Emerging concepts in colorectal neoplasia

Inflammation and cancer IV. Colorectal cancer in inflammatory bowel disease: the role of inflammation

Patients with ulcerative colitis and Crohn's disease are at increased risk for developing colorectal cancer. To date, no known genetic basis has been identified to explain colorectal cancer predisposition in these inflammatory bowel diseases. Instead, it is assumed that chronic inflammation is what causes cancer. This is supported by the fact that colon cancer risk increases with longer duration of colitis, greater anatomic extent of colitis, the concomitant presence of other inflammatory manifestations such as primary sclerosing cholangitis, and the fact that certain drugs used to treat inflammation, such as 5-aminosalicylates and steroids, may prevent the development of colorectal cancer. The major carcinogenic pathways that lead to sporadic colorectal cancer, namely chromosomal instability, microsatellite instability, and hypermethylation, also occur in colitis-associated colorectal cancers. Unlike normal colonic mucosa, however, inflamed colonic mucosa demonstrates abnormalities in these molecular pathways even before any histological evidence of dysplasia or cancer. Whereas the reasons for this are unknown, oxidative stress likely plays a role. Reactive oxygen and nitrogen species produced by inflammatory cells can interact with key genes involved in carcinogenic pathways such as p53, DNA mismatch repair genes, and even DNA base excision-repair genes. Other factors such as NF-kappaB and cyclooxygenases may also contribute. Administering agents that cause colitis in healthy rodents or genetically engineered cancer-prone mice accelerates the development of colorectal cancer. Mice genetically prone to inflammatory bowel disease also develop colorectal cancer especially in the presence of bacterial colonization. These observations offer compelling support for the role of inflammation in colon carcinogenesis.

The relationship between cyclooxygenase-2 expression and characteristics of malignant transformation in human colorectal adenomas

BACKGROUND AND AIMS

Cyclooxygenase 2 (COX-2) is a target of aspirin and other non-steroidal anti-inflammatory drugs and is implicated in the pathogenesis of colorectal cancer. The objective of this study was to evaluate the extent of COX-2 in pre-malignant colorectal polyps and to assess the relationship between COX-2 and the level of dysplasia in these lesions.

METHODS

Whole polypectomy specimens were retrieved from 123 patients by endoscopic or surgical resection. Following formalin fixation and paraffin embedding, the polyps were evaluated histologically for size, type and grade of dysplasia. The extent of COX-2 expression was measured by the avidin-biotin immunohistochemical technique using a monoclonal COX-2 antibody. The extent of COX-2 expression was graded according to percentage epithelial COX-2 expression.

RESULTS

The polyps were of the following histological types: 10 hyperplastic, 35 tubular adenomas, 61 tubulovillous adenomas and 17 villous adenomas. Twenty showed mild dysplasia, 65 moderate dysplasia, and 28 focal or severe dysplasia (including eight with focal invasion). The average polyp size was 1.7 cm. Nine hyperplastic polyps were COX-2-negative and one was COX-2-positive. COX-2 expression was more extensive in larger polyps and in polyps with a higher villous component. There was a significant increase in the extent of COX-2 protein with increasing severity of dysplasia. Within a polyp, there was a focal corresponding increase in COX-2 expression within epithelium showing a higher grade of dysplasia.

CONCLUSIONS

COX-2 expression is related directly to colorectal adenomatous polyp size, type and grade of dysplasia. This suggests that the role of COX-2 in colorectal cancer may be at an early stage in the adenoma-to-carcinoma sequence and supports the suggestion that inhibition of COX-2 may be useful chemoprevention for this disease.

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

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

Diagnosis and management of dysplasia in patients with inflammatory bowel diseases

Patients with ulcerative colitis and Crohn's colitis face an increased lifetime risk of developing colorectal cancer. Factors associated with increased risk include long duration of colitis, extensive colonic involvement, primary sclerosing cholangitis, a family history of colorectal cancer, and, according to some studies, early disease onset and more severely active inflammation. Although prophylactic proctocolectomy can essentially eliminate the risk of cancer, most patients and their physicians opt instead for a lifelong program of surveillance. This entails regular medical follow-up, management with antiinflammatory and putative chemopreventive agents, and periodic colonoscopic examinations combined with extensive biopsy sampling throughout the colon. The main objective of regular colonoscopy is to detect neoplasia at a surgically curative and preferably preinvasive stage, i.e., dysplasia. An initial screening colonoscopy should be performed 7-8 years from disease onset or immediately in patients with primary sclerosing cholangitis. Surveillance should then continue annually or biennially so long as no dysplasia is found or suspected. Biopsy specimens are graded pathologically as negative, indefinite for dysplasia, low-grade dysplasia, high-grade dysplasia, or invasive cancer. The diagnosis and grading of dysplasia can be very challenging and should be confirmed by an expert pathologist whenever intervention or a change in management is contemplated. If 1 or more biopsy specimens are indefinite for dysplasia, colonoscopy intervals should be reduced. A patient with low- or high-grade dysplasia found in a discrete adenoma-like polyp, but nowhere else, can be safely managed with polypectomy and accelerated surveillance. However, dysplasia of any grade found in an endoscopically nonresectable polyp and high-grade dysplasia found in flat mucosa are both strong indications for proctocolectomy. Evidence further suggests that the same may be true even of low-grade dysplasia in flat mucosa. Chromoendoscopy holds promise for facilitating the endoscopic detection of neoplasia. The clinical application of newer molecular methods to detect neoplasia, particularly gene microarrays and stool DNA testing, also deserve further study.

Clinical significance of small colorectal polyps

PURPOSE

Since the concept of "advanced" or "dangerous" adenomas was introduced in 1992, less concern has been directed to diminutive colorectal adenomas. They apparently confer no increased risk of metachronous colorectal cancer and some investigators have suggested that they need neither follow-up nor treatment. This study is intended to discover how often small colorectal adenomas have unfavorable histologic features.

METHODS

Since 1995 the details of all colorectal polyps have been entered into a database, along with data concerning patients, symptoms, treatment, and outcome. Using this database all adenomas were categorized into three groups: Group I, <6 mm diameter, Group II, 6 to 10 mm diameter, and Group III, >10 mm diameter. "High risk" adenomas were defined as those containing >25 percent villous architecture, those with severe dysplasia, and those over 10 mm in size. Thus all Group III adenomas are high-risk by definition. The effects of family history, patient age, and polyp location on the proportions of Group I and Group II adenomas that were histologically high risk were examined.

RESULTS

There were 5,722 polyps of which 4,381 (76.6 percent) were Group I, 666 (11.6 percent) were Group II, and 675 (11.8 percent) were Group III. These included 24 invasive cancers (2 in Group I, 1 in Group II, and 21 in Group III. Of the Group I adenomas, 91/2,064 (4.4 percent) were high risk compared to 65/417 (15.6 percent) in Group II. Of the 564 Group III adenomas, 326 (57.8 percent) had unfavorable histology. There was no effect of age, family history, or site of the polyp on the proportion of polyps that were high risk.

CONCLUSIONS

Four percent of adenomas less than 6 mm diameter and 16 percent of those between 6 and 10 mm have unfavorable histology. Small adenomas can still be clinically significant and should not be ignored. Since the concept of "advanced" or "dangerous" adenomas was introduced in 1992, less concern has been directed to diminutive colorectal adenomas. They apparently confer no increased risk of metachronous colorectal cancer and some investigators have suggested that they need neither follow-up nor treatment. This study is intended to discover how often small colorectal adenomas have unfavorable histologic features.

Gene mutations in advanced colonic polyps: potential marker selection for stool-based mutated human DNA assays for colon cancer screening

The detection and removal of advanced colonic polyps (ACPs) can help prevent the development of colorectal cancer. A set of DNA mutations known to be associated with colorectal carcinoma was tested against resected ACPs to determine the set s potential utility as a marker panel for ACPs. A sensitive mutation marker panel could be used by stool-based assays that look for mutated human DNA to detect the presence of ACPs. DNA from 32 ACPs = 1.0 cm in diameter was amplified and tested for 19 colorectal cancer associated DNA mutations and for deletions in BAT-26 (microsatellite instability). One or more mutations were identified by microsequencing in 28 of the 32 ACPs (88%). Mutations were identified in k-ras (59%), APC (33%), and p53 (22%). BAT-26 mutation, a marker for microsatellite instability, was not identified. Stool DNA based assays that can identify these mutations may significantly increase the identification of patients with potentially premalignant ACPs for evaluation and treatment by colonoscopy.

Genome wide array comparative genomic hybridisation analysis of premalignant lesions of the stomach

BACKGROUND

Gastric cancer is one of the most frequent malignancies in the world, ranking fifth in the Netherlands as a cause of cancer death. Surgery is the only curative treatment for advanced cases, but results of gastrectomy largely depend on the stage of the disease. A better understanding of the mechanisms of progression from a preneoplastic condition through intraepithelial neoplasia to invasive cancer may provide information relevant to designing focused prevention strategies.

METHODS

Because the pattern of chromosomal aberrations in precursors of gastric cancer is unclear, 11 gastric polyps with intraepithelial neoplasia (three hyperplastic polyps and eight adenomas) were analysed by microarray comparative genomic hybridisation to study chromosomal instability in precursors of gastric cancer.

RESULTS

Chromosomal aberrations were detected in all specimens. Adenomas showed no more chromosomal aberrations than did the hyperplastic polyps. The most frequent aberrations were gain of 7q36 and 20q12, and loss of 5q14-q21 in the adenomas, and loss of 15q11-14, 1p21-31, and 21q11-21.2 in the hyperplastic polyps. The most frequent chromosomal aberration in common to both types was loss of 9p21.3.

CONCLUSION

Hyperplastic polyps showed many chromosomal aberrations, confirming that neoplastic transformation can occur in these lesions. These observations are consistent with the existence of two morphologically and genetically distinct pathways to gastric cancer-the hyperplastic polyp pathway and the (intestinal type) adenoma pathway. The relative contribution of each to gastric carcinogenesis in general, and how they compare to patterns of chromosomal aberrations in the more prevalent flat foci of intraepithelial neoplasia remain to be determined.

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.

Colorectal proliferation and apoptosis in serrated versus conventional adenoma-carcinoma pathway: growth, progression and survival

BACKGROUND

Hyperplastic polyp, serrated adenoma and serrated adenocarcinoma form a morphological continuum, and are likely to be biologically related. The growth rate and malignant conversion rate of serrated adenoma are postulated to be higher than those of conventional adenoma.

METHODS

Immunohistochemistry for M30 and Ki67 was used to compare apoptosis and proliferation in colorectal hyperplastic polyps, serrated adenomas and serrated adenocarcinomas, and in relation to conventional adenomas and adenocarcinomas.

RESULTS

There was an abrupt increase in the apoptosis in carcinomas of serrated adenoma-serrated adenocarcinoma pathway, indicating that inhibition of apoptosis is not maintained in serrated adenocarcinomas. Proliferation was significantly lower at the invasive margin than in the central part in adenocarcinomas, particularly in serrated adenocarcinomas (P < 0.005, Wilcoxon). Apoptosis was lower at the invasive margin than in the central part in serrated adenocarcinomas, but not in conventional adenocarcinomas.

CONCLUSIONS

Disordered regulation of apoptosis occurs later in serrated pathway than in conventional adenoma-carcinoma pathway during malignant conversion. Serrated adenoma growth is not likely to be slower than adenoma growth, as judged by the proliferation and apoptosis rates in serrated adenomas and adenomas. In cancer, the decrease of proliferation and apoptosis in the invasive margin is likely to influence the behaviour of the tumour.

High frequency of genetic aberrations in enteropathy-type T-cell lymphoma

To define genetic aberrations playing a role in the development of enteropathy-type T-cell lymphoma (ETL), we examined 26 such tumors using a battery of 47 microsatellite markers. The most frequent aberration (seen in 40% of informative genotypes) was amplification of genomic material in region 9q34 encompassing c-abl and Notch-1 gene loci. Other frequent amplifications were detected in regions 5q33.3-34 and 7q31 (both in more than 30%). Multiple losses of heterozygosity were detected in 6p24, 7p21, 17q23-25, regions containing putative tumor suppressor genes, and in the p53 locus in 17p13.1. Analysis of the pattern of occurrence of these aberrations revealed existence of two ETL subgroups: one of them characterized by the 9q34 aberration and another smaller one showing allelic imbalances in 3q27. These two aberrations were mutually exclusive. Microsatellite instability (MSI) was detected in 69% of the examined lymphomas; the percentage of MSI-positive genotypes per tumor ranged from 2% to 12%. The spectrum of genetic alterations detected showed patterns dependent on morphology. Monomorpic ETLs displayed frequently biallelic TCR-gamma gene rearrangement (p = 0078, chi(2) test). They showed a different pattern and fewer allelic imbalances (no 3q27, 4q28, 13q14, fewer 5q21, or 5q33.3-34 aberrations) and a lower frequency of MSI than pleomorphic ETLs.

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

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

Human intestinal epithelial crypt cell survival and death: Complex modulations of Bcl-2 homologs by Fak, PI3-K/Akt-1, MEK/Erk, and p38 signaling pathways

To investigate the mechanisms responsible for survival and apoptosis/anoikis in normal human intestinal epithelial crypt cells, we analyzed the roles of various signaling pathways and cell adhesion on the expression of six Bcl-2 homologs (Bcl-2, Bcl-XL, Mcl-1, Bax, Bak, Bad) in the well established HIEC-6 cell model. Pharmacological inhibitors and/or dominant-negative constructs were used to inhibit focal adhesion kinase (Fak) and p38 isoforms, as well as the phosphatidylinositol 3'-kinase (PI3-K)/Akt-1 and mitogen-activated protein kinase [MAPK] kinase (MEK)/extracellular regulated kinases (Erk) pathways. Cell adhesion was disrupted by antibody-inhibition of integrin binding or forced cell suspension. The activation levels of studied kinase pathways were also analyzed. Herein, we report that beta1 integrins, Fak, and the PI3-K/Akt-1 pathway, but not beta4 integrins or the MEK/Erk pathway, are crucial for the survival of HIEC-6 cells. Conversely, p38beta, but not p38alpha or gamma, is required for the induction of apoptosis/anoikis in HIEC-6 cells. However, each of the signaling molecules/pathways analyzed were found to affect distinctively the individual expression of the Bcl-2 homologs studied. For example, the inhibition of the PI3-K/Akt-1 pathway down-regulated Bcl-XL, Mcl-1, and Bad, while at the same time up-regulating Bax, whereas the inhibition of Fak up-regulated both Bax and Bak, down-regulated Bad, and did not affect the other Bcl-2 homologs analyzed. These results indicate that integrins, Fak, PI3-K/Akt-1, MEK/Erk, and p38 isoforms perform distinct roles in the regulation of HIEC-6 cell survival and/or death. In addition, our data show that the functions performed by these molecules/pathways in promoting cell survival or apoptosis/anoikis translate into complex, differential modulations of individual Bcl-2 homologs.

Possible influence of glutathione S-transferase GSTT1 null genotype on age of onset of sporadic colorectal adenocarcinoma

INTRODUCTION

Glutathione S-transferase enzymes mediate exposure to cytotoxic and genotoxic agents and may be involved in cancer susceptibility. Both glutathione S-transferase mu 1 (GSTM1) and GST theta 1 (GSTT1) genes have a null variant allele in which the entire gene is absent. The association of glutathione S-transferase null genotype and risk of developing colorectal cancer is not yet fully clarified.

METHODS

We tested whether the null genotypes for GSTM1 and GSTT1 genes altered the risk for sporadic colorectal adenocarcinoma in Brazilian patients. Genomic DNA from 102 sporadic colorectal adenocarcinoma patients and 300 controls was analyzed by polymerase chain reaction.

RESULTS

Frequencies of GSTM1, GSTT1, and null combined genotypes were similar in patients and controls (49.9 vs. 44.6 percent, 16.6 vs. 17.3 percent, and 8.8 vs. 8 percent, respectively). We found a 1.03-fold (95 percent confidence interval, 0.96-1.10) and 1.08-fold (95 percent confidence interval, 0.99-1.18) increased risk associated with GSTM1 and GSTT1 null genotypes, respectively (P = 0.45 and P = 0.08) and a 1.18-fold (95 percent confidence interval, 0.47-2.90) increased risk associated with the combined null genotype (P = 0.74). The GSTT1 null genotype was more common in patients who were diagnosed before the age of 60 years than in those who were diagnosed at an older age (28.8 vs. 4 percent, respectively; P = 0.0008).

CONCLUSIONS

The results suggest that inherited absence of this carcinogen detoxification pathway may not be associated with sporadic colorectal adenocarcinoma in the present cases. However, a higher frequency of GSTT1 null genotype in patients diagnosed before the age of 60 years suggests that this genotype could influence the age of disease onset in Brazil.

Apc+/Min colonic epithelial cells express TNF receptors and ICAM-1 when they are co-cultured with large intestine intra-epithelial lymphocytes

Adenomatous polyposis coli (APC) functions are involved in the heterotypic interactions occurring between intestinal epithelial cells (IECs) and intra-epithelial lymphocytes (IELs). These interactions may be of interest in cancer prevention, since recent data provide evidence for lymphocyte mediated immunosurveillance of epithelial cancers. The present study attempts to determine if APC inactivation induces changes in the cross-talk between IEC and large intestine IEL (LI-IEL) through intercellular adhesion molecule (ICAM-1)/leukocyte function-associated (LFA-1) interactions. Mouse Apc+/+ and Apc+/Min colonocytes were co-cultivated with LI-IEL. When co-cultured with LI-IEL Apc+/Min IEC but not Apc+/+ IEC expressed high levels of ICAM-1. The presence of ICAM-1 was linked to TNFalpha production in both co-cultures and TNFR expression only in co-cultivated Apc+/Min IEC. Finally, butyrate enhanced the expression of ICAM-1 in Apc+/Min IEC co-cultured with LI-IEL, and the secretion of TNFalpha by both types of co-cultures. These events could participate in determining the Apc+/Min IEC immunogenicity under different in vivo conditions.

The relationship between hypomethylation and CpG island methylation in colorectal neoplasia

Tumors are often characterized by an imbalance in cytosine methylation as manifested both by hypermethylation of CpG islands and by genome hypomethylation. These epigenetic changes were assessed in colorectal neoplasia to determine whether they arose through a common mechanism or indeed were distinct and unrelated phenomena. Fresh representative samples of adenomas, hyperplastic polyps, colorectal cancers, and normal mucosa were used in this study. Global methylation levels were measured by analyzing the methyl-accepting capacity of DNA. Methylation of p16, hMLH1, and MINT 1, 2, 12, and 31 were assessed by bisulfite polymerase chain reaction. Microsatellite status was determined by polymerase chain reaction using six markers and hMLH1 and proliferating cell nuclear antigen expression was assessed by immunohistochemistry. Normal colonic mucosa had a higher endogenous 5-methyl cytosine content than all proliferative lesions of the colon (P < 0.001). The extent of demethylation in hyperplastic polyps and adenomas was significantly related to its proliferative rate. Right-sided hyperplastic polyps were more likely to be methylated than adenomas (odds ratio, 2.3; confidence interval, 1.1 to 4.6). There was no relationship between the level of global hypomethylation and hypermethylation. Some hyperplastic colorectal polyps have a propensity to develop dense CpG island methylation. Hypermethylation and hypomethylation contribute separately to the process of carcinogenesis.

Challenges to cancer control by screening

Population-based screening seems to be a common-sense strategy for controlling cancer, but recent reports have raised controversy concerning the benefits of common screening procedures. Intense efforts to develop and evaluate novel screening technologies are underway; however, effective use of any screening method must take into account any underlying biological considerations. What are these biological issues, and what challenges do clinicians face in screening for common cancers?

Methylation of hMLH1 and hMSH2 promoter in colorectal cancer with microsatellite instability

AIM: To explore methylation of hMLH1 and hMSH2 promoter with microsatellite instability (MSI) in colorectal carcinomas.

METHODS: Methylation of hMLH1 and hMSH2 promoter was measured with methylation-specific PCR; MSI was analyzed by PCR-based methods.

RESULTS: No methylation of hMLH1 and hMSH2 promoter was found in 10 normal colorectal mucosas. Seventy-six cases of sporadic colorectal carcinoma were studied for methylation of hMLH1 and hMSH2 promoter and MSI. Methylation of hMLH1 promoter was detected in 8 (10.5%)colorectal carcinomas and none in hMSH2. Frequence of hMLH1 methylation on right-sided colorectal cancer (23.1%)was significantly higher than that on left one (4.0%, P < 0.05). MSI was detected in at least one locus in 26.3%(20/76) of the tumors analyzed with five microsatellite markers. Frequence of hMLH1 methylation in gastric cancer with MSI-H (80.0%)was significantly higher than that in gastric cancer with MSI-L (20.0%, P < 0.01) and with MSS (10.7%, P < 0.001).

CONCLUSION: Methylation of hMLH1 promoter is related to right-sided colorectal cancer and involved in the MSI pathway.

DNA repair defects in colon cancer

Defects in DNA-repair pathways lead to an accumulation of mutations in genomic DNA that result from non-repair or mis-repair of modifications introduced into the DNA by endogenous or exogenous agents or by the malfunction of DNA metabolic pathways. Until recently, only two repair pathways, postreplicative mismatch repair and nucleotide excision repair, have been linked to cancer in mammals, but these have been joined in recent months also by the damage-reversal and base-excision-repair processes, which have been shown to be inactivated, either through mutation or epigenetically, in human cancer.

[Clinical, pathological and molecular prognostic factors in colorectal carcinomas]

Various aspects of the progression and prognosis of colorectal carcinoma have been investigated in numerous publications during recent years. An exact macroscopic and microscopic examination is still of basic importance but different factors of the molecular pathogenesis of colorectal carcinoma could be described by immunohistochemistry and molecular biology. Furthermore, they have been evaluated regarding their importance for the course of disease and prognosis and in particular, the different pathways of carcinogenesis and microsatellite instability were included. The detection of micrometastasis was investigated applying mostly molecular genetic methods. Numerous oncogenes, tumor suppressor genes and regulators of the cell cycle, markers of proliferation and apoptosis, cell adhesion antigens and angiogenetic factors were characterized with regard to their prognostic potential. In the future, so-called response predictors will presumably gain a certain relevance in the context of neoadjuvant (radiotherapy) chemotherapy. The present review summarizes these results and discusses the future clinical relevance.