Deletion of 1p loci and microsatellite instability in colorectal polyps

Molecular characteristics of colorectal hyperplastic polyp subgroups

BACKGROUND/AIMS

The importance of hyperplastic polyps during colorectal carcinogenesis is appreciated related to the understanding of serrated pathway. The morphologic subtypes of hyperplastic polyps in carcinogenesis and the nomenculature of lesions with both hyperplastic and adenomatous areas are controversial. We aimed to reveal the molecular properties of hyperplastic polyp subtypes and the molecular changes in polyps containing both hyperplastic and adenomatous areas. Matherial and Methods: 49 hyperplastic polyps [19 microvesicular (MVHP), 19 goblet-rich (GRHP), 11 mucin-poor (MPHP)] and 10 mixed hyperplastic and adenomatous polyps were analysed for KRAS, BRAF mutations and MSI with real-time PCR.

RESULTS

68,4% of MVHPs and 81% of MPHPs which were localized in right colon had BRAF mutations. While none of the GRHPs showing a KRAS mutation with a rate of 73% was localized in the ascending colon, 63% of them were localized in the rectosigmoid area. In five (50%) of the mixed polyps, KRAS mutation was detected both in the hyperplastic and adenoma components. There was no BRAF mutation in any of the mixed polyps. However, in two cases, the hyperplastic component was MSI-H and the adenoma area was MSS.

CONCLUSION

Hyperplastic polyps, even if smaller than 5 mm, are precancerous lesions bearing different mutations. GRHPs with predominant KRAS mutations and MVHPs and MPHSs with predominant BRAF mutations are precancerous. Although the molecular investigations for HPP/SP are not necessary the morphological subtyping should be included if the case is diagnosed with HPP/SP as it will be useful for attracting the gastroenterologist's attention.

Low Gene Dosage of Cdc42 Is Not Associated with Protein Dysfunction in Patients with Colorectal Cancer

High incidence of Rho Cdc42-GTPase overexpression has been found in Colorectal Cancer (CRC) samples, suggesting its potential role in tumor development. However, no conclusive studies have shown the lack of mutations and/or copy number of Cdc42 gene in this type of samples. To understand mutation/deletion and copy number status of Cdc42 gene, CRC patients were evaluated for both parameters. More than Cdc42 mutants, single-nucleotide variants were found. Analysis of regions flanking the Cdc42 gene showed allelic imbalance; 58.7% were loss of heterozygosity (LOH) positive and 14.8% presented microsatellite instability. The highest LOH percentage was located between microsatellite markers D1S199 and D1S2674, where the Cdc42 gene is located. No association between gender, age, and tumor stage was found. LOH validation through gene dosage analysis showed most CRC patients with allelic imbalance also presented a low gene dosage of Cdc42, although equal amounts of Cdc42 mRNA were detected in all samples. Although changes in Cdc42 expression were not found in any condition, Cdc42 activation was different between high and normal gene dosage samples, but not between samples with normal and low copy number. Low dosage of Cdc42 was also not related to changes in methylation status at the Cdc42 promoter region. Results suggest that low copy of Cdc42 gene is not associated with Cdc42 protein dysfunction in CRC patients.

Regulator of Chromosome Condensation 2 Identifies High-Risk Patients within Both Major Phenotypes of Colorectal Cancer

PURPOSE

Colorectal cancer has high incidence and mortality worldwide. Patients with microsatellite instable (MSI) tumors have significantly better prognosis than patients with microsatellite stable (MSS) tumors. Considerable variation in disease outcome remains a challenge within each subgroup, and our purpose was to identify biomarkers that improve prediction of colorectal cancer prognosis.

EXPERIMENTAL DESIGN

Mutation analyses of 42 MSI target genes were performed in two independent MSI tumor series (n = 209). Markers that were significantly associated with prognosis in the test series were assessed in the validation series, followed by functional and genetic explorations. The clinical potential was further investigated by immunohistochemistry in a population-based colorectal cancer series (n = 903).

RESULTS

We identified the cell-cycle gene regulator of chromosome condensation 2 (RCC2) as a cancer biomarker. We found a mutation in the 5' UTR region of RCC2 that in univariate and multivariate analyses was significantly associated with improved outcome in the MSI group. This mutation caused reduction of protein expression in dual luciferase gene reporter assays. siRNA knockdown in MSI colon cancer cells (HCT15) caused reduced cell proliferation, cell-cycle arrest, and increased apoptosis. Massive parallel sequencing revealed few RCC2 mutations in MSS tumors. However, weak RCC2 protein expression was significantly associated with poor prognosis, independent of clinical high-risk parameters, and stratifies clinically important patient subgroups with MSS tumors, including elderly patients (>75 years), stage II patients, and those with rectal cancer.

CONCLUSIONS

Impaired RCC2 affects functional and clinical endpoints of colorectal cancer. High-risk patients with either MSI or MSS tumors can be identified with cost-effective routine RCC2 assays.

Role of MYH polymorphisms in sporadic colorectal cancer in China: a case-control, population-based study

PURPOSE

Biallelic germline variants of the 8-hydroxyguanine (8-OG) repair gene MYH have been associated with colorectal neoplasms that display somatic G:C?T:A transversions. However, the effect of single germline variants has not been widely studied, prompting the present investigation of monoallelic MYH variants and susceptibility to sporadic colorectal cancer (CRC) in a Chinese population.

PATIENTS AND METHODS

Between January 2006 and December 2012, 400 cases of sporadic CRC and 600 age- and sex-matched normal blood donors were screened randomly for 7 potentially pathogenic germline MYH exons using genetic testing technology. Variants of heterozygosity at the MYH locus were assessed in both sporadic cancer patients and healthy controls. Univariate and multivariate analyses were performed to determine risk factors for cancer onset.

RESULTS

Five monoallelic single nucleotide polymorphisms (SNPs) were identified in the 7 exon regions of MYH, which were detected in 75 (18.75%) of 400 CRC patients as well as 42 (7%) of 600 normal controls. The region of exon 1 proved to be a linked polymorphic region for the first time, a triple linked variant including exon 1-316 G?A, exon 1-292 G?A and intron 1+11 C?T, being identified in 13 CRC patients and 2 normal blood donors. A variant of base replacement, intron 10-2 A?G, was identified in the exon 10 region in 21 cases and 7 controls, while a similar type of variant in the exon 13 region, intron 13+12 C?T, was identified in 8 cases and 6 controls. Not the only but a newly missense variant in the present study, p. V463E (Exon 14+74 T?A), was identified in exon 14 in 6 patients and 1 normal control. In exon 16, nt. 1678-80 del GTT with loss of heterozygosity (LOH) was identified in 27 CRC cases and 26 controls. There was no Y165C in exon 7 or G382D in exon 14, the hot- spot variants which have been reported most frequently in Caucasian studies. After univariate analysis and multivariate analysis, the linked variant in exon 1 region (p=0.002), intron 10-2 A?G (p=0.004) and p. V463E (p=0.036) in the MYH gene were selected as 3 independent risk factors for CRC.

CONCLUSIONS

According to these results, the linked variant in Exon 1 region, Intron 10-2 A?G of base replacement and p. V463E of missense variant, the 3 heterozygosity variants of MYH gene in a Chinese population, may relate to the susceptibility to sporadic CRC. Lack of the hot-spot variants of Caucasians in the present study may due to the ethnic difference in MYH gene.

Predicting survival in head and neck squamous cell carcinoma from TP53 mutation

For TP53-mutated head and neck squamous cell carcinomas (HNSCCs), the codon and specific amino acid sequence change resulting from a patient's mutation can be prognostic. Thus, developing a framework to predict patient survival for specific mutations in TP53 would be valuable. There are many bioinformatics and functional methods for predicting the phenotypic impact of genetic variation, but their overall clinical value remains unclear. Here, we assess the ability of 15 different methods to predict HNSCC patient survival from TP53 mutation, using TP53 mutation and clinical data from patients enrolled in E4393 by the Eastern Cooperative Oncology Group (ECOG), which investigated whether TP53 mutations in surgical margins were predictive of disease recurrence. These methods include: server-based computational tools SIFT, PolyPhen-2, and Align-GVGD; our in-house POSE and VEST algorithms; the rules devised in Poeta et al. with and without considerations for splice-site mutations; location of mutation in the DNA-bound TP53 protein structure; and a functional assay measuring WAF1 transactivation in TP53-mutated yeast. We assessed method performance using overall survival (OS) and progression-free survival (PFS) from 420 HNSCC patients, of whom 224 had TP53 mutations. Each mutation was categorized as "disruptive" or "non-disruptive". For each method, we compared the outcome between the disruptive group vs. the non-disruptive group. The rules devised by Poeta et al. with or without our splice-site modification were observed to be superior to others. While the differences in OS (disruptive vs. non-disruptive) appear to be marginally significant (Poeta rules + splice rules, P = 0.089; Poeta rules, P = 0.053), both algorithms identified the disruptive group as having significantly worse PFS outcome (Poeta rules + splice rules, P = 0.011; Poeta rules, P = 0.027). In general, prognostic performance was low among assessed methods. Further studies are required to develop and validate methods that can predict functional and clinical significance of TP53 mutations in HNSCC patients.

A study of genomic instability in early preneoplastic colonic lesions

It is difficult to explain the differential rates of progression of premalignant colonic lesions and differences in behaviour of morphologically similar lesions. Heterogeneity for microsatellite instability (MSI) and promoter methylation in driving these phenomena forward may explain this; however, no previous analysis has examined this in detail at the gland level, the smallest unit of colorectal premalignant lesions. We aimed to carry out an analysis of gland level genomic instability for MSI and promoter methylation. MSI occurred significantly more frequently (20%) in colonic glands than has previously been observed in whole colorectal polyps. Significant promoter methylation was seen in MLH1, PMS2, MLH3 and MSH3 as well as significant heterogeneity for both MSI and promoter methylation. Methylation and MSI may have a significant role in driving forward colorectal carcinogenesis, although in the case of MSI, this association is less clear as it occurs significantly more frequently than previously thought, and may simply be a passenger in the adenoma-carcinoma sequence. Promoter methylation in MLH1, MLH3, MSH3 and PMS2 was also found to be significantly associated with MSI and should be investigated further. A total of 273 colorectal glands (126 hyperplastic, 147 adenomatous) were isolated via laser capture microdissection (targeted at regions of MLH1 loss) from 93 colonic polyps and tested for MSI, and promoter methylation of the DNA mismatch repair genes MLH1, MSH2, MLH3, MSH6, PMS2, MGMT and MLH3 via methylation specific multiplex ligation-dependent probe amplification. Logistic regression modelling was then used to identify significant associations between promoter methylation and gland histological type and MSI status.

The code structure of the p53 DNA-binding domain and the prognosis of breast cancer patients

MOTIVATION

The tumor-suppressor gene TP53 mutations are diverse in the central region encoding the DNA-binding domain. It has not been clear whether the prognostic significance for survival in breast cancer patients is the same for all types of mutations. Are there specific types of mutations carrying a worse prognosis? To understand the correlation between the mutations in the gene encoding the DNA-binding domain and the prognosis of breast cancer, we studied the code structure of the DNA-binding domain of breast cancer patients by using various artificial codes in information transmission.

RESULTS

We indicated that the prognostic significance of all types of mutations in the DNA-binding domain is not the same, and that the DNA-binding domain having a certain code structure is important for estimating the prognosis of breast cancer patients.

CONTACT

keiko@is.noda.tus.ac.jp or hara@is.noda.tus.ac.jp.

The stem cell marker CD133 is highly expressed in sessile serrated adenoma and its borderline variant compared with hyperplastic polyp

Non-dysplastic serrated polyps (ND-SP) represent a heterogeneous group of colorectal lesions that comprise hyperplastic polyp (HP) and the non-dysplastic subset of sessile serrated adenoma/polyp/lesion (SSA/P/L) and its borderline variant (BSSA/P/L). Given the observer variation in their histological typing, the identification of reliable markers that assist in the characterisation is warranted. Most important is the identification of polyp qualities that may reflect the patients' risk of developing colorectal cancer. To address these issues, CD133 may represent a potential adjunct. Here we studied the discriminatory value of CD133 expression in the classification of ND-SPs and its distribution pattern in relation to synchronous colorectal carcinoma (SCRC). 39 SSA/P/Ls, 27 BSSA/P/Ls and 21 matched HPs were immunostained for CD133. The data were further correlated to the presence of SCRC and to polyp site and size. Ignoring SCRC status, CD133 was expressed more prominently in SSA/P/Ls than in HPs. The values for BSSA/P/Ls fell in between, yet closer to the SSA/P/L scorings. This observation was retained in the context of SCRC and for SSA/P/Ls not associated with SCRC. Right-sidedness and large size of the polyps more commonly associated with increased CD133 expression. CD133 expression was not a significant discriminator as to the SCRC status. BSSA/P/Ls are more closely aligned to SSA/P/L and further that SSA/P/L and BSSA/P/Ls fundamentally differ from HP by their CD133 immunoprofile, a notion that can be exploited in the diagnostic routine practice. Recorded data further indirectly support the idea that SSA/P/Ls are more prone to neoplastic progression than are HPs.

Reduced expression of ELAVL4 in male meningioma patients

Meningioma is a frequently occurring tumor of the central nervous system. Among many genetic alternations, the loss of the short arm of chromosome 1 is the second most frequent chromosomal abnormality observed in these tumors. Here, we focused on the previously described and well-established minimal deletion regions of chromosome 1. In accordance with the Knudson suppressor theory, we designed an analysis of putative suppressor genes localized in the described minimal deletion regions. The purpose was to determine the molecular background of the gender-specific occurrence of meningiomas. A total of 149 samples were examined for loss of heterozygosity (LOH). In addition, 57 tumor samples were analyzed using real-time polymerase chain reaction. We examined the association between the expression of selected genes and patient age, gender, tumor grade and presence of 1p loss. Furthermore, we performed an analysis of the most stable internal control for real-time analysis in meningiomas. LOH analysis revealed gender-specific discrepancies in the frequency of 1p aberrations. Moreover, statistical correlation between the gene expression level and gender was significant for the ELAVL4 gene as we found it to be lower in males than in females. We conclude that meningiomas present different features depending on patient gender. We suggest that ELAVL4 can be involved in the pathogenesis of meningiomas in male patients.

Characterization of a major colon cancer susceptibility locus (Ccs3) on mouse chromosome 3

Treatment of mice with the carcinogen azoxymethane (AOM) induces a number of lesions in the colon, including hyperplastic lesions, as well adenomas and carcinomas in situ. Inbred strains of mice show different responses to AOM-induced carcinogenesis. A/J mice are highly susceptible and develop a greater number of hyperplastic lesions and tumors (15-70 tumors per mouse) than resistant C57BL/6J mice (0-6 tumors per mouse). Susceptibility to AOM-induced tumors segregates as a co-dominant trait in (A x B6)F1 hybrids. Using a set of 23 AcB and BcA recombinant congenic mouse strains derived from A/J (susceptible) and B6 (resistant) parents, we observed that the number of hyperplastic lesions and tumors induced by AOM was under different genetic controls in AcB/BcA strains. The multiplicity of AOM-induced tumors is controlled by a major locus that we have mapped on the distal portion of chromosome 3, to which we have given the temporary designation colon cancer susceptibility locus 3 (Ccs3). B6 and A/J alleles at Ccs3 are associated with resistance and susceptibility, respectively. Haplotype analysis in key informative AcB/BcA strains restricts the size of the Ccs3 locus to a 14 Mb segment that contains 94 annotated genes. The expression level of all these genes in normal colon has been established by transcript profiling with microarrays, and has led to the identification of a subset of positional candidates that are expressed at high levels in this tissue. The 4q and 1p human chromosomal segments sharing syntenic homology with the mouse Ccs3 segment are known to be associated with inflammatory bowel diseases and colorectal tumors in humans, suggesting that the study of the mouse Ccs3 locus may help further the pathogenesis of these human conditions.

Germline MutY human homologue mutations and colorectal cancer: a multisite case-control study

BACKGROUND & AIMS

The MutY human homologue (MYH) gene is a member of the base-excision repair pathway involved in the repair of oxidative DNA damage. The objective of this study was to determine colorectal cancer (CRC) risk associated with mutations in the MYH gene.

METHODS

A total of 3811 CRC cases and 2802 controls collected from a multisite CRC registry were screened for 9 germline MYH mutations; subjects with any mutation underwent screening of the entire MYH gene. Logistic regression was used to estimate age- and sex-adjusted odds ratios (AOR). Clinicopathologic and epidemiologic data were reviewed to describe the phenotype associated with MYH mutation status and assess for potential confounding and effect modification.

RESULTS

Twenty-seven cases and 1 control subject carried homozygous or compound heterozygous MYH mutations (AOR, 18.1; 95% confidence interval, 2.5-132.7). CRC cases with homozygous/compound heterozygous mutations were younger at diagnosis (P=.01), had a higher proportion of right-sided (P=.01), synchronous cancers (P<.01), and personal history of adenomatous polyps (P=.003). Heterozygous MYH mutations were identified in 87 CRC cases and 43 controls; carriers were at increased risk of CRC (AOR, 1.48; 95% confidence interval, 1.02-2.16). There was a higher prevalence of low-frequency microsatellite instability (MSI) in tumors from heterozygous and homozygous/compound heterozygous MYH mutation carriers (P=.02); MSI status modified the CRC risk associated with heterozygous MYH mutations (P interaction<.001).

CONCLUSIONS

Homozygous/compound heterozygous MYH mutations account for less than 1% of CRC cases. Heterozygous carriers are at increased risk of CRC. Further studies are needed to understand the possible interaction between the base excision repair and low-frequency MSI pathways.

Genetic and epigenetic changes in aberrant crypt foci and serrated polyps

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

A comprehensive review of the treatment of Merkel cell carcinoma

Merkel cell carcinoma (MCC) is an uncommon but malignant cutaneous neuroendocrine carcinoma with a high incidence of local recurrence, regional lymph node metastases, and subsequent distant metastases. The etiology of MCC remains unknown. It usually occurs in sun-exposed areas in elderly people, many of whom have a history of other synchronous or metachronous sun-associated skin lesions. The outcome for most patients with MCC is generally poor. Surgery is the mainstay of treatment. The role of adjuvant therapy has been debated. However, data from recent development support a multimodality approach, including surgical excision of primary tumor with adequate margins and sentinel lymph node dissection followed by postoperative radiotherapy in most cases, as current choice of practice with better locoregional control and disease-free survival. Patients with regional nodal involvement or advanced disease should undergo nodal dissection followed by adjuvant radiotherapy and, perhaps, systemic platinum-based chemotherapy in most cases.

Targeting aberrant chromatin structure in colorectal carcinomas

Epigenetic processes such as DNA methylation and histone modifications are now recognized as critical events for regulation of gene expression in mammalian cells and affect gene function without a change in coding sequence. Neoplastic cells often show profound epigenetic alterations that contribute to tumorigenesis by altering expression of critical genes. In colorectal tumorigenesis, detailed analysis led to a hypothesis on a critical role for epigenetic changes in age-related cancer susceptibility and separately identified a distinct phenotype termed the CpG island methylator phenotype. CpG island methylator phenotype-positive colorectal cancers have significant associations with female sex, older age, proximal location, mucinous histology, KRAS and BRAF mutations, wild-type p53, and microsatellite instability. Histone modifications that affect chromatin structures are also closely implicated in tumor suppressor gene inactivation and DNA methylation and histone modifications seem to form reinforcing networks for stable gene silencing. Much of the excitement in this field relates to the possibility of therapeutic reversal of epigenetic changes by chromatin-modifying drugs. In CpG island methylator phenotype-positive colorectal cancers, DNA methylation inhibitors restore key silenced pathways in vivo (eg, mismatch repair defects), and hypomethylation can largely abolish tumorigenesis in a mouse model. Drugs that inhibit DNA methylation and histone deacetylation are in use in the clinic and should be tested in colorectal malignancy.

Microsatellite instability in long-standing ulcerative colitis

OBJECTIVE

Ulcerative colitis (UC) is a chronic inflammatory disease of the colon associated with a high risk of developing colorectal cancer. Several genetic alterations have been documented in dysplasia and cancer developing in UC. Concerning microsatellite instability (MSI), many contradictory results have been published. We therefore analysed a large, well-characterized UC material for MSI to elucidate its significance in long-standing UC.

MATERIAL AND METHODS

From 33 patients, a total of 159 microdissected lesions and 165 mucosa samples obtained adjacent to the tissue blocks were analysed for MSI using the five standard markers recommended by the National Cancer Institute; D2S123, D5S346, D17S250, BAT-25 and BAT-26. In addition, 12 of the patients were investigated by a mini-satellite marker at the D1S7 locus.

RESULTS

High-level MSI (MSI-H) was detected in one villous adenoma with high-grade dysplasia and right-sided location. This represents 3.6% (1/28) of dysplastic mucosa investigated. No other lesions showed MSI in the five standard markers or at the D1S7 locus.

CONCLUSIONS

This study suggests that MSI is rare in UC-related neoplasia as well as non-neoplastic lesions, and does not contribute to the development of dysplasia.

[Emerging concepts in colorectal serrated polyps]

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

Patched2 modulates tumorigenesis in patched1 heterozygous mice

The sonic hedgehog (SHH) receptor Patched 1 (Ptch1) is critical for embryonic development, and its loss is linked to tumorigenesis. Germ line inactivation of one copy of Ptch1 predisposes to basal cell carcinoma and medulloblastoma in mouse and man. In many cases, medulloblastoma arising from perturbations of Ptch1 function leads to a concomitant up-regulation of a highly similar gene, Patched2 (Ptch2). As increased expression of Ptch2 is associated with medulloblastoma and other tumors, we investigated the role of Ptch2 in tumor suppression by generating Ptch2-deficient mice. In striking contrast to Ptch1-/- mice, Ptch2-/- animals were born alive and showed no obvious defects and were not cancer prone. However, loss of Ptch2 markedly affected tumor formation in combination with Ptch1 haploinsufficiency. Ptch1+/-Ptch2-/- and Ptch1+/-Ptch2+/- animals showed a higher incidence of tumors and a broader spectrum of tumor types compared with Ptch1+/- animals. Therefore, Ptch2 modulates tumorigenesis associated with Ptch1 haploinsufficiency.

Germline mutations in the MYH gene in Swedish familial and sporadic colorectal cancer

Biallelic germline mutations in the base excision repair gene MYH have been shown to predispose to a proportion of multiple colorectal adenomas and cancer. To evaluate the contribution of MYH mutations to non- FAP, non-HNPCC familial colorectal cancer, 84 unrelated Swedish individuals affected with colorectal cancer from such families were screened for germline mutations in the coding sequence of the gene. None of the cases was found to carry any pathogenic sequence change. We then determined the prevalence of the two most common pathogenic MYH mutations found in Caucasians, Y165C and G382D, in 450 Swedish sporadic colorectal cancer cases and 480 Swedish healthy controls. The frequency of both variants in Swedish cases and controls was similar to those previously reported. In addition, we found that previously unknown sequence variations at the position of amino acid 423 (R423Q, R423P, and R423R) appear to occur more frequently in cases than in controls (p = 0.02), a finding that warrants future studies.

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.

Low rate of microsatellite instability in young patients with adenomas: reassessing the Bethesda guidelines

BACKGROUND AND AIM

Screening adenomas for microsatellite instability (MSI) in patients younger than 40 yr of age has been recommended by the Bethesda Guidelines as a means of identifying patients at risk for hereditary nonpolyposis colorectal cancer (HNPCC). We sought to determine the rate of MSI in adenomas removed from individuals under 40 yr of age over a 5-yr period in a university general gastroenterology practice.

METHODS

We identified patients between 18 and 39 yr of age with endoscopically removed adenomatous colorectal polyps. Patients with polyposis syndromes, inflammatory bowel disease, or colorectal carcinoma were excluded. A three-generation family history was obtained via telephone interview. Endoscopic and histology reports were reviewed. Adenomas were tested for MSI using the BAT26 and BAT40 microsatellite markers, and expression of the MSH2 and MLH1 proteins was assessed by immunostaining.

RESULTS

A total of 34 patients had 46 adenomas removed endoscopically. Out of 34 patients, 14 (41%) had a family history of colorectal cancer and 3 were from Amsterdam criteria positive families. A total of 28 of 46 adenomas (61%) were distal to the splenic flexure. Polyps ranged in size from 2 to 20 mm and averaged 6.6 mm. Five polyps (11%) were tubulovillous adenomas, and the remainder were tubular adenomas. None of the polyps were serrated adenomas and none demonstrated high-grade dysplasia. Among the 40 adenomas available for testing, none demonstrated MSI using either BAT26 (0/40) or BAT40 (0/21), nor did any of the polyps tested demonstrate loss of either MSH2 or MLH1 expression (0/16).

CONCLUSION

Screening adenomas from patients younger than 40 yr of age for MSI was ineffective in identifying potentially new cases of HNPCC. New strategies that improve on the current clinical and molecular screening methods should be developed so that at-risk individuals can be identified and referred for germline testing before developing their first cancer.

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.

Comparative molecular pathology of sporadic hyperplastic polyps and neoplastic lesions from the same individual

AIM

The biology of colorectal hyperplastic polyps is of considerable relevance, because recent evidence suggests that under certain circumstances hyperplastic polyps may be precursors of neoplasms. The aim of this study was to assess and compare the clinical and molecular characteristics of hyperplastic polyps and neoplastic lesions removed from patients without the hyperplastic polyposis syndrome.

METHODS

One hundred and twenty six patients were identified through a series of genetic epidemiological studies. Each patient had at least one neoplastic lesion and one hyperplastic polyp; there was a total of 147 hyperplastic polyps. All lesions were evaluated for K-ras mutations, loss of heterozygosity (LOH) of the adenomatous polyposis coli (APC) gene, and microsatellite instability.

RESULTS

K-ras mutation was detected in 15 (10%) hyperplastic polyps, all from the rectosigmoid colon. No hyperplastic polyp had APC LOH or microsatellite instability. Patients with adenomas or carcinomas showing K-ras mutations were not more likely to have hyperplastic polyps with K-ras mutations. The average number of adenomas did not differ between those patients with hyperplastic polyps with K-ras mutations and those without K-ras mutations. There was no association between the hyperplastic polyp and the adenoma regarding the colon segments from which the two lesions were removed.

CONCLUSIONS

The sporadic hyperplastic polyp is a lesion with limited molecular change and no relation to patients' neoplastic lesions.

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.

The multiple colorectal adenoma phenotype and MYH, a base excision repair gene

We summarize the genetic and clinical features of the colorectal adenomas and cancers that occur in MYH-associated polyposis (MAP). MAP results from biallelic germline mutations in the base excision repair gene, mutY homologue (MYH). MAP has a phenotype that is often indistinguishable from classical or attenuated familial adenomatous polyposis (FAP), but the former is inherited as a recessive condition, whereas the latter is a dominantly inherited disease caused by germline mutations of the APC gene. MYH mutations seem to act by increasing the frequency of somatic APC mutations. MAP tumors may then progress to cancer along a distinct genetic pathway. MAP occurs in several different ethnic groups, the mutation spectrum appearing to differ among groups. It remains unknown, however, as to why carriers of MYH mutations specifically develop tumors of the gastrointestinal tract. In general, carriers of biallelic MYH mutations should be treated and followed up as for FAP patients with a similar phenotype. Relatives of MAP patients should be counseled as for any other recessive condition, although it remains possible that carriers of single mutations are at a modestly increased risk of colorectal cancer.

Role of inherited defects ofMYH in the development of sporadic colorectal cancer

Biallelic germ-line variants of the 8-hydroxyguanine repair gene MYH have been associated with multiple colorectal adenomas that display somatic G:C-->T:A transversions in APC. However, the effect of single germ-line variants has not been widely studied. To examine the relationship between monoallelic MYH variants and susceptibility to sporadic colorectal cancer (CRC), 92 cases of sporadic CRC, 19 cases of familial CRC not meeting the Bethesda guidelines, 17 cases with multiple adenomas, and 53 normal blood donors were screened for 8 potentially pathogenic germ-line MYH variants. Loss of heterozygosity (LOH) at 1p adjacent to the MYH locus, microsatellite instability (MSI) status, and somatic mutations in KRAS2 and APC were analyzed in sporadic cancers. Neither homozygote nor compound heterozygote MYH variants were observed in the germ-line of any subjects with sporadic CRC. There was no difference in the incidence of monoallelic variants between this group (20 of 92, 22%) and cancer-free controls (14 of 53, 26%). However, the presence of monoallelic germ-line MYH variants was negatively associated with an MSI-high (MSI-H) tumor phenotype, with an incidence of only 1 of 23 (4%) MSI-H CRCs as contrasted with 19 of 69 (28%) non-MSI-H (P=0.02). Further, 4 of 5 tumors with 1p LOH contained monoallelic MYH variants compared with 15 of 53 without 1p LOH (P=0.04) and the normal population (P=0.03). The presence of G:C-->T:A transversions in KRAS2 or APC was significantly more common in single MYH variant tumors (9 of 12) than in MYH wild-type tumors (11 of 33; P=0.02). These results suggest that single germ-line variants of MYH may influence genetic pathways in CRC.

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.

Genetic and protein markers related to in situ growth and multiplicity in small sporadic colorectal adenomas

BACKGROUND

Some early genetic events in the development of colorectal adenomas are known, but their relationship to in vivo growth characteristics is uncertain. This study compared in situ size changes and other clinicopathological variables with selected genetic and protein markers.

METHODS

56 adenomas (< or = 10 mm) from 39 patients were analysed for APC, CTNNB1 and K-ras mutations, allelic imbalance on 1p and 18q, microsatellite instability and immunohistochemical expression of HLA-DR, BAX, BCL-2 and Ki-67. For 42 of the adenomas, in situ growth was measured over 3 years. The total number of polyps in each patient was recorded.

RESULTS

K-ras was mutated in 8/56 adenomas. None of the regressing adenomas revealed such mutations, compared to 20% in those that maintained or increased their size. Multivariate linear regression analysis showed that tumour growth was higher in females compared to males, and was even higher in the presence of a K-ras mutation. APC mutations were found in 37/56 adenomas. CTNNB1 mutations were found in 2/19 adenomas without APC mutation. Deletions of 1p were found in 12/56 adenomas and, seemingly, most frequent in patients with few tumours. The most frequently expressed protein was BAX (33/41), but neither this nor the other proteins showed associations with an in situ growth pattern.

CONCLUSION

The multivariate linear regression model showed that patient gender and the presence of K-ras mutation had significant effects on tumour growth. The lack of the proliferative stimulus resulting from a K-ras mutation may contribute to the process of adenoma regression.

Genetic tumor markers with prognostic impact in Dukes' stages B and C colorectal cancer patients

PURPOSE

To examine several genetic changes in primary colorectal carcinomas (CRCs) from patients with 10 years of follow-up and associate the findings with clinicopathologic variables.

MATERIAL AND METHODS

DNA from 220 CRCs were analyzed for allelic imbalances at 12 loci on chromosome arms 1p, 14q, 17p, 18q, and 20q, and the microsatellite instability (MSI) status was determined. The clinical significance of the tumor protein 53 (TP53) mutations was re-evaluated.

RESULTS

Patients with tumors containing 17p or 18q deletions had shorter survival than those without these alterations (P =.021, P =.008, respectively). This was also significant for the Dukes' B group (P =.025, P =.010, respectively). Furthermore, patients with tumors showing losses of both chromosome arms revealed an even poorer disease outcome than those with either 17p or 18q loss. Patients with low increase in 20q copy number in their tumors had longer survival compared with those without changes (P =.009) or those with a high increase of copy number (P =.037). This was also evident for the Dukes' C group (P =.018, P =.030, respectively). MSI was seemingly a beneficial marker for survival (P =.071). A significant association between mutations affecting the L3 zinc-binding domain of TP53 and survival was confirmed in this cohort after 10 years of follow-up, and also was found to apply for patients in the Dukes' B group. Several associations were found among genetic and pathologic data.

CONCLUSION

The present study indicates that 17p, 18q, and 20q genotypes, and TP53 mutation status add information in the subclassification of Dukes' B and C patients and may have impact on the choice of treatment.

Multiple colorectal adenomas, classic adenomatous polyposis, and germ-line mutations in MYH

BACKGROUND

Germ-line mutations in the base-excision-repair gene MYH have been associated with recessive inheritance of multiple colorectal adenomas. Tumors from affected persons displayed excess somatic transversions of a guanine-cytosine pair to a thymine-adenine pair (G:C-->T:A) in the APC gene.

METHODS

We screened for germ-line MYH mutations in 152 patients with multiple (3 to 100) colorectal adenomas and 107 APC-mutation-negative probands with classic familial adenomatous polyposis (>100 adenomas). Subgroups were analyzed for changes in the related genes MTH1 and OGG1. Adenomas were tested for somatic APC mutations.

RESULTS

Six patients with multiple adenomas and eight patients with polyposis had biallelic germline MYH variants. Missense and protein-truncating mutations were found, and the spectrums of mutations were very similar in the two groups of patients. In the tumors of carriers of biallelic mutations, all somatic APC mutations were G:C-->T:A transversions. In the group with multiple adenomas, about one third of patients with more than 15 adenomas had biallelic MYH mutations. In the polyposis group, no patient with biallelic MYH mutations had severe disease (>1000 adenomas), but three had extracolonic disease. No clearly pathogenic MTH1 or OGG1 mutations were identified.

CONCLUSIONS

Germ-line MYH mutations predispose persons to a recessive phenotype, multiple adenomas, or polyposis coli. For patients with about 15 or more colorectal adenomas--especially if no germ-line APC mutation has been identified and the family history is compatible with recessive inheritance--genetic testing of MYH is indicated for diagnosis and calculation of the level of risk in relatives. Clinical care of patients with biallelic MYH mutations should be similar to that of patients with classic or attenuated familial adenomatous polyposis.

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.

The colorectal adenoma-carcinoma sequence

BACKGROUND

It is widely accepted that the adenoma-carcinoma sequence represents the process by which most, if not all, colorectal cancers arise. The evidence supporting this hypothesis has increased rapidly in recent years and the purpose of this article is to review this evidence critically and highlight its clinical significance.

METHODS

Medline searches were used to identify recent key articles relating to the adenoma-carcinoma sequence. Further pertinent articles were obtained by manual scanning of the reference lists of identified papers.

RESULTS

The evidence supporting the adenoma-carcinoma sequence can be classified as epidemiological, clinicopathological and genetic. The most recent and largest body of data relates to molecular genetic events and their cellular effects; however, many other approaches, such as cytogenetics, molecular cytogenetics and cytometry, have also yielded valuable information.

CONCLUSION

Recent work continues to support the adenoma-carcinoma sequence, but there is a paucity of data on the interrelationship between different genetic mutations and on the relationship between molecular and other types of genetic abnormalities. The clinical utility of the observations described has yet to be fully realized and global genetic analysis of colorectal tumours may prove to be central in rational adenoma management.

CpG island methylation in aberrant crypt foci of the colorectum

Aberrant crypt foci (ACF) are postulated to be the earliest precursor lesion in colorectal carcinogenesis, and CpG island methylation has been described as an important molecular pathway. We therefore studied methylation in ACF from patients with familial adenomatous polyposis (FAP) or sporadic colorectal cancer. We assessed methylation status of the p16 tumor suppressor gene, MINT1 (methylated in tumor 1), MINT2, MINT31, O(6)-methylguanine-DNA methyltransferase gene, and hMLH1 mismatch repair gene. We compared methylation to ACF histopathology, K-ras proto-oncogene mutation, loss of heterozygosity at chromosome 1p, and microsatellite instability. Methylation was present in 34% (21 of 61) of ACF, including both FAP and sporadic types, but was more frequent in sporadic ACF [53% (18 of 34) versus 11% (3 of 27), P = 0.002], especially dysplastic sporadic ACF [75% (3 of 4) versus 8% (2 of 24), P = 0.004]. MINT31 was more frequently methylated in heteroplastic ACF than dysplastic ACF [35% (11 of 31) versus 7% (2 of 30), P = 0.01]. Strong associations of ACF methylation with K-ras mutation (P = 0.007) and with loss of chromosome 1p (P = 0.04) were observed, but methylation was the only molecular abnormality identified in 16% (10 of 61) of ACF. Our findings suggest that methylation in ACF is an early event in the pathogenesis of a subset of colorectal carcinomas, and that ACF from FAP patients and patients with sporadic colorectal cancer have distinct epigenetic changes that reflect differences in molecular pathogenesis.

Molecular alterations in chronic ulcerative colitis-associated and sporadic hyperplastic polyps: a comparative analysis

OBJECTIVES

There is growing interest in the biological and molecular features and neoplastic potential of colonic hyperplastic polyps because of the recent finding of K-ras mutations in many of these lesions. Hyperplastic polyps may also develop in chronic ulcerative colitis (CUC), but it is unclear if these are biologically similar to the sporadic type. The aim of this study was to evaluate and compare the molecular profile of CUC-associated hyperplastic polyps with sporadic hyperplastic polyps of the colon.

METHODS

Thirty-nine hyperplastic polyps from 26 CUC patients, 39 sporadic hyperplastic polyps from 29 age- and sex-matched patients without CUC, and 26 colonic mucosal biopsies from 22 patients with CUC but without hyperplastic polyps were analyzed by polymerase chain reaction for loss of heterozygosity of APC, 3p, p53, and p16 and for mutations in codons 12, 13, and 61 of the K-ras gene. Immunohistochemical evaluations for the proliferation-associated nuclear peptide Ki67 (MIB-1) and p27 were also performed on a subset of hyperplastic polyps.

RESULTS

CUC-associated hyperplastic polyps showed a proportion of genetic alterations (47%) similar to that of sporadic hyperplastic polyps (33%) (p > 0.05), and neither significantly differed from chronically inflamed mucosae in CUC patients without hyperplastic polyps. Furthermore, in a small group of CUC patients in which informative tissue was available from both their hyperplastic polyps and adjacent flat colitic mucosae, the polyps contained mutations that were not present in the underlying mucosa. Loss of heterozygosity of APC, 3p, p53, p16, and K-ras mutations were present in 21%, 40%, 27%, 20%, and 19% of CUC patients with hyperplastic polyps, respectively, and in 0%, 11%, 20%, 13%, and 13% of non-CUC patients with sporadic polyps, respectively. Both CUC-associated and sporadic hyperplastic polyps showed a substantial number of cases (46% and 64% of cases, respectively) with loss of p27 expression, and both types of lesions showed similar MIB-1 proliferation indices.

CONCLUSIONS

These data suggest that CUC-associated hyperplastic polyps are genotypically similar to the sporadic type. This study adds to the expanding list of molecular alterations that have been discovered in hyperplastic polyps, and lends further support to the controversial theory that these lesions may have neoplastic potential.

Loss of heterozygosity, microsatellite instability, and mismatch repair protein alterations in the radial growth phase of cutaneous malignant melanomas

Little is known about genomic alterations during development of the radial growth phase (RGP) of cutaneous malignant melanomas (CMMs). In this investigation polymerase chain reaction-based microsatellite assays were applied to analyze 13 RGP-CMMs with 18 microsatellite markers at six chromosomal regions: 1p, 3p, 4q, 6q, 9p, and 10q. Loss of heterozygosity (LOH) was found in eight cases (62%), at 9p22, 1p36, and 10q11, suggesting the presence of tumor-suppressor genes at these regions. LOH was encountered frequently at the interferon-alpha (31%) and D10S249 loci (15%). Low-level microsatellite instability (MSI) (11-16% of investigated loci unstable) was noted in three cases (23%). Two MSI banding patterns were seen: band shift and the presence of additional bands. To investigate the underlying mechanisms of the low-level MSI pattern, we analyzed the lesions for expression of mismatch repair (MMR) proteins with immunoperoxidase methods and mouse monoclonal antibodies. The average percentages of positively stained cells for human MutL homolog 1 (hMLH1), human MutS homolog 2 (hMSH2), and human MutS homolog 6 (hMSH6) in RGP-CMM (75.6 +/- 3.4%, 67.20 +/- 7.71%, and 76.6 +/- 2.1%, respectively) were reduced compared with benign nevi. No statistically significant differences in MMR protein expression were found between microsatellite-stable and low-level MSI lesions (P = 0.173, P = 0.458, and P = 0.385 for hMLH1, hMSH2, and hMSH6, respectively). There was a direct correlation between values for percentages of positively stained cells for hMSH2 and hMSH6 (r = +0.9, P = 0.03), suggesting that common mechanisms regulate their expression. In conclusion, LOH, MSI, and reduced MMR protein expression appear to be present in at least some RGP-CMMs and may play a role in their pathogenesis. Further studies are necessary to support these finding and to determine their diagnostic and prognostic significance.

Genetic alterations in serrated adenomas: comparison to conventional adenomas and hyperplastic polyps

Serrated adenoma is a recently described entity characterized by the presence of a hyperplastic (serrated) growth pattern combined with cytologic features of dysplasia. In contrast to conventional (nonserrated) adenomas, the molecular features of serrated adenomas have been poorly studied. Thus, it remains unclear if serrated adenomas are simply a morphologic variant of conventional adenomas or represent a different biologic entity. In this study, 46 serrated adenomas from 39 patients, 32 conventional (nonserrated) adenomas from 31 patients, and 18 hyperplastic polyps from 16 patients were evaluated for loss of heterozygosity (LOH) of APC, p53, p16, and 3p and for K-ras mutations of codons 12, 13, and 61 by polymerase chain reaction (PCR) analysis. Serrated adenomas demonstrated LOH of at least one genetic locus in 32.6% of cases. LOH of the APC gene, 3p, p53, and p16 was seen in 19.4%, 14.2%, 9.3%, and 13.8% of cases, respectively. K-ras mutations were observed in 18% of cases. Similar to serrated adenomas, conventional adenomas demonstrated at least one LOH event in 37.5% of cases and K-ras mutations in another 19% of cases. LOH of APC, 3p, p53, and p16 was observed in 22%, 33%, 5.8%, and 13.4% of cases, respectively. There were no significant differences in either the total number of genetic events or the presence of LOH of any of the individual markers between serrated adenomas and conventional adenomas. However, hyperplastic polyps showed LOH in 22% of cases and a single K-ras mutation (11%). The prevalence of LOH in hyperplastic polyps was lower than both serrated adenomas and conventional adenomas (P < .05). These results support the hypothesis that serrated adenomas represent a biologically similar morphologic variant of conventional adenomas.

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).

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.

Comprehensive analysis of 112 melanocytic skin lesions demonstrates microsatellite instability in melanomas and dysplastic nevi, but not in benign nevi

INTRODUCTION

the length of DNA repetitive sequences (microsatellite instability (MSI)) represent distinct tumorigenic pathways associated with several familial and sporadic tumors.

MATERIAL AND METHODS

To investigate the prevalence and frequency of MSI in melanocytic lesions, the polymerase chain reaction (PCR)-based microsatellite assay was used to examine formalin-fixed, paraffin-embedded tissues of 30 benign melanocytic nevi, 60 melanocytic dysplastic nevi (MDN), and 22 primary vertical growth phase cutaneous malignant melanomas (CMM). Twenty-four microsatellite markers at the 1p, 2p, 3p, 4q and 9p chromosomal regions were used.

RESULTS

MSI was found at 1p and 9p in MDN and CMM but not in benign melanocytic nevi. The overall prevalence of MSI was 17/60 (28%) in MDN and 7/22 (31%) in CMM. The frequency of MSI ranged from 2/24 (9%) to 4/24 (17%) and was most commonly found at D9S162. There was a statistically significant correlation between degree of atypia and frequency of MSI (p<0.001) in MDN. There were two MSI banding patterns: band shifts and additional bands.

CONCLUSIONS

The data presented revealed the presence of low-frequency MSI (MSI-L) at the 1p and 9p regions in both MDN and CMM. Whether the MSI-L pattern reflects a defect in mismatch repair genes is still to be determined.

Pathology of colorectal cancer

The earliest phases of colorectal tumourigenesis initiate in the normal mucosa, with a generalised disorder of cell replication, and with the appearance of clusters of enlarged crypts (aberrant crypts) showing proliferative, biochemical and biomolecular abnormalities. The large majority of colorectal malignancies develop from adenomatous polyps. These can be defined as well demarcated masses of epithelial dysplasia, with uncontrolled crypt cell division. An adenoma can be considered malignant when neoplastic cells pass through the muscularis mucosae and infiltrate the submucosa. Definitions like "carcinoma in situ" or "intramucosal carcinoma" should be abandoned, since they lead to confusion. Although several lines of evidence indicate that carcinomas usually originate from pre-existing adenomas, this does not imply that all polyps undergo malignant changes, and does not exclude "de novo" carcinogenesis. Besides adenomas, other types of polypoid lesions include hyperplastic polyps (showing elongated crypts often with cystic dilatation), serrated adenomas (with a serrated glandular pattern], flat adenomas (flat lesions which are difficult to detect in routine lower endoscopy, but may possess malignant potential), hamartomatous polyps (which show a complex branching pattern of smooth muscle supporting normal lamina propria and glands), and inflammatory polyps. Colorectal carcinomas are one of the most frequent neoplasms in Western society; the macroscopic appearance of these lesions may be that of a polypoid vegetating mass or of a flat infiltrating lesion. Most of these tumours are adenocarcinomas (96%), that, in some cases, show a mucinous component. More rare malignancies of the large bowel include signet-ring cell carcinoma, squamous carcinoma, undifferentiated neoplasms and medullary type adenocarcinoma (solid carcinoma with minimal glandular differentiation or slight cellular pleomorphism). Colorectal carcinoma can be graded into well, moderately and poorly differentiated lesions; there is little evidence, however, that grading may be of help in evaluating prognosis of affected patients. In conclusion, colorectal tumours cover a wide range of premalignant and malignant lesions, many of which can easily be removed at endoscopy. It follows that colorectal neoplasms might be prevented by interfering with the various steps of carcinogenesis, which begins with uncontrolled epithelial cell replication, continues with the formation of adenomas of various dimensions, and eventually evolves into malignancy.

Colorectal carcinoma associated with serrated adenoma--prevalence, histological features, and prognosis

Serrated adenoma has been proposed to be a distinct entity among colorectal neoplasms. Progression to frank carcinoma has been suggested in individual cases, but the prevalence of carcinomas originating from serrated adenomas and their clinico-pathological characteristics are not known. In the present study, a large series of colorectal cancers was analysed for the occurrence of serrated adenoma in association with carcinoma and clinico-pathological features were compared in cases with and without serrated adenoma. Specimens from 466 colorectal carcinoma patients undergoing operations between 1986 and 1996 were re-evaluated for the presence of juxtaposed serrated adenoma and carcinoma. Clinico-pathological features such as location, Dukes' stage, histological grade, mucinous differentiation, and prognosis were evaluated. Twenty-seven carcinomas (5.8%) were found in association with an adjacent serrated adenoma. Eight of the patients were male and 19 were female. All of these adenocarcinomas showed a serrated appearance resembling that of serrated adenomas. Nine (33%) cases were mucinous and a mucinous component was present in 11 (41%) additional cases. The majority of the tumours were located either in the caecum (14 cases; 51%) or in the rectum (9 cases; 33%). DNA microsatellite instability was more common in carcinomas associated with serrated adenoma (37.5%) than in other carcinomas (11.0%). It is concluded that carcinoma associated with serrated adenoma is a distinct type of colorectal neoplasm, accounting for 5.8% of all colorectal carcinoma cases in this study. Predilection for the caecum and the rectum may reflect their aetiological factors. Female preponderance is contrary to that reported for hyperplastic polyps and serrated adenomas.

Hyperplastic polyposis: association with colorectal cancer

Hyperplastic polyposis is a loosely defined syndrome initially thought not to confer a clinically important predisposition to colorectal cancer. The aim of the current study was to examine the clinical, histologic, and molecular features of a prospective series of cases meeting a strict definition of the condition. Twelve patients were identified, seven of whom had developed colorectal cancer. Most polyps were hyperplastic, but 11 patients also had polyps containing dysplasia as either serrated adenomas. mixed polyps, or traditional adenomas. The mean percentage of dysplastic polyps in patients with cancer was 35%, and in patients without cancer, 11% (p < 0.05). Microsatellite instability (MSI) was present in 3 of 47 hyperplastic polyps and two of eight serrated adenomas. Kras was mutated in 8 of 47 hyperplastic polyps and two of eight serrated adenomas. No polyps showed loss of heterozygosity of chromosomes 5q, 1p, or 18q. Two of seven cancers showed a high level of MSI. It is concluded that hyperplastic polyposis is associated with a high risk of colorectal cancer. Hyperplastic polyps are the dominant type of polyp, but most cases have some dysplastic epithelium. A higher proportion of dysplastic polyps is associated with increased cancer risk. Clonal genetic changes are observed in some hyperplastic polyps and serrated adenomas.

Distal deletion of 1p in colorectal tumors: an initial event and/or a step in carcinogenesis? Study by fluorescence in situ hybridization interphase cytogenetics

Cytogenetics studies have suggested that short arm deletion in chromosome 1 is involved in triggering colorectal tumor development. To elucidate the role of 1p under-representation in the tumoral process, we investigated by fluorescence in situ hybridization interphase cytogenetics, using simultaneously centromeric and p36 telomeric probes for chromosome 1, 27 primary adenocarcinomas, 5 metastases, 5 adenomas and as control 4 normal mucous membranes. The 1p under-representation in paradiploid tumoral cells, interpreted as a 1p deletion, was observed in 8/27 adenocarcinomas, 2/5 metastases and 3/5 adenomas. Thus, in diploid cells 1p deletion was observed in some tumors independently of the stage of the process. The 1p under-representation in total number of examined cells, i.e., diploid and aneuploid, was observed in 14/16 grade B1-B2 tumors, in 5/8 grade C1-C2 tumors, and all grade D tumors (3/3) and all metastases (5/5). There were no correlations with location or histological characteristics of cancers, gender or age of patients. These results show high frequency of 1p under-representation in intestinal tumors, and lead to separate the under-representation of 1p in diploid cells, which correspond to a 1p deletion probably implicated in the initiation of the process, from the under-representation in aneuploid cells, which mainly may be the consequence of complex rearrangements in relation to extension of the malignant process.

Low frequency of allelic imbalance at the prostate cancer susceptibility loci HPC1 and 1p36 in Swedish men with hereditary prostate cancer

The aim of this study was to investigate allelic imbalance at the major human prostate cancer susceptibility locus HPC1 at 1q24-25 and the recently reported, putative, susceptibility locus at 1p36 in prostate tumors from Swedish families with hereditary prostate cancer. We analyzed 31 prostate tumors and two lymph node metastases from 33 Swedish men in 22 families with hereditary prostate cancer for the presence of allelic imbalance using microsatellite markers D1S158, D1S422, and D1S238 for the HPC1 locus and D1S1597, D1S407, and D1S489 for the 1p36 locus. Frequencies of allelic imbalance at the two investigated loci were quite low, 3 of 27 informative tumors at the 1p36 locus and 3 of 27 informative tumors at the HPC1 locus. Interestingly, two tumors showed allelic imbalance at both loci investigated, suggesting that they may have lost a great part of chromosome 1. Taking this possibility into consideration, the specific loss of the two investigated loci may be even lower (1 of 27 informative tumors for either locus). The very low level of allelic imbalance found at HPC1 and 1p36 makes it unlikely that these loci encode genes that are acting as classic tumor suppressor genes in the initiation or progression of hereditary prostate cancer. Of the eight tumors from HPC1-linked families, only two showed AI at the HPC1 locus, one of which had lost the wild-type allele.

Evaluation of 1p losses in primary carcinomas, local recurrences and peripheral metastases from colorectal cancer patients

Cytogenetic and molecular genetic analyses of colorectal adenomas and carcinomas have shown that loss of the distal part of chromosome arm 1p is common, particularly in tumors of the left colon. Because the importance of 1p loss in colorectal cancer metastases is unknown, we compared the frequency, exact site and extent of 1p deletions in primary carcinomas (n=28), local recurrences (n=19) and metastases (n=33) from 67 colorectal cancer patients using 14 markers in an allelic imbalance study. Loss of 1p was found in 50% of the primary carcinomas, 33% of the local recurrences, and 64% of the metastases, revealing a significant difference between the local recurrences and the metastases (P=.04). The smallest region of 1p deletion overlap (SRO) defined separately for each group of lesions had the region between markers D1S2647 and D1S2644, at 1p35-36, in common. The genes PLA2G2A (1p35.1-36) and TP73 (1p36.3) were shown to lie outside this consistently lost region, suggesting that neither of them are targets for the 1p loss. In the second part of the study, microdissected primary carcinomas and distant metastases from the same colorectal cancer patients (n=18) were analyzed, and the same 1p genotype was found in the majority of patients (12/18, 67%). The finding that primary carcinoma cells with metastatic ability usually contain 1p deletions, and that some cases lacking 1p alterations in the primary tumor acquire such changes during growth of a metastatic lesion, supports the notion that 1p loss may be important both early and late in colorectal carcinogenesis, with the apparent exception of local recurrences.

Hyperplastic polyps and DNA microsatellite unstable cancers of the colorectum

Although the scientific and clinical rationale for classifying colorectal cancer according to mechanisms underlying genetic instability is well supported, little is known of the early morphogenesis of sporadic cancer showing high levels of DNA microsatellite instability (MSI-H). Evidence is accumulating that the traditional adenoma-carcinoma sequence may not apply to sporadic MSI-H colorectal cancer. The serrated pathway comprising hyperplastic polyps, mixed polyps and serrated adenomas may serve as the missing link. This review relates the recently described CpG island methylator phenotype (CIMP) to the serrated pathway. Two rate-limiting genetic steps may underlie the neoplastic pathway associated with CIMP. A transmembrane receptor expressed by pericryptal myofibroblasts (HPP1) may be implicated in the transition from normal to hyperplasia whereas inactivation of hMLH1 is responsible for the conversion of hyperplasia to dysplasia through loss of DNA mismatch repair. These mechanisms fit with clinical observations relating to sporadic MSI-H colorectal cancer, specifically proximal location, multiplicity, higher frequency among females and rapid evolution of early cancer.

Phenotypic and molecular characteristics of hyperplastic polyposis

BACKGROUND & AIMS

Patients with hyperplastic polyposis are reported to have multiple and/or large hyperplastic polyps (HPs) and an increased risk of colorectal cancer, but the phenotype and genetic alterations in hyperplastic polyposis have not been studied in detail.

METHODS

We evaluated clinical-pathological and molecular characteristics of 129 HPs, 6 serrated adenomas, and 3 admixed hyperplastic-adenomatous polyps from 13 patients with hyperplastic polyposis (more than 20 HPs), 5 patients with a large HP (>/=1 cm in diameter), and 5 patients with multiple HPs (5-10 HPs).

RESULTS

HPs in the right colon in contrast to the left colorectum had more frequent topographic dysregulation of p21(Waf-1/Cip1) expression (94% vs. 76%, P = 0.03) and of proliferation (92% vs. 53%, P = 0. 0001), but less frequent allelic loss of chromosome 1p (4% vs. 17%, P = 0.03). K-ras mutation was present in 8% of HPs, p53 gene product overexpression in none, and microsatellite instability in 3% without relationship to microsatellite instability in synchronous cancer. Patients with a large HP differed from those with multiple HPs in having a high frequency of right-sided HP (63% vs. 22%, P = 0.01) and of right-sided colon cancer (100% vs. 8%, P = 0.003). Hyperplastic polyposis was associated with a family history of colorectal cancer (P = 0.01) and with loss of chromosome 1p in HP (21% vs. 0%, P = 0.001).

CONCLUSIONS

A hyperplastic polyp/dysplasia-to-adenocarcinoma sequence can be manifested in 3 distinct phenotypes consisting of patients with hyperplastic polyposis and chromosome 1p allelic loss in some HPs, in contrast to patients who have large, right-sided HPs or small numbers of HPs that lack 1p loss.

APC mutations are sufficient for the growth of early colorectal adenomas

It is not clear whether APC mutations are sufficient for early colorectal adenomas to grow or whether additional mutations at other loci are required. We previously have screened 210 early colorectal adenomas from familial adenomatous polyposis patients for mutations and allelic loss at APC. Here, we determined whether allelic loss at APC had any effect on the nearby alpha-catenin gene. However, loss on 5q in familial adenomatous polyposis adenomas rarely extended as far as alpha-catenin, and no differences in alpha-catenin protein expression were found in tumors that showed loss encompassing both APC and alpha-catenin. We then screened all 210 tumors for mutations at candidate loci other than APC (K-ras, beta-catenin, and allelic loss at 1p33-p35 and 1p36) and for microsatellite instability (MSI). Each of these loci has been implicated previously in early colorectal tumorigenesis. One tumor harbored a beta-catenin mutation and another MSI, but none showed K-ras mutation or allelic loss at 1p33-p35 or 1p36. These data support the following hypotheses derived from sporadic colorectal tumors: beta-catenin mutations are generally an alternative to mutations at APC, MSI is not usually an early phenomenon in colorectal tumorigenesis, and K-ras mutations are more typical of large- and moderate-sized adenomas. Contrary to some previous reports, chromosome 1p allelic loss is infrequent in very early adenomas. APC mutations are generally sufficient for colorectal tumors to grow to about 1-cm diameter, although chance mutations at other loci can provide these early colorectal adenomas with a selective advantage, and some colorectal tumors may develop along a pathway not involving APC.