Significance of Micromorphological Characteristics and Expression of Intermediate Filament Proteins CK7 and CK20 in the Differential Diagnosis of Serrated Lesions of the Colorectum

Serrated lesions in the colorectum include all epithelial neoplastic lesions, which show a sawtooth-like morphology in the epithelial crypts. Classification systems nosologically divide colon serrated polyps into three different categories, primarily emphasizing their micromorphological growth pattern and cytodifferentiation: (1) hyperplastic polyps, (2) sessile serrated adenomas/polyps and (3) traditional serrated adenomas. Overall, 109 patients with serrated lesions of the colon, who underwent endoscopic or surgical polypectomy/tumorectomy during one or multiple endoscopic or surgical interventions, over a four-year period, were analyzed. The average age of patients was 62.8 ± 11.6 years. The frequency of serrated lesions of the colon in male patients was 2.4 times higher than in females (70.6% vs. 29.4%). All sessile serrated lesions without dysplasia were positive for CK7 and statistically significant compared to other serrated lesions, if this positivity was present in the complete crypt (p = 0.005). CK20 positivity, which is limited to the upper half of the crypt, is a special feature of hyperplastic polyps compared to other serrated lesions, which is statistically significant (p = 0.0078). Whereas, CK20 positivity of complete crypts is a statistically significant feature of traditional serrated adenomas (p < 0.01). Differences in the expression pattern of cytokeratin 7 and 20 in different serrated lesions may indicate different pathways of colorectal carcinogenesis, and be diagnostically and prognostically useful.

Mucins in neoplastic spectrum of colorectal polyps: can they provide predictions?

Background

The significance of expression of different mucins in succession of malignant transformation of colorectal polyps is not determined yet. The aim of the present study was to determine the pattern of expression of MUC1, MUC2, MUC5AC and MUC6 in colorectal polyps and to evaluate the applicability of using mucin expression in predicting the extent of malignant transformation in colorectal polyps.

Methods

A total of 454 polyp specimens comprising 36 hyperplastic polyps, 15 serrated adenomas, 258 tubular adenomas, 114 tubulovillous adenomas, and 31 villous adenomas were included in this study, and were immunostained for MUC1, MUC2, MUC5AC and MUC6 by using mucin specific antibodies.

Results

MUC1 and MUC6 were absent in all hyperplastic polyps and their expression was higher in serrated and traditional adenomas. Only 5 cases including 2 serrated adenomas, 1 tubulovillous adenoma, and 2 villous adenomas stained negative for MUC2. The highest expression of MUC5AC was observed in serrated adenomas followed by tubular adenomas. Binary logistic regression analysis indicated that positive staining for MUC1, and MUC6, and negative staining for MUC2 would increase the risk of invasion to mucosa or the muscularis mucosae in colorectal polyps. Ordinal regression analysis demonstrated a positive association between the level of staining for MUC1 and risk of being of high configuration/grade in colorectal polyps.

Conclusions

MUC1, MUC2, MUC5AC, and MUC6 have the potential to be used as predictors of malignant transformation and invasion to mucosa or the muscularis mucosae in colorectal polyps. The most reliable predictions can be achieved by determining the level of expression of MUC1.

Gene profiling of colonic serrated adenomas by using oligonucleotide microarray

PURPOSE

The serrated pathway has been proposed as an important concept explaining the colorectal carcinogenesis. However, the key molecules of the serrated pathway which contribute to the formation of serrated polyp are still poorly understood. To elucidate the molecular genetic basis of the serrated pathway, we performed an initial oligonucleotide microarray to analyze the gene expression pattern of patients with colonic serrated adenomas.

METHODS

Oligonucleotide microarrays containing 3,096 genes were used to compare individual gene profiles of serrated adenoma samples (n = 5) and normal mucosal samples obtained from colon in patients by colonoscopy. Three genes were further investigated by means of quantitative reverse transcription polymerase chain reaction (RT-PCR) for validation. The Significance Analysis of Microarray (SAM) package method was used to identify differentially expressed genes.

RESULTS

Compared with normal colonic mucosa tissue, 73 genes were upregulated at least twofold, and 51 genes were downregulated by at least 50% in serrated polyp samples (approximately 3.6% of genes evaluated) with a p-value of less than 0.05. Moreover, some of the gene expression patterns observed were similar to those of previously reported in colorectal cancer, suggesting reinforcement of tendency to malignancy. Three genes (TNFRSF10A, BENE, RARA) with strongly significant expression intensities in the oligonucleotide microarray results were validated by quantitative RT-PCR. TNFRSF10A had upregulated expression patterns while BENE, RARA had downregulated expression pattern.

CONCLUSION

Although our report presents only preliminary results, we think they provide important data regarding serrated adenomas not only to better define the precise mechanism of genetic changes involved as the main member in serrated pathway of colorectal carcinogenesis but also to yield practical information for identifying optimized diagnostic modalities.

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.

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.

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.

A prospective study of the clinical, genetic, screening, and pathologic features of a family with hereditary mixed polyposis syndrome

In 1997, hereditary mixed polyposis syndrome (HMPS) was described in an Ashkenazi pedigree having colorectal polyps with mixed histology and risk for colorectal cancer (CRC). The mutation is now localized to 15q13-14. Since 1980, compliant relatives of an HMPS family were seen annually, tested genetically, and had colonoscopy offered every 1 to 2 yr from age 20 yr. The Israeli pedigree has 37 members (17 clinically affected by CRC or polyps), and seven of 13 available relatives entered our screening program. The others, followed-up elsewhere, provided clinical information. Half of our screened group had rectal bleeding; others were asymptomatic. Colonoscopy, performed a mean of four times, identified polyps in all seven patients (mean age 28 yr). Polyps were removed and included juvenile adenomas, mixed juvenile adenomas, hyperplastic polyps, mixed hyperplastic adenomas, serrated adenomas, and tubular adenomas. None of our screened patients developed CRC or extracolonic neoplasia. Linkage analysis localized their mutation to 15q13-14. This high-penetrance founder mutation so far is described only in Ashkenazim. The CRC pathway seems to be through juvenile and hyperplastic polyps. Mutation identification will aid screening for and evaluation of HMPS prevalence in Jewish and non-Jewish populations. Meanwhile, a cancer pedigree and correct classification of polyps will identify HMPS families. They require early and frequent colonoscopy, polypectomy, and elective extensive colectomy when indicated.

Histopathological and clinical evaluation of serrated adenomas of the colon and rectum

We evaluated the diagnostic utility of the histological characteristics ascribed in the literature to serrated adenomas and developed a practical working model to allow their reliable identification. We also documented the frequency and location of serrated adenomas identified in an unselected series of individuals undergoing colonoscopic evaluation, as well as the clinical characteristics of those individuals. One hundred forty consecutive individuals (prospective polyp data set; 97 male, 43 female; age mean: 63.3 y; age range: 29-98 y) with 255 polyps were identified from 919 individuals undergoing colonoscopy. Further polyps previously removed from these individuals were added for the purpose of histological assessment (extended polyp data set, n = 380). All polyps were assessed by two independent examiners for eight selected architectural and cytological features of serrated adenomas. In the prospective polyp data set, 56 patients had 72 hyperplastic polyps, 7 had 9 serrated adenomas, 3 had 4 admixed polyps, and 98 had 170 conventional adenomas. There was no difference in the age, sex, or cancer association of the seven patients with serrated adenomas when compared with the case of other individuals with polyps. The prevalence of serrated adenomas was 9/919 (1%) in our population, with an average size of 5.8 mm. When assessing serrated adenomas histologically, the combination of nuclear dysplasia and serration of >/=20% of crypts provided the most accurate model for detection of these lesions (sensitivity 100%, specificity 97%). Other criteria provided supportive evidence but did not increase the diagnostic yield. The optimum model for the histological identification of the serrated adenoma includes the presence of a serrated architecture in >/=20% of crypts in association with surface epithelial dysplasia.

Emerging concepts in colorectal neoplasia

An understanding of the mechanisms that explain the initiation and early evolution of colorectal cancer should facilitate the development of new approaches to effective prevention and intervention. This review highlights deficiencies in the current model for colorectal neoplasia in which APC mutation is placed at the point of initiation. Other genes implicated in the regulation of apoptosis and DNA repair may underlie the early development of colorectal cancer. Inactivation of these genes may occur not by mutation or loss but through silencing mediated by methylation of the gene's promoter region. hMLH1 and MGMT are examples of DNA repair genes that are silenced by methylation. Loss of expression of hMLH1 and MGMT protein has been demonstrated immunohistochemically in serrated polyps. Multiple lines of evidence point to a "serrated" pathway of neoplasia that is driven by inhibition of apoptosis and the subsequent inactivation of DNA repair genes by promoter methylation. The earliest lesions in this pathway are aberrant crypt foci (ACF). These may develop into hyperplastic polyps or transform while still of microscopic size into admixed polyps, serrated adenomas, or traditional adenomas. Cancers developing from these lesions may show high- or low-level microsatellite instability (MSI-H and MSI-L, respectively) or may be microsatellite stable (MSS). The suggested clinical model for this alternative pathway is the condition hyperplastic polyposis. If colorectal cancer is a heterogeneous disease comprising discrete subsets that evolve through different pathways, it is evident that these subsets will need to be studied individually in the future.