also not associated with advanced colorectal neoplasia.

CONCLUSIONS

Our results suggest that there is not a strong association between SSA/Ps and subsequent advanced colorectal neoplasia during the 5 years following SSA/P removal.

DNA methylation changes that precede onset of dysplasia in advanced sessile serrated adenomas

Background

Sessile serrated adenomas (SSAs) are common polyps which give rise to 20–30% of colorectal cancer (CRC). SSAs display clinicopathologic features which present challenges in surveillance, including overrepresentation in young patients, proclivity for the proximal colon and rarity of histologic dysplasia (referred to then as SSAs with dysplasia, SSADs). Once dysplasia develops, there is rapid progression to CRC, even at a small size. There is therefore a clinical need to separate the “advanced” SSAs at high risk of progression to SSAD and cancer from ordinary SSAs. Since SSAs are known to accumulate methylation over time prior to the development of dysplasia, SSAD backgrounds (the remnant SSA present within an SSAD) likely harbour additional methylation events compared with ordinary SSAs. We therefore performed MethyLight and comprehensive methylation array (Illumina MethylationEPIC) on 40 SSAD backgrounds and 40 matched ordinary SSAs, and compared the methylation results with CRC methylation, CRC expression and immunohistochemical data.

Results

SSAD backgrounds demonstrated significant hypermethylation of CpG islands compared with ordinary SSAs, and the proportion of hypermethylated probes decreased progressively in the shore, shelf and open sea regions. Hypomethylation occurred in concert with hypermethylation, which showed a reverse pattern, increasing progressively away from the island regions. These methylation changes were also identified in BRAF-mutant hypermethylated CRCs. When compared with CRC expression data, SV2B, MLH1/EPM2AIP1, C16orf62, RCOR3, BAIAP3, OGDHL, HDHD3 and ATP1B2 demonstrated both promoter hypermethylation and decreased expression. Although SSAD backgrounds were histologically indistinguishable from ordinary SSAs, MLH1 methylation was detectable via MethyLight in 62.9% of SSAD backgrounds, and focal immunohistochemical MLH1 loss was seen in 52.5% of SSAD backgrounds.

Conclusions

Significant hyper- and hypomethylation events occur during SSA progression well before the development of histologically identifiable changes. Methylation is a heterogeneous process within individual SSAs, as typified by MLH1, where both MLH1 methylation and focal immunohistochemical MLH1 loss can be seen in the absence of dysplasia. This heterogeneity is likely a generalised phenomenon and should be taken into account in future methylation-based studies and the development of clinical methylation panels.

Electronic supplementary material

The online version of this article (10.1186/s13148-019-0691-4) contains supplementary material, which is available to authorized users.

Molecular characterization of "sessile serrated" adenoma to carcinoma transition in six early colorectal cancers

Colorectal cancer (CRC) is a heterogeneous group of diseases both from the morphological and molecular point of view. The sessile serrated adenoma/polyp (SSA/P) has been proposed as the precursor lesion of CRCs characterized by CpG island methylator phenotype (CIMP), DNA mismatch repair (MMR) system deficiency, and BRAF gene mutations. However, no study so far investigated the molecular landscape of "sessile serrated" adenoma to carcinoma transition in early CRCs. Six formalin-fixed paraffin-embedded CRCs developed within SSA/P were profiled for the immunohistochemical expression of MMR proteins (MLH1, MSH2, MSH6, PMS2, and Ep-CAM), p16, and β-catenin. DNA was extracted from the two components of each sample, after microdissection, and characterized for CIMP status and by applying a custom hotspot multigene mutational profiling of 164 hotspot regions of eleven CRC-associated genes (AKT1, APC, BRAF, CTNNB1, KIT, KRAS, NRAS, PDGFRA, PIK3CA, PTEN, and TP53). Five out of the six CRCs shared the same molecular profile (i.e. CIMP positive, MSI status, and BRAF mutation) with their SSA/P components. One out of five CRCs was also APC mutated, whereas another one showed an additional TP53 mutation. The remaining case was CIMP negative and MMR proficient in both the components, harbored a BRAF mutation in the SSA/P counterpart, whereas the CRC one was APC and TP53 mutated and showed p16 and β-catenin dysregulation. This study provides the molecular evidence that SSA/P, even without cytological dysplasia, is a precursor lesion of CRC and that conventional CRC might arise from mixed polyp.

Efficacy of CapeOX plus Cetuximab Treatment as a First-Line Therapy for Patients with Extended RAS/BRAF/PIK3CA Wild-Type Advanced or Metastatic Colorectal Cancer

Background: Oxaliplatin and capecitabine (CapeOX) combined with cetuximab is rarely used to treat advanced and metastatic colorectal cancer (mCRC). The present study aimed to clarify the clinical benefits of this treatment regimen when used as a first-line therapy in patients with expanded RAS/BRAF/PIK3CA wild-type mCRC, using the data and tumor specimens from two previously published Phase II clinical trials.

Methods: The gene mutation status and clinical data of 102 patients with KRAS wild-type mCRC, who received either of CapeOX + cetuximab or FOLFOX + cetuximab, were analyzed. The primary endpoint was response rate (RR) of CapeOX + cetuximab treatment in patients with extended RAS/BRAF/PIK3CA wild-type mCRC. RR comparisons and maximum tumor size changes between different treatment regimens and gene mutation status were set as key secondary endpoints.

Results: We identified 88 patients with extended RAS/BRAF/PIK3CA wild-type mCRC. Those treated with CapeOX + cetuximab (n = 52) had a 61.5% RR (95% CI, 47.0-74.7%), while those treated with FOLFOX + cetuximab (n = 36) had a 66.7% RR (95% CI, 49.0-81.4%). Patients with any mutation (n = 14) had a 42.9% RR (95% CI, 17.1-71.1%). There were no significant differences between these three groups (P = 0.298). The disease control rate was 86.5% (95% CI, 74.2-94.4%) in the CapeOX + cetuximab group, and 88.9% (95% CI, 73.9-96.9%) in the FOLFOX + cetuximab group. Maximum tumor size changes were largest in patients with wild-type mCRC treated with FOLFOX + cetuximab followed by patients with wild-type mCRC treated with CapeOX + cetuximab, and then by those with any mutation (-63.2%, -52.6%, and -27.3%, respectively; P = 0.035).

Conclusions: Patients with RAS/BRAF/PIK3CA wild-type mCRC had a sufficient RR following first-line treatment with CapeOX + cetuximab. These results suggest that this combination therapy should be considered as a treatment option for patients with advanced mCRC.

The proto CpG island methylator phenotype of sessile serrated adenomas/polyps

Sessile serrated adenomas/polyps (SSA/Ps) are the putative precursors of the ~20% of colon cancers with the CpG island methylator phenotype (CIMP). To investigate the epigenetic phenotype of these precancers, we prospectively collected fresh-tissue samples of 17 SSA/Ps and 15 conventional adenomas (cADNs), each with a matched sample of normal mucosa. Their DNA was subjected to bisulfite next-generation sequencing to assess methylation levels at ~2.7 million CpGs located predominantly in gene regulatory regions and spanning 80.5Mb; RNA was sequenced to define the samples' transcriptomes. Compared with normal mucosa, SSA/Ps and cADNs exhibited markedly remodeled methylomes. In cADNs, hypomethylated regions were far more numerous (18,417 vs 4288 in SSA/Ps) and rarely affected CpG islands/shores. SSA/Ps seemed to have escaped this wave of demethylation. Cytosine hypermethylation in SSA/Ps was more pervasive (hypermethylated regions: 22,147 vs 15,965 in cADNs; hypermethylated genes: 4938 vs 3443 in cADNs) and more extensive (region for region), and it occurred mainly within CpG islands and shores. Given its resemblance to the CIMP typical of SSA/Ps' putative descendant colon cancers, we refer to the SSA/P methylation phenotype as proto-CIMP. Verification studies of six hypermethylated regions in an independent series of precancers demonstrated DNA methylation markers' high potential for predicting the diagnosis of SSA/Ps and cADNs. Surprisingly, proto-CIMP in SSA/Ps was associated with upregulated gene expression; downregulation was more common in cADNs. In conclusion, the epigenetic landscape of SSA/Ps differs markedly from that of cADNs. These differences are a potentially rich source of novel tissue-based and noninvasive biomarkers.

Molecular characterization of sessile serrated adenoma/polyps with dysplasia/carcinoma based on immunohistochemistry, next-generation sequencing, and microsatellite instability testing: a case series study

Background

Colorectal sessile serrated adenoma/polyps (SSA/Ps) are considered early precursor lesions in the serrated neoplasia pathway. Recent studies have shown associations of SSA/Ps with lost MLH1 expression, a CpG island methylator phenotype, and BRAF mutations. However, the molecular biological features of SSA/Ps with early neoplastic progression have not yet been fully elucidated, owing to the rarity of cases of SSA/P with advanced histology such as cytologic dysplasia or invasive carcinoma. In this study, we aimed to elucidate the molecular biological features of SSA/Ps with dysplasia/carcinoma, representing relatively early stages of the serrated neoplasia pathway.

Methods

We performed immunostaining for β-catenin, MLH1, and mucins (e.g., MUC2, MUC5AC, MUC6, and CD10); targeted next-generation sequencing; and microsatellite instability (MSI) testing in 8 SSA/P lesions comprised of 4 SSA/Ps with high-grade dysplasia and 4 SSA/Ps with submucosal carcinoma.

Results

Lost MLH1 expression was found in 5 cases. All lesions studied were positive for nuclear β-catenin expression. Regarding phenotypic mucin expression, all lesions were positive for MUC2, but negative for CD10. MUC5AC and MUC6 positivity was observed in 7 cases. Genetically, the most frequently mutated gene was BRAF (7 cases), and other mutations were detected in FBXW7 (3 cases); TP53 (2 cases), and KIT, PTEN, SMAD4, and SMARCB1 (1 case each). Furthermore, 4 of 8 lesions were MSI-high and the remaining 4 lesions were microsatellite-stable (MSS). Interestingly, all 4 MSI-high lesions displayed MLH1 loss, 3 of which harbored a FBXW7 mutation, but not a TP53 mutation. However, 2 MSS lesions harbored a TP53 mutation, although none harbored a FBXW7 mutation.

Conclusions

SSA/Ps with dysplasia/carcinoma frequently harbored BRAF mutations. Activation of the WNT/β-catenin signaling pathway may facilitate the development of dysplasia in SSA/Ps and progression to carcinoma. Furthermore, our results suggested that these lesions might be associated with both MSI-high and MSS colorectal cancer, which might be distinguished by distinct molecular biological features such as lost MLH1 expression, FBXW7 mutations, and TP53 mutations.

Endoscopic diagnosis of sessile serrated adenoma/polyp with and without dysplasia/carcinoma

Sessile serrated adenoma/polyps (SSA/Ps) are early precursor lesions in the serrated neoplasia pathway, which results in colorectal carcinomas with BRAF mutations, methylation for DNA repair genes, a CpG island methylator phenotype, and high levels of microsatellite instability. Some of these lesions can rapidly become dysplastic or invasive carcinomas that exhibit high lymphatic invasion and lymph node metastasis potentials. Detecting serrated lesions, including SSA/Ps with and without dysplasia/carcinoma, is critical, but SSA/Ps can be difficult to detect, are inconsistently identified by endoscopists and pathologists, and are often incompletely resected. Therefore, SSA/Ps are considered to be major contributors to “interval cancers”. If colonoscopists can identify the specific endoscopic characteristics of SSA/Ps, their detection and the effectiveness of colonoscopy may improve. Here, the endoscopic features of SSA/Ps with and without dysplasia/carcinoma, including the characteristics determined using magnifying endoscopy, are reviewed in the context of previous reports. Endoscopically, these subtle polyps are like hyperplastic polyps, because they are slightly elevated and pale. Unlike hyperplastic polyps, SSA/Ps are usually larger than 5 mm, frequently covered by a thin layer called the ‘‘mucus cap’’, and are more commonly located in the proximal colon. Magnifying narrow-band imaging findings, which include dark spots inside the crypts and varicose microvascular vessels, in addition to the type II-open pit patterns detected using magnifying chromoendoscopy, effectively differentiate SSA/Ps from hyperplastic polyps. The lesions’ endoscopic characteristics, which include their (semi)pedunculated morphologies, double elevations, central depressions, and reddishness, and the use of magnifying endoscopy, might help to detect dysplasia/carcinoma within SSA/Ps. Greater awareness may promote further research into improving the detection, identification, and complete resection rates of SSA/Ps with and without dysplasia/carcinoma and reduce the interval cancer rates.

Serrated Polyps of Colon and Rectum: a Clinicopathologic Review

BACKGROUND

In the past decade, there have been significant changes in the classification and nomenclature of colorectal polyps. Previously, only two groups of lesions were widely recognized, the adenoma and the hyperplastic polyp. Adenomas were considered the only precursor of colorectal cancer, and hyperplastic polyps were considered innocent with no malignant potential. However, recent discoveries about molecular pathways of colorectal cancers have significantly changed our understanding of these neoplasms. Serrated polyps-previously uniformly called hyperplastic polyps-are now known to comprise a heterogeneous family of neoplasms united by their characteristic saw tooth morphology but differing in many important ways, including their malignant potential and molecular profile. This group of neoplasms includes both hyperplastic polyps and the more recently recognized serrated adenomas. Serrated adenomas can be subdivided into the traditional serrated adenoma and the sessile serrated adenoma/polyp. Both of these lesions show characteristic molecular changes, which differ from traditional colorectal adenomatous polyps.

OBJECTIVES

In this review, we will discuss the morphologic features of serrated colorectal lesions, the molecular alterations that characterize them, and their role in colorectal cancer development.

MATERIAL AND METHODS

The English literature regarding the new nomenclature will be reviewed and the key diagnostic points will be recorded.

RESULTS AND DISCUSSION

This large group of polyps has recently been better classified which needs specific attention by pathologists, gastroenterologists and even surgeons.

The role of epigenetic therapies in colorectal cancer

Although developments in the diagnosis and therapy of colorectal cancer (CRC) have been made in the last decade, much work remains to be done as it remains the second leading cause of cancer death. It is now well established that epigenetic events, together with genetic alterations, are key events in initiation and progression of CRC. Epigenetics refers to heritable alterations in gene expression that do not involve changes in the DNA sequence. These alterations include DNA methylation, histone alterations, chromatin remodelers, and noncoding RNAs. In CRC, aberrations in epigenome may also involve in the development of drug resistance to conventional drugs such as 5-fluorouracil, oxaliplatin, and irinotecan. Thus, it has been suggested that combined therapies with epigenetic agents may reverse drug resistance. In this regard, DNA methyltransferase inhibitors and histone deacetylase inhibitors have been extensively investigated in CRC. The aim of this review is to provide a brief overview of the preclinical data that represent a proof of principle for the employment of epigenetic agents in CRC with a focus on the advantages of combinatorial therapy over single-drug treatment. We will also critically discuss the results and limitations of initial clinical experiences of epigenetic-based therapy in CRC and summarize ongoing clinical trials. Nevertheless, since recent translational research suggest that epigenetic modulators play a key role in augmenting immunogenicity of the tumor microenvironment and in restoring immune recognition, we will also highlight the recent developments of combinations strategies of immunotherapies and epigenetic therapies in CRC, summarizing preclinical, and clinical data to signify this evolving and promising field for CRC treatment.

Diagnosis and predictors of sessile serrated adenoma after educational training in a large, community-based, integrated healthcare setting

BACKGROUND AND AIMS

Sessile serrated adenomas (SSAs) are precursors of 15% to 30% of colorectal cancers but are frequently underdiagnosed. We sought to measure the SSA detection rate (SDR) and predictors of SSA detection after educational training for community gastroenterologists and pathologists.

METHODS

Colonoscopy and pathology data (2010-2014) from 3 medical centers at Kaiser Permanente Northern California were accessed electronically. Gastroenterologists and pathologists attended a training session on SSA diagnosis in 2012. Mean SDRs and patient-level predictors of SSA detection post-training (2013-2014) were investigated.

RESULTS

Mean SDRs increased from .6% in 2010-2012 to 3.7% in 2013-2014. The increase in the detection of proximal SSAs was accompanied by a decrease in the detection of proximal hyperplastic polyps (HPs). Among 34,161 colonoscopies performed in 2013 to 2014, SDRs for screening, fecal immunochemical test positivity, surveillance, and diagnostic indication were 4.2%, 4.5%, 4.9%, and 3.0%, respectively. SSA detection was lower among Asians (adjusted odds ratio [aOR], .46; 95% confidence interval [CI], .31-.69) and Hispanics (aOR, .59; 95% CI, .36-.95) compared with non-Hispanic whites and higher among patients with synchronous conventional adenoma (aOR, 1.46; 95% CI, 1.15-1.86), HP (aOR, 1.74; 95% CI, 1.30-2.34), and current smokers (aOR, 1.78; 95% CI, 1.17-2.72). SDRs varied widely among experienced gastroenterologists, even after training (1.1%-8.1%). There was a moderately strong correlation between adenoma detection rate (ADR) and SDR for any SSA (r = .64, P = .0003) and for right-sided SSAs (r = .71, P < .0001).

CONCLUSIONS

Educational training significantly increased the detection of SSA, but a wide variation in SDR remained across gastroenterologists. SSA detection was inversely associated with Asian and Hispanic race/ethnicity and positively associated with the presence of conventional adenoma, HP, and current smoking. There was a moderately strong correlation between ADR and SDR.

Distinct histopathological characteristics in colorectal submucosal invasive carcinoma arising in sessile serrated adenoma/polyp and conventional tubular adenoma

The histopathological characteristics of colorectal submucosal invasive carcinoma arising in sessile serrated adenoma/polyp (SSA/P), a rare malignant tumour, have not yet been fully elucidated. To investigate the features of such, we retrospectively analysed 40 submucosal invasive carcinomas with SSA/P (CA-SSA/P) and compared them to 129 cases of submucosal invasive carcinoma with conventional tubular adenoma (CA-AD). We additionally performed hMLH1 immunostaining. CA-SSA/Ps were significantly smaller than CA-ADs (P < 0.001). Histologically, well to moderately differentiated adenocarcinoma was predominant in both CA-SSA/Ps and CA-ADs. No significant differences in depth of invasion were found between the two groups. However, lymphatic invasion was more often found in CA-SSA/Ps (30%) than in CA-ADs (13%; P = 0.028), as was lymph node metastasis (CA-SSA/Ps, 28%; CA-ADs, 7%; P = 0.011). Furthermore, mucinous component and serrated architecture were significantly more frequent in CA-SSA/Ps (30 and 63%) than in CA-ADs (5 and 18%; P < 0.001, respectively). Tumour-infiltrating lymphocytes and Crohn-like inflammatory reaction were also more frequently found in CA-SSA/Ps (70 and 30%) than in CA-ADs (31 and 9%; P ≤ 0.001, respectively), whereas the opposite was true of desmoplastic reaction (CA-SSA/Ps, 35%; CA-ADs, 67%; P < 0.001). Loss of hMLH1 expression was more frequent in CA-SSA/P cases (93%) than in CA-AD cases (5%; P < 0.001). In conclusion, CA-SSA/P lesions exhibit a higher potential for lymphatic invasion and lymph node metastasis and have distinct histopathological features, including mucinous component, serrated architecture, tumour-infiltrating lymphocytes, Crohn-like inflammatory reaction, and absence of desmoplastic reaction, compared to their conventional counterparts.

Prognostic Value of BRAF and KRAS Mutations in MSI and MSS Stage III Colon Cancer

Background

The prognostic value of BRAF and KRAS mutations within microsatellite-unstable (MSI) and microsatellite-stable (MSS) subgroups of resected colon carcinoma patients remains controversial. We examined this question in prospectively collected biospecimens from stage III colon cancer with separate analysis of MSI and MSS tumors from patients receiving adjuvant FOLFOX +/- cetuximab in two adjuvant therapy trials.

Methods

Three groups were defined: BRAF Mutant, KRAS Mutant, and double wild-type. The analytic strategy involved estimation of study-specific effects, assessment of homogeneity of results, and then analysis of pooled data as no differences in patient outcome were found between treatment arms in both trials. Associations of mutations with patient outcome were analyzed, and multivariable models were adjusted for treatment and relevant factors.

Results

Four thousand four hundred eleven tumors were evaluable for BRAF and KRAS mutations and mismatch repair status; 3934 were MSS and 477 were MSI. In MSS patients, all BRAF V600E mutations (hazard ratio [HR] = 1.54, 95% confidence interval [CI] = 1.23 to 1.92, P < .001), KRAS codon 12 alterations, and p.G13D mutations (HR = 1.60, 95% CI = 1.40 to 1.83, P < .001) were associated with shorter time to recurrence (TTR) and shorter survival after relapse (SAR; HR = 3.02 , 95% CI = 2.32 to 3.93, P < .001, and HR = 1.20, 95% CI = 1.01 to 1.44, P = .04, respectively). Overall survival (OS) in MSS patients was poorer for BRAF-mutant patients (HR = 2.01, 95% CI = 1.56 to 2.57, P < .001) and KRAS-mutant patients (HR = 1.62, 95% CI = 1.38 to 1.91, P < .001) vs wild-type. No prognostic role of KRAS or BRAF mutations was seen in MSI patients. Furthermore, no interaction was found between treatment arm (with or without cetuximab) and KRAS and BRAF mutations for TTR or OS in MSS patients.

Conclusions

In a pooled analysis of resected stage III colon cancer patients receiving adjuvant FOLFOX, BRAF or KRAS mutations are independently associated with shorter TTR, SAR, and OS in patients with MSS, but not MSI, tumors. Future clinical trials in the adjuvant setting should consider these mutations as important stratification factors.

Comprehensive DNA Methylation and Mutation Analyses Reveal a Methylation Signature in Colorectal Sessile Serrated Adenomas

Colorectal sessile serrated adenomas (SSA) are hypothesized to be precursor lesions of an alternative, serrated pathway of colorectal cancer, abundant in genes with aberrant promoter DNA hypermethylation. In our present pilot study, we explored DNA methylation profiles and examined selected gene mutations in SSA. Biopsy samples from patients undergoing screening colonoscopy were obtained during endoscopic examination. After DNA isolation and quality analysis, SSAs (n = 4) and healthy controls (n = 5) were chosen for further analysis. DNA methylation status of 96 candidate genes was screened by q(RT)PCR using Methyl-Profiler PCR array system. Amplicons for 12 gene mutations were sequenced by GS Junior Instrument using ligated and barcoded adaptors. Analysis of DNA methylation revealed 9 hypermethylated genes in both normal and SSA samples. 12 genes (CALCA, DKK2, GALR2, OPCML, PCDH10, SFRP1, SFRP2, SLIT3, SST, TAC1, VIM, WIF1) were hypermethylated in all SSAs and 2 additional genes (BNC1 and PDLIM4) were hypermethylated in 3 out of 4 SSAs, but in none of the normal samples. 2 SSAs exhibited BRAF mutation and synchronous MLH1 hypermethylation and were microsatellite instable by immunohistochemical analysis. Our combined mutation and DNA methylation analysis revealed that there is a common DNA methylation signature present in pre-neoplastic SSAs. This study advocates for the use of DNA methylation as a potential biomarker for the detection of SSA; however, further investigation is needed to better characterize the molecular background of these newly recognized colorectal lesions.

Molecular Analysis of Single Tumor Glands Using the Crypt Isolation Method in Endometrial Carcinomas

OBJECTIVE

Endometrial adenocarcinomas are characterized by the presence of many single tumor glands in which multiple genetic changes have accumulated. To elucidate the differences in molecular abnormalities among single tumor glands, individual tumor glands were analyzed and microsatellite alterations (loss of heterozygosity (LOH) and microsatellite instability [MSI]) were examined using the crypt isolation method in glands from each tumor from patients with endometrial carcinoma.

METHODS

Twenty-five patients with endometrial adenocarcinoma who underwent surgery were included in this study. We obtained cancerous individual isolated tumor glands from each patient using the crypt isolation method. For LOH and MSI analyses, we used 15 microsatellite markers (3p, 5q, 10q, 13q, 17p, 18q, BAT25, and BAT26) and the promoter regions of 6 genes (transforming growth factor beta receptor II, BAX, insulin-like growth factor II receptor, E2F4, MutS homolog 3, and MSH6).

RESULTS

Loss of heterozygosity was detected in 8 (32%) of 25 patients, and MSI was detected in 9 (36%) of 25 patients. Some MSI-positive carcinomas had LOH in single tumor gland samples, and the coexistence of LOH and MSI was confirmed. In 16 (64%) of 25 cases, intratumoral genetic heterogeneity among single tumor gland samples was detected.

CONCLUSIONS

By analyzing multiple single tumor glands within the same tumor, we found that endometrial adenocarcinoma was composed of various tumor glands with different molecular abnormalities, even in a limited region within the same tumor.

Genetic instability, CpG island methylator phenotype, and proliferative activity are distinct differences between diminutive and small tubular adenoma of the colorectum

It is recommended that small (6-10 mm) lesions be treated with endoscopic resection (ER), whereas diminutive (≤5 mm) lesions are not currently an indication for ER according to the Japanese guidelines. The aim of this study was to evaluate the molecular alterations, and therefore treatment indications, in diminutive versus small tubular adenoma (TA). We prospectively analyzed genetic instability, including microsatellite instability and loss of heterozygosity, methylation status, KRAS/BRAF mutations, and Ki-67 staining in 96 TAs without a villous component. Although no microsatellite instability was identified in either diminutive or small TAs, genetic instability was seen in small TAs (9.1%) but not diminutive TAs (P = .04). In addition, the low-level CpG island methylator phenotype (CIMP-L) was more frequently observed in small TAs (31.8%) than in diminutive TAs (P = .01). Thus, genetic instability and CIMP-L were associated with small TAs, and only CIMP-L was an independent predictive marker for small TAs (odds ratio, 3.29; P = .03). Intriguingly, the Ki-67 proliferative index tended to be higher in small TAs than in diminutive TAs (P = .06) and higher in TAs with CIMP-L than in those without CIMP (P = .08). KRAS mutations were seen in codon 12 in 5.2% of TAs, but no BRAF gene mutations were found. As the molecular events and proliferative activity for the progression may increase from diminutive to small TAs, small TAs should be treated with ER, whereas a "predict, resect, and discard" strategy may be acceptable in most diminutive lesions except flat and depressed-type lesions, in keeping with the current strategy in the West.

TP53 mutation at early stage of colorectal cancer progression from two types of laterally spreading tumors

Although most sporadic colorectal cancers (CRC) are thought to develop from protruded adenomas through the adenoma-carcinoma sequence, some CRC develop through flat lesions, so-called laterally spreading tumors (LST). We previously analyzed epigenetic aberrations in LST and found that LST are clearly classified into two molecular subtypes: intermediate-methylation with KRAS mutation and low-methylation with absence of oncogene mutation. Intermediate-methylation LST were mostly granular type LST (LST-G) and low-methylation LST were mostly non-granular LST (LST-NG). In the present study, we conducted a targeted exon sequencing study including 38 candidate CRC driver genes to gain insight into how these genes modulate the development of LST. We identified a mean of 11.5 suspected nonpolymorphic variants per sample, including indels and non-synonymous mutations, although there was no significant difference in the frequency of total mutations between LST-G and LST-NG. Genes associated with RTK/RAS signaling pathway were mutated more frequently in LST-G than LST-NG (P = 0.004), especially KRAS mutation occurring at 70% (30/43) of LST-G but 26% (13/50) of LST-NG (P < 0.0001). Both LST showed high frequency of APC mutation, even at adenoma stage, suggesting its involvement in the initiation stage of LST, as it is involved at early stage of colorectal carcinogenesis via adenoma-carcinoma sequence. TP53 mutation was never observed in adenomas, but was specifically detected in cancer samples. TP53 mutation occurred during development of intramucosal cancer in LST-NG, but during development of cancer with submucosal invasion in LST-G. It is suggested that TP53 mutation occurs in the early stages of cancer development from adenoma in both LST-G and LST-NG, but is involved at an earlier stage in LST-NG.

Serrated colorectal cancer: Molecular classification, prognosis, and response to chemotherapy

Molecular advances support the existence of an alternative pathway of colorectal carcinogenesis that is based on the hypermethylation of specific DNA regions that silences tumor suppressor genes. This alternative pathway has been called the serrated pathway due to the serrated appearance of tumors in histological analysis. New classifications for colorectal cancer (CRC) were proposed recently based on genetic profiles that show four types of molecular alterations: BRAF gene mutations, KRAS gene mutations, microsatellite instability, and hypermethylation of CpG islands. This review summarizes what is known about the serrated pathway of CRC, including CRC molecular and clinical features, prognosis, and response to chemotherapy.

Increased Risk of Colorectal Cancer Development Among Patients With Serrated Polyps

BACKGROUND & AIMS

Sessile serrated adenomas/polyps (SSA/Ps) and traditional serrated adenomas (TSAs) are now distinguished from hyperplastic polyps and recognized as precursors to colorectal cancer (CRC). We studied CRC risks associated with serrated polyps.

METHODS

By using Danish databases (1977-2009), we conducted a nationwide population-based, case-control study nested within individuals who had received colonoscopies (n = 272,342), and identified 2045 CRC cases and 8105 CRC-free individuals (controls). For each case and control, we identified the first colorectal polyp(s) that underwent a biopsy or were excised during or after the initial colonoscopy, and obtained tissue blocks for hyperplastic lesions. Four expert pathologists reviewed these lesions using current terminology for serrated polyps. We used logistic regression to compute odds ratios (ORs) to associate the risk of CRC with polyp type and estimated the absolute risks by multiplying the risk in patients with no polyps by these ORs.

RESULTS

Seventy-nine cases and 142 controls had SSA/Ps (OR, 3.07; 95% confidence interval [CI], 2.30-4.10). SSA/Ps with cytology markers of dysplasia were associated with a particularly high OR (4.76; 95% CI, 2.59-8.73). Women with SSA/P had a higher risk for CRC than men with SSA/P (OR for women, 5.05; 95% CI, 3.05-8.37 vs OR for men, 2.18; 95% CI, 1.24-3.82); patients with SSA/P proximal to the splenic flexure had the highest risk for CRC (OR, 12.42; 95% CI, 4.88-31.58). The OR for CRC was 4.84 in the 14 cases vs 17 controls with TSAs (95% CI, 2.36-9.93), 2.51 in the 757 cases vs 1698 controls with conventional adenomas (95% CI, 2.25-2.80), and 1.30 in the 55 cases vs 235 controls with hyperplastic polyps (95% CI, 0.96-1.77). The 10-year risk for CRC was 4.4% for patients with SSA/P with dysplasia, 4.5% for patients with TSAs, and 2.3% for patients with conventional adenomas.

CONCLUSION

Patients with SSA/P or TSA are at increased risk for CRC; their level of risk is similar to or higher than that of patients with conventional adenomas.

Reappraisal of hMLH1 promoter methylation and protein expression status in the serrated neoplasia pathway

AIMS

The aim of this study was to determine whether human mutL homologue 1 (hMLH1) inactivation precedes the progression of sessile serrated lesion (SSL) into SSL with cytological dysplasia (SSL/D) and to define the histological stage at which promoter methylation and inactivation of hMLH1 occur.

METHODS AND RESULTS

Using the MassARRAY EpiTYPER assay and immunohistochemistry, we examined methylation levels and the protein expression status of hMLH1 in 33 SSL/Ds with conventional epithelial dysplasia and compared the results with those of control hyperplastic polyps (HPs) and SSLs. The methylation level of hMLH1 was higher in the dysplastic component than in the non-dysplastic component of SSL/Ds (P = 0.005), and differed significantly with regard to the degree of dysplasia (P = 0.002). The methylation levels of hMLH1 in the dysplastic component of SSL/Ds tended to be higher than those of control SSLs and HPs (P = 0.063 and P = 0.017, respectively). The loss of hMLH1 protein expression was identified in only 13 of 33 (39.39%) dysplastic components of SSL/Ds.

CONCLUSION

Promoter methylation and loss of protein expression of hMLH1 are not parallel processes that occur concurrently. hMLH1 methylation is an early molecular event which occurs even in HP. However, the loss of hMLH1 expression is a much later step, found in approximately 40% of SSL/Ds at various histological stages. Notably, the loss of hMLH1 protein expression does not necessarily precede the development of cytological dysplasia in SSL.

Genetic and epigenetic aberrations occurring in colorectal tumors associated with serrated pathway

To clarify molecular alterations in serrated pathway of colorectal cancer (CRC), we performed epigenetic and genetic analyses in sessile serrated adenoma/polyps (SSA/P), traditional serrated adenomas (TSAs) and high-methylation CRC. The methylation levels of six Group-1 and 14 Group-2 markers, established in our previous studies, were analyzed quantitatively using pyrosequencing. Subsequently, we performed targeted exon sequencing analyses of 126 candidate driver genes and examined molecular alterations that are associated with cancer development. SSA/P showed high methylation levels of both Group-1 and Group-2 markers, frequent BRAF mutation and occurrence in proximal colon, which were features of high-methylation CRC. But TSA showed low-methylation levels of Group-1 markers, less frequent BRAF mutation and occurrence at distal colon. SSA/P, but not TSA, is thus considered to be precursor of high-methylation CRC. High-methylation CRC had even higher methylation levels of some genes, e.g., MLH1, than SSA/P, and significant frequency of somatic mutations in nonsynonymous mutations (p < 0.0001) and insertion/deletions (p = 0.002). MLH1-methylated SSA/P showed lower methylation level of MLH1 compared with high-methylation CRC, and rarely accompanied silencing of MLH1 expression. The mutation frequencies were not different between MLH1-methylated and MLH1-unmethylated SSA/P, suggesting that MLH1 methylation might be insufficient in SSA/P to acquire a hypermutation phenotype. Mutations of mismatch repair genes, e.g., MSH3 and MSH6, and genes in PI3K, WNT, TGF-β and BMP signaling (but not in TP53 signaling) were significantly involved in high-methylation CRC compared with adenoma, suggesting importance of abrogation of these genes in serrated pathway.

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.

Molecular and histologic considerations in the assessment of serrated polyps

CONTEXT : Colorectal cancer is a heterogeneous disease resulting from different molecular pathways of carcinogenesis. Recent data evaluating the histologic features and molecular basis of the serrated polyp-carcinoma pathway have significantly contributed to more comprehensive classifications of and treatment recommendations for these tumors.

OBJECTIVE

To integrate the most recent molecular findings in the context of histologic classifications of serrated lesions and their implications in diagnostic pathology and colorectal cancer surveillance.

DATA SOURCES

Published literature focused on serrated polyps and their association with colorectal cancer.

CONCLUSIONS

Three types of serrated polyps are currently recognized: hyperplastic polyps, sessile serrated adenomas/polyps, and traditional serrated adenomas. The BRAF V600E mutation is one of the most frequent molecular abnormalities identified in hyperplastic polyps and sessile serrated adenomas. In contrast, in traditional serrated adenomas, either BRAF V600E or KRAS mutations can be frequently identified. CpG methylation has emerged as a critical molecular mechanism in the sessile serrated pathway. CpG methylation of MLH1 often leads to reduced or lost expression in dysplastic foci and carcinomas arising in sessile serrated adenomas/polyps.

Serrated neoplasia-role in colorectal carcinogenesis and clinical implications

Colorectal cancer (CRC) is considered a heterogeneous disease, both regarding pathogenesis and clinical behaviour. Four decades ago, the adenoma-carcinoma pathway was presented as the main pathway towards CRC, a conclusion that was largely based on evidence from observational morphological studies. This concept was later substantiated at the genomic level. Over the past decade, evidence has been generated for alternative routes in which CRC might develop, in particular the serrated neoplasia pathway. Providing indisputable evidence for the neoplastic potential of serrated polyps has been difficult. Reasons include the absence of reliable longitudinal observations on individual serrated lesions that progress to cancer, a shortage of available animal models for serrated lesions and challenging culture conditions when generating organoids of serrated lesions for in vitro studies. However, a growing body of circumstantial evidence has been accumulated, which indicates that ≥15% of CRCs might arise through the serrated neoplasia pathway. An even larger amount of post-colonoscopy colorectal carcinomas (carcinomas occurring within the surveillance interval after a complete colonoscopy) have been suggested to originate from serrated polyps. The aim of this Review is to assess the current status of the serrated neoplasia pathway in CRC and highlight clinical implications.

Traditional serrated adenoma: an update

Although recognized 25 years ago, the traditional serrated adenoma (TSA) remains an ongoing source of diagnostic and biologic debate. Recent research has greatly improved our understanding of the morphological and molecular aspects of these polyps. In particular, the recognition of ectopic crypt foci (ECFs) in combination with typical cytology and slitlike serrations improves diagnostic reproducibility. Awareness that many TSAs, particularly BRAF-mutated TSAs, arise in precursor microvesicular hyperplastic polyps and sessile serrated adenomas can aid in making this diagnosis and should not be confused with a sessile serrated adenoma with dysplasia. At a molecular level, TSAs can be divided into 2 groups based on their BRAF or KRAS mutation status. The development of overt cytologic dysplasia is accompanied by TP53 mutation, Wnt pathway activation, and, in some cases, silencing of CDKN2A. Importantly, however, mismatch repair enzyme function is retained. Thus, the TSA is an important precursor of aggressive molecular subtypes of colorectal carcinoma.

Sporadic microsatellite instability-high colon cancers rarely display immunohistochemical evidence of Wnt signaling activation

Most sporadic colonic adenocarcinomas are microsatellite stable (MSS) and arise from conventional adenomas by dysregulation of the APC/β-catenin/Wnt signaling pathway. Sporadic adenocarcinomas with a high degree of microsatellite instability (MSI) likely arise from sessile serrated polyps through the serrated neoplastic pathway. These polyps contain BRAF mutations and are prone to epigenetic methylation that ultimately silences MLH1, leading to MSI and heralding progression of dysplasia to invasive adenocarcinoma. Most investigators believe that these 2 models of cancer progression are mutually exclusive, although recent studies describe Wnt signaling activation in serrated polyps and propose that it plays a role in the development of sporadic colonic adenocarcinomas with MSI. We sought to test this hypothesis by evaluating β-catenin immunoexpression in 44 sporadic microsatellite unstable adenocarcinomas and 44 MSS colon cancers. We defined sporadic MSI-high carcinomas as those with loss of MLH1 and PMS2 immunostaining and BRAF V600E mutations that occurred in patients 50 years of age or older without a family history of colonic adenocarcinoma or Lynch syndrome. Forty-one (93%) of these carcinomas displayed membranous β-catenin staining only, compared with 28 (64%) site-matched MSS tumors with abnormal nuclear β-catenin staining.