Morphologic reappraisal of serrated colorectal polyps

Serrated polyps of the large intestine

Serrated polyps of the large intestine comprise a family of lesions bearing some histological similarities, including an overall serrated configuration caused at least in part by inhibition of apoptosis by mutations in one of two genes. Over the past decade, it has become apparent that these lesions can be subdivided by histological criteria into lesions with differing degrees of relationship to the development of carcinoma, including sporadic microsatellite instable (MSI) carcinomas and probably carcinomas demonstrating the CpG island methylator phenotype (CIMP), which includes both MSI and microsatellite stable tumors. These differing histological subtypes can in part predict some of the molecular features of these lesions, and the combination of histological and molecular features is beginning to give us better insight into the potential natural history and therefore management of these lesions. This review will present the histological classification of these lesions, relate that histological classification to molecular aspects of the lesions, and present recommendations for management.

Advanced colorectal polyps with the molecular and morphological features of serrated polyps and adenomas: concept of a 'fusion' pathway to colorectal cancer

AIM

To establish and explain the pattern of molecular signatures across colorectal polyps.

METHODS AND RESULTS

Thirty-two sessile serrated adenomas (SSA), 10 mixed polyps (MP), 15 traditional serrated adenomas (SA), 49 hyperplastic polyps (HP) and 84 adenomas were assessed for mutation of KRAS and BRAF and aberrant expression of p53. The findings were correlated with loss of expression of O-6-methylguanine DNA methyltransferase (MGMT). KRAS mutation occurred more frequently (26.5%) than BRAF mutation (4.8%) in adenomas (P < 0.001) and particularly in adenomas with villous architecture (50%). Loss of expression of MGMT correlated with KRAS mutation in small tubular adenomas (P < 0.04). BRAF mutation was frequent in HPs (67%) and SSAs (81%), while KRAS mutation was infrequent (4% and 3%, respectively). Of MPs and SAs, 72% had either BRAF or KRAS mutation. Aberrant expression of p53 was uncommon overall, but occurred more frequently in MPs and SAs (12%) than adenomas (1%) (P < 0.04) and there was concordant loss of expression of MGMT.

CONCLUSIONS

Molecular alterations that are characteristic of the serrated pathway and adenoma-carcinoma sequence can co-occur in a minority of advanced colorectal polyps that then show morphological features of both pathways. These lesions account for only 2% of colorectal polyps, but may be relatively aggressive.

[Serrated neoplasia of the gastro-intestinal tract]

Serrated neoplasia of the gastro-intestinal tract have peculiar microscopic and molecular features that are still incompletely described. Some serrated polyps seem to be involved in a new carcinogenic pathway in the colon: the serrated neoplasia pathway, with hypermethylation of the cytosine-guanine dinucleotides, located in the promoter of some genes such as h-MLH1, BRAF and MGMT. The natural history of the serrated polyps and their risk for progression to malignancy are still unclear. There is no official guideline for the management of serrated polyps. The aim of this article is to describe the epidemiological, morphological, immunohistochemical and molecular characteristics of the serrated neoplasia of the gastrointestinal tract: hyperplastic polyps, "traditional" serrated adenomas, mixed hyperplastic and adenomatous polyps, sessile serrated adenomas, hyperplastic polyposis and serrated adenocarcinomas.

Morphology and microsatellite instability in sporadic serrated and non-serrated colorectal cancer

Colorectal serrated adenocarcinoma originates from serrated adenoma, but definite histological criteria have not yet been established. It presents with frequent DNA microsatellite instability (MSI), but the frequency of low-level (MSI-L) and high-level MSI (MSI-H) and the expression of mismatch-repair (MMR) enzymes in serrated adenocarcinoma are not known. To address these questions, morphological criteria for serrated cancers were established, their validity was tested, and MSI analysis was performed with NIH consensus markers and MMR enzyme immunohistochemistry for hMLH1, hMSH2, and hMSH6 in 35 serrated and 75 non-serrated colorectal carcinomas. Serrated carcinomas frequently showed a serrated, mucinous or trabecular growth pattern; abundant eosinophilic cytoplasm; chromatin condensation; preserved polarity; and the absence of necrosis. With these features, it was possible to distinguish them from non-serrated cancers, with the mean kappa score for five observers being 0.509. MSI analysis was successful in 31 serrated and 73 non-serrated carcinomas. 54.8% of serrated carcinomas were microsatellite-stable (MSS), 29.0% presented with MSI-L, and 16.1% presented with MSI-H, whereas 78.1% of non-serrated carcinomas were MSS, 13.7% were MSI-L, and 8.2% were MSI-H. MSI-L was more common in serrated cancers (p=0.035) and it was associated with patchy immunohistochemical staining (33.3%) of MLH1. MSI-H did not differ between serrated and non-serrated cancers (p=0.14). These results suggest that the biological background of serrated carcinomas differs from sporadic non-serrated colorectal cancer, but is not directly related to MSI.

Serrated adenoma of the colorectum and the DNA-methylator phenotype

Serrated adenomas (SA) of the colorectum show features intermediate between hyperplastic polyps (HP) and adenomas. HP and SA are related lesions and there is now strong evidence for a 'serrated-polyp pathway' to colorectal cancer (CRC) that is largely independent of the classic adenoma-to-carcinoma sequence. A recently recognized lesion in this pathway is a HP variant characterized by relatively large size, atypical histology and proximal location in the colorectum. This HP variant has been given a variety of names in the literature including 'sessile SA' and 'type I SA'. Because this lesion lacks the traditional cytology of colorectal adenoma and in order to avoid confusion with SA, it is referred to in this review as sessile serrated polyp. SA are characterized by a heterogeneous group of changes at the molecular level, but a high proportion have BRAFmutations and DNA methylation. They may develop in HP or sessile serrated polyps, or may arise de novo. In the serratedpolyp pathway, the advent of genetic instability is likely to be an important rate-limiting step that drives rapid neoplastic evolution. Methylation and inactivation of the DNA repair genes MLH1 and MGMT (O-6-methylguanine-DNA methyltransferase) have been proposed as critical steps leading to genetic instability. Stretches of DNA rich in the bases guanine and cytosine (CpG islands; where p represents a phosphodiester bond linking adjacent cytosine and guanine bases) that are normally unmethylated may become methylated in malignant human colorectal tumors. Subsets of colorectal cancers with an unusually high number of methylated CpG islands have been described as having the 'CpG-island-methylator phenotype' It is possible that many, if not all, CRCs with the CpG-island-methylator phenotype evolve through the serrated-polyp pathway that would, therefore, explain approximately 20% of all CRCs. The current lack of guidelines for managing serrated polyps may explain the static incidence of proximal CRC, despite the falling incidence rates for left-sided CRC during the same time period.

Demographic and pathological characteristics of serrated polyps of colorectum

AIMS

To characterize a series of colorectal polyps, focusing on the clinicopathological features of serrated adenoma (SA), mixed polyp (MP) and the recently recognized sessile serrated adenoma (SSA).

METHODS AND RESULTS

Eight hundred and ninety-one conventional adenomas (AD), 298 hyperplastic polyps (HP), 27 SSA, 10 MP and 24 traditional SA were obtained from patients during colonoscopic examination. SSA were more likely to be proximally located than other polyps. All SA, MP and SSA and a randomly selected subset of HP (n = 61) and ADs (n = 93) were assessed for expression of mucin, MLH1, MGMT, and Ki67. SSA expressed more MUC5AC than either HP or SA. Loss of MLH1 was not observed in any serrated polyps and in only one AD. Loss of MGMT occurred in 13% of AD, and showed no correlation with histological type, size or location. Loss of MGMT occurred in 24% of SSA, MP and SA (combined), and was more frequent in proximal lesions and larger lesions. SSA had a higher proliferative index than HP. In MP, the proliferative index of the non-dysplastic component was closer to HP than SSA, while the dysplastic component was intermediate between SA and AD.

CONCLUSIONS

SSA differ from other serrated polyps of colorectum in terms of location, morphology and immunophenotype.

Sessile Serrated Polyp Mimicry in Patients With Solitary Rectal Ulcer Syndrome: Is There Evidence of Preneoplastic Change?

Context.—Solitary rectal ulcer syndrome (SRUS) is associated with erythema and ulceration of the rectal wall. Serrated lesions of the colon are divided into conventional hyperplastic polyps and a new set of lesions that are variably called sessile serrated polyps (SSPs) and sessile serrated adenomas. The SSPs are epithelial proliferative lesions that appear to act as a unique pathway to colorectal carcinogenesis. No association between SRUS and SSPs has been previously reported.

Objective.—To assess a possible association between SRUS and morphologic features that mimic SSPs.

Design.—Twenty-six patients with SRUS, who presented to our institution between January 1, 1999, and November 14, 2004, were retrospectively reviewed for SSP-type morphologic features by 3 pathologists. Ki-67 and hMLH1 immunohistochemical stains were used. Control tissues included 10 conventional left-sided hyperplastic polyps, 10 right-sided large SSPs, 7 adenocarcinomas with known loss of hMLH1 gene expression, and 4 normal human tonsil tissues.

Results.—Ten (38%) of 26 SRUS specimens demonstrated histologic features consistent with SSPs. These features included exaggerated serration within the lower crypt compartments, crypt branching, hypermucinous appearance of epithelium, and horizontal extension of crypt bases along the muscularis mucosa. All 10 cases of SRUS had positive basal Ki-67 staining in 10% to 20% of cells. Two (20%) of the 10 cases demonstrated focal superficial loss of hMLH1 mismatch repair gene expression within areas of serrated morphologic features. One hyperplastic polyp superimposed on SRUS showed a reduced number of surface epithelial cells that express hMLH1 protein.

Conclusions.—Up to 38% of patients with SRUS have histologic changes that mimic SSPs. More importantly, 20% of these serrated lesions were found to have focal loss of hMLH1 gene expression, indicating a potential of preneoplastic change. This phenomenon may reflect an increased propensity for neoplastic progression in response to repeated trauma and repair process in certain cases of SRUS.

Tracing origin of serrated adenomas with BRAF and KRAS mutations

Serrated neoplasm of the colorectum raised many as-yet unanswered issues. To characterize serrated neoplasia pathway, we investigated BRAF and KRAS mutations in 35 traditional serrated adenomas. BRAF exons 11 and 15, and KRAS exon 2 were amplified by polymerase chain reaction and directly sequenced. BRAF V599E mutation was found in 27 serrated adenomas (77.1%), and KRAS mutations were found in 3 (8.6%) of 35 traditional serrated adenomas. In 13 cases, mixed polyps composed of traditional serrated adenomas and hyperplastic (serrated) polyps were observed, and seven of them showed the same BRAF mutations in both components. Somatic mutations of BRAF and KRAS genes were mutually exclusive. These findings suggest that BRAF mutations are early and a critical event in the serrated adenomas, and most serrated adenomas in both sides of colon may progress from microvesicular hyperplastic polyps via BRAF mutations, and some left-sided serrated adenomas develop via KRAS mutations.

Multinucleated epithelial giant cells in colorectal polyps: a potential mimic of viropathic and/or dysplastic changes

Multinucleated epithelial giant cells (MEG) simulating viral cytopathic effect and/or dysplasia have been reported in the esophagus in association with inflammation, but the occurrence of similar cells in the colon has not been documented. Twenty-three colon specimens (22 biopsies and 1 partial colectomy) featuring MEG from 21 patients were evaluated for a variety of histologic features and correlated with clinical, endoscopic, and follow-up data. Patients included 9 males and 12 females (mean age, 64.9 years; range, 45-86 years). Eleven cases were obtained from 10 asymptomatic patients undergoing surveillance biopsies. Presenting symptoms in the remaining patients were dyspepsia, anemia, abdominal pain, and hematochezia. Over half (13 of 23) of the specimens were from descending and rectosigmoid colon, and almost all were visualized as polyps on endoscopy. Microscopically, all but 1 of the cases featured multiple MEG (range, 6 to >50 cells per biopsy) in the base and mid crypt zones of inflamed polyps with serrated architecture. Immunohistochemical stains for CMV, HSV, adenovirus, EBV, and polyoma virus were negative and no viral particles were identified on ultrastructural examination. Nuclear staining for hMLH1 and hMSH2, markers of microsatellite instability, was similar in distribution to adjacent serrated crypts, but reduced staining intensity was noted in occasional multinucleated cells. Expression of Ki-67 and cleaved caspase 3 was consistent with a quiescent or low proliferative state. Clinical follow-up was available for 9 patients (mean duration, 22.7 months). One patient died of heart failure; all others were well at last follow-up. Bizarre MEG may occasionally be seen within the crypts of inflamed polyps with serrated architecture, raising concern for dysplasia or viral infection. Immunohistochemical and ultrastructural studies fail to establish a viral etiology, and follow-up does not indicate clinically aggressive disease. These changes appear to represent a nonspecific, possibly degenerative response to inflammation and injury, and should be distinguished from dysplasia.

BRAF mutations in aberrant crypt foci and hyperplastic polyposis

Patients with hyperplastic polyposis have multiple hyperplastic polyps (HPs) and increased risk of colorectal carcinomas. Aberrant crypt foci (ACF) are postulated to be the earliest precursor lesions in colorectal carcinogenesis. We evaluated BRAF mutations by DNA sequencing in 53 ACF from patients with sporadic colorectal carcinomas and familial adenomatous polyposis, in 18 sporadic HPs from patients with resected colorectal cancer, and in 70 HPs, 4 serrated adenomas, 3 admixed hyperplastic-adenomatous polyps, 10 tubular adenomas, and 6 carcinomas from 17 patients with multiple/large HPs and/or hyperplastic polyposis. BRAF mutation status was compared with clinicopathological features and other genetic alterations by marginal logistic regression. BRAF mutation was present in only 2% of ACF and 6% of sporadic HPs. In contrast, BRAF mutation was present in 43% of HPs (P = 0.01 versus sporadic HPs), 75% of serrated adenomas, 33% of admixed hyperplastic-adenomatous polyps, 30% of tubular adenomas, and 33% of carcinomas from patients with multiple/large HPs and/or hyperplastic polyposis. BRAF mutation status in patients with multiple/large HPs and/or hyperplastic polyposis correlated with HPs from the same patient (odds ratio, 5.8; P = 0.0002) but associated with younger age (odds ratio, 0.83; P = 0.006 compared to older age), with a large HP (odds ratio, 22.5; P = 0.01 compared with patients with multiple HPs), with location of HPs in the right colon (odds ratio, 3.0; P = 0.03), and with methylation of the p16 gene and the MINT31 locus [odds ratio, 12.2 (P = 0.0001) and 4.4 (P = 0.02), respectively]. Our study shows that BRAF mutation status is heterogeneous among patients with multiple/large HPs and/or hyperplastic polyposis, suggesting differences in pathogenesis of HPs that indicate subsets within this phenotype.

Cell turnover of serrated adenomas

Serrated adenomas of the colon are characterized by epithelial neoplasia combining the architectural features of hyperplastic polyps and the cytological features of adenomas. Cell turnover, which is related to the malignant potential of these polyps, has not been thoroughly investigated. The aim of this study was to investigate epithelial cell proliferation, apoptosis, and oncoprotein expression in serrated adenomas. Twenty-five hyperplastic polyps, 25 serrated adenomas, and 25 tubulovillous adenomas resected from the colons of 75 patients were studied by immunohistochemical staining using monoclonal antibodies against MIB-1, Bcl-2, Bax, p53, and the TUNEL method for the detection of apoptosis. In serrated adenomas, the proliferation rate was significantly lower than in tubulovillous adenomas in both the lower and the upper parts of the crypts, and higher than that of hyperplastic polyps. Apoptosis was also significantly lower in serrated than in tubulovillous adenomas, but higher than in hyperplastic polyps. p53 oncoprotein expression was significantly greater in both serrated and tubulovillous adenomas than in hyperplastic polyps. bcl-2 protein expression was higher only in tubulovillous adenomas. Bax index was significantly different between tubullovillous and serrated adenomas, but the lowest values were observed in hyperplastic polyps. Serrated adenomas are highly proliferative polyps. They should be considered a biologically different entity from hyperplastic polyps. The intermediate features between serrated adenomas, hyperplastic polyps, and tubulovillous adenomas using the antibodies analysed in this study could have implications for the rate or the mechanism of development of malignancy in this type of polyp.

The risk of metachronous neoplasia in patients with serrated adenoma

Serrated adenomas are the precursors of at least 5.8% of colorectal cancers; otherwise little is known of their clinical significance in comparison with conventional adenomas and hyperplastic polyps. We compared the risk of metachronous lesions in colorectal serrated adenomas, conventional adenomas, and hyperplastic polyps. A consecutive series of patients with colorectal polyps first diagnosed from January 1978 to December 1982 and follow-up specimens to the end of 2000 was reviewed, and 239 polyps fulfilling the selection criteria were chosen as index polyps. The type of polyp seen in follow-up correlated significantly with the type of the initial lesion. Serrated adenomas were estimated to grow faster than conventional adenomas, but the incidence of colorectal cancer did not differ significantly between serrated (2/38 [5%]) and conventional adenomas (2.2%). The results indicate that serrated adenomas are lesions with a significant risk of metachronous serrated adenomas and the development of cancer. We emphasize the need for the proper recognition and management of serrated adenomas.

BRAF and KRAS Mutations in hyperplastic polyps and serrated adenomas of the colorectum: relationship to histology and CpG island methylation status

The aim of this study was to test the hypothesis that mutations of the oncogenes BRAF or KRAS are early events in the putative serrated polyp neoplasia pathway and more advanced pathology is associated with acquired mutator and suppressor gene inactivation by CpG island methylation of promoter regions. We assayed 79 sporadic hyperplastic polyps (HPs) classified according to the schema of Torlakovic et al and 25 serrated adenomas (SAs) for BRAF and KRAS mutations and related the findings to histologic characteristics and CpG island methylation phenotype (CIMP). Mutations at exon 15, codon 599, of BRAF were assayed using an allele-specific PCR (AS-PCR) technique and confirmed in a sample of AS-PCR- positive cases by direct sequencing of exon 15. AS-PCR-negative HPs and SAs were also sequenced on exon 15 and exon 11 to detect additional mutations. PCR-RFLP was used to assay KRAS codon 12 and 13 mutations, and these mutations were further validated by direct sequencing of the KRAS gene. BRAF599 mutations were identified in a total of 55 HPs (69.6%) and KRAS mutations in a total of 13 (16.5%). BRAF599 mutations occurred with similar frequencies among microvesicular serrated polyp (76.3%) and serrated polyp with abnormal proliferation (82.1%) subtypes but less frequently in goblet cell serrated polyps (23.1%). Conversely, KRAS mutations were most frequent in goblet cell serrated polyp (46.2%) and less frequent in microvesicular serrated polyp (13.2%) and serrated polyp with abnormal proliferation (7.1%). BRAF599 and KRAS mutations were present in 15 (60.0%) and 7 (28.0%) of SAs, respectively. BRAF 599 mutation and KRAS were mutually exclusive findings in the polyps studied and one or the other occurred in 68 of 79 (86.1%) HPs and 22 of 25 (88.0%) SAs. CpG island methylation involving 2 or more genes (CIMP-H) was present in 80.0% of SAs, 75% serrated polyp with abnormal proliferations, 47.4% of microvesicular serrated polyps, and 15.4% of goblet cell serrated polyps. SAs were significantly more likely to be CIMP-H than HPs (odds ratio 3.7; 95% confidence interval, 1.27-10.86; P = 0.017). A similar high frequency of KRAS or BRAF mutations across the histologic spectrum of the serrated polyps assayed suggests that these are early events in the serrated polyp neoplasia pathway. In contrast, the association of higher levels of CpG island methylation with more advanced histologic changes suggests that CpG island methylation plays a role in serrated polyp progression toward colorectal carcinoma.

Distinct secreted Frizzled receptor protein 1 staining pattern in patients with hyperplastic polyposis coli syndrome

CONTEXT

Patients with hyperplastic polyposis coli syndrome are thought to harbor precursor lesions of a proposed hyperplasia-carcinoma pathway in colorectal cancer, but morphologic recognition of such lesions remains difficult. Hypermethylation of the secreted Frizzled receptor protein 1 gene on chromosome 8p12 is one of the earliest molecular alterations in colorectal carcinogenesis, potentially disrupting the Wnt signaling cascade of cellular growth control.

OBJECTIVE

To determine if hyperplastic polyps from patients with hyperplastic polyposis coli syndrome show a distinct immunohistochemical expression pattern for mismatch repair proteins and secreted Frizzled receptor protein 1 compared to their sporadic counterparts.

DESIGN

Immunohistochemical studies (secreted Frizzled receptor protein 1, 3 mismatch repair proteins, and p53) were performed on 23 hyperplastic polyps, 6 synchronous colon cancers, and normal colonic mucosa from 6 patients with hyperplastic polyposis coli syndrome and were compared with studies of sporadic hyperplastic polyps obtained from 13 matched control subjects.

RESULTS

The staining pattern for the mismatch repair proteins MLH-1, MSH-2, and MSH-6 did not differ between sporadic and syndromic hyperplastic polyps. In contrast, 52% of syndromic hyperplastic polyps showed a reproducible and distinct staining pattern for secreted Frizzled receptor protein 1 that was not seen in control specimens and that was associated with larger polyp size (P =.002) and location in the proximal colon (P =.01).

CONCLUSIONS

Some hyperplastic polyps from patients with hyperplastic polyposis coli syndrome show a secreted Frizzled receptor protein 1 immunophenotype that could indicate alterations of cellular growth control. These findings may help identify precursor lesions in the proposed hyperplasia-carcinoma pathway of colorectal carcinogenesis.

Progressive methylation during the serrated neoplasia pathway of the colorectum

Serrated adenoma is a recently described entity characterized by having combined architectural features of hyperplastic polyps and classical adenoma. To understand the role of gene regulation in the progression of the serrated neoplasia pathway, we examined the methylation profiles of the promoter regions of 19 genes, DNA ploidy, and mutator phenotype status. In all, 40 sporadic, classical serrated adenomas were pathologically reviewed and divided into four pathologic groups according to their histologic grades. Methylation-specific PCR was performed using primers for p16, hMLH1, RASSF1A, APC, HIC-1, DAPK, MGMT, SLC5A8, RB1, H-Cadherin, E-Cadherin, TIMP3, PTEN, THBS1, LKB1, p14, p15, FHIT, and VHL. Dual flow-cytometric analyses using cytokeratin and DAPI and MSI studies using BAT26 were also performed. Methylation was observed in 2.5-82.5% (mean 33.9%) of the CpG islands in the promoter regions of 16 genes. The tumors with higher histologic grades, including carcinomas, showed more extensive methylation compared to those with lower grades, and serrated adenomas in the right colon showed more frequent methylation than those in the left (P<0.05). Tumor-specific promoter methylation of SLC5A8 was observed in 33 (82.5%) of the serrated adenomas. Aneuploidization with near-diploid DNA indices was detected in four out of 28 cases examined (14.3%); two were low-grade serrated adenomas and two were carcinomas in the left colon. The high mutator phenotype was not observed in any of the cases examined. Our results indicate that: (1) aberrant, widespread methylation of CpG islands increases with the histological progression of serrated adenomas; (2) methylation of SLC5A8 is an early event; and (3) additional methylation of the p16, p14, MGMT, TIMP3, and FHIT genes are important tumorigenic steps in the serrated neoplasia pathway.

Support for hMLH1 and MGMT silencing as a mechanism of tumorigenesis in the hyperplastic–adenoma-carcinoma (serrated) carcinogenic pathway in the colon

BACKGROUND

Down-regulation of DNA repair genes has been proposed as an important mechanism of tumorigenesis in some colon cancers. This mechanism has also recently been implicated in the newly postulated hyperplastic polyp-serrated adenoma-carcinoma ("serrated") pathway of carcinogenesis, although this has never been investigated thoroughly. The aim of this study was to evaluate hMLH1, hMSH2, MGMT, as well as MIB-1, p53, and beta-catenin immunoexpression in an uncommon cohort of mixed colonic polyps that contain a combination of hyperplastic and adenomatous features (n = 21), and in some (n = 7), carcinoma as well.

DESIGN

The clinical, pathological, and immunophenotypic (hMLH1, hMSH2, MGMT, MIB-1, p53, and beta-catenin) properties of 28 mixed hyperplastic and adenomatous polyps of the colon (7 of which also contained carcinoma within the same lesion) were evaluated for the above immunopeptides in each of the different morphologic areas of the polyps, and the results were compared to traditional hyperplastic polyps, serrated adenomas, and conventional (nonserrated) adenomas.

RESULTS

Clinically, most mixed polyps with carcinoma occurred in the ascending colon (86%), and pathologically, the adenomatous component of most mixed polyps was serrated (96%). Mixed polyps, particularly those with carcinoma, showed loss of hMLH1 (33%), MGMT (37%), and even hMSH2 (11%) with significantly higher frequency compared to hyperplastic polyps, conventional adenomas, and serrated adenomas. More specifically, loss of hMLH1 and MGMT were more frequent in epithelium of higher neoplastic grade in mixed polyps. However, hMSH2 loss was only present in the adenoma component and never in the hyperplastic or carcinomatous areas of these polyps. Defects in MIB-1 proliferation indices and p53 were not significantly different among the same epithelial components in each of the polyp groups. However, conventional adenomas showed significantly higher rates of nuclear beta -catenin staining (100%) in comparison to the adenomatous component of mixed polyps (60%).

CONCLUSIONS

Loss of hMLH1 and MGMT play a prominent role in the serrated pathway of carcinogenesis in the colon.

Hyperplastic polyps and serrated adenomas: colonoscopic surveillance?

Hyperplastic polyps are not thought to carry a malignant potential. They are, therefore, not regularly screened by the majority of clinicians. We present two case reports of serrated adenomas that add to a small but expanding body of clinical and histological evidence that suggests a hyperplastic to neoplastic pathway. Regular colonoscopic surveillance may be indicated in at least some cases of hyperplastic polyposis

Hyperplastic polyposis and the risk of colorectal cancer

PURPOSE

Hyperplastic polyps are usually considered to be an innocent finding with little or no potential to progress to colorectal cancer. However, recent literature suggests that some of these polyps may be morphologically and genetically distinct and lead to microsatellite unstable colorectal cancers. The purpose of this study was to define the cancer risk associated with hyperplastic polyposis.

METHODS

All patients with hyperplastic polyposis diagnosed by a single colorectal surgeon at a university hospital were followed prospectively. The diagnosis of hyperplastic polyposis was made by the presence of more than 20 hyperplastic polyps distributed throughout the colon and/or a hyperplastic polyp at least 1 cm in size in diameter in the right colon. Patient demographics, family history, size, location, and distribution of polyps and the development of colorectal cancer were noted.

RESULTS

Thirteen patients who met the criteria for hyperplastic polyposis were identified and followed prospectively. All of these patients had at least 30 polyps distributed throughout the colon, often > 100. Nine of 13 also had a hyperplastic polyp at least 1 cm in size, usually in the right colon. Of particular note, 7 of 13 patients (54 percent) were diagnosed with colorectal cancer during the study period. Four had cancer on initial diagnosis and three patients developed cancer despite frequent colonoscopic surveillance. Five of seven colorectal cancers were located in the right colon.

CONCLUSIONS

Patients with hyperplastic polyposis are at high risk for colorectal cancer. Failure to identify this subset of patients could have dire consequences.

Molecular differences between sporadic serrated and conventional colorectal adenomas

PURPOSE

The purpose is to compare the molecular characteristics of serrated adenomas (SAs) with those of conventional adenomas (CADs) and hyperplastic polyps (HPs).

EXPERIMENTAL DESIGN

We evaluated the proliferative activity and molecular alterations in 47 SAs (25 pure-type and 22 mixed-type), 71 CADs, and 23 HPs.

RESULTS

The proliferative activity of SAs, as evaluated by Ki-67 expression, was intermediate between CADs and HPs. There was no significant difference in the incidence of KRAS or p53 mutations between the three histological groups. In the microsatellite instability (MSI) analysis, 21% of SAs (9 of 43) showed MSI at two or more loci (MSI-H); corresponding values were 5% of CADs (3 of 64) and 8% of HPs (1 of 13; SAs versus CADs, P = 0.0125). MSI-H was more likely to be found in pure-type SAs (36%; 8 of 22) than in mixed-type SAs (5%; 1 of 21; P = 0.0212). Loss of hMLH-1 expression was found in 8 of 9 SAs with MSI-H. The incidence of BRAF or KRAS mutations was 36 and 15% of SAs, respectively; the combined incidence of BRAF and KRAS mutations occurred in 49% of SAs. However, there was no significant difference in the incidence of BRAF or KRAS mutations between SAs with and without MSI-H.

CONCLUSIONS

Genetic instability is more frequently implicated in the tumorigenesis of SAs, especially pure-type SAs, than in that of CADs. In contrast, activation of the Ras/Raf/MEK/MAP kinase cascade by BRAF or KRAS mutation, independently of the genetic instability, may be associated with the progression of about half of SAs.

Proximal versus distal hyperplastic polyps of the colorectum: different lesions or a biological spectrum?

BACKGROUND

Because of their suggested link with microsatellite instability high colorectal cancers, right sided hyperplastic polyps (HPs) may differ from their distally located counterparts. This is highlighted by the recognition of a variant HP, termed sessile serrated adenoma (SSA), which predominates in the proximal colon. HPs displaying the morphological features now associated with SSAs have been shown to have altered expression of "cancer associated" markers, but no studies have investigated whether this is dependent on anatomical location of the polyps.

AIMS

To evaluate morphological and functional features in right versus left sided HPs from patients without colorectal cancer with the aim of identifying distinguishing characteristics.

METHODS

HPs originating in the proximal and distal colorectum were histochemically and immunohistochemically stained to evaluate a panel of markers related to proliferation and differentiation. In addition, a series of morphological features was evaluated for each polyp.

RESULTS

Crypt serration, crypt dilatation, and horizontal crypt growth were more common among HPs from the right side, whereas histochemical factors including mucin changes, global methylation status, and expression of carcinoembryonic antigen were not significantly different. An age disparity was also seen between patients with right versus left sided lesions, with patients with right sided lesions being an average of more than 10 years younger than those with left sided lesions.

CONCLUSIONS

These findings suggest that right and left sided HPs differ mainly in terms of growth regulation rather than cellular differentiation, implying that these lesions belong to a continuous spectrum of serrated polyps that differ quantitatively rather than qualitatively.

My approach to serrated polyps of the colorectum

Hyperplastic polyps of the colorectum are heterogeneous lesions, a subset of which is now regarded as the precursor of colorectal cancer with DNA microsatellite instability. Some authors have distinguished this subset from classic hyperplastic polyps and have introduced the term "sessile serrated adenoma". These lesions frequently show BRAF mutation and DNA methylation. This personal perspective reviews recent insights into serrated polyps and highlights the importance of inhibition of apoptosis as a unifying mechanism. It is estimated that around 25 hyperplastic polyps of the proximal colon exist for every colorectal cancer with DNA microsatellite instability. Further research is required to identify additional risk factors for hyperplastic polyps other than anatomical location. These may be demographic, clinical, morphological, or molecular. It is not recommended that the term sessile serrated adenoma be used in routine reporting, but it is desirable that potentially aggressive hyperplastic polyps should be identified for the purposes of both clinical practice and research.

Hyperplastic (serrated) polyps of the colorectum: relationship of CpG island methylator phenotype and K-ras mutation to location and histologic subtype

We investigated the frequency of promoter region CpG island methylation (CIM) of hMLH1, MGMT, MINT1, MINT2, and p16 and K-ras mutations in a total of 79 hyperplastic (serrated) polyps (HPs) from 75 patients and correlated the molecular profiles to polyp location in the colorectum, histologic variation, and other factors. Methylation-specific PCR (MS-PCR) was used to assay CIM status. HPs that showed CIM of one or more or two or more of the genes assayed were classified as CpG island methylator phenotype (CIMP) and CIMP-high (CIMP-H), respectively. PCR restriction fragment length polymorphism was used to assay K-ras codon 12 and 13 mutations. Logistic regression indicated a statistically significant trend for increasing odds for CIMP (P = 0.002) and CIMP-H (P < 0.001) according to proximity to the cecum or distance from the rectum. Conversely, K-ras codon 12 mutation was present in 13 of 40 (32.5%) distally located HPs compared with 2 of 39 (5.1%) proximal HPs (P = 0.006). Histologic subtype distribution varied by proximal and distal locations. Frequency of CIMP in serrated polyps with abnormal proliferation (SPAPs), differed significantly from goblet cell serrated polyps (GCSPs) (24 of 26, 92.3% vs. 6 of 13, 46.2%) (P = 0.003) and microvesicular serrated polyps (MVSPs) (26 of 38, 68.4%) (P = 0.03). Frequency of K-ras mutation in GCSPs (7 of 13, 54%) differed from that of MVSPs (6 of 38, 16%) (P = 0.01) and SPAPs (2 of 26, 8%) (P = 0.003). Location in the colorectum and histologic subtype were major determinants of the molecular profile of HPs. The molecular findings of CIMP and K-ras mutations appear to encompass most if not all HPs; CIMP profiles suggest that SPAP is the most advanced morphologic variant. We postulate that MVSP and GCSP may be precursor lesions that, if proximally located or larger, can progress to SPAP. Frequent K-ras mutations and infrequent CIMP distinguish the distal GCSP variant.

Serrated colorectal polyps: emerging evidence suggests the need for a reappraisal

A set of polyps that superficially resemble ordinary hyperplastic polyps of the left colon but with divergent morphology and probably divergent biology has become apparent. Such polyps differ from typical small left-sided hyperplasic polyps by the large sizes they may attain, their tendency to be right-sided, and subtle morphologic differences. It is important to separate these polyps, which some have called "sessile serrated polyps" from hyperplastic polyps as they are associated with progression to carcinoma probably through mismatch repair defects.

Primary epithelial neoplasms and other epithelial lesions of the appendix (excluding carcinoid tumors)

Epithelial tumors of the appendix range from low-grade mucosal-based tumors which, when confined to the appendix, have an excellent prognosis but, once outside the appendix, have a fair prognosis and often a prolonged disease course, to high grade invasive carcinomas that are rapidly fatal. Low grade mucinous neoplasms may rupture and spread to the peritoneum as pseudomyxoma peritonei, and the nomenclature of these tumors has been the subject of considerable disagreement among pathologists; the designation "low grade appendiceal mucinous neoplasm" has recently been proposed for reasons discussed herein. Demonstrating rupture of these neoplasms may require particularly diligent gross and microscopic evaluation as the rupture site often heals over leaving only subtle evidence of its presence. Invasive adenocarcinomas are often mucinous and may also spread to the peritoneum. Against this backdrop, the clinical and pathologic features of low grade appendiceal mucinous neoplasms and mucinous adenocarcinomas, as well as other types such as typical colorectal type and signet-ring cell type, are reviewed. In addition, emerging entities, serrated polyps and serrated adenomas, whose significance is only beginning to be understood, are considered. Retention cysts, hyperplastic polyps, and diffuse mucosal hyperplasia, although not necessarily neoplastic, are reviewed here as they may enter into the differential diagnosis of appendiceal mucinous neoplasms.