Morphologic reappraisal of serrated colorectal polyps

Paneth cell differentiation in colonic epithelial neoplasms: evidence for the role of the Apc/beta-catenin/Tcf pathway

Paneth cell differentiation may occur in colonic epithelial neoplasms. However, its significance and mechanism of development remains unclear. Human defensin 5 is a specific marker of Paneth cells and has been shown to represent one of the target genes of the Apc/beta-catenin/Tcf pathway. The aim of this study was to evaluate the frequency of Paneth cell differentiation in a variety of colonic neoplasms, and to investigate the role of human defensin 5 and beta-catenin in this process. The clinical and pathologic findings, including histologic evidence of Paneth cell differentiation and immunostaining for human defensin 5 and beta-catenin, were evaluated in 29 samples of nonneoplastic colonic mucosa, 18 hyperplastic polyps, 10 sessile serrated adenomas, 12 traditional serrated adenomas, 21 mixed polyps, 39 conventional adenomas, and 40 adenocarcinomas. Human defensin-5 and beta-catenin expression were evaluated for the location and degree of staining in all cell types (dysplastic and nondysplastic) and correlated with histologic areas of Paneth cell differentiation in all types of polyps. Histologic evidence of Paneth cell differentiation was observed in 15 conventional adenomas (38.5%) and 1 adenocarcinoma (2.5%) but not in other types of polyps. Human defensin-5 immunostaining was positive in the cytoplasm of all nonneoplastic Paneth cells and all neoplastic cells with Paneth cell differentiation. Human defensin-5 expression was noted in 0% of hyperplastic polyps, 10% of sessile serrated adenomas, 25% of traditional serrated adenomas, 33.3% of mixed polyps, 82.1% of conventional adenomas, and 17.5% of adenocarcinomas: human defensin 5 expression was significantly higher in conventional adenomas compared to all other groups (P < .01). Seventeen (53.1%) of 32 human defensin 5 positive conventional adenomas, 6 (86%) of 7 of human defensin 5 positive adenocarcinomas, and all human defensin 5-positive sessile serrated adenomas, traditional serrated adenomas, and mixed polyps did not show histologic evidence of Paneth cell differentiation. All mixed polyps (100%) that revealed human defensin 5 expression (7; 33.3%) revealed conventional dysplasia. In the positive mixed polyp cases, human defensin 5 was only positive in areas of conventional dysplasia. Of the 31 conventional adenomas with nuclear beta-catenin staining, 15 (48.4%) revealed histologic evidence of Paneth cell differentiation, and all of the neoplastic cells with Paneth cell differentiation showed nuclear beta-catenin staining, whereas nonneoplastic Paneth cells consistently showed a normal pattern of membranous beta-catenin staining. A strong topographical correlation was noted between human defensin 5 expression and nuclear beta-catenin expression in conventional adenomas and in conventional dysplastic epithelium of mixed polyps. Paneth cell differentiation is common in early colonic neoplasms that develop via the conventional adenoma-carcinoma carcinogenic pathway. Activation of Apc/beta-catenin/Tcf pathway may play a role in Paneth cell differentiation in human colonic neoplasms.

Pathologic features and biologic importance of colorectal serrated polyps

Serrated polyps of the large intestine comprise a heterogeneous group of mucosal lesions that includes nondysplastic polyps, such as hyperplastic polyps and sessile serrated polyps, and polyps that show overt cytologic dysplasia, namely serrated adenomas and mixed hyperplastic/adenomatous polyps. These polyps have received increased recognition over the past 2 decades, as emerging evidence suggests that a subset may be precursors to colorectal carcinomas that lack chromosomal instability. Several investigators have proposed the concept of the "serrated neoplastic pathway" according to which nondysplastic serrated lesions develop progressively severe dysplasia culminating in the development of microsatellite unstable carcinomas that show DNA hypermethylation and BRAF mutations. A subset of hyperplastic polyps and sessile serrated polyps show mutations in the BRAF gene and abnormal DNA methylation, which can, ultimately, affect the promoter regions of key DNA-repair and tumor suppressor genes, such as MLH1 and MGMT, leading to their decreased transcription and microsatellite instability. On the basis of this hypothesis, many authors have proposed that sessile serrated polyps should be treated and surveilled similar to conventional adenomas, although prospective data are lacking. This review describes the clinicopathologic and molecular features of serrated polyps and discusses the current data regarding their biologic significance.

Association of large serrated polyps with synchronous advanced colorectal neoplasia

OBJECTIVES

Serrated polyps of the colorectum are a histologically and genetically heterogeneous group of lesions, which include classic hyperplasic polyps, sessile serrated adenomas (SSAs), and traditional serrated adenomas. Accumulating evidence suggests that they may have different malignancy potentials. This study sought to determine the association between the presence of large serrated colorectal polyps and synchronous advanced colorectal neoplasia.

METHODS

Among 4,714 asymptomatic subjects who underwent screening colonoscopy, cases of advanced colorectal neoplasia (tubular adenoma > or =1 cm, adenoma with any villous histology, adenoma with carcinoma in situ / high-grade dysplasia, or invasive adenocarcinoma) were compared with controls without advanced neoplasia with respect to candidate predictors, including age, sex, family history of colorectal cancer, body mass index, the presence and number of small tubular adenomas (<1 cm), the presence of multiple small serrated polyps (<1 cm), and the presence of large serrated polyps (> or =1 cm). Independent predictors of advanced neoplasia were determined by multivariate logistic regression analysis.

RESULTS

Among 467 cases and 4,247 controls, independent predictors of advanced colorectal neoplasia were increasing age (odds ratio (OR)=4.51; 95% confidence interval (CI), 1.43-14.3; P=0.01 for subjects > or =80 years vs. 50-54 years of age); non-advanced tubular adenomas (OR=2.33; 95% CI 1.37-3.96, P=0.0017 for 3 or more); and large serrated polyps (OR=3.24; 95% CI 2.05-5.13, P<0.0001). In total, 109 subjects (2.3% of the study population) had large serrated polyps. Right- and left-sided large serrated polyps had a similar association with advanced colorectal neoplasia (OR=3.38 vs. 2.66, P=0.62).

CONCLUSIONS

Large serrated polyps are strongly and independently associated with synchronous advanced colorectal neoplasia. Our results suggest that large serrated polyps may be a marker for advanced colorectal neoplasia. Further studies are needed to determine whether the association with advanced neoplasia differs among subsets of serrated polyps, particularly SSAs and classic hyperplastic polyps.

RUNX3 inactivation in colorectal polyps arising through different pathways of colonic carcinogenesis

OBJECTIVES

We hypothesized that RUNX3 inactivation by promoter hypermethylation in colorectal polyps is an early molecular event in colorectal carcinogenesis.

METHODS

RUNX3 protein expression was analyzed immunohistochemically in 50 sporadic colorectal polyps comprising 19 hyperplastic polyps (HPs), 14 traditional serrated adenomas (TSAs), and 17 sporadic traditional adenomas (sTAs) as well as in 19 familial adenomatous polyposis (FAP) samples from 10 patients showing aberrant crypt foci (ACF) (n=91), small adenomas (SmAds) (n=40), and large adenomas (LAds) (n=13). In addition, we assessed the frequency of promoter hypermethylation of RUNX3 by methylation-specific PCR (MSP) in all the 50 sporadic polyps as well as 38 microdissected FAP polyps comprising ACF, SmAds, and LAds obtained from 7 FAP samples. A total of 12 normal colon samples were also included for RUNX3 MSP analysis.

RESULTS

Compared to normal colon (2 of 12, 16%) and sTAs (3 of 17, 18%), HPs (15 of 19, 79%) and TSAs (8 of 14, 57%) displayed significant inactivation of RUNX3 (P<0.05). In FAP, RUNX3 inactivation was more frequently seen in ACF (78 of 91, 86%), SmAds (25 of 40, 62%), and LAds (6 of 13, 46%) compared to normal mucosa (0 of 19, 0%) in the same samples (all P<0.05). Promoter hypermethylation of RUNX3 was significantly higher in colorectal polyps (64 of 87, 74%) compared to normal colon (2 of 12, 16%) (P=0.001). Serrated polyps such as HPs (17 of 19, 89%) and TSAs (12 of 14, 86%) were significantly more methylated than sTAs (7 of 17, 44%) (P=0.004). RUNX3 hypermethylation was observed in 28 of the total 38 (74%) FAP polyps. Overall, RUNX3 promoter methylation correlated with inactivation of RUNX3 expression in sporadic (27 of 36, 75%) (P=0.022) and FAP (21 of 28, 75%) (P=0.021) polyps.

CONCLUSIONS

Our data suggest that RUNX3 inactivation due to promoter hypermethylation in colorectal polyps represents an early event in colorectal cancer (CRC) progression. In addition, epigenetic RUNX3 inactivation is a frequent event in the serrated colonic polyps as well as in the ACF of FAP polyps.

Narrow-band imaging without high magnification to differentiate polyps during real-time colonoscopy: improvement with experience

BACKGROUND

There is no widely adopted, easily applied method for distinguishing between adenomatous and nonadenomatous polyps during real-time colonoscopy.

OBJECTIVE

To compare white light (WL) with narrow-band imaging (NBI) for the differentiation of colorectal polyps in vivo and to assess for a learning curve.

DESIGN

A prospective polyp series.

PATIENTS AND SETTING

A total of 302 patients referred for colonoscopy, between August 2006 and July 2007, to a single tertiary-referral center in the United States.

INTERVENTION

Standard WL colonoscopy was performed with Olympus 180-series colonoscopes. Each detected polyp was first characterized by WL and then by NBI. Modified Kudo pit pattern and vascular color intensity (VCI) were recorded, and the histology was predicted. Endoscopists were given feedback every 2 weeks.

MAIN OUTCOME MEASUREMENTS

Overall accuracy and sensitivity and specificity of endoscopic diagnosis by using WL alone and with NBI, as well as improvement in endoscopists' performance.

RESULTS

A total of 265 polyps were found in 131 patients. Diagnostic accuracy was 80% with NBI and 77% with WL (P = .35). NBI performed better than WL in diagnosing adenomas (sensitivity 80% vs 69%, P < .05). Nonadenomatous polyps were more likely to have a "light" VCI compared with adenomas (71% vs 29%, P < .001). During the second half of the study, NBI accuracy improved, from 74% to 87%, and outperformed an unchanged WL accuracy of 79% (P < .05).

CONCLUSIONS

Overall, NBI was not more accurate than WL in differentiating colorectal polyps in vivo; however, once a learning curve was achieved, NBI performed significantly better. Further refinements of an NBI pit-pattern classification and VCI scale are needed before broad application to clinical decisions regarding the necessity of polypectomy.

Significance of serrated polyps of the colon

The fundamental view that colon adenocarcinomas arise only from conventional adenomas has been challenged by the now recognized hyperplastic polyp-serrated adenoma-adenocarcinoma pathway. This article describes the history of the serrated adenoma (both the traditional serrated adenoma and the sessile serrated adenoma) as well as the histology and endoscopic appearance of these lesions in comparison with hyperplastic polyps and mixed polyps. Although the exact pathway is the subject of ongoing research, compelling histologic associations and molecular phenotypes that define the model of the serrated polyp-carcinoma sequence, including microsatellite instability, BRAF/KRAS mutations, and CpG island methylator phenotype, provide strong evidence that this is a genuine pathway. Management of serrated neoplasia of the colon includes careful colonoscopy, complete removal of colonic polyps, sampling fields of diminutive polyps of the rectosigmoid, and basing surveillance on histology of removed polyps.

Colorectal polyposes: from phenotype to diagnosis

The colorectal polyposes are uncommon and frequently present diagnostic difficulties. Although the final diagnostic arbiter is the demonstration of a germline mutation, this may not always be demonstrable, and some forms of colorectal polyposis have no known genetic basis. Therefore, an accurate description of the phenotype by the pathologist is central to the establishment of a working diagnosis. This can direct the search for the underlying genetic cause (if any) and is also essential for establishing the magnitude of risk of colorectal malignancy for the patient and the patient's relatives. The pathologist may be provided with only a small and selected sample of endoscopically resected polyps or with prodigious numbers of polyps (too many to sample) when receiving a surgical specimen. Each type of polyposis presents its own particular diagnostic problems that may relate to polyp numbers, gross recognition of small or flat polyps, incomplete development of the full phenotype at the stage of investigation, and the histological classification of unusual or mixed polyps. The aim of this review is to highlight the principles and pitfalls in achieving a comprehensive description of the various types of colorectal polyposis, including classical FAP, attenuated FAP, MUTYH- (formerly MYH-) associated polyposis (MAP), other presentations of multiple adenomas, Peutz-Jeghers syndrome (P-JS), juvenile polyposis syndrome (JPS), Cowden syndrome (CS), hereditary mixed polyposis syndrome (HMPS), and hyperplastic polyposis syndrome (HPS).

Selective expression of gastric mucin MUC6 in colonic sessile serrated adenoma but not in hyperplastic polyp aids in morphological diagnosis of serrated polyps

Colonic sessile serrated adenoma, in contrast to hyperplastic polyp, is thought to be related to sporadic colorectal cancers with high microsatellite instability. However, the morphological distinction between these entities is difficult and subject to observer and sampling variation. Therefore, we elected to investigate the expression of gastric mucin MUC6 as a potential marker to separate the two in the hope of finding an objective and reproducible adjunct to morphological diagnosis. Endoscopic biopsies of colonic polyps with serrated architecture, but without cytological dysplasia were studied and categorized as sessile serrated adenoma or hyperplastic polyp, using previously published morphological criteria. Smaller groups of serrated polyps with cytological dysplasia (traditional serrated adenomas, filiform serrated adenomas and sessile serrated adenomas with cytological dysplasia) were also included. In total, 94 polyps were immunohistochemically stained with antibodies to MUC6 and to MLH-1. MUC6 was found to have 100% specificity in distinguishing sessile serrated adenoma (N=26; positive staining) from hyperplastic polyp (N=48; negative staining). Traditional serrated adenomas and filiform serrated adenomas were also negative for MUC6. Sessile serrated adenomas with cytological dysplasia were found to lose expression of MLH-1 in dysplastic areas, while retaining MUC6 expression. Neither anatomic location in the right or left colon nor polyp size appears to account for the differences in MUC6 expression.

Genetic and epigenetic changes in aberrant crypt foci and serrated polyps

Aberrant crypt foci (ACF) in colorectal mucosa are the earliest known morphological precursors to colorectal cancer and can be subclassified as dysplastic, heteroplastic (non-dysplastic), and mixed types. Serrated adenoma (SA) is a polyp with serrated architecture and dysplasia, and can be subclassified as traditional SA or sessile SA. Sessile SA is thought to be preneoplastic and differs from most lesions in the traditional SA category because of their flat morphology and general lack of cytological dysplasia. Serrated polyps include hyperplastic polyps (HP), SA, and admixed hyperplastic-adenomatous polyps and are considered a morphological continuum encompassing heteroplastic ACF, HP, admixed hyperplastic-adenomatous polyps, and SA. Recent studies have uncovered other developmental pathways including a heteroplastic ACF-HP/SA-carcinoma sequence and a heteroplastic ACF-adenoma-carcinoma sequence. Heteroplastic ACF histopathologically resemble HP and SA. Sporadic HP are usually present in the left colon, are small, and are considered benign. However, adenocarcinoma arising in the setting of colorectal HP or SA, especially in patients with hyperplastic polyposis, has been described. The relationship between heteroplastic ACF, HP, and colorectal cancer is less certain than that of dysplastic ACF. Here, we discuss the current understanding of genetic and epigenetic alterations in the development of colorectal cancer. Our goal is to provide a conceptual framework for understanding the heteroplastic ACF-HP/SA-carcinoma sequence.

Carcinogenesis and microsatellite instability: the interrelationship between genetics and epigenetics

DNA mismatch repair (MMR) deficiency results in a strong mutator phenotype and high-frequency microsatellite instability (MSI-H), which are the hallmarks of tumors arising within Lynch syndrome. MSI-H is characterized by length alterations within simple repeated sequences, microsatellites. Lynch syndrome is primarily due to germline mutations in one of the DNA MMR genes; mainly hMLH1 or hMSH2 and less frequently hMSH6 and rarely hPMS2. Germline hemiallelic methylation of MLH1, termed epimutation, has been reported to be a new cause of Lynch syndrome. MSI-H is also observed in approximately 15% of colorectal, gastric and endometrial cancers and in lower frequencies in a minority of other tumors, where it is associated with the hypermethylation of the promoter region of hMLH1. MSI-H underlies a distinctive tumorigenic pathway because cancers with MSI-H exhibit many differences in genotype and phenotype relative to cancers without MSI-H, irrespective of their hereditary or sporadic origins. Genetic, epigenetic and transcriptomic differences exist between cancers with and those without the MSI-H. The BRAF V600E mutation is associated with sporadic MSI-H colorectal cancers (CRCs) harboring hMLH1 methylation but not Lynch syndrome-related CRCs. The differences in genotype and phenotype between cancers with and those without MSI-H are likely to be causally linked to their differences in biological and clinical features. Therefore, the diagnosis of MSI-H in cancers is thus considered to be of increasing relevance, because MSI-H is a useful screening marker for identifying patients with Lynch syndrome, a better prognostic factor and could affect the efficacy of chemotherapy. This review addresses recent advances in the field of microsatellite instability research.

Hyperplastic/serrated polyposis in inflammatory bowel disease: a case series of a previously undescribed entity

Herein, we describe the clinical, pathologic, immunohistochemical, and molecular features of 3 unique patients with long standing inflammatory bowel disease, all of whom developed numerous discrete hyperplastic/serrated colonic polyps similar to those described in the hyperplastic/serrated polyposis syndrome. The 3 patients (2 with ulcerative colitis and 1 with Crohn ileo-colitis) were evaluated for a variety of clinical, histologic (including the type, location and number of polyps in the colon), and immunohistochemical features [MLH-1, MSH-2, MGMT (O(6)-methylguanine-DNA methyltransferase), beta-catenin, and p53]. KRAS and BRAF mutation analysis was also performed on a subset of polyps from 2 patients. All patients had moderate-severe pancolitis of more than 10 years duration and had >20 colonic polyps. None had polyps in the upper gastrointestinal tract. Pathologically, a combination of conventional hyperplastic polyps and sessile serrated polyps (adenomas) were present in the 3 cases. In addition, serrated adenomas were present in 2 and conventional adenomas in 1. Two patients also had synchronous adenocarcinoma. All 3 cases showed retention of MLH-1 and MSH-2, and a membranous beta-catenin staining pattern. However, 2 cases showed loss of MGMT in several serrated polyps, and one also in adjacent colitic mucosa. KRAS mutations were detected in 5/11 serrated polyps. However, BRAF mutations were not present in any of the polyps tested. These findings suggest the possibility of a serrated pathway of carcinogenesis in inflammatory bowel disease characterized by silencing of MGMT, most likely by gene promoter methylation, KRAS mutations, and possibly other, as yet, uncharacterized molecular alterations, resulting eventually in progression to adenocarcinoma.

Sessile serrated adenoma (SSA) vs. traditional serrated adenoma (TSA)

The morphologic distinction between various serrated polyps of the colorectum may be challenging. The distinction between sessile serrated adenoma (SSA) and traditional serrated adenoma (TSA) may be difficult using currently available criteria mostly based on cytologic characteristics. We have evaluated 66 serrated polyps including 29 SSA, 18 TSA, and 19 hyperplastic polyps for overall shape of the polyps, architectural features of individual crypts, the presence of eosinophilic cytoplasm, size and distribution of the proliferation and maturation zones, as well as Ki-67 and CK20 expression. The extent of the expression of CK20 and Ki-67 could not distinguish between the 3 types of serrated polyps, but the distribution of their expression was very helpful and differences were statistically significant. The distribution of Ki-67+ cells was the single most helpful distinguishing feature of the serrated polyp type (P<0.0001, chi test). Hyperplastic polyps had regular, symmetric, and increased Ki-67 expression. SSA had irregular, asymmetric, and highly variable expression of Ki-67. TSA had low Ki-67 expression, which was limited to "ectopic crypts" and admixed tubular adenomalike areas. In serrated polyps, ectopic crypt formation (ECF) defined by the presence of ectopic crypts with their bases not seated adjacent to the muscularis mucosae was nearly exclusive to TSA and was found in all cases, while the presence of cytologic atypia and eosinophilia of the cytoplasm were characteristic, but not limited to TSA. No evidence of ECF, but nevertheless abnormal distribution of proliferation zone was characteristic of SSA, whereas HP had neither. The presence of the ECF defines TSA in a more rigorous fashion than previous diagnostic criteria and also explains the biologic basis of exuberant protuberant growth associated with TSA and the lack of such growth in SSA. Recognition of this phenomenon may also help in exploring the genetic and molecular basis for differences between SSA and TSA, because these architectural abnormalities may well be a reflection of abnormalities in genetically programmed mucosal development.

Sessile serrated adenoma: challenging discrimination from other serrated colonic polyps

Sessile serrated adenoma (SSA) is the proposed precursor for microsatellite unstable colorectal carcinomas and some authorities recommend that SSAs should be managed similar to adenomas. The aim of our study was to determine whether serrated polyps can be classified with sufficient consistency to support current treatment recommendations. One hundred eighty-five serrated polyps were classified as hyperplastic polyp (HP), SSA, or traditional serrated adenoma (TSA) by 5 pathologists blinded to clinical data. The observers documented which histologic features they considered most helpful in reaching their diagnosis in each case. In a second round, the observers were provided with polyp site and size. After reaching a consensus on minimum criteria for SSA and TSA, the pathologists classified another set of 50 polyps. The interobserver concordance was calculated using kappa statistics. In the first round, the overall interobserver agreement was moderate (kappa=0.55). Concordance for HP and SSA was moderate whereas it was nearly perfect for TSA. In the second round, there was no improvement in the concordance. All observers relied more often on architectural features than on cytologic ones to distinguish SSA from HP and agreement was reached that architectural features should provide the basis for the diagnosis of SSA. Subsequently, interobserver concordance was slightly improved but remained moderate (kappa=0.58). Interobserver agreement for the diagnosis of serrated polyps is moderate. However, this level of variability is acceptable because the presence of SSA indicates increased risk of developing additional serrated polyps and carcinoma, and surveillance is appropriate.

Pathophysiology, clinical presentation, and management of colon cancer

Colon cancer is believed to arise from two types of precursor polyps via two distinct pathways: conventional adenomas by the conventional adenoma-to-carcinoma sequence and serrated adenomas according to the serrated adenoma-to-carcinoma theory. Conventional adenomas arise from mutation of the APC gene; progression to colon cancer is a multistep process. The fundamental genetic defect in serrated adenomas is unknown. Environmental factors can increase the risk for colon cancer. Advanced colon cancer often presents with symptoms, but early colon cancer and premalignant adenomatous polyps commonly are asymptomatic, rendering them difficult to detect and providing the rationale for mass screening of adults over age 50.

Sporadic and syndromic hyperplastic polyps and serrated adenomas of the colon: classification, molecular genetics, natural history, and clinical management

There is now strong evidence for an alternative pathway of colorectal carcinogenesis implicating hyperplastic polyps and serrated adenomas. This article briefly reviews the evidence for this serrated pathway, provides diagnostic criteria for clinically significant hyperplastic polyps and allied serrated polyps, and suggests how this information may be translated into safe, effective guidelines for colonoscopy-based colon cancer prevention. Consideration also is given to the definition and management of hyperplastic polyposis syndrome. The currently proposed management plan for serrated polyps is tentative because of incomplete knowledge of the nature and behavior of these polyps. This article highlights key areas warranting further research.

Surveillance of patients at increased risk of colon cancer: inflammatory bowel disease and other conditions

Colorectal cancer (CRC) is the second most common cause of cancer-related mortality in the United States. Colonoscopic screening with removal of adenomatous polyps in individuals at average risk is known to decrease the incidence and associated mortality from colon cancer. Certain conditions, notably inflammatory bowel disease involving the colon, a family history of polyps or cancer, a personal history of colon cancer or polyps, and other conditions such as acromegaly, ureterosigmoidostomy, and Streptococcus bovis bacteremia are associated with an increased risk of colonic neoplasia. This article reviews the CRC risks associated with these conditions and the currently recommended surveillance strategies.

Reducing the incidence and mortality of colon cancer: mass screening and colonoscopic polypectomy

Most colon cancers arise from conventional adenomatous polyps (conventional adenoma-to-carcinoma sequence), while some colon cancers appear to arise from the recently recognized serrated adenomatous polyp (serrated adenoma-to-carcinoma theory). Because conventional adenomas and serrated adenomas are usually asymptomatic, mass screening of asymptomatic patients has become the cornerstone for detecting and eliminating these precursor lesions to reduce the risk of colon cancer. Colonoscopy has become the primary screening test because of its high sensitivity and specificity, and the ability to perform polypectomy. Other screening tests include guaiac tests or fecal immunochemical tests (FIT) for fecal occult blood, and flexible sigmoidoscopy. A minimal colonoscopic withdrawal time of 6 minutes is important to maximize polyp detection at colonoscopy. Chromoendoscopy is an experimental technique used to highlight abnormal colonic areas to identify neoplastic tissue and to potentially determine the histology of colonic polyps at colonoscopy based on superficial pit anatomy.

Cyclooxygenase-2 overexpression is common in serrated and non-serrated colorectal adenoma, but uncommon in hyperplastic polyp and sessile serrated polyp/adenoma

BACKGROUND

Cyclooxygenase-2 (COX-2, PTGS2) plays an important role in colorectal carcinogenesis. COX-2 overexpression in colorectal cancer is inversely associated with microsatellite instability (MSI) and the CpG island methylator phenotype (CIMP). Evidence suggests that MSI/CIMP+ colorectal cancer may arise through the serrated tumorigenic pathway through various forms of serrated neoplasias. Therefore, we hypothesized that COX-2 may play a less important role in the serrated pathway.

METHODS

By immunohistochemistry, we assessed COX-2 expression in 24 hyperplastic polyps, 7 sessile serrated polyp/adenomas (SSA), 5 mixed polyps with SSA and adenoma, 27 traditional serrated adenomas, 515 non-serrated adenomas (tubular adenoma, tubulovillous adenoma and villous adenoma), 33 adenomas with intramucosal carcinomas, 96 adenocarcinomas with serration (corkscrew gland) and 111 adenocarcinomas without serration.

RESULTS

Strong (2+) COX-2 overexpression was more common in non-serrated adenomas (28% = 143/515) than in hyperplastic polyps (4.2% = 1/24, p = 0.008) and serrated polyps (7 SSAs and 5 mixed polyps) (0% = 0/12, p = 0.04). Furthermore, any (1+/2+) COX-2 overexpression was more frequent in non-serrated adenomas (60% = 307/515) than in hyperplastic polyps (13% = 3/24, p < 0.0001) and serrated polyps (SSAs and mixed polyps) (25% = 3/12, p = 0.03). Traditional serrated adenomas and non-serrated adenomas showed similar frequencies of COX-2 overexpression. Regardless of serration, COX-2 overexpression was frequent (approximately 85%) in colorectal adenocarcinomas. Tumor location was not significantly correlated with COX-2 overexpression, although there was a trend towards higher frequencies of COX-2 overexpression in distal tumors (than proximal tumors) among hyperplastic polyps, SSAs, mixed polyps, traditional serrated adenomas and adenocarcinomas.

CONCLUSION

COX-2 overexpression is infrequent in hyperplastic polyp, SSA and mixed polyp with SSA and adenoma, compared to non-serrated and serrated adenoma. COX-2 overexpression becomes more frequent as tumors progress to higher grade neoplasias. Our observations suggest that COX-2 may play a less significant role in the serrated pathway of tumorigenesis; however, COX-2 may still play a role in later stage of the serrated pathway.

Gastrointestinal polyposes: clinical, pathological and molecular features

This article focuses mainly on noninflammatory epithelial polyposes, particularly the diagnostically important morphological and molecular features of the more recently recognized and/or more poorly understood conditions. One of the most important, but often neglected, of these is hyperplastic polyposis.

Hyperplastic and serrated polyps of the colorectum

The serrated polyp pathway is a histopathological sequence that begins in a hyperplastic polyp, or precursor serrated aberrant crypt focus, and has the potential to end in a colonic adenocarcinoma that is CIMP-high and, in most cases, also MSI. An activating mutation of the BRAF oncogene is a marker for this pathway. There is evidence that aberrant CpG-island methylation is the molecular engine that drives the progression through sequential steps of the pathway, from hyperplastic polyp to a form of atypical hyperplastic polyp (termed sessile serrated adenoma) to dysplastic serrated polyp and, ultimately to serrated carcinoma. A second serrated pathway, identified by mutations of KRAS in serrated adenoma, is delineated less completely. Its endpoint is a colorectal carcinoma that is CIMP-low and MSS, and both the advanced serrated adenoma and carcinoma stages of this pathway show molecular genetic and morphologic features that overlap with those of the conventional APC carcinogenic pathway. Clinical studies are needed to elucidate the natural history of serrated neoplasia, and provide evidence-based guidance for risk assessment and surveillance of individuals discovered to harbor its various serrated polyp precursors.

Molecular heterogeneity of colorectal cancer: Implications for cancer control

Colorectal cancer (CRC) is a multi-pathway disease. A molecular approach to the classification of CRC utilises: (1) the type of genetic instability, specifically microsatellite instability (MSI) versus stable (MSS), and (2) the presence of DNA methylation or the CpG island methylator phenotype (CIMP). The MSS/CIMP-neg subset evolves through the classical adenoma-carcinoma sequence while the MSI/CIMP-pos and MSS/CIMP-pos subsets evolve through the recently recognised 'serrated pathway'. This review will show that the existence of two or more independent pathways to CRC is relevant to cancer prevention. In particular, new strategies for detecting and managing sessile serrated polyps will need to be developed and evaluated.

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

Whereas the generally accepted carcinogenesis pathway of the microsatellite instabile high (MSI-H) colorectal carcinoma (CRC) involves the traditional adenoma in patients with Lynch syndrome, a serrate pathway involving serrate adenomas (SA) and sessile serrate polyps (SSP) characterize the sporadic MSI-H counterpart. Recent studies have, however, challenged such simple one-pathway models, inviting the consideration of alternative, unexpected pathways. Here, the issue as to the possible role of SSP, primarily in the context of Lynch syndrome, but also in subjects from familial CRC families (FCF) is addressed. Polyps coded as hyperplastic polyps (HP) from subjects with Lynch syndrome and FCF enrolled in the HNPCC-register at the Hvidovre University Hospital as well as adenomas from this population were retrieved and reviewed for features of SSP. Ninety-eight polyps coded as HP and 41 polyps coded as adenoma from 14 individuals with Lynch syndrome as well as 17 individuals from FCF constituted the study material. Seven of the 98 polyps coded as HP displayed histological features that, to varying extent, deviated from the traditional HP (THP), yet, merely two of these, both from the FCF, were considered examples of probable SSP. None of the 41 cases coded as adenoma possessed a morphology that qualified as SSP. The prevalence of SSP was not increased as compared to the background population and thus, this serrated lesion does not appear to play a tumorigenic role in Lynch syndrome, nor in FCF.

Molecular classification and genetic pathways in hyperplastic polyposis syndrome

Hyperplastic Polyposis (HPPS) is a poorly characterized syndrome that increases colorectal cancer (CRC) risk. We aimed to provide a molecular classification of HPPS. We obtained 282 tumours from 32 putative HPPS patients with >or= 10 hyperplastic polyps (HPs); some patients also had adenomas and CRCs. We found no good evidence of microsatellite instability (MSI) in our samples. The epithelium of HPs was monoclonal. Somatic BRAF mutations occurred in two-thirds of our patients' HPs, and KRAS2 mutations in 10%; both mutations were more common in younger cases. The respective mutation frequencies in a set of 'sporadic' HPs were 18% and 10%. Importantly, the putative HPPS patients generally fell into two readily defined groups, one set whose polyps had BRAF mutations, and another set whose polyps had KRAS2 mutations. The most plausible explanation for this observation is that there exist different forms of inherited predisposition to HPPS, and that these determine whether polyps follow a BRAF or KRAS2 pathway. Most adenomas and CRCs from our putative HPPS patients had 'classical' morphology and few of these lesions had BRAF or KRAS2 mutations. These findings suggest that tumourigenesis in HPPS does not necessarily follow the 'serrated' pathway. Although current definitions of HPPS are sub-optimal, we suggest that diagnosis could benefit from molecular analysis. Specifically, testing BRAF and KRAS2 mutations, and perhaps MSI, in multiple polyps could help to distinguish HPPS from sporadic HPs. We propose a specific model which would have diagnosed five more of our cases as HPPS compared with the WHO clinical criteria.

Hyperplastic polyps and sessile serrated 'adenomas' of the colon and rectum display gastric pyloric differentiation

The serrated polyp-neoplasia pathway is a novel concept that has been demonstrated to differ from the conventional adenoma-carcinoma pathway. To characterize the phenotypic patterns of differentiation in colorectal serrated polyps, we examined the immunohistochemical expression profile of gastric (MUC5AC, TFF1, MUC6, GlcNAcalpha1 --> 4Gal --> R, and PDX1) and intestinal (MUC2, TFF3, and CDX2) epithelial markers in 15 hyperplastic polyps (HPs), 29 sessile serrated adenomas (SSAs),12 traditional serrated adenomas (TSAs), and 16 conventional adenomas (CAs). MUC5AC and TFF1 were upregulated in the HPs, SSAs, and TSAs. MUC6 was expressed in the HPs and SSAs. GlcNAcalpha1 --> 4Gal --> R was expressed only in the SSAs. Although MUC2 expression was preserved, TFF3 was downregulated in the HPs, SSAs, and TSAs. PDX1 was upregulated in the HPs, SSAs, and TSAs. On the other hand, CDX2 was downregulated in the HPs and SSAs. The colorectal serrated polyps showed higher expression of gastric makers than CAs. The HPs and SSAs showed gastric and intestinal mixed phenotype expression with gastric pyloric organoid differentiation and almost identical, but different from the TSAs, marker profile. PDX1 up-regulation and CDX2 down-regulation could be important for the induction of a gastric pyloric pattern of cell differentiation in colorectal serrated polyps.

Filiform serrated adenomas: a clinicopathologic and immunophenotypic study of 18 cases

In this study, we describe a previously uncharacterized type of adenomatous polyp of the colorectum that shows prominent, thin, elongated projections of neoplastic epithelium with a serrated contour, which we have termed "filiform serrated adenoma" (SA). Routinely processed polypectomy specimens from 18 patients with filiform SA and 23 controls with traditional (nonfiliform) SA were evaluated for their clinical and pathologic features, and immunohistochemically stained for a variety of markers (O-methylguanine methyltransferase, MLH1, MSH2, CDX2, nuclear beta-catenin, p53, and Ki-67) designed to evaluate their molecular and proliferative characteristics. DNA was extracted from the paraffin-embedded materials, amplified by polymerase chain reaction, and analyzed for microsatellite instability, BRAF, K-ras, and p53 mutational status. Five cases contained sufficient non-neoplastic tissue for dissection and DNA extraction, allowing analysis of loss of heterozygosity. The study group consisted of 7 males and 11 females of mean age 64 years (range: 42 to 89 y). All 18 filiform SAs were located in the left colon, including 15 (83%) that occurred in the rectum, compared with 43% of the control group (P=0.03). Filiform SAs were also larger (1.6 cm) than SAs (mean: 1.2 cm, P=0.02), but no other clinical differences were noted. Most (56%) filiform SAs contained marked stromal edema and tall nonmucinous cells with abundant eosinophilic cytoplasm (61%). High-grade dysplasia was present in 4/18 (22%) cases. Four (22%) filiform SAs also contained nonserrated adenomatous elements with a villous (3 cases) or tubular (1 case) growth pattern. Two (11%) cases contained adjacent areas of sessile SAs and 4 (22%) had hyperplastic areas. None of the polyps in the control group showed stromal edema, high-grade dysplasia, or mixed elements. Polyps in both groups demonstrated comparable staining patterns for O-methylguanine methyltransferase, MLH-1, MSH-2, CDX2, beta-catenin, and Ki-67, and none showed increased nuclear p53 expression. Low-frequency microsatellite instability was present in 5/12 (42%) filiform SAs, 7/12 (58%) were microsatellite stable. Mitogen-activated protein kinase pathway abnormalities were present in 71% of the cases [7/14 (50%) with BRAF and 3/14 (21%) with K-ras mutations]. Four cases showed silent p53 mutations upon direct sequencing and 4 revealed loss of heterozygosity at the loci evaluated, including 1 at D5S346 [adenomatous polyposis coli (APC) gene], 1 at D17S250 (p53 gene), and 2 at MYCL (chromosome 1p34). We conclude that filiform SA potentially represents an unusual variant of SA with a predilection for the left colon, particularly the rectum.

Serrated neoplasia of the colorectum

Serrated polyps of the colorectum form a group of related lesions which include aberrant crypt foci (ACF), conventional hyperplastic polyps, mixed (admixed) polyps, serrated adenomas and sessile serrated adenomas. In recent years the molecular differences between these morphologically similar lesions have been highlighted, and their differing biological potential has been realised. In particular, the sessile serrated adenoma has become recognised as the precursor lesion to a group of sporadic colorectal carcinomas characterised by morphological and molecular features distinct from conventional adenomas. These recent findings have challenged the long held paradigm that all colorectal carcinomas arise via the traditional adenoma-carcinoma sequence. In addition, they present a major challenge for the early detection and management of colorectal cancer, which is no longer regarded as a homogeneous entity.

Role of BRAF-V600E in the serrated pathway of colorectal tumourigenesis

There is increasing evidence for an alternative pathway of sporadic colorectal tumourigenesis that is associated with DNA microsatellite instability (MSI), due to methylation and loss of expression of the mismatch repair gene MLH1. Recent studies have highlighted a serrated pathway of colorectal cancer (CRC) in which serrated polyps with activating mutations in BRAF progress to CRCs with MSI following methylation and silencing of MLH1. The present study provides a novel mechanistic experimental model for these clinical observations. We investigated the role of BRAF activating mutation (BRAF-V600E) in colorectal tumourigenesis by studying the effects of forced expression of BRAF-V600E in the 'normal' colon epithelial NCM460 cell line and by targeting endogenous BRAF-V600E in MSI-High (MSI-H) colon cancer cell lines. The findings indicate that BRAF mutation in colon epithelial cells contributes to a gain in resistance towards apoptotic stimuli, which is likely to be an important characteristic of pre-malignant serrated lesions. BRAF-V600E also plays a role in the development and maintenance of transformed and invasive phenotypes in colon epithelial cells. Our findings also suggest that BRAF mutation potentiates promoter hypermethylation of the MLH1 gene promoter. Together, these results highlight BRAF as a potential target for therapeutic intervention in sporadic MSI-H colorectal cancers.

Hyperplastic polyposis associated with two asynchronous colon cancers

We report a patient with hyperplastic polyposis who had two asynchronous colon cancers, a combined adenoma-hyperplastic polyp, a serrated adenoma, and tubular adenomas. Hyperplastic polyposis is thought to be a precancerous lesion; and adenocarcinoma arises from hyperplastic polyposis through the hyperplastic polyp-adenoma-carcinoma sequence. Most polyps in patients with hyperplastic polyposis present as bland-looking hyperplastic polyps, which are regarded as non-neoplastic lesions; however, the risk of malignancy should not be underestimated. In patients with multiple hyperplastic polyps, hyperplastic polyposis should be identified and followed up carefully in order to detect malignant transformation in the early stage.

The case for a genetic predisposition to serrated neoplasia in the colorectum: hypothesis and review of the literature

In recent years, an alternative pathway of colorectal cancer development has been described in which serrated polyps replace the traditional adenoma as the precursor lesion. Importantly, serrated polyps and a subset of colorectal cancer show largely nonoverlapping mutation profiles to those found in adenomas and the majority of colorectal cancer. These genetic alterations include activating mutation of the BRAF proto-oncogene and widespread gene promoter hypermethylation (CpG island methylator phenotype or CIMP). Up to 15% of colorectal cancer is likely to develop on the basis of a strong genetic predisposition. The two most well-characterized syndromes, familial adenomatous polyposis and hereditary nonpolyposis colorectal cancer (Lynch syndrome), both develop via the adenoma-carcinoma pathway and together account for approximately one third of familial colorectal cancer. We have recently described 11 families in which there is evidence that the genetic predisposition to autosomal dominant colorectal cancer is linked to the serrated pathway. This condition, serrated pathway syndrome, and the related condition, hyperplastic polyposis, the presentation of which suggests a recessive mode of inheritance, represent two syndromes in which BRAF mutation and methylation co-occur within serrated precursor lesions. Further, CIMP is observed in the normal colonic mucosa of individuals with hyperplastic polyposis consistent with a field defect in epigenetic regulation. The spectrum of serrated neoplasia may also implicate the apparently sporadic and later onset subset of colorectal cancer with high levels of microsatellite instability. The tendency for these lesions to be multiple, associated with smoking, and to show frequent BRAF mutation and CIMP points to a defect that may result from interactions between the environment and a weakly penetrant genetic alteration.

Histopathology of serrated adenoma, its variants, and differentiation from conventional adenomatous and hyperplastic polyps

CONTEXT

Serrated adenomas can be morphologically subdivided into traditional and sessile types. They are thought to have a comparable rate of cancer progression like conventional adenomas, but they potentially have a faster rate of growth through methylation pathway(s). They share similar morphologic features with both the conventional adenoma and the hyperplastic polyp in a fashion that is different from a mixed adenoma and a hyperplastic polyp.

OBJECTIVE

To describe the histopathologic features of traditional serrated adenoma and sessile serrated adenoma and their comparison with traditional adenomas and hyperplastic polyp.

DATA SOURCES

Relevant articles in peer-review journals and the authors' working experience as practicing surgical pathologists with a specific interest in gastrointestinal pathology.

CONCLUSIONS

Both types of serrated adenomas, traditional serrated adenoma and sessile serrated adenoma, are morphologically distinct, clinically important entities, and they can be diagnosed accurately in routine practice.

A multinational, internet-based assessment of observer variability in the diagnosis of serrated colorectal polyps

This Internet-based quiz (http://kathrin.unibas.ch/polyp/) tested the diagnostic variability of 168 pathologists in the diagnosis of 20 colorectal polyps on 3 representative images, including hyperplastic polyps (HPs), traditional serrated adenomas (TSAs), sessile serrated adenomas (SSAs), and tubulovillous adenomas (TVAs). Interobserver variability for each of the 20 lesions was significant and was most pronounced for SSAs. Correct answers were independent of the participant's experience with TVAs, HPs, and TSAs. Participants with gastrointestinal subspecialty training and those who had read a reference article on serrated polyps gave a significantly higher percentage of correct answers for SSAs. The nomenclature used for serrated polyps was generally inconsistent. Our results suggest significant shortcomings in the routine H&E diagnosis of serrated colorectal polyps. A diagnostically unifying concept for lesions of the serrated neoplasia pathway, standardization of nomenclature, training of pathologists, and possibly development of ancillary techniques are of paramount importance for accurate patient management.

Mutations in BRAF and KRAS differentially distinguish serrated versus non-serrated hyperplastic aberrant crypt foci in humans

We previously reported that colon carcinomas, adenomas, and hyperplastic polyps exhibiting a serrated histology were very likely to possess BRAF mutations, whereas when these same advanced colonic lesions exhibited non-serrated histology, they were wild type for BRAF; among hyperplastic polyps, KRAS mutations were found mainly in a non-serrated variant. On this basis, we predicted that hyperplastic aberrant crypt foci (ACF), a putative precancerous lesion found in the colon, exhibiting a serrated phenotype would also harbor BRAF mutations and that non-serrated ACF would not. In contrast, KRAS mutations would be found more often in the non-serrated ACF. We examined 55 ACF collected during screening colonoscopy from a total of 28 patients. Following laser capture microdissection, DNA was isolated, and mutations in BRAF and KRAS were determined by direct PCR sequencing. When hyperplastic lesions were further classified into serrated and non-serrated histologies, there was a strong inverse relationship between BRAF and KRAS mutations: a BRAF(V600E) mutation was identified in 10 of 16 serrated compared with 1 of 33 non-serrated lesions (P = 0.001); conversely, KRAS mutations were present in 3 of 16 serrated compared with 14 of 33 non-serrated lesions. Our finding of a strong association between BRAF mutations and serrated histology in hyperplastic ACF supports the idea that these lesions are an early, sentinel, or a potentially initiating step on the serrated pathway to colorectal carcinoma.

[Emerging concepts in colorectal serrated polyps]

Colorectal serrated polyps are heterogeneous epithelial lesions characterized by a serrated architecture. They include the classical hyperplastic polyps and the much rarer serrated adenomas and mixed polyps. Whereas serrated adenomas are composed of an unequivocal adenomatous epithelium with architectural serrated, mixed polyps include two separate hyperplastic and adenomatous components. During the past few years, another type of serrated polyp with only very subtle proliferation abnormalities has been described. These atypical serrated polyps may occur either sporadically or in the context of colorectal polyposis. Despite their close resemblance to traditional hyperplastic polyps, some authors argued that they should be regarded as authentically neoplastic lesions and have proposed to call them "sessile serrated adenomas". Their malignant potential requires their removal when discovered during colonoscopy. This article reviews the histological features, the endoscopic appearance, the natural history and the molecular phenotype of the different categories of serrated polyps and introduces the concept of "serrated neoplastic pathway" in the development of colorectal cancer.

Survivin and hedgehog protein expression in serrated colorectal polyps: an immunohistochemical study

Sessile serrated adenomas and traditional serrated adenomas are pathogenetically related to inhibition of apoptosis. Survivin and hedgehog proteins, including sonic hedgehog, patched, and smoothened, inhibit apoptosis, with hedgehog proteins forming a signal transduction cascade implicated in digestive cancers. This study compares survivin and hedgehog protein expression in serrated polyps and tubulovillous adenomas. Biopsies of sessile serrated adenomas (48) and traditional serrated adenomas (10) diagnosed during 2005 were retrieved from our files. Biopsies of normal mucosa (10), hyperplastic polyps (14), and tubulovillous adenomas (22) were used for comparison. Immunohistochemistry for survivin, sonic hedgehog, patched, and smoothened was graded as high or low grade. chi(2) tests were used to evaluate correlation between polyp type and survivin and hedgehog expression. Traditional serrated adenomas were also compared to sessile serrated adenomas with foci of cytological dysplasia (11 cases) with respect to MLH1 and p53 expression. Sessile serrated adenomas showed high-grade nuclear and cytoplasmic expression of survivin at the bottom of crypts more frequently than tubulovillous adenomas (60% versus 18%, P = .001 [nuclear]; 54% versus 18%, P = .005 [cytoplasm]), the latter showing a top-heavy pattern of staining. Survivin expression in hyperplastic polyps was similar to sessile serrated adenomas, being bottom-heavy, whereas traditional serrated adenomas showed diffuse staining throughout crypts. Although traditional serrated adenomas showed high-grade expression of sonic hedgehog more frequently than tubulovillous adenomas (90% versus 18%; P < .001), sonic hedgehog, patched, and smoothened expression was low grade among normal mucosa, hyperplastic polyps, and sessile serrated adenomas. All cytological dysplasias showed increased p53 expression within dysplastic foci, and MLH1 was also lost within dysplastic foci in 4 cases; traditional serrated adenomas showed intact MLH1 expression and minimal p53 expression throughout. Survivin expression is localized to the bottom of crypts in sessile serrated adenomas and hyperplastic polyps, whereas tubulovillous adenomas show top-heavy expression. Traditional serrated adenomas express survivin throughout crypts, suggesting intersection between the serrated and conventional adenoma-cancer pathways. Sonic hedgehog up-regulation is characteristic of traditional serrated adenomas, distinguishing this entity from other colorectal polyps.

Colorectal serrated adenocarcinoma

Colorectal cancer (CRC) ranks among the three most common cancers in terms of both cancer incidence and cancer-related deaths in most Western countries. Serrated adenocarcinoma is a recently described, distinct variant of CRC, accounting for about 7.5% of all CRCs and up to 17.5% of most proximal CRCs. It has been postulated that about 10-15% of sporadic CRCs would have their origin in serrated polyps that harbour a significant malignant potential. These lesions include hyperplastic-type aberrant crypt foci, hyperplastic polyps, sessile serrated adenomas, admixed polyps and serrated adenomas, and constitute the so-called 'serrated pathway', which is distinct from both the conventional adenoma-carcinoma pathway and the mutator pathway of hereditary non-polyposis CRC and is characterized by early involvement of oncogenic BRAF mutations, excess CpG island methylation (CIM) and subsequent low- or high-level DNA microsatellite instability (MSI). Methylation of hMLH1 is likely to explain the increased frequency of high-level MSI (16%) and methylation of MGMT is postulated to explain the low-level MSI (29%) in serrated adenocarcinomas. Reproducible histopathological criteria for serrated adenocarcinoma have recently been established and they have been qualified by DNA expression analysis for 7928 genes, showing clustering of serrated adenocarcinomas into a molecular entity apart from conventional adenocarcinoma, and representing with distinct down-regulation of EPHB2, PTCH and up-regulation of HIF1alpha.

Classification of colorectal cancer based on correlation of clinical, morphological and molecular features

Over the last 20 years it has become clear that colorectal cancer (CRC) evolves through multiple pathways. These pathways may be defined on the basis of two molecular features: (i) DNA microsatellite instability (MSI) status stratified as MSI-high (MSI-H), MSI-low (MSI-L) and MS stable (MSS), and (ii) CpG island methylator phenotype (CIMP) stratified as CIMP-high, CIMP-low and CIMP-negative (CIMP-neg). In this review the morphological correlates of five molecular subtypes are outlined: Type 1 (CIMP-high/MSI-H/BRAF mutation), Type 2 (CIMP-high/MSI-L or MSS/BRAF mutation), Type 3 (CIMP-low/MSS or MSI-L/KRAS mutation), Type 4 (CIMP-neg/MSS) and Type 5 or Lynch syndrome (CIMP-neg/MSI-H). The molecular pathways are determined at an early evolutionary stage and are fully established within precancerous lesions. Serrated polyps are the precursors of Types 1 and 2 CRC, whereas Types 4 and 5 evolve through the adenoma-carcinoma sequence. Type 3 CRC may arise within either type of polyp. Types 1 and 4 are conceived as having few, if any, molecular overlaps with each other, whereas Types 2, 3 and 5 combine the molecular features of Types 1 and 4 in different ways. This approach to the classification of CRC should accelerate understanding of causation and will impact on clinical management in the areas of both prevention and treatment.

Comparison of microsatellite instability, CpG island methylation phenotype, BRAF and KRAS status in serrated polyps and traditional adenomas indicates separate pathways to distinct colorectal carcinoma end points

The aim of this study was to compare BRAF and KRAS, CpG island methylator phenotype (CIMP), and microsatellite instability (MSI) status in each of the histologic categories, including end-point carcinomas with residual adenoma, of the serrated polyp neoplasia pathway and the traditional (nonserrated) adenoma-carcinoma sequence. Deoxyribonucleic acid (DNA) was extracted from the selected samples and assayed for BRAF, KRAS2 codon12, 13, CIMP using markers hMLH1, MGMT, MINT1, MINT2, p16, and MSI using an assay for BAT25 and BAT26. A BRAF mutation was present in 82% of serrated carcinomas (SCas), 62% of serrated adenomas (SAs), 83% of serrated polyps with abnormal proliferation (SPAPs-syn. sessile serrated adenoma [SSA]), 76% of microvesicular serrated polyps (MVSPs), and was not found in any of the histologic categories of the traditional adenoma-carcinoma sequence. KRAS2 mutations were found in 43% of the goblet cell serrated polyp (GCSP) category, 13% of MVSPs, 7% of SPAPs, and 24% of SAs; in 26% of large traditional adenoma (lTAs) compared with small traditional adenomas (sTAs) (0/30; P<0.005) and in 37.3% of traditional carcinomas (TCa). CIMP-H (>1 marker positive) was significantly more frequent in SPAP, SA, and SCa compared with MVSP (P<0.05); CIMP-H was present in 10% of sTAs but was found more frequently in lTA (44.4%; OR 7.2; P=0.007) and TCa (38.9%; OR 5.8; P=0.007). Higher CIMP levels (4 or more markers positive) were significantly more frequent in advanced categories of the serrated pathway (SAs [31%] and SCas [30%]) compared with lTAs [0%] and TCAs [3.4%] (OR 12.2; P=0.02). MSI-H was identified only in the adenocarcinoma component of SCas (9/11) or in the contiguous SAs (3/7). The findings indicate that a BRAF mutation is a specific marker for a serrated polyp pathway that has its origin in a hyperplastic polyp (MVSP) and a potential end point as MSI carcinoma. CIMP-High (CIMP-H) develops early in this sequence and MSI-H develops late. The data provided a less complete picture of a second serrated pathway, identified by a KRAS2 mutation in SAs, but showed that the progressive stages of both iterations of the serrated neoplasia pathway are separate and distinct from those of the traditional adenoma-carcinoma sequence.

High prevalence of sessile serrated adenomas with BRAF mutations: a prospective study of patients undergoing colonoscopy

BACKGROUND & AIMS

Sporadic colorectal cancers with a high degree of microsatellite instability are a clinically distinct subgroup with a high incidence of BRAF mutation and are widely considered to develop from serrated polyps. Previous studies of serrated polyps have been highly selected and largely retrospective. This prospective study examined the prevalence of sessile serrated adenomas and determined the incidence of BRAF and K-ras mutations in different types of polyps.

METHODS

An unselected consecutive series of 190 patients underwent magnifying chromoendoscopy. Polyp location, size, and histologic classification were recorded. All polyps were screened for BRAF V600E and K-ras codon 12 and 13 mutations.

RESULTS

Polyps were detected in 72% of patients. Most (60%) were adenomas (tubular adenomas, tubulovillous adenomas), followed by hyperplastic polyps (29%), sessile serrated adenomas (SSAs; 9%), traditional serrated adenomas (0.7%), and mixed polyps (1.7%). Adenomas were more prevalent in the proximal colon (73%), as were SSAs (75%), which tended to be large (64% >5 mm). The presence of at least one SSA was associated with increased polyp burden (5.0 vs 2.5; P < .0001) and female sex (P < .05). BRAF mutation was rare in adenomas (1/248 [0.4%]) but common in SSAs (78%), traditional serrated adenomas (66%), mixed polyps (57%), and microvesicular hyperplastic polyps (70%). K-ras mutations were significantly associated with goblet cell hyperplastic polyps and tubulovillous adenomas (P < .001).

CONCLUSIONS

The prevalence of SSAs is approximately 9% in patients undergoing colonoscopy. They are associated with BRAF mutation, proximal location, female sex, and presence of multiple polyps. These findings emphasize the importance of identifying and removing these lesions for endoscopic prevention of colorectal cancer.

Hyperplastic polyposis and cancer of the colon with gastrinoma of the duodenum

BACKGROUND

A 64-year-old woman presented to the emergency room with a 3-month history of intermittent abdominal cramps, accompanied by nausea, vomiting, anorexia, and decreased bowel movements consistent with a partial intestinal obstruction. She had a 12-year history of peptic ulcers, which had been treated with histamine-2 blockers.

INVESTIGATIONS

Physical examination, abdominal X-ray, abdominal CT scan, colonoscopy and assessment of gastrin levels.

DIAGNOSIS

Duodenal neuroendocrine neoplasm showing gastrin expression and stage III (T3N2M0), poorly differentiated adenocarcinoma of the cecum arising from hyperplastic polyposis.

MANAGEMENT

Right-sided hemicolectomy with ileocolonic anastomosis, duodenal resection, leucovorin and 5-fluorouracil chemotherapy, annual colonoscopic surveillance, and polypectomy.

Complementary analysis of microsatellite tumor profile and mismatch repair defects in colorectal carcinomas

Microsatellite instability (MSI) is a prognostic factor and a marker of deficient mismatch repair (MMR) in colorectal adenocarcinomas (CRC). However, a proper application of this marker requires understanding the following: (1) The MSI concept: The PCR approach must amplify the correct locus and accurately identify the microsatellite pattern in the patient’s normal tissue. MSI is demonstrated when the length of DNA sequences in a tumor differs from that of nontumor tissue. Any anomalous expansion or reduction of tandem repeats results in extra-bands normally located in the expected size range (100 bp, above or below the expected product), differ from the germline pattern by some multiple of the repeating unit, and must show appropriate stutter. (2) MSI mechanisms: MMR gene inactivation (by either mutation or protein down-regulation as frequently present in deep CRC compartments) leads to mutation accumulation in a cell with every cellular division, resulting in malignant transformation. These mechanisms can express tumor progression and result in a decreased prevalence of aneuploid cells and loss of the physiologic cell kinetic correlations in the deep CRC compartments. MSI molecular mechanisms are not necessarily independent from chromosomal instability and may coexist in a given CRC. (3) Because of intratumoural heterogeneity, at least two samples from each CRC should be screened, preferably from the superficial (tumor cells above the muscularis propria) and deep (tumor cells infiltrating the muscularis propria) CRC compartments to cover the topographic tumor heterogeneity. (4) Pathologists play a critical role in identifying microsatellite-unstable CRC, such as occur in young patients with synchronous or metachronous tumors or with tumors showing classic histologic features. In these cases, MSI testing and/or MMR immunohistochemistry are advisable, along with gene sequencing and genetic counseling if appropriate. MSI is an excellent functional and prognostically useful marker, whereas MMR immunohistochemistry can guide gene sequencing.

Sessile serrated adenomas with low- and high-grade dysplasia and early carcinomas: an immunohistochemical study of serrated lesions "caught in the act"

Sessile serrated adenomas (SSAs) show serrations typical of hyperplastic polyps but display architectural differences and lack traditional dysplasia. SSAs with foci of low- (LGD) or high-grade dysplasia (HGD) or early invasive carcinoma are seldom biopsied and, thus, are not well studied. Immunohistochemical analysis for MLH1, MSH2, MSH6, and PMS2 (mismatch repair gene products) was performed on colon biopsy specimens from 11 patients (age range, 54-87 years; 4 men and 7 women) showing SSA with LGD (n = 1), HGD (n = 5), or focal invasive carcinoma (n = 5). All 11 cases showed intact nuclear staining for MSH2 and MSH6 in the SSA component; in foci of LGD, HGD, or carcinoma; and in background normal mucosa. In contrast, there was tandem loss of MLH1 and PMS2 in zones of LGD (1/1) or HGD (3/5) and early carcinoma (2/4; with concordant loss in associated HGD) but retention in SSA areas (11/11) and normal mucosa (11/11). No patient was known to have hereditary nonpolyposis colorectal cancer/Lynch syndrome. This study offers additional strong evidence that SSA is truly a precursor to at least a subset of sporadic microsatellite-unstable colorectal cancer.