Hyperplastic polyps and DNA microsatellite unstable cancers of the colorectum

The relation of magnesium and calcium intakes and a genetic polymorphism in the magnesium transporter to colorectal neoplasia risk

BACKGROUND

Mean magnesium intake in the US population does not differ from that in East Asian populations with traditionally low risks of colorectal cancer and other chronic diseases, but the ratio of calcium to magnesium (Ca:Mg) intake is much higher in the US population. Transient receptor potential melastatin 7 (TRPM7) is a newly found gene essential to magnesium absorption and homeostasis.

OBJECTIVE

We aimed to test whether the association of colorectal polyps with intake of calcium, magnesium, or both and Thr1482Ile polymorphism in the TRPM7 gene is modified by the Ca:Mg intake.

DESIGN

Included in the study were a total of 688 adenoma cases, 210 hyperplastic polyp cases, and 1306 polyp-free controls from the Tennessee Colorectal Polyp Study.

RESULTS

We found that total magnesium consumption was linked to a significantly lower risk of colorectal adenoma, particularly in those subjects with a low Ca:Mg intake. An inverse association trend was found for hyperplastic polyps. We also found that the common Thr1482Ile polymorphism was associated with an elevated risk of both adenomatous and hyperplastic polyps. Moreover, this polymorphism significantly interacted with the Ca:Mg intake in relation to both adenomatous and hyperplastic polyps. The subjects who carried >or=1 1482Ile allele and who consumed diets with a high Ca:Mg intake were at a higher risk of adenoma (odds ratio: 1.60; 95% CI: 1.12, 2.29) and hyperplastic polyps (odds ratio: 1.85; 95% CI: 1.09, 3.14) than were the subjects who did not carry the polymorphism.

CONCLUSION

These findings, if confirmed, may provide a new avenue for the personalized prevention of magnesium deficiency and, thus, colorectal cancer.

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.

Incorporation of somatic BRAF mutation testing into an algorithm for the investigation of hereditary non-polyposis colorectal cancer

Patients suspected on clinical grounds to have hereditary non-polyposis colorectal cancer (HNPCC) may be offered laboratory testing in order to confirm the diagnosis and to facilitate screening of pre-symptomatic family members. Tumours from an affected family member are usually pre-screened for microsatellite instability (MSI) and/or loss of immunohistochemical expression of mismatch repair (MMR) genes prior to germline MMR gene mutation testing. The efficiency of this triage process is compromised by the more frequent occurrence of sporadic colorectal cancer (CRC) showing high levels of MSI (MSI-H) due to epigenetic loss of MLH1 expression. Somatic BRAF mutations, most frequently V600E, have been described in a significant proportion of sporadic MSI-H CRC but not in HNPCC-associated cancers. BRAF mutation testing has therefore been proposed as a means to more definitively identify and exclude sporadic MSI-H CRC cases from germline MMR gene testing. However, the clinical validity and utility of this approach have not been previously evaluated in a familial cancer clinic setting. Testing for the V600E mutation was performed on MSI-H CRC samples from 68 individuals referred for laboratory investigation of suspected HNPCC. The V600E mutation was identified in 17 of 40 (42%) tumours showing loss of MLH1 protein expression by immunohistochemistry but in none of the 28 tumours that exhibited loss of MSH2 expression (P < 0.001). The assay was negative in all patients with an identified germline MMR gene mutation. Although biased by the fact that germline testing was not pursued beyond direct sequencing in many cases lacking a high clinical index of suspicion of HNPCC, BRAF V600E detection was therefore considered to be 100% specific and 48% sensitive in detecting sporadic MSI-H CRC amongst those cases showing loss of MLH1 protein expression, in a population of patients with MSI-H CRC and clinical features suggestive of HNPCC. Accordingly, we recommend the incorporation of BRAF V600E mutation testing into the laboratory algorithm for pre-screening patients with suspected HNPCC, whose CRCs show loss of expression of MLH1. In such tumours, the presence of a BRAF V600E mutation indicates the tumour is not related to HNPCC and that germline testing of MLH1 in that individual is not warranted. We also recommend that in families where the clinical suspicion of HNPCC is high, germline testing should not be performed on an individual whose CRC harbours a somatic BRAF mutation, as this may compromise identification of the familial mutation.

Rare CpG island methylator phenotype in ulcerative colitis-associated neoplasias

BACKGROUND & AIMS

We previously reported that a high degree of age-related methylation was found in both the dysplastic and nondysplastic mucosa of patients with ulcerative colitis (UC). Whether this translates into hypermethylation in UC-associated cancers (UC-Cs) is not known.

METHODS

We evaluated the methylation status of 11 genes (MINT1, 2, 31, hMLH1, p16, p14, MGMT, HPP1, SFRP1, ERalpha, and LINE-1) in 48 UC-Cs, 21 UC-associated dysplasias, and 69 sporadic colorectal cancers (S-CRCs) using a quantitative bisulfite pyrosequencing analysis.

RESULTS

Methylation levels in UC-Cs were lower than S-CRCs for all the genes except MGMT. A methylation index based on the average of Z-scores, for type C (cancer-specific genes: MINT1, MINT2, MINT31, hMLH1, p16, and p14) was -.97 in UC-Cs and .92 in S-CRCs (P = .009). That of type A (age-related genes: HPP1, SFRP1, and ERalpha) was -1.97 in UC-Cs and 1.24 in S-CRCs (P < .001). We observed a significant difference in the incidence of CpG island methylator phenotype between UC-Cs and S-CRCs (8 of 48 [17%] and 26 of 69 [38%]; P = .022). UC-associated dysplasias had significantly higher methylation of type A gene than UC-Cs (Z-score: .07 and -1.97, respectively; P < .001). By contrast, global DNA methylation measured using a LINE-1 assay was significantly higher in UC-Cs than in S-CRCs (58.2% vs 51.0%, P < .001).

CONCLUSIONS

DNA methylation alterations are uncommon in UC cancers. Given that both genetic and epigenetic changes are common in UC mucosa and dysplasias, we speculate that the genetic changes lead to a more aggressive clinical course than epigenetic changes.

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.

Microsatellite instability in interval colon cancers

BACKGROUND & AIMS

Colon cancers that develop after a complete colonoscopy may be the result of "failure of colonoscopy" or rapid tumor growth. Tumors that develop via the mismatch repair gene pathway demonstrate rapid tumor growth. The aim of this study was to determine if interval colon cancers were more likely than noninterval cancers to result from the loss of function of mismatch repair genes and hence demonstrate microsatellite instability (MSI).

METHODS

We searched our institution's cancer registry for interval cancers, defined as colon cancers that developed within 5 years of a complete colonoscopy. These were frequency matched in a 1:2 ratio by age and sex to patients with noninterval cancers (defined as colon cancers diagnosed on a patient's first recorded colonoscopy). Archived cancer specimens for all subjects were retrieved and tested for MSI.

RESULTS

Of the 993 colon cancers diagnosed during the study period, 51 (5.1%) were identified as an interval cancer, and 112 subjects with noninterval cancer served as a comparison group. Study subjects were almost all men. MSI was found in 30.4% of interval cancers compared with 10.3% of noninterval cancers (P = .003). After adjusting for age, interval cancers were 3.7 times more likely to show MSI than noninterval cancers (95% confidence interval, 1.5-9.1). This association was strongest for tumors located in the distal colon (odds ratio, 17.5; P = .008). No difference in TNM stage at diagnosis, histologic type or grade, or 5-year survival was found between groups.

CONCLUSIONS

Interval colon cancers were almost 4 times as likely as noninterval colon cancers to be associated with mismatch repair gene dysfunction.

Risk of microsatellite-unstable colorectal cancer is associated jointly with smoking and nonsteroidal anti-inflammatory drug use

Smoking has been consistently associated with an increased risk of colorectal adenomas and hyperplastic polyps as well as colorectal cancer. Conversely, nonsteroidal anti-inflammatory drugs (NSAID) have been associated with reduced colorectal cancer risk. We conducted a population-based case-control study to evaluate the joint association between smoking and regular NSAID use with colorectal cancer risk; we also examined these associations stratified by tumor microsatellite instability (MSI). We analyzed 1,792 incident colorectal cancer cases and 1,501 population controls in the Seattle, Washington area from 1998-2002. MSI, defined as MSI high (MSI-H) or MSI-low/microsatellite stable (MSI-L/MSS), was assessed in tumors of 1,202 cases. Compared with nonsmokers, colorectal cancer risk was modestly increased among individuals who had ever smoked. Current NSAID use was associated with a 30% lower risk compared with nonusers. There was a statistically significant interaction between smoking duration and use of NSAIDs (P(interaction) = 0.05): relative to current NSAID users who never smoked, individuals who had both smoked for >40 years and had never used NSAIDs were at the highest risk for colorectal cancer (adjusted odds ratio, 2.8; 95% confidence intervals, 1.8-4.1). Compared with nonsmokers, there was a stronger association within MSI-H tumors with current smoking than there was within MSI-L/MSS tumors. Smokers of long duration were at elevated risk of MSI-H tumors even with NSAID use. The risk of MSI-L/MSS tumors was not elevated among long-duration smokers with long exposure to NSAIDs but was elevated among long-duration smokers who had never used NSAIDs. There seems to be a synergistic inverse association (implying protection) against colorectal cancer overall as a result of NSAID use and nonsmoking, but risk of MSI-H colorectal cancer remains elevated among smokers even when they have a history of NSAID use.

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.

Changing trends in the incidence, stage, survival, and screen-detection of colorectal cancer: a population-based study

BACKGROUND & AIMS

Colorectal cancer (CRC) screening has been advocated increasingly during the past 2 decades, but there is little direct evidence that it has affected cancer incidence or presentation at the population level. This study assessed concurrent trends in CRC incidence, presentation, survival, mortality, and polypectomies in Olmsted County, Minnesota.

METHODS

Longitudinal observational study was conducted of all Olmsted County residents with colorectal adenocarcinoma first diagnosed in 1980-1999.

RESULTS

Altogether, 889 invasive CRCs were diagnosed among Olmsted County residents from 1980 through 1999. Annual age- and sex-adjusted CRC incidence rates decreased significantly during this period (P = .02) with a 23% decline from 60 per 100,000 in 1980-1984 to 46 per 100,000 in 1995-1999. This was primarily accounted for by a 40% reduction in left-sided CRC (P < .001). The incidence of right-sided CRC remained unchanged, but the proportion of right-sided CRC increased from 46% to 58%. Cancer stage shifted downward, and survival improved over time. The overall proportion of screen-detected CRC rose from 8% to 17%. Annual adjusted adenomatous polypectomy rates increased dramatically from 86 to 320 per 100,000 (P < .001).

CONCLUSIONS

The incidence of CRC in Olmsted County has declined in recent years. An impact of screening is suggested by the observed upward trend in screen-detected cases, a favorable stage shift, and a concurrent rise in polypectomy rates. However, the incidence of right-sided cancer remains unaltered and might be less affected by historically used screening interventions. Most CRCs still present symptomatically, and more effective population screening is needed.

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.

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.

Defective mismatch repair in the pathogenesis of low-grade appendiceal mucinous neoplasms and adenocarcinomas

Defective DNA mismatch repair has been proposed as a second pathway for colonic carcinogenesis, particularly in tumors arising in the right colon. We investigated whether tumors arising in the appendix are associated with defective DNA mismatch repair using immunohistochemistry for mismatch repair enzymes hMLH-1, hMSH-2, hMSH-6, and hPMS-2. These immunoassays have been shown to be highly sensitive and specific for defective DNA mismatch repair in sporadic and familial adenocarcinomas. Sporadic adenocarcinomas with defective DNA mismatch repair essentially always show loss of hMLH-1, while loss of hMSH-2, hMSH-6, or hPMS-2 is almost always due to germline mutation. In all, 35 cases of appendiceal epithelial neoplasms were evaluated, comprising 18 low-grade appendiceal mucinous neoplasms confined to the appendix; eight low-grade appendiceal mucinous neoplasms with extra-appendiceal spread (five peritoneum and ovaries, two peritoneum, one ovaries only); and nine invasive adenocarcinomas (three with metastatic disease). All immunohistochemical slides were reviewed by two pathologists. One (11%) invasive adenocarcinoma showed absent expression of hMSH-2 and hMSH-6, but preserved hMLH-1 and hPMS-2 expression. This case was a 26-year-old female with a history of synovial sarcoma who presented with acute appendicitis and appendiceal perforation (median age for other invasive carcinomas, 62 years; range 38-76 years). The appendiceal tumor was a moderately differentiated, colonic-type adenocarcinoma without significant extracellular mucin or tumor-infiltrating lymphocytes. The remaining invasive carcinomas and low-grade appendiceal mucinous neoplasms demonstrated preserved expression of all mismatch repair enzymes, including the seven cases in which extra-appendiceal tumor was also evaluated. We conclude that defective DNA mismatch repair does not play a role in the pathogenesis of low-grade appendiceal mucinous neoplasms. Defective DNA mismatch was found in 11% of invasive carcinomas, likely due to a germline mutation. These findings suggest that sporadic appendiceal neoplasia rarely arises through the defective DNA mismatch repair (mutator) pathway.

HNPCC and sporadic MSI-H colorectal cancer: a review of the morphological similarities and differences

Morphological features may serve as diagnostically useful markers of colorectal cancer (CRC) with the microsatellite instability-high (MSI-H) phenotype. The most important of these are lymphocytic infiltration, mucin secretion and poor differentiation. These features are apparent in both sporadic MSI-H CRC and CRC occurring in the context of hereditary non-polyposis colorectal cancer (HNPCC). There is now strong evidence that that the two principal subtypes of MSI-H CRC evolve through different pathways. Sporadic MSI-H CRC orginate within serrated polyps with BRAF mutation and DNA methylation while CRC in HNPCC arise within conventional adenomas in which there is frequent mutation of APC or beta -catenin and/or K- ras. These early differences in pathogenesis translate into multiple morphological distinctions in the cancers developing through the two pathways. Lymphocytic infiltration, tumour budding (de-differentiation), and co-existing adenomas are more evident in HNPCC while mucin secretion, poor differentiation, tumour heterogeneity and glandular serration, and co-existing serrated polyps are more evident in sporadic MSI-H CRC. Sporadic MSI-H CRC are also characterized by cytoplasmic eosinophilia and nuclei that are large, round, vesicular and contain a prominent nucleolus while in HNPCC the cytological features recapitulate the basophilia and nuclear characteristics of conventional adenomas. In practice, lymphocytic infiltration is the most sensitive marker of MSI-H status in both sporadic CRC and HNPCC. The crucial distinction between HNPCC and sporadic MSI-H CRC should be achieved by means of all available data including family history, age at onset of malignancy and molecular features. There is increasing evidence that genetic factors may predispose to DNA methylation. This can result in familial clustering of MSI-H CRC in which the underlying mechanism is methylation of hMLH1 rather than germline mutation. Morphological features can assist is distinguishing such families from bona fide HNPCC families which they closely mimic.

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.

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.

Phenotypic alteration in malignant transformation of colonic villous tumours: with special reference to a comparison with tubular tumours

AIMS

To clarify the cellular differentiation of colorectal villous tumours in malignant transformation, compared with that of tubular tumours (tubular adenoma and adenocarcinoma arising in tubular adenoma).

METHODS AND RESULTS

Forty-nine cases of colorectal villous tumours [six cases of low-grade villous adenoma, 21 of high-grade villous adenoma (VA), nine of invasive carcinoma in villous adenoma (CIVA), and 13 of pure villous carcinoma (PVC)] and 46 cases of tubular tumours [14 cases of low-grade and 17 of high-grade tubular adenoma (TA), and 15 cases of carcinoma in tubular adenoma (CITA)] were selected for this study based on their expression patterns of CD10 (small intestinal brush border), MUC2 (intestinal goblet cell), and HGM (gastric foveolar epithelium). HGM was more frequently expressed in the adenomatous components of villous tumours (63%) than in those of tubular tumours (14%) (P < 0.05). CD10 expression of high-grade TAs (47%) and carcinomas arising in TA (60%) was significantly higher than that of villous tumours (0%) (P < 0.05).

CONCLUSIONS

There were significant differences in the phenotypic expression of adenoma and adenocarcinoma between villous and tubular tumours, respectively. Villous tumours have a pathway of malignant transformation different from that of tubular tumours. Because of biological differences, colorectal villous tumours should be distinguished from tubular neoplasia. The analysis of the phenotype of colorectal neoplasms is useful for the evaluation of tumour progression.

Relationship between MUC5AC and altered expression of MLH1 protein in mucinous and non-mucinous colorectal carcinomas

The main purpose of this study was to examine the expression of mucins and mismatch repair proteins in colorectal carcinomas. The immunohistochemical distribution of apomucins MUC2, MUC5AC, and the expression of MLH1 and MSH2 proteins were examined in 76 mucinous and 60 non-mucinous colorectal carcinomas. MUC2 was noted in all mucinous carcinomas, whereas MUC5AC was present in 41 cases only (54%). In non-mucinous carcinomas, MUC2 was expressed in 61.7% of the tumors; by contrast, MUC5AC was present in 20% of the cases. The expression level of apomucins was significantly different in mucinous and non-mucinous lesions (p<0.001). Twenty-seven (35.5%) of the mucinous carcinomas showed no MLH1 expression, whereas 11 (18.3%) of the non-mucinous tumors did. This difference was statistically significant (p<0.005). Altered expression of MSH2 protein was never observed. The lack of MLH1 expression was considerably more frequent in carcinomas with secretion of MUC5AC (p<0.005). Our study has demonstrated this close relationship by immunohistochemical methods. In summary, our data show: (1) differences in the expression of mucins between mucinous and non-mucinous tumors; (2) a high frequency of altered MLH1 protein expression (35.5%) in mucinous carcinomas; (3) a significant relationship between the presence of MUC5AC and the altered expression of MLH1 protein in colorectal carcinomas.

No major tumorigenic role for beta-catenin in serrated as opposed to conventional colorectal adenomas

Intracellular redistribution of beta-catenin through mutation of the adenomatous polyposis coli (APC) gene has been proposed as an early tumorigenic event in most colorectal tumours. In serrated adenoma (SA), a newly recognised subtype of colorectal adenoma, APC mutations are uncommon, and the contribution of beta-catenin to tumorigenesis remains unclear. We compared intracellular localisation of beta-catenin and presence of mutations in exon 3 of beta-catenin between 45 SAs, with 71 conventional adenomas (CADs), and eight carcinomas invading the submucosa (SCAs). Widespread or focal nuclear beta-catenin expression was demonstrated in 7% of SAs (three out of 45), 61% of CADs (43 out of 71), and 88% of SCAs (seven out of eight). Cytoplasmic immunostaining for beta-catenin was demonstrated in 16% of SAs (seven out of 45), 77% of CADs (55 out of 71), and 88% of SCAs (seven out of eight). No mutation in exon 3 of beta-catenin was found in SAs or SCAs, while 7% of CADs (five out of 71) had beta-catenin mutations. No nuclear or cytoplasmic expression of beta-catenin was observed in the hyperplastic or conventionally adenomatous epithelium of mixed-type SAs. These findings suggest that beta-catenin mutation is unlikely to contribute to the tumorigenesis in SA, and that intracellular localisation of beta-catenin may not be associated with an early event of the tumour progression in most SAs.

Proliferation kinetics and apoptosis of serrated adenoma of the colorectum

To elucidate the proliferation kinetics and cell loss by apoptosis of serrated adenoma (SA) of the colorectum, we performed Ki-67 immunohistochemistry and the terminal deoxynucleotidyl transferase (TdT)-mediated biotinylated deoxyuridine-triphosphate nick-end labeling (TUNEL) method for 24 SA, and compared the results to those of normal colonic mucosa (n = 15), hyperplastic polyp (HP) (n = 18) and traditional tubular adenoma (TA) (n = 55). The growth fraction (Ki-67 labeling index) of SA was 18.8%, which was significantly lower than those of TA (40.1%) and HP (23.8%), while the apoptotic index of SA (0.14%) was significantly lower than that of TA (1.17%). The proliferative compartment in SA was distributed either basally (47%, 60/117 crypts), or in the intermediate portion (51.3%, 55/117 crypts), and there was no superficial translocation of the proliferative compartment, which was seen in 81.2% (361/445 crypts) of TA crypts. These results indicate that SA is a tumor with low proliferative activity and its growth would be maintained by a low extent of cell loss by apoptosis. The results also indicate the neoplastic process in SA is characterized by the disorder of cell migration, maturation and exfoliation similar to HP, and its epithelial cell maturation and migration occasionally occur bidirectionally, toward the surface and to the bottom of the crypt.

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.

Cellular differentiation status of epithelial polyps of the colorectum: the gastric foveolar cell-type in hyperplastic polyps

AIMS

The 'metaplastic' polyp of the colorectum, a synonym for the hyperplastic polyp, was named based only on features of the crypt epithelium. It is considered non-neoplastic, but the precise cellular differentiation status remains to be proven.

METHODS AND RESULTS

Forty-eight hyperplastic polyps, 12 serrated adenomas, 45 tubular adenomas and five juvenile polyps were studied for their phenotypic expression using gastric (foveolar or pyloric gland cell), small intestinal (goblet cell), and colonic (goblet cell) cellular markers by immunohistochemical and mucin histochemical techniques. Gastric foveolar cell-type differentiation was significantly expressed in hyperplastic polyps, while colonic differentiation was also consistently preserved. Neither gastric pyloric-type nor small intestinal differentiation was observed. The same cell differentiation status as hyperplastic polyps was observed in serrated adenomas but not in tubular adenomas or juvenile polyps.

CONCLUSIONS

A large proportion of hyperplastic polyps are composed of hybrid epithelium, with bidirectional differentiation to both gastric foveolar and colonic epithelial cells in the same crypt. Therefore hyperplastic polyps might be interpreted as the outcome of abnormal cell differentiation of stem cells. The same phenotypic expression suggests that hyperplastic polyps and serrated adenomas share the same cell lineage.

Frequent CpG island methylation in serrated adenomas of the colorectum

Serrated adenomas are characterized by a saw-toothed growth pattern with epithelial dysplasia (intraepithelial neoplasia). The CpG island methylator phenotype (CIMP) is a recently described mechanism for tumorigenesis in colorectal carcinomas and adenomas characterized by methylation of multiple CpG islands. The role of these epigenetic alterations in the pathogenesis of serrated adenomas is not clear. We therefore evaluated CIMP in 22 sporadic serrated adenomas and 6 serrated adenomas with multiple (6 to 10) hyperplastic polyps, including 5 with admixed hyperplastic glands and adenomatous glands, and compared the results with 34 conventional adenomas. Bisulfite methylation-specific polymerase chain reaction was used for the p16 and hMLH1 genes, and three MINT (methylated in tumor) loci (MINT1, MINT2, and MINT31). Patients with sporadic serrated adenomas had a higher frequency of hyperplastic polyps (1.3 +/- 1.6) as compared to patients with tubular adenomas (0.4 +/- 0.9, P = 0.02). Mean number of methylated sites was significantly higher in sporadic serrated adenomas (2.0 +/- 1.7) than in tubular adenomas (0.8 +/- 0.9, P = 0.00001). Sporadic serrated adenomas had significantly more frequent methylation of MINT1 (48%, 10 of 22) and MINT2 (71%, 15 of 21) than tubular adenomas (9%, 3 of 34, P = 0.001; and 18%, 6 of 34, P = 0.0001), respectively. Concordant methylation of two or more sites (CIMP-high) was also more frequent in sporadic serrated adenomas (68%, 15 of 22) than in tubular adenomas (18%, 6 of 34, P = 0.0005). All five serrated adenomas with admixed hyperplastic glands and adenomatous glands were CIMP-high. Our results indicate that CpG island methylation is common in sporadic serrated adenomas and may play an important role in their pathogenesis.

Expression of Ki-67 and cytokeratin 20 in hyperplastic polyps of the colorectum

AIMS

To study the expression of Ki-67 and cytokeratin 20 (CK20) in a group of hyperplastic polyps (including a group with "atypical" features) with the aim of determining whether upper crypt Ki-67 staining and lower crypt CK20 staining correlated with these atypical features, as assessed by light microscopy.

METHODS

Fifty seven formalin fixed, paraffin wax embedded hyperplastic colorectal polyps from 53 patients were selected on histological grounds; these comprised 26 typical polyps and 31 with atypical features, which included nuclear hyperchromatism, basal crowding, and increased mitotic activity. These polyps were examined using a standard immunohistochemical method with antibodies against CK20 and Ki-67. Comparisons were made with normal mucosa, adenomatous polyps, and carcinomas.

RESULTS

Of the 26 typical polyps, 17 showed the usual pattern of lower crypt Ki-67 and upper crypt CK20 staining; one with upper crypt Ki-67 staining but normal surface CK20 staining; seven with Ki-67 confined to the lower half of crypts but with scattered lower crypt CK20; and one with both upper crypt Ki-67 staining, together with scattered CK20 basal staining. Of the 31 polyps with atypical features, 11 showed the usual staining pattern of lower crypt Ki-67 staining and surface staining with CK20; two showed Ki-67 staining extending into the upper half of crypts, but with a normal surface staining with CK20; 14 showed Ki-67 confined to the lower half of crypts, but scattered lower crypt staining with CK20; and four showed upper crypt Ki-67 staining together with scattered CK20 lower crypt staining.

CONCLUSIONS

The normal pattern of lower crypt Ki-67 and upper crypt CK20 was seen in 28 of the 57 hyperplastic polyps and, in general, this corresponded with standard light microscopic appearances. Twenty one of the 57 polyps showed lower crypt mosaic CK20 staining, which in general corresponded with basal abnormalities on light microscopy, although seven specimens had normal appearances. Two smaller subsets emerged, one showing upper crypt Ki-67 staining in the presence of normal CK20 expression (three cases) and another in which a combination of lower crypt CK20 and upper crypt Ki-67 expression was seen (five cases). This last pattern was similar to that of neoplastic polyps and raises the possibility that a subgroup of hyperplastic polyps exists that may be a variant with malignant potential. Further studies with markers of mismatch repair genes and K-ras mutations may help to clarify this issue.

Morphologic reappraisal of serrated colorectal polyps

The "hyperplastic polyp" is considered a benign lesion with no malignant potential, whereas "serrated adenoma" is a precursor of adenocarcinoma. The morphologic complexity of the serrated adenoma varies from being clearly adenomatous to being difficult to distinguish from hyperplastic polyp, which creates a need for more detailed morphologic analysis of all serrated polyps. We evaluated 24 morphologic variables in 289 serrated polyps from the colon and rectum. Cluster analysis and discriminant analysis were performed. A subset of polyps was immunostained for hMLH1 and hMSH2. Major differences were found between right-sided and left-sided polyps. A distinct group of serrated polyps with abnormal proliferation was identified throughout the colon and rectum. These polyps demonstrated decreased expression of hMHL1 and hMSH2 compared with polyps with normal proliferation. Left-sided serrated polyps with normal proliferation further clustered into three groups: vesicular cell-type, goblet cell-type, and mucin-poor-type. We recommend evaluation of the localization, size, and morphologic features when serrated polyps are included in colorectal carcinogenesis research. Polyps with abnormal proliferation are similar to the polyps in "hyperplastic polyposis" and, because of their decreased expression of hMLH1 and hMSH2, may be the subset of polyps associated with the development of colorectal carcinoma via the microsatellite instability pathway.

Colorectal polyps and other precursor lesions. Need for an expanded view

The traditional understanding of adenomas serving as precursors for a homogeneous group of adenocarcinomas is being assailed from all sides. Clearly, the relationship between precursor lesions and adenocarcinomas with defective DNA mismatch repair is much more complex and appears to include right-sided hyperplastic polyps as precursor lesions in some cases. Additional data will be forthcoming regarding this risk of adenocarcinoma development in right-sided hyperplastic polyps, both through defective DNA mismatch repair and methylation of the MGMT gene. This will likely be accompanied by an attempt to reclassify at least some larger hyperplastic polyps as serrated adenomas either on subtle morphologic or molecular grounds.

Pathogenesis and clinical management of hereditary non-polyposis colorectal cancer

BACKGROUND

Hereditary non-polyposis colorectal cancer (HNPCC) is an inherited genetic condition associated with microsatellite instability; it accounts for around 5 per cent of all cases of colorectal cancer. This review examines recent data on management strategies for this condition.

METHODS

A Medline-based literature search was performed using the keywords 'HNPCC' and 'microsatellite instability'. Additional original papers were obtained from citations in articles identified by the initial search.

RESULTS AND CONCLUSION

The Amsterdam criteria identify patients in whom the presence of an inherited mutation should be investigated. Those with a mutation should be offered counselling and screening. The role of prophylactic surgery has been superseded by regular colonoscopy, which dramatically reduces the risk of colorectal cancer. Screening for extracolonic malignancy is also advocated, but the benefits are uncertain. Chemoprevention may be of value in lowering the incidence of bowel cancer in affected patients, but further studies are required.

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.

[Prognosis in patients with potentially treatable colorectal carcinoma]

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Does MSI-low exist?

Microsatellite instability is a well-recognised phenomenon. Ten to 15% of sporadic colorectal cancers with a high level of MSI form a well defined group with distinct clinicopathological features. The set of tumours with low level of microsatellite instability (MSI-low), though widely referred to, is not a clearly defined group. The definitions of MSI-low have varied among groups and between different studies from the same group. Some studies have found associations between the MSI-L phenotype and molecular features, notably a higher frequency of K-ras mutations, and, possibly, methylation of methylguanine methyltransferase. Two recent independent studies, however, showed respectively that 68% and 79%, non-MSI-H cancers showed some MSI and could therefore be classed nominally as MSI-L. There was no evidence for a qualitatively discrete MSI-L group, but quantitative differences in the level of MSI were found.

Distinction between familial and sporadic forms of colorectal cancer showing DNA microsatellite instability

Attempts to classify colorectal cancer into subtypes based upon molecular characterisation are overshadowed by the classical stepwise model in which the adenoma-carcinoma sequence serves as the morphological counterpart. Clarity is achieved when cancers showing DNA microsatellite instability (MSI) are distinguished as sporadic MSI-low (MSI-L), sporadic MSI-high (MSI-H) and hereditary non-polyposis colorectal cancer (HNPCC). Divergence of the 'methylator' pathway into MSI-L and MSI-H is at least partly determined by the respective silencing of MGMT and hMLH1. Multiple differences can be demonstrated between sporadic and familial (HNPCC) MSI-H colorectal cancer with respect to early mechanisms, evolution, molecular characterisation, demographics and morphology. By acknowledging the existence of multiple pathways, rapid advances in the fields of basic and translational research will occur and this will lead to improved strategies for the prevention, early detection and treatment of colorectal cancer.

Apoptosis index and apoptosis-related antigen expression in serrated adenoma of the colorectum: the saw-toothed structure may be related to inhibition of apoptosis

Serrated adenoma of the colorectum is a recently proposed entity characterized by a saw-toothed structure of hyperplastic polyp and cytologic atypia of tubular adenoma. To clarify the role of apoptosis in morphogenesis of serrated adenoma, we investigated apoptotic indices and expression of apoptosis-related antigens in the tumor cells. Thirty-eight serrated adenomas were examined by the nick-end DNA labeling method and immunostained for CD95 (Fas), bcl-2, bax, and p53. Thirty-seven hyperplastic polyps, 48 tubular adenomas, and 16 sections containing normal colonic mucosa were similarly examined for comparison. The apoptotic indices in the upper and middle zones of the crypts of serrated adenomas and hyperplastic polyps were lower than those of normal colon mucosa and tubular adenomas with statistically significant differences. The CD95 expression was diffusely observed throughout the epithelium of normal crypts and tubular adenomas, whereas it was reduced in serrated adenomas and hyperplastic polyps. The bcl-2 expression was confined to the basal crypts in the latter two lesions but was diffuse throughout the neoplastic epithelium in tubular adenomas. The bax expression was increased in serrated adenomas and tubular adenomas but was decreased in hyperplastic polyps. Overexpression of p53 protein was observed in 50% of serrated adenomas, none of hyperplastic polyps, and 14% of tubular adenomas. These findings suggest that inhibition of apoptosis is caused by reduced CD95 expression in serrated adenomas and hyperplastic polyps, which may induce the characteristic saw-toothed structure in these lesions. Based on the similarities and differences between serrated adenoma and hyperplastic polyp observed in the present study, a progression from the latter to the former lesion may be postulated.

Evolution of colorectal cancer: change of pace and change of direction

This review compiles evidence for an alternative to the classical adenoma-carcinoma sequence in the evolution of colorectal cancer. It is suggested that between 30 and 50 of colorectal cancers are not initiated by mutation of the tumor suppressor gene APC, but through the epigenetic silencing of genes implicated in the control of differentiation, cell cycle control and DNA repair proficiency. The precursor polyps are often characterized by a serrated architecture, and include hyperplastic polyps, admixed polyps and serrated adenomas. The alternative pathway is heterogeneous and may culminate in cancers showing low or high level DNA microsatellite instability (MSI-L and MSI-H, respectively), and in cancers that are microsatellite stable (MSS). Cancers showing DNA MSI may be characterized by an accelerated evolution. Cancers in hereditary non-polyposis colorectal cancer show features of both classical (adenoma and APC mutation) and alternative pathways (rapid evolution, MSI-H and lack of chromosomal instability).

Features of colorectal cancers with high-level microsatellite instability occurring in familial and sporadic settings: parallel pathways of tumorigenesis

High-level microsatellite instability (MSI-H) is demonstrated in 10 to 15% of sporadic colorectal cancers and in most cancers presenting in the inherited condition hereditary nonpolyposis colorectal cancer (HNPCC). Distinction between these categories of MSI-H cancer is of clinical importance and the aim of this study was to assess clinical, pathological, and molecular features that might be discriminatory. One hundred and twelve MSI-H colorectal cancers from families fulfilling the Bethesda criteria were compared with 57 sporadic MSI-H colorectal cancers. HNPCC cancers presented at a lower age (P < 0.001) with no sporadic MSI-H cancer being diagnosed before the age of 57 years. MSI was less extensive in HNPCC cancers with 72% microsatellite markers showing band shifts compared with 87% in sporadic tumors (P < 0.001). Absent immunostaining for hMSH2 was only found in HNPCC tumors. Methylation of hMLH1 was observed in 87% of sporadic cancers but also in 55% of HNPCC tumors that showed loss of expression of hMLH1 (P = 0.02). HNPCC cancers were more frequently characterized by aberrant beta-catenin immunostaining as evidenced by nuclear positivity (P < 0.001). Aberrant p53 immunostaining was infrequent in both groups. There were no differences with respect to 5q loss of heterozygosity or codon 12 K-ras mutation, which were infrequent in both groups. Sporadic MSI-H cancers were more frequently heterogeneous (P < 0.001), poorly differentiated (P = 0.02), mucinous (P = 0.02), and proximally located (P = 0.04) than HNPCC tumors. In sporadic MSI-H cancers, contiguous adenomas were likely to be serrated whereas traditional adenomas were dominant in HNPCC. Lymphocytic infiltration was more pronounced in HNPCC but the results did not reach statistical significance. Overall, HNPCC cancers were more like common colorectal cancer in terms of morphology and expression of beta-catenin whereas sporadic MSI-H cancers displayed features consistent with a different morphogenesis. No individual feature was discriminatory for all HNPCC cancers. However, a model based on four features was able to classify 94.5% of tumors as sporadic or HNPCC. The finding of multiple differences between sporadic and familial MSI-H colorectal cancer with respect to both genotype and phenotype is consistent with tumorigenesis through parallel evolutionary pathways and emphasizes the importance of studying the two groups separately.

Sporadic colorectal cancers with microsatellite instability and their possible origin in hyperplastic polyps and serrated adenomas

BACKGROUND

Microsatellite instability (MSI) is seen in 10%-15% of sporadic colorectal cancers mostly in the right colon, but the precursors of cancers with MSI remain unknown. We examined whether sporadic cancers with MSI arise from pre-existing benign proliferative lesions (such as hyperplastic polyps or serrated adenomas [together denoted as "serrated polyps"]).

METHODS

The frequency of benign epithelial lesions (serrated polyps and conventional adenomas) was determined by histologic review of resection specimens from individuals (n = 29) with sporadic colorectal cancer with MSI and from a matched control group (n = 29) with cancer showing microsatellite stability (MSS). MSI status, expression of mismatch repair enzyme (product of the human mut-L homologue 1 [hMLH1] gene), and hMLH1 gene promoter methylation in the benign lesions were determined. Data were analyzed by the chi-square test, by Wilcoxon's rank-sum test, and by conditional logistic regression as appropriate, and a two-sided probability less than.05 was considered to be statistically significant.

RESULTS

Individuals with cancers showing MSI were more likely to harbor at least one serrated polyp than individuals with cancers showing MSS (odds ratio = 4.0; 95% confidence interval = 1.1 to 14.2; P =.03), but the frequency of conventional adenomas was the same in both groups (P =.52, Mann-Whitney test). Loss of hMLH1 protein expression was seen in lesions from 10 of 13 patients with MSI, but no loss was seen in lesions from four patients with MSS (P =.02, Fisher's exact test). Loss of hMLH1 protein expression was associated with MSI in assessable lesions. The hMLH1 promoter was methylated in all assessable serrated polyps from patients with cancers showing MSI but in none of the lesions from patients with MSS cancers.

CONCLUSIONS

Some right-sided hyperplastic polyps may give rise to sporadic colorectal carcinomas with MSI. Methylation of the hMLH1 gene promoter within neoplastic cell subpopulations may be a critical step in the progression to carcinoma. The frequency with which benign lesions progress to cancer with MSI is unknown.

Altered mucin expression in the gastrointestinal tract: a review

Early studies of changes in mucin expression in disorders of the gastrointestinal tract focused on alterations in the carbohydrate chain. This review briefly considers the various mechanisms by which such alterations may come about: (a) normal variation, (b) sialic acid alterations, (c) defective assembly of carbohydrate side-chains, (d) changed expression of core proteins and (e) epithelial metaplasia. The availability of monoclonal antibodies to mucin core proteins adds a new dimension to mucin histochemistry. It is now possible to offer explanations for traditional mucin histochemical findings on the basis of lineage-specific patterns of mucin core protein expression. Changes in core protein expression are described in inflammatory, metaplastic and neoplastic disorders of the gastrointestinal tract. The possibility that mucin change could be important in the aetiology of some diseases such as ulcerative colitis and H. pylori gastritis is considered. It is more probable, however, that changes in mucin expression are secondary to reprogramming of cellular differentiation and altered cell turnover. As such they may serve as markers to explain pathogenesis and provide novel diagnostic and prognostic information.

Hyperplastic polyps of the colorectum-innocent or guilty?

Hyperplastic polyps have traditionally been regarded as nonneoplastic polyps lacking malignant potential. The demonstration of genetic alterations within these lesions indicates an underlying neoplastic cause. There is evidence that hyperplastic polyps are heterogeneous. Most are innocuous, but subsets may have malignant potential. Risk factors for neoplastic progression include multiple, large, and proximally located polyps. Aberrant methylation resulting in the silencing of cancer genes may be an important underlying mechanism, particularly in pathways progressing to tumors with DNA microsatellite instability. Lesions intermediate between hyperplastic polyp and cancer include admixed polyps and serrated adenomas. Currently, pathologists have different thresholds for diagnosing serrated adenomas, including the distinction from large hyperplastic polyps. Reasons for over looking this pathway in the past may include rapid tumor progression and the fact that proximally located hyperplastic polyps may be flat and not especially numerous. Management of the serrated pathway of colorectal neoplasia may require novel approaches to screening, early detection, and prevention.