Characterisation of a subtype of colorectal cancer combining features of the suppressor and mild mutator pathways

Serrated polyps and colorectal cancer: new pathway to malignancy

Until recently, two major forms of colorectal epithelial polyp were recognized: the adenoma and the hyperplastic polyp. Adenomas were perceived to represent the precursor to colorectal cancer, whereas hyperplastic polyps were viewed as innocuous lesions with no potential for progression to malignancy. We now recognize, however, that the lesions formerly classified as hyperplastic actually represent a heterogeneous group of polyps, some of which have a significant risk for neoplastic transformation. These serrated polyps include not only hyperplastic polyps but also traditional serrated adenomas and sessile serrated adenomas. These polyps demonstrate characteristic molecular alterations not commonly seen in colorectal adenomas, and they probably progress to colorectal cancer by means of a new pathway: the serrated neoplasia pathway. The morphologic features of serrated colorectal lesions, the molecular alterations that characterize them, and their role in colorectal cancer development are discussed herein.

Sporadic colorectal carcinomas with low-level microsatellite instability in Korea: do they form a distinct subgroup with distinguished clinicopathological features?

BACKGROUND

The biologic significance of low-level microsatellite instability (MSI) in colorectal cancers (CRCs) remains unclear. This study aimed to elucidate whether sporadic MSI-low CRCs in Korea displayed distinguished clinicopathological characteristics from microsatellite stable (MSS) and MSI-high CRCs.

METHODS

We consecutively enrolled 657 patients who underwent their first surgical resections for stage I-IV sporadic CRCs and compared their clinicopathological features and prognosis after resection according to MSI status (574 MSS, 30 MSI-low and 53 MSI-high CRCs).

RESULTS

When compared with MSS CRCs, MSI-low CRCs showed significantly more frequent association with poorly differentiated histology, mucinous carcinoma, and large tumour size. In addition, MSI-low CRCs demonstrated significantly less frequent lymph node metastasis and advanced tumour stage than MSS CRCs. When compared with MSI-high CRCs, MSI-low CRCs were significantly more frequently located in distal colon. Three-year overall and disease-free survival rates of MSS, MSI-low and MSI-high CRCs were 83.5%, 90.0% and 91.7% and 82.0%, 89.1% and 87.5%, respectively and neither demonstrated significant difference between three groups.

CONCLUSIONS

These results indicated that sporadic MSI-low CRCs in Korea displayed distinguished clinicopathological features and might form a distinct subgroup especially from MSS CRCs. Further large studies are required to evaluate the impact of MSI-low status on prognosis.

Deficient DNA mismatch repair is common in Lynch syndrome-associated colorectal adenomas

Lynch syndrome is caused by germline mutations in DNA mismatch repair (MMR) genes. Both microsatellite instability (MSI) testing and immunohistochemical analyses (IHC) of colon cancers are valuable diagnostic strategies for Lynch syndrome. We sought to determine whether these markers of MMR deficiency were also detectable in pre-cancerous colorectal adenomas. Fifteen subjects with a germline MMR gene mutation who had 44 adenomas removed during surveillance colonoscopy were identified. MSI testing and IHC for MLH1, MSH2, and MSH6 were performed. MSI was detected in 23 adenomas. There was a significant association between MSI and high-grade dysplasia (P = 0.006) and distal location (P = 0.0008). Loss of MMR protein by IHC was detected in 31 adenomas. A significant association was observed between loss of staining by IHC and high-grade dysplasia (P = 0.04). Among the 40 adenomas in which both MSI tests and IHC were performed, the presence of a germline mutation correlated with an abnormal MSI result in 58% of cases, an abnormal IHC result in 70% of cases, and either an abnormal MSI or IHC result in 73% of cases. The combination of MSI and IHC testing in colorectal adenomas is a sensitive screen for the detection of Lynch syndrome and may be particularly useful when Lynch syndrome is suspected and adenomatous polyps are the only tissues available for analysis.

Microsatellite instability-low colorectal cancer acquires a KRAS mutation during the progression from Dukes' A to Dukes' B

The classification of colorectal cancer (CRC) by microsatellite instability (MSI) status is important for effective clinical management. In fact, microsatellite instability-high (MSI-H) cancer has distinctive clinicopathological and molecular features. However, microsatellite instability-low (MSI-L) cancer is not clearly defined. The objective of this study was to further clarify the characteristics of MSI-L CRC. A consecutive series of 940 primary CRCs were subdivided into three groups according to the level of MSI and analyzed the clinicopathological features and genetic changes in the KRAS, BRAF and p53 mutation and the loss of heterozygosity (LOH) of adenomatous polyposis coli (APC) gene and methylation status of the O(6)-methylguanine-DNA methyltransferase (MGMT) and MLH1 promoter. Of the 940 CRCs, 5.9% were MSI-H, 7.1% were MSI-L and 87% were microsatellite stable (MSS). KRAS and BRAF mutations were detected in 39.4 and 4.6% of the CRCs, respectively. The frequency of KRAS mutations in MSI-H, MSI-L and MSS cancer was 30, 48 and 39%, respectively. The proportion of KRAS mutations in MSI-L cancer increased from 16 to 63% accompanying the progression from Dukes' A to Dukes' B. While the LOH of D5S346, which is located near the APC gene, and p53 mutation was observed in 75 and 67% of MSI-L CRC at Dukes' A, respectively. These results indicated that the LOH of APC and p53 mutation has already occurred by the Dukes' A lake 'suppressor pathway' but not the KRAS mutation in MSI-L CRCs. The genes involving MSI-L carcinogenesis are similar to MSS but the timing and frequency of the KRAS mutation is different.

Comprehensive biostatistical analysis of CpG island methylator phenotype in colorectal cancer using a large population-based sample

Background

The CpG island methylator phenotype (CIMP) is a distinct phenotype associated with microsatellite instability (MSI) and BRAF mutation in colon cancer. Recent investigations have selected 5 promoters (CACNA1G, IGF2, NEUROG1, RUNX3 and SOCS1) as surrogate markers for CIMP-high. However, no study has comprehensively evaluated an expanded set of methylation markers (including these 5 markers) using a large number of tumors, or deciphered the complex clinical and molecular associations with CIMP-high determined by the validated marker panel.

Metholodology/Principal Findings

DNA methylation at 16 CpG islands [the above 5 plus CDKN2A (p16), CHFR, CRABP1, HIC1, IGFBP3, MGMT, MINT1, MINT31, MLH1, p14 (CDKN2A/ARF) and WRN] was quantified in 904 colorectal cancers by real-time PCR (MethyLight). In unsupervised hierarchical clustering analysis, the 5 markers (CACNA1G, IGF2, NEUROG1, RUNX3 and SOCS1), CDKN2A, CRABP1, MINT31, MLH1, p14 and WRN were generally clustered with each other and with MSI and BRAF mutation. KRAS mutation was not clustered with any methylation marker, suggesting its association with a random methylation pattern in CIMP-low tumors. Utilizing the validated CIMP marker panel (including the 5 markers), multivariate logistic regression demonstrated that CIMP-high was independently associated with older age, proximal location, poor differentiation, MSI-high, BRAF mutation, and inversely with LINE-1 hypomethylation and β-catenin (CTNNB1) activation. Mucinous feature, signet ring cells, and p53-negativity were associated with CIMP-high in only univariate analysis. In stratified analyses, the relations of CIMP-high with poor differentiation, KRAS mutation and LINE-1 hypomethylation significantly differed according to MSI status.

Conclusions

Our study provides valuable data for standardization of the use of CIMP-high-specific methylation markers. CIMP-high is independently associated with clinical and key molecular features in colorectal cancer. Our data also suggest that KRAS mutation is related with a random CpG island methylation pattern which may lead to CIMP-low tumors.

PIK3CA mutation in colorectal cancer: relationship with genetic and epigenetic alterations

Somatic PIK3CA mutations are often present in colorectal cancer. Mutant PIK3CA activates AKT signaling, which up-regulates fatty acid synthase (FASN). Microsatellite instability (MSI) and CpG island methylator phenotype (CIMP) are important molecular classifiers in colorectal cancer. However, the relationship between PIK3CA mutation, MSI and CIMP remains uncertain. Using Pyrosequencing technology, we detected PIK3CA mutations in 91 (15%) of 590 population-based colorectal cancers. To determine CIMP status, we quantified DNA methylation in eight CIMP-specific promoters [CACNA1G, CDKN2A (p16), CRABP1, IGF2, MLH1, NEUROG1, RUNX3, and SOCS1] by real-time polymerase chain reaction (MethyLight). PIK3CA mutation was significantly associated with mucinous tumors [P = .0002; odds ratio (OR) = 2.44], KRAS mutation (P < .0001; OR = 2.68), CIMP-high (P = .03; OR = 2.08), phospho-ribosomal protein S6 expression (P = .002; OR = 2.19), and FASN expression (P = .02; OR = 1.85) and inversely with p53 expression (P = .01; OR = 0.54) and beta-catenin (CTNNB1) alteration (P = .004; OR = 0.43). In addition, PIK3CA G-to-A mutations were associated with MGMT loss (P = .001; OR = 3.24) but not with MGMT promoter methylation. In conclusion, PIK3CA mutation is significantly associated with other key molecular events in colorectal cancer, and MGMT loss likely contributes to the development of PIK3CA G>A mutation. In addition, Pyrosequencing is useful in detecting PIK3CA mutation in archival paraffin tumor tissue. PIK3CA mutational data further emphasize heterogeneity of colorectal cancer at the molecular level.

Most low-level microsatellite instability in colorectal cancers can be explained without an elevated slippage rate

Many cancers show a low level of microsatellite slippage and are labelled MSI-L (microsatellite instability--low). However, it is unclear whether this slippage can be attributed to some underlying genetic change that results in a mutator phenotype, analogous to mismatch repair deficiency in MSI-H cancers, or whether the apparent instability is the result of relatively frequent normal somatic slippage. Here, we have used a mathematical model of microsatellite slippage during cancer growth to estimate the degree of microsatellite slippage expected in a cancer due to normal somatic slippage. We compared the model to the slippage observed in 42 non-MSI-H cancers that were macro-dissected into four distinct regions and genotyped at N = 9 microsatellite loci. When the slippage rate was set at mu = 10(-5) per locus per division, ten cancers showed a level of slippage in at least one region that was too severe to be expected from normal somatic slippage alone, suggesting that these cancers had acquired MSI-L. Only one of these ten cancers had putative MSI-L in all four regions. When we considered a slightly higher slippage rate of mu = 5 x 10(-5), none of the cancers showed a degree of slippage that could not be reasonably explained by normal somatic slippage. Counting the number of 'unstable' loci was a poor indicator of putative MSI-L status. We conclude that most low-level microsatellite instability in colorectal cancers can be explained without requiring an elevated slippage rate during neoplastic development, and hence there is little evidence for a discrete MSI-L group of cancers. Putative MSI-L status is indicated by the presence of at least one locus that has multiple alleles that differ by at least five motif repeats from the germline. If an underlying genetic change does cause MSI-L, it appears to be a relatively uncommon event that occurs late in oncogenesis.

Gene profiling of colonic serrated adenomas by using oligonucleotide microarray

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Bone morphogenic protein 3 inactivation is an early and frequent event in colorectal cancer development

Bone morphogenic proteins (BMPs) are members of the TGFB growth factor superfamily with well-described functions in bone formation. Although disrupted BMP signalling in tumor development has more recently been investigated, a role for BMP3 in colorectal cancer (CRC) has remained largely unexplored. The aim of this study was to investigate BMP3 disruption in CRCs in relation to both the traditional and serrated pathways of tumor progression. BMP3 was down-regulated as assessed by real-time PCR in 50 of 56 primary tumors (89%). Bisulfite sequencing of the putative promoter revealed extensive hypermethylation in the cell line HT29, in which expression could be restored by treatment with a methyltransferase inhibitor. Aberrant hypermethylation was observed in 33/60 (55%) tumors and was highly correlated with microsatellite instability (P < 0.01), the CpG Island Methylator Phenotype (P < 0.01), BRAF oncogene mutation (P < 0.01), and proximal location (P < 0.001). Methylation was also frequently observed in serrated and traditional adenomatous polyps (22/29, 76%). Re-introduction of BMP3 into cell lines revealed marked growth suppression supporting the functional relevance of this alteration in colorectal tumor development. This study provides molecular and functional data supporting the importance of BMP3 silencing as an early and frequent event in colorectal tumors progressing via the serrated and traditional pathways.

Sessile serrated adenoma: challenging discrimination from other serrated colonic polyps

Sessile serrated adenoma (SSA) is the proposed precursor for microsatellite unstable colorectal carcinomas and some authorities recommend that SSAs should be managed similar to adenomas. The aim of our study was to determine whether serrated polyps can be classified with sufficient consistency to support current treatment recommendations. One hundred eighty-five serrated polyps were classified as hyperplastic polyp (HP), SSA, or traditional serrated adenoma (TSA) by 5 pathologists blinded to clinical data. The observers documented which histologic features they considered most helpful in reaching their diagnosis in each case. In a second round, the observers were provided with polyp site and size. After reaching a consensus on minimum criteria for SSA and TSA, the pathologists classified another set of 50 polyps. The interobserver concordance was calculated using kappa statistics. In the first round, the overall interobserver agreement was moderate (kappa=0.55). Concordance for HP and SSA was moderate whereas it was nearly perfect for TSA. In the second round, there was no improvement in the concordance. All observers relied more often on architectural features than on cytologic ones to distinguish SSA from HP and agreement was reached that architectural features should provide the basis for the diagnosis of SSA. Subsequently, interobserver concordance was slightly improved but remained moderate (kappa=0.58). Interobserver agreement for the diagnosis of serrated polyps is moderate. However, this level of variability is acceptable because the presence of SSA indicates increased risk of developing additional serrated polyps and carcinoma, and surveillance is appropriate.

Molecular classification and correlates in colorectal cancer

Molecular classification of colorectal cancer is evolving. As our understanding of colorectal carcinogenesis improves, we are incorporating new knowledge into the classification system. In particular, global genomic status [microsatellite instability (MSI) status and chromosomal instability (CIN) status] and epigenomic status [CpG island methylator phenotype (CIMP) status] play a significant role in determining clinical, pathological and biological characteristics of colorectal cancer. In this review, we discuss molecular classification and molecular correlates based on MSI status and CIMP status in colorectal cancer. Studying molecular correlates is important in cancer research because it can 1) provide clues to pathogenesis, 2) propose or support the existence of a new molecular subtype, 3) alert investigators to be aware of potential confounding factors in association studies, and 4) suggest surrogate markers in clinical or research settings.

Low level of microsatellite instability in paediatric malignant astrocytomas

AIM

Microsatellite instability (MSI) has been proposed as a possible mechanism in the development of cancer. The aim of the current study was to determine whether MSI is involved in the pathogenesis of paediatric malignant astrocytomas.

METHODS

We screened a cohort of 126 high-grade astrocytoma samples for MSI using a sensitive and precise method of DNA analysis including a panel of five mononucleotide repeats, in combination with immunohistochemistry for DNA mismatch repair (MMR) proteins.

RESULTS

We identified low level of MSI (MSI-L) in four of 126 (3.2%) paediatric malignant astrocytic tumours. To analyse the molecular profile associated with MSI-L positive tumours, we performed immunohistochemistry for protein expression of hMSH6 and p53 as well as mutational analysis of the K-ras gene. In MSI-L paediatric malignant astrocytic tumours we detected retained nuclear expression of hMSH6 protein and strong nuclear accumulation of p53 protein indicating possible mutations of TP53. There was no correlation between K-ras mutational status and frequency of MSI in this patient population.

CONCLUSION

Our results suggest that the MSI-L phenotype is associated with p53 accumulation and/or mutations. However, this represents only a small subgroup of paediatric gliomas with possible distinct biological features, and the deficiencies of DNA MMR genes do not play a main role in the tumourigenesis of the majority of paediatric malignant astrocytomas.

Differences between familial and sporadic forms of colorectal cancer with DNA microsatellite instability

Microsatellite instability (MSI) is observed in approximately 13% of colorectal cancers. Genes containing a mononucleotide microsatellite in the coding sequence are particularly prone to inactivation in MSI tumourigenesis, and much work has been conducted to identify genes with high repetitive tract mutation rates in these tumours. MSI caused by deficient DNA mismatch-repair functions is a hallmark of cancers associated with the hereditary non-polyposis colorectal cancer syndrome but is also found in about 15% of all sporadic tumours.

Molecular correlates with MGMT promoter methylation and silencing support CpG island methylator phenotype-low (CIMP-low) in colorectal cancer

BACKGROUND

The CpG island methylator phenotype (CIMP or CIMP-high) with widespread promoter methylation is a distinct epigenetic phenotype in colorectal cancer. In contrast, a phenotype with less widespread promoter methylation (CIMP-low) has not been well characterised. O-6-methylguanine-DNA methyltransferase (MGMT) promoter methylation and silencing have been associated with G>A mutations and microsatellite instability-low (MSI-low).

AIM

To examine molecular correlates with MGMT methylation/silencing in colorectal cancer.

METHODS

Utilising MethyLight technology, we quantified DNA methylation in MGMT and eight other markers (a CIMP-diagnostic panel; CACNA1G, CDKN2A (p16), CRABP1, IGF2, MLH1, NEUROG1, RUNX3 and SOCS1) in 920 population-based colorectal cancers.

RESULTS

Tumours with both MGMT methylation and loss were correlated positively with MSI-low (p = 0.02), CIMP-high (>or=6/8 methylated CIMP markers, p = 0.005), CIMP-low (1/8-5/8 methylated CIMP markers, p = 0.002, compared to CIMP-0 with 0/8 methylated markers), KRAS G>A mutation (p = 0.02), and inversely with 18q loss of heterozygosity (p = 0.0002). Tumours were classified into nine MSI/CIMP subtypes. Among the CIMP-low group, tumours with both MGMT methylation and loss were far more frequent in MSI-low tumours (67%, 12/18) than MSI-high tumours (5.6%, 1/18; p = 0.0003) and microsatellite stable (MSS) tumours (33%, 52/160; p = 0.008). However, no such relationship was observed among the CIMP-high or CIMP-0 groups.

CONCLUSION

The relationship between MGMT methylation/silencing and MSI-low is limited to only CIMP-low tumours, supporting the suggestion that CIMP-low in colorectal cancer may be a different molecular phenotype from CIMP-high and CIMP-0. Our data support a molecular difference between MSI-low and MSS in colorectal cancer, and a possible link between CIMP-low, MSI-low, MGMT methylation/loss and KRAS mutation.

Correlation of beta-catenin localization with cyclooxygenase-2 expression and CpG island methylator phenotype (CIMP) in colorectal cancer

The WNT/beta-catenin (CTNNB1) pathway is commonly activated in the carcinogenic process. Cross-talks between the WNT and cyclooxygenase-2 (COX-2 or PTGS2)/prostaglandin pathways have been suggested. The relationship between beta-catenin activation and microsatellite instability (MSI) in colorectal cancer has been controversial. The CpG island methylator phenotype (CIMP or CIMP-high) with widespread promoter methylation is a distinct epigenetic phenotype in colorectal cancer, which is associated with MSI-high. However, no study has examined the relationship between beta-catenin activation and CIMP status. Using 832 population-based colorectal cancer specimens, we assessed beta-catenin localization by immunohistochemistry. We quantified DNA methylation in eight CIMP-specific promoters [CACNA1G, CDKN2A(p16), CRABP1, IGF2, MLH1, NEUROG1, RUNX3, and SOCS1] by real-time polymerase chain reaction (MethyLight). MSI-high, CIMP-high, and BRAF mutation were associated inversely with cytoplasmic and nuclear beta-catenin expressions (i.e., beta-catenin activation) and associated positively with membrane expression. The inverse relation between beta-catenin activation and CIMP was independent of MSI. COX-2 overexpression correlated with cytoplasmic beta-catenin expression (even after tumors were stratified by CIMP status), but did not correlate significantly with nuclear or membrane expression. In conclusion, beta-catenin activation is inversely associated with CIMP-high independent of MSI status. Cytoplasmic beta-catenin is associated with COX-2 overexpression, supporting the role of cytoplasmic beta-catenin in stabilizing PTGS2 (COX-2) mRNA.

Senescence and serration: a new twist to an old tale

Interest in the role of oncogene-induced senescence in tumorigenesis is mounting. Raf-associated senescence in cutaneous nevi has been advanced as an example of this process occurring in the context of a human tumour. In this model, conversion from a senescent nevus to a malignant melanoma is accompanied by loss of expression of p16. Serrated polyps of the colorectum may provide a further example of oncogene-induced senescence. BRAF and KRAS mutation may initiate different pathways of senescence-associated serrated neoplasia in the colorectum, the former linked to CpG island methylator phenotype (CIMP)-high (CIMP1) and microsatellite instability (MSI)-high status and the latter with CIMP-low (CIMP2) and MSI-low status. The role of methylation in both Raf- and Ras-associated pathways is to drive tumorigenesis by silencing pro-apoptotic and cell cycle inhibitory genes. Both pathways are associated with mutation of Ras-induced senescence 1 (RIS1), but the biological role of RIS1 requires further elucidation.

High-resolution fluorescent analysis of microsatellite instability in gastric cancer

BACKGROUND

Microsatellite instability (MSI) is associated with various human malignancies and regarded as reflecting cellular deficiency in DNA mismatch repair (MMR). Analysis of MSI has been prevalent in the field of oncology, and numerous data have accumulated in the literature. It has been reported that the MSI+ phenotype is relatively frequent in gastric cancer. The reported frequencies of MSI+ gastric tumors, however, are diverse.

AIM AND METHODS

To determine the frequencies of the MSI+ phenotype and defective MMR in gastric cancer, we examined tumors derived from 167 patients with sporadic gastric cancer, using our unique fluorescent technique, 'high-resolution fluorescent microsatellite analysis'.

RESULTS

High-resolution fluorescent microsatellite analysis allowed us the unequivocal designation of MSI. The frequencies of MSI-H and MSI-L were 11 and 9.6%, respectively. In addition to the distinction based on the frequency of microsatellite changes, MSI was classifiable into two distinct categories, type A and type B, according to the mode of length changes in the dinucleotide microsatellites. Type A and type B MSI were observed in 14 and 6.6%, respectively. The overall frequency of MSI was 21%. Intriguingly, MSI did not correlate with any of commonly used clinicopathological variables. In addition, neither MSI-H nor MSI-L correlated with family history of malignancies or patient history of multiple cancers. Instead, type B MSI was significantly more frequent in patients with family history of gastric cancer. Type A MSI appeared to occur more frequently in tumors of patients with a history of double cancer, which, however, was not statistically significant.

CONCLUSION

In gastric cancer, contribution of defective MMR to the risk of multiple cancer or familial predisposition appears more limited than has been expected. The relationship between MSI and high risk of cancer may have been oversimplified, at least in gastric cancer.

Serrated neoplasia of the colorectum

Serrated polyps of the colorectum form a group of related lesions which include aberrant crypt foci (ACF), conventional hyperplastic polyps, mixed (admixed) polyps, serrated adenomas and sessile serrated adenomas. In recent years the molecular differences between these morphologically similar lesions have been highlighted, and their differing biological potential has been realised. In particular, the sessile serrated adenoma has become recognised as the precursor lesion to a group of sporadic colorectal carcinomas characterised by morphological and molecular features distinct from conventional adenomas. These recent findings have challenged the long held paradigm that all colorectal carcinomas arise via the traditional adenoma-carcinoma sequence. In addition, they present a major challenge for the early detection and management of colorectal cancer, which is no longer regarded as a homogeneous entity.

Colorectal carcinogenesis: Road maps to cancer

This review explores the chief genetic and epigenetic events that promote pathological progression in colorectal carcinogenesis. This article discusses the molecular and pathological basis for classifying colorectal neoplasia into suppressor, mutator and methylator pathways. These differing mechanisms of genomic instability are associated with specific cancer characteristics, and may provide the opportunity for more effective prevention and surveillance strategies in the future. This is the first review in a series of five topics outlining important and developing aspects of colorectal cancer.

18q loss of heterozygosity in microsatellite stable colorectal cancer is correlated with CpG island methylator phenotype-negative (CIMP-0) and inversely with CIMP-low and CIMP-high

Background:

The CpG island methylator phenotype (CIMP) with widespread promoter methylation is a distinct epigenetic phenotype in colorectal cancer, associated with microsatellite instability-high (MSI-high) and BRAF mutations. 18q loss of heterozygosity (LOH) commonly present in colorectal cancer with chromosomal instability (CIN) is associated with global hypomethylation in tumor cell. A recent study has shown an inverse correlation between CIN and CIMP (determined by MINTs, p16, p14 and MLH1 methylation) in colorectal cancer. However, no study has examined 18q LOH in relation to CIMP-high, CIMP-low (less extensive promoter methylation) and CIMP-0 (CIMP-negative), determined by quantitative DNA methylation analysis.

Methods:

Utilizing MethyLight technology (real-time PCR), we quantified DNA methylation in 8 CIMP-specific promoters {CACNA1G, CDKN2A (p16), CRABP1, IGF2, MLH1, NEUROG1, RUNX3 and SOCS1} in 758 non-MSI-high colorectal cancers obtained from two large prospective cohorts. Using four 18q microsatellite markers (D18S55, D18S56, D18S67 and D18S487) and stringent criteria for 18q LOH, we selected 374 tumors (236 LOH-positive tumors with ≥ 2 markers showing LOH; and 138 LOH-negative tumors with ≥ 3 informative markers and no LOH).

Results:

CIMP-0 (0/8 methylated promoters) was significantly more common in 18q LOH-positive tumors (59% = 139/236, p = 0.002) than 18q LOH-negative tumors (44% = 61/138), while CIMP-low/high (1/8–8/8 methylated promoters) was significantly more common (56%) in 18q LOH-negative tumors than 18q LOH-positive tumors (41%). These relations persisted after stratification by sex, location, or the status of MSI, p53 expression (by immunohistochemistry), or KRAS/BRAF mutation.

Conclusion:

18q LOH is correlated positively with CIMP-0 and inversely with CIMP-low and CIMP-high. Our findings provide supporting evidence for relationship between CIMP-0 and 18q LOH as well as a molecular difference between CIMP-0 and CIMP-low in colorectal cancer.

Performance of different microsatellite marker panels for detection of mismatch repair-deficient colorectal tumors

BACKGROUND

Colorectal tumors caused by failure of the DNA mismatch repair system commonly show microsatellite instability. Our goals were to compare the performance of two panels of markers (a panel previously recommended by the National Cancer Institute [NCI] and a pentaplex of mononucleotide repeats) and to devise the simplest diagnostic strategy for identification of patients with colorectal cancer characterized by defects in mismatch repair.

METHODS

We recruited 1058 patients who were newly diagnosed with colorectal cancer. DNA from fresh-frozen and paraffin-embedded tumors was tested for microsatellite instability, using the NCI-recommended panel of microsatellite markers and the pentaplex panel of mononucleotide repeats, respectively, as templates for polymerase chain reactions (PCRs). Microsatellite instability in fresh-frozen tumors was also assessed using the pentaplex panel of mononucleotides in a crossover analysis. The expression of mismatch repair proteins (MLH1, MSH2, MSH6, and PMS2) in the tumors was determined immunohistochemically. The sensitivity and specificity with which the marker panels identified tumors with deficiencies in the expression of mismatch repair proteins were calculated. All statistical tests were two-sided.

RESULTS

The sensitivity and positive predictive value of the NCI panel were 76.5% (95% confidence interval [CI] = 61% to 92%) and 65.0% (95% CI = 49% to 81%), respectively; corresponding values for the mononucleotide pentaplex panel were 95.8% (95% CI = 89% to 103%) and 88.5% (95% CI = 79% to 98%), respectively. A panel consisting of the mononucleotide repeat markers BAT26 and NR24 alone had the same predictive value as the pentaplex panel of mononucleotide repeats.

CONCLUSIONS

The pentaplex panel of mononucleotide repeats performs better than the NCI panel for the detection of mismatch repair-deficient tumors. Simultaneous assessment of the instability of BAT26 and NR24 is as effective as use of the pentaplex panel for diagnosing mismatch repair deficiency.

Colorectal serrated adenocarcinoma

Colorectal cancer (CRC) ranks among the three most common cancers in terms of both cancer incidence and cancer-related deaths in most Western countries. Serrated adenocarcinoma is a recently described, distinct variant of CRC, accounting for about 7.5% of all CRCs and up to 17.5% of most proximal CRCs. It has been postulated that about 10-15% of sporadic CRCs would have their origin in serrated polyps that harbour a significant malignant potential. These lesions include hyperplastic-type aberrant crypt foci, hyperplastic polyps, sessile serrated adenomas, admixed polyps and serrated adenomas, and constitute the so-called 'serrated pathway', which is distinct from both the conventional adenoma-carcinoma pathway and the mutator pathway of hereditary non-polyposis CRC and is characterized by early involvement of oncogenic BRAF mutations, excess CpG island methylation (CIM) and subsequent low- or high-level DNA microsatellite instability (MSI). Methylation of hMLH1 is likely to explain the increased frequency of high-level MSI (16%) and methylation of MGMT is postulated to explain the low-level MSI (29%) in serrated adenocarcinomas. Reproducible histopathological criteria for serrated adenocarcinoma have recently been established and they have been qualified by DNA expression analysis for 7928 genes, showing clustering of serrated adenocarcinomas into a molecular entity apart from conventional adenocarcinoma, and representing with distinct down-regulation of EPHB2, PTCH and up-regulation of HIF1alpha.

Classification of colorectal cancer based on correlation of clinical, morphological and molecular features

Over the last 20 years it has become clear that colorectal cancer (CRC) evolves through multiple pathways. These pathways may be defined on the basis of two molecular features: (i) DNA microsatellite instability (MSI) status stratified as MSI-high (MSI-H), MSI-low (MSI-L) and MS stable (MSS), and (ii) CpG island methylator phenotype (CIMP) stratified as CIMP-high, CIMP-low and CIMP-negative (CIMP-neg). In this review the morphological correlates of five molecular subtypes are outlined: Type 1 (CIMP-high/MSI-H/BRAF mutation), Type 2 (CIMP-high/MSI-L or MSS/BRAF mutation), Type 3 (CIMP-low/MSS or MSI-L/KRAS mutation), Type 4 (CIMP-neg/MSS) and Type 5 or Lynch syndrome (CIMP-neg/MSI-H). The molecular pathways are determined at an early evolutionary stage and are fully established within precancerous lesions. Serrated polyps are the precursors of Types 1 and 2 CRC, whereas Types 4 and 5 evolve through the adenoma-carcinoma sequence. Type 3 CRC may arise within either type of polyp. Types 1 and 4 are conceived as having few, if any, molecular overlaps with each other, whereas Types 2, 3 and 5 combine the molecular features of Types 1 and 4 in different ways. This approach to the classification of CRC should accelerate understanding of causation and will impact on clinical management in the areas of both prevention and treatment.

Unfavorable pathological characteristics in familial colorectal cancer with low-level microsatellite instability

A high degree of microsatellite instability (MSI) in colorectal cancer (CRC) is a hallmark of hereditary non-polyposis colorectal cancer (HNPCC), caused by germline defects in the mismatch repair (MMR) genes. A low degree of instability (less than 30% of the microsatellites) is seen in a subset of tumors. To clarify the significance of this low degree of MSI phenotype, we studied the differences between patients with colorectal tumors with high-level, low-level and no MSI. Colorectal tumors with no (n = 68) and low-level (n = 18) MSI of patients clinically suspected of HNPCC were compared to colorectal tumors with high-level MSI (n = 12) of patients that carry a pathogenic germline mutation in a MMR gene. Compared to tumors with no MSI, tumors with low-level MSI were classified more frequently as stage T3 or T4 (100% vs 68% respectively), and showed less immune response (P = 0.02). No significant differences in familial CRC risk were found by comparing pedigrees of these two groups of tumors. Compared to the group of tumors with high-level MSI, the group of tumors with low-level MSI had a less suspicious family history, a higher percentage of lymph node metastasis (56 vs 17%), and less immune response. Thus, with respect to genetic risks, familial CRC can be divided into two groups: Tumors with high-level MSI and tumors with low-level or no MSI. However, tumors with low-level MSI show unfavorable pathological characteristics compared to tumors with no and tumors with high-level MSI. These differences suggest a distinct underlying biology of CRC with low-level MSI.

Overexpression of the receptor for hyaluronic acid mediated motility is an independent adverse prognostic factor in colorectal cancer

RHAMM, a member of the microtubule-associated protein family that interacts with the mitogen-activated protein kinase pathway, is associated with tumor progression, aggressive disease and shortened survival in several tumor types. This study aimed to determine the prognostic value of RHAMM in colorectal cancer (CRC). A series of 1420 unselected, nonconsecutive CRC resections were subdivided into three groups: (1) DNA mismatch repair (MMR)-proficient, (2) MLH1 negative and (3) presumed Lynch syndrome. Immunohistochemical analysis of RHAMM expression (0 vs >0%), increasing expression (increasing percentage positivity) and complete expression (100 vs <100%) was performed using tissue microarray technique and the results were correlated with clinicopathological parameters. Fifty-seven tissue samples of normal colonic mucosa were included as a control group. In a univariate analysis increasing and complete expression of RHAMM were associated with higher N stage (P=0.023 and 0.021) and worse survival (P<0.0001) in MMR-proficient CRC. Complete expression of RHAMM was associated with worse survival in presumed Lynch syndrome (P=0.016). In MLH1-negative CRC there was no association between RHAMM expression and the clinicopathological features. In a multivariate analysis, increasing RHAMM expression was an independent adverse prognostic factor in MMR-proficient CRC (P<0.0001) and complete expression in MMR-proficient CRC and presumed Lynch syndrome (P<0.0001 and P=0.031, respectively). Nuclear pERK expression was associated with increasing RHAMM expression in MMR-proficient CRC (P=0.012) and with complete RHAMM expression in presumed HNPCC (P=0.03). Increasing and complete RHAMM expressions are independent adverse prognostic factors in MMR-proficient CRC and presumed Lynch syndrome.

Tumor buds show reduced expression of laminin-5 gamma 2 chain in DNA mismatch repair deficient colorectal cancer

PURPOSE

Tumor budding at the invasive margin of colorectal cancer is an important adverse prognostic factor. The subset of colorectal cancer that is deficient in DNA mismatch repair has been associated with a good prognosis. It is hypothesized that tumor budding in this subset may lack biologic aggressiveness because it is not associated with aberrant expression of the independent prognostic factor, laminin-5 gamma 2.

METHODS

Eighty colorectal cancers with high-grade tumor budding were studied, including nine sporadic colorectal cancers with immunohistochemical loss of expression of MLH1 (MLH1(-)), seven colorectal cancers from patients with hereditary nonpolyposis colorectal cancer, and 64 sporadic colorectal cancers expressing both MLH1 and MSH2 (MLH1(+)). Two regulatory mechanisms for laminin-5 gamma 2 expression were explored, including aberrant nuclear expression of beta-catenin by immunohistochemistry and promoter methylation of laminin-5 gamma 2 by methylation-specific polymerase chain reaction.

RESULTS

Only three of nine MLH1(-) colorectal cancers showed expression of laminin-5 gamma 2 compared with 46 of 64 MLH1(+) colorectal cancers (P = 0.05). Only two of seven hereditary nonpolyposis colorectal cancers expressed laminin-5 gamma 2 compared with MLH1(+) colorectal cancers (P= 0.03). Expression of nuclear beta-catenin was more frequent (58 percent) in MLH1(+) colorectal cancers compared with MLH1(-) colorectal cancers (11 percent, P = 0.01). Methylation of laminin-5 gamma 2 was found in 5 of 38 (13 percent) cases but did not differ among colorectal cancer subsets. Four of five colorectal cancers with methylation of laminin-5 gamma 2 were scored as negative for laminin-5 gamma 2 by immunohistochemistry.

CONCLUSIONS

The reduced expression of laminin-5 gamma 2 in colorectal cancers with deficient DNA mismatch repair may underlie a variant of tumor budding that is relatively nonaggressive.

Do MSI-L Sporadic Colorectal Tumors Develop Through “Mild Mutator Pathway”?

BACKGROUND

The mutator pathway implied in the development of colorectal cancer (CRC) is characterized by microsatellite instability (MSI). MSI tumors can be subdivided according to the level of instability: MSI-H (high), MSI-L (low) or stable MSS. MSI-H CRC displays a well described distinct phenotype, but the true biologic significance of MSI-L is still uncertain. The objective of this study was to further clarify if the MSI-L phenotype could reflect a distinct pathway of tumor development with a different clinical behavior.

METHODS

We analyzed the clinicopathological and genetic variables of 156 patients with sporadic CRC in relation with the level of MSI of the tumors.

RESULTS

We have found that MSI-L tumors are someway in the middle of MSI-H and MSS CRC, as they share some features with each of the other 2 subgroups: left side location, lower incidence of LOH at MSH2 as MSS and Dukes B (stage II TNM) like MSI-H. Moreover, MSI-L tumors show higher incidence of KRAS mutations.

CONCLUSION

We believe that MSI-L tumors could be considered a distinct phenotype that develops through a "mild mutator pathway."

Mismatch repair polymorphisms and colorectal polyps: hMLH1-93G>A variant modifies risk associated with smoking

BACKGROUND AND AIM

Mutations in the mismatch repair (MMR) enzymes hMLH1 and hMSH6 are known causes of hereditary nonpolyposis colorectal cancer and act by inducing a mutator phenotype characterized by microsatellite instability. The aim of our study was to determine if polymorphisms in the DNA MMR genes hMLH1 and hMSH6 are associated with an increased risk of colorectal polyps, and to evaluate interactions with exposures known to cause DNA damage.

METHODS

In a Minnesota-based case-control study of individuals with adenomas (N=401), hyperplastic polyps (N=195), or both adenomas and hyperplastic polyps (N=123) versus polyp-free controls (N=624), we investigated the role of hMLH1-93G>A, hMLH1 I219V, and hMSH6 G39E polymorphisms in increasing the risk of colorectal polyps. Polytomous multivariate logistic regression analysis was used, adjusting for age, sex, body mass index, postmenopausal hormone use, aspirin use, and NSAID use.

RESULTS

Overall, no evidence of an association between any of the three polymorphisms or hMLH1 haplotypes and colorectal polyps was observed. However, risk associated with the hMLH1-93A variant differed by smoking: smoking-associated risks were stronger among those with variant -93AA or -93AG genotypes, showing a twofold greater risk of adenoma with >25 pack-years of smoking compared with nonsmokers, and a corresponding eightfold greater risk of hyperplastic polyps (genotype smoking: p-interaction=0.02 for hyperplastic polyps and p-interaction=0.08 for adenomas).

CONCLUSIONS

These data are consistent with the observation that smoking is associated with MMR in colorectal neoplasia and suggest that the risk increase with smoking may differ by hMLH1-93G>A genotype.

A prospective analysis of microsatellite instability as a molecular marker in colorectal cancer

BACKGROUND

Microsatellite instability (MSI) may be a molecular marker of colorectal tumor biology. We sought to evaluate the incidence and significance of MSI in an unselected colorectal cancer population.

METHODS

Colorectal cancer cases from a community health system were prospectively evaluated for MSI and patient outcomes monitored.

RESULTS

Of 240 eligible, 140 underwent testing; 43 (31%) had high-frequency MSI (MSI-H). Those with MSI-H tumors presented with earlier disease stage (P = .014) and lymphocytic infiltration (P < .001). Stage III MSI-H patients trended toward improved disease-free survival (P = .065). MSI-H patients were more likely to have other primary malignancies.

CONCLUSIONS

Prevalence of MSI-H in the general colorectal cancer population is higher than previously reported. MSI testing of colorectal cancers is useful as part of a molecular profile to stratify patients for prognosis, treatment, and further study. Patients with MSI-H tumors are more likely to have other primary malignancies, suggesting a role for heightened screening.

Optimization of antibodies for detection of the mismatch repair proteins MLH1, MSH2, MSH6, and PMS2 using a biotin-free visualization system

Testing for microsatellite instability (MSI) has become an important step in the planning of therapeutic and follow-up procedures for patients with colorectal cancer, both as a prognostic marker and as a screening tool for hereditary non-polyposis colorectal cancer. Today the gold standard for MSI testing is based on the polymerase chain reaction. Immunohistochemistry may represent an alternative or complement to molecular MSI testing. Antibodies against the protein products of the most commonly affected mismatch repair genes (hMLH1, hMSH2, hMSH6, and hPMS2) have been available for some time now. However, the quality of the primary antibody and optimization of the antigen retrieval methods are essential to get reproducible results. The aim of the present study was to test and optimize a panel of antibodies against the mismatch repair proteins MLH1, MSH2, MSH6, and PMS2 using biotin-free, polymer-based visualization systems. The antibodies were tested on multitissue blocks containing normal tissue and tumor tissue from patients with known microsatellite-stable and microsatellite-instable tumors. For all four antibody groups, the chosen clones gave specific and reproducible staining. Furthermore, with the PowerVision+ detection system, the influence of endogenous biotin was eliminated, the incubation time with the primary antibody was significantly reduced, and the primary antibody could be further diluted. The authors found that immunohistochemistry may provide a cost-effective and time-saving complement to the molecular MSI analysis, and using the PowerVision+ detection system has greatly decreased the turnaround time as well as reduced the cost of immunohistochemistry in the authors' laboratory.

Microsatellite instability in gastrointestinal tract cancers: a brief update

Microsatellite instability (MSI) was initially reported in colorectal cancer and, particularly, in hereditary nonpolyposis colorectal cancer (HNPCC). Since mutations in the genes functioning in DNA mismatch repair (MMR) were found in HNPCC kindred, this phenotype has been connected to a deficiency in MMR. The MSI(+) phenotype is associated with various human malignancies. As MSI(+) tumors appear to form a unique clinicopathological and molecular entity that is clearly distinct from that of classical colorectal tumors, which are accompanied by chromosomal instability (CIN), an exclusive pathway of tumorigenesis has been proposed in colorectal cancer. However, this scheme, comprising two mutually exclusive pathways, is now being reexamined, in light of a series of evidence accumulating in the literature, which relates to (a) distinction between high-level MSI (MSI-H) and low-level MSI (MSI-L), (b) heterogeneity in MSI-H, particularly in the sporadic and hereditary settings, (c) molecular mechanisms underlying the MSI(+) phenotypes, and (d) relationships between the MSI(+) and CIN phenotypes. Several molecular mechanisms may underlie repeat instability in eukaryotic cells. The relationship between MSI and defective MMR may be more complicated than has been suspected. The role of MMR deficiency in tumorigenesis in the digestive tract appears to be diverse and is not simple, even in the colorectum.

Characterization of tumour-infiltrating lymphocytes and apoptosis in colitis-associated neoplasia: comparison with sporadic colorectal cancer

The development of colorectal cancer is a major complication for patients with chronic idiopathic colitis. Colitis-associated tumours tend to occur at a younger age and be more aggressive than sporadic colorectal cancers. While we have previously associated the presence of tumour-infiltrating lymphocytes (TILs) and increased apoptosis in sporadic colorectal cancer with high-level microsatellite instability and improved prognosis, little is known of the relationship between these variables in colitis-associated colorectal cancer. The aim of this study was to correlate TILs and tumour cell apoptosis in colitis-associated neoplasms stratified according to microsatellite instability. Twenty tumour and 11 dysplastic samples resected from 21 patients with long-standing colitis were analysed for microsatellite instability at 10 microsatellite markers. TIL distribution (CD3, CD8) and function (granzyme B) were quantified by immunohistochemistry. Neoplastic cell apoptosis was assessed using the M30 CytoDEATH antibody. These findings were compared with 40 microsatellite stable (MSS) sporadic colorectal cancers previously evaluated for TILs and neoplastic apoptosis. Low-level microsatellite instability was found in 1/20 colitis-associated tumours. All other colitis-associated lesions were designated MSS. CD3(+) and CD8(+) TIL counts were significantly higher in colitis-associated lesions compared with MSS sporadic colorectal cancer (p < 0.0001, p = 0.001 respectively). Despite their higher TIL density, colitis-associated tumours were more likely to present late (Dukes' stage C or D) (p = 0.02). Functionally, colitis-associated TILs demonstrated significantly less granzyme B expression compared to sporadic cancers (p = 0.002). The level of tumour cell apoptosis was similar between the two groups (sporadic, 1.53%; colitis cancers, 1.45%). In conclusion, MSS colitis-associated tumours have a higher prevalence of CD3(+)/CD8(+) TILs but no associated increase in tumour cell killing by apoptosis. Unlike cytotoxic T cells in sporadic colorectal cancer, TILs do not appear to enhance the prognosis of colitis-associated colorectal cancer. This may be related to an impairment of granzyme B expression within these lesions.

DNA methylation patterns in adenomas from FAP, multiple adenoma and sporadic colorectal carcinoma patients

Colorectal adenomas have traditionally been regarded as homogeneous. The aim of our study was to identify molecular features that may differentiate sporadic adenomas from familial adenomas such as Familial Adenomatous Polyposis (FAP) and Multiple Adenoma patients. DNA methylation was tested at Methylated IN Tumor (MINT) loci (1,2,12,31) and the CpG promoter region of genes MLH1, HPP1, MGMT, p14ARF and p16INK4a in FAP-associated adenomas (33) from 5 patients with a known APC mutation (Group 1, FAP), adenomas (29) from 4 Multiple Adenoma patients (Group 2 Multiple), adenomas (14) from 3 patients with sporadic colorectal cancers showing high microsatellite instability (Group 3, MSI-H) and adenomas (16) from 7 patients, with sporadic colorectal cancers showing microsatellite stable or low level instability (Group 4, MSS/MSI-L). Aberrant Crypt Foci (ACFs), Hyperplastic Polyps (HPs) and cancers were also examined for methylation status as well as K-ras mutation. Multiple Adenoma patients were examined for germline polymorphisms in the base excision repair gene, MYH. The familial syndrome, FAP -associated adenomas showed a significantly low frequency of MINT methylation (15.5%,) compared to sporadic MSS/MSI-L-associated adenomas (35.5%). Group 3 (MSI-H) adenomas were different in that many showed serration and a high level of methylation (57.1%). Group 2, Multiple Adenoma cases, resembled sporadic MSS/MSI-L-associated adenomas. However the promoter regions of key genes, MGMT, p14ARF and p16INK4a were methylated to a greater extent than MINTs in both sporadic and familial adenomas. Genetic profiling of adenomas supports the concept that adenomas belonging to familial syndromes pursue a different pathway to tumorigenesis than their sporadic counterpar/ts from their earliest formation.

Expression of angiogenic VEGF-A (soluble isoforms 121, 165) and lymphangiogenic VEGF-C in colorectal cancers with micro-satellite instability

BACKGROUND AND OBJECTIVES

Colorectal cancers (CRC) with high-level micro-satellite instability (MSI-H) show reduced metastatic potential and better prognosis compared to stage-matched stable (MSS) cancers. Angiogenesis/lymphangiogenesis, central to tumour growth and spread, is mediated by vascular endothelial growth factor (VEGF) cytokines, but little is known of their relationship to MSI.

METHODS

In this study, 67 sporadic CRC with identified MSI status, and 8 samples of normal colon were analysed for VEGF-A soluble isoforms (VEGF-121/VEGF-165) and VEGF-C gene transcription (by RT-PCR and scanning densitometry), and blood vessel density (BVD; measuring angiogenesis) and VEGF-C protein expression (measuring lymphangiogenesis).

RESULTS

Compared to normal colon, VEGF-165 transcription was reduced (P < 0.05), but VEGF-121 transcription was higher in MSS (P < 0.06) and MSI-L (P < 0.01) cancers (but similar in MSI-H). VEGF-165 transcription was unrelated to MSI, but VEGF-121 transcription was elevated in MSI-L (P < 0.06). There was a weak inverse correlation with VEGF-121 transcription and Dukes stage (P < 0.09), and with BVD and MSI (P < 0.09). With a singular di-nucleotide loci mutation (MSI-L), VEGF-121 (P < 0.03) and VEGF-C (P < 0.04) transcription was elevated.

CONCLUSIONS

MSI-H cancers have reduced angiogenic/lymphangiogenic potential, and transcription of VEGF-121 may be important in early growth and spread of CRC. Elevated VEGF-121 and VEGF-C transcription with singular di-nucleotide mutations may aid in the identification of distinct MSI-L cancers.

Use of microsatellite instability and immunohistochemistry testing for the identification of individuals at risk for Lynch syndrome

It is now generally recognized that a specific subset of those patients clinically defined as having hereditary non polyposis colon cancer (HNPCC) have germline mutations in any one of several genes involved in DNA mismatch repair (MMR). This important subset of HNPCC families is now defined as having Lynch syndrome. A considerable amount of data has shown that tumors from patients with Lynch syndrome have characteristic features resulting from the underlying molecular involvement of defective MMR, that is, the presence of microsatellite instability (MSI) and the absence of MMR protein expression by immunohistochemistry (IHC). As a result, identifying patients with Lynch syndrome can now be accomplished by testing tumors for these tumor-related changes. Together, MSI and IHC are powerful tools that help identify individuals at risk for having Lynch syndrome and to distinguish these cases from HNPCC cases with other hereditary gene defects. Furthermore, IHC analysis provides valuable clues as to which MMR gene is mutated, allowing for comprehensive mutational analyses of that gene. Here, we discuss the current and historical perspectives regarding MSI and IHC analyses in tumors from sporadic colon cancer and from patients with Lynch syndrome. Given this background, we also provide a testing strategy for the identification of patients at risk for Lynch syndrome and subsequent gene testing.

Low microsatellite instability is associated with poor prognosis in stage C colon cancer

PURPOSE

The significance of low microsatellite instability (MSI-L) in colorectal cancer is poorly understood. No clear biologic distinction has been found between MSI-L and microsatellite stable (MSS) colorectal cancer, and these two phenotypes are usually combined when analyzed against the well-defined high MSI (MSI-H) phenotype. Evidence is emerging that an O(6)-methylguanine DNA methyltransferase (MGMT) gene defect is associated with MSI-L. Therefore, to further define this phenotype, we undertook a detailed analysis of the prognostic significance of MSI-L and loss of MGMT expression in colon cancer.

PATIENTS AND METHODS

The study cohort was 183 patients with clinicopathologic stage C colon cancer who had not received adjuvant therapy. We analyzed MSI status, MGMT, and mismatch repair protein expression, as well as MGMT and p16 promoter hypermethylation.

RESULTS

We showed that MSI-L defines a group of patients with poorer survival (P = .026) than MSS patients, and that MSI-L was an independent prognostic indicator (P = .005) in stage C colon cancer. Loss of MGMT protein expression was associated with the MSI-L phenotype but was not a prognostic factor for overall survival in colon cancer. p16 methylation was significantly less frequent in MSI-L than in MSI-H and MSS tumors and was not associated with survival.

CONCLUSION

MSI-L characterizes a distinct subgroup of stage C colon cancer patients, including the MSI-L subset of proximal colon cancer, who have a poorer outcome. Neither the MGMT defect nor p16 methylation are likely to contribute to the worse prognosis of the MSI-L phenotype.

Two modes of microsatellite instability in human cancer: differential connection of defective DNA mismatch repair to dinucleotide repeat instability

Microsatellite instability (MSI) is associated with defective DNA mismatch repair in various human malignancies. Using a unique fluorescent technique, we have observed two distinct modes of dinucleotide microsatellite alterations in human colorectal cancer. Type A alterations are defined as length changes of < or =6 bp. Type B changes are more drastic and involve modifications of > or =8 bp. We show here that defective mismatch repair is necessary and sufficient for Type A changes. These changes were observed in cell lines and in tumours from mismatch repair gene-knockout mice. No Type B instability was seen in these cells or tumours. In a panel of human colorectal tumours, both Type A MSI and Type B instability were observed. Both types of MSI were associated with hMSH2 or hMLH1 mismatch repair gene alterations. Intriguingly, p53 mutations, which are generally regarded as uncommon in human tumours of the MSI+ phenotype, were frequently associated with Type A instability, whereas none was found in tumours with Type B instability, reflecting the prevailing viewpoint. Inspection of published data reveals that the microsatellite instability that has been observed in various malignancies, including those associated with Hereditary Non-Polyposis Colorectal Cancer (HNPCC), is predominantly Type B. Our findings indicate that Type B instability is not a simple reflection of a repair defect. We suggest that there are at least two qualitatively distinct modes of dinucleotide MSI in human colorectal cancer, and that different molecular mechanisms may underlie these modes of MSI. The relationship between MSI and defective mismatch repair may be more complex than hitherto suspected.

PTGS2 (COX-2) -765G > C Promoter Variant Reduces Risk of Colorectal Adenoma among Nonusers of Nonsteroidal Anti-inflammatory Drugs

Prostaglandin H synthase 2 (PTGS2) or cyclooxygenase-2 (COX-2) has been shown to play a key role in the regulation of inflammation, and its inhibition is associated with a reduced risk of colon cancer. The PTGS2 (COX-2) -765G > C promoter variant is located in a putative SP1 binding site and reduces PTGS2 expression. In a Minnesota-based case-control study of cases with adenomatous (n = 494) or hyperplastic polyps (n = 186) versus polyp-free controls (n = 584), we investigated the role of the PTGS2 -765G > C promoter polymorphism. Multiple logistic regression analysis was used, adjusting for age, body mass index, caloric intake, alcohol, fiber, sex, hormone use, and smoking. For colorectal adenoma, odds ratios (OR) compared with PTGS2 -765GG as reference were GC 1.00 [95% confidence interval (95% CI), 0.74-1.35] and CC 0.53 (95% CI, 0.22-1.28). For hyperplastic polyps, the comparable adjusted odds ratios were GC 0.97 (95% CI, 0.65-1.46) and CC 0.24 (95% CI, 0.05-1.11). Risk associated with the -765G > C variant differed by aspirin or other nonsteroidal anti-inflammatory drug (NSAID) use. Among nonusers of aspirin or other NSAIDs, the CC genotype conferred a significant decrease in risk of adenoma (OR, 0.26; 95% CI, 0.07-0.89). Use of aspirin or other NSAIDs reduced risk of adenoma only among those with the -765GG (wild type) and possibly -765CG genotypes (OR, 0.66; 95% CI, 0.48-0.92 and OR, 0.64; 95% CI, 0.40-1.02, respectively). These data suggest that COX-2 expression or activity may be beneficially suppressed, and risk of colorectal polyps reduced, by aspirin or other NSAIDs in PTGS2 -765GG (wild type) individuals and by the -765 CC variant genotype in nonusers of NSAIDs.

Progressive methylation during the serrated neoplasia pathway of the colorectum

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

Low level microsatellite instability may be associated with reduced cancer specific survival in sporadic stage C colorectal carcinoma

BACKGROUND

Colorectal cancers (CRCs) may be categorised according to the degree of microsatellite instability (MSI) exhibited, as MSI-high (MSI-H), MSI-low (MSI-L), or microsatellite stable (MSS). MSI-H status confers a survival advantage to patients with sporadic CRC.

AIMS

To determine if low levels of MSI are related to the clinicopathological features and prognosis of sporadic stage C CRC.

PATIENTS

A total of 255 patients who underwent resection for sporadic stage C CRC were studied. No patient received chemotherapy. Minimum follow up was five years.

METHODS

DNA extracted from archival malignant and non-malignant tissue was amplified by polymerase chain reaction using a panel of 11 microsatellites. MSI-H was defined as instability at > or =40% of markers, MSS as no instability, and MSI-L as instability at >0% but <40% of markers. Patients with MSI-H CRC were excluded from analysis as they have previously been shown to have better survival.

RESULTS

Thirty three MSI-L and 176 MSS CRCs were identified. There was no difference in biological characteristics or overall survival of MSI-L compared with MSS CRC but MSI-L was associated with poorer cancer specific survival (hazard ratio 2.0 (95% confidence interval 1.1-3.6)).

CONCLUSIONS

Sporadic MSI-L and MSS CRCs have comparable clinicopathological features. Further studies are required to assess the impact of MSI-L on prognosis.

Low level microsatellite instability may be associated with reduced cancer specific survival in sporadic stage C colorectal carcinoma

BACKGROUND

Colorectal cancers (CRCs) may be categorised according to the degree of microsatellite instability (MSI) exhibited, as MSI-high (MSI-H), MSI-low (MSI-L), or microsatellite stable (MSS). MSI-H status confers a survival advantage to patients with sporadic CRC.

AIMS

To determine if low levels of MSI are related to the clinicopathological features and prognosis of sporadic stage C CRC.

PATIENTS

A total of 255 patients who underwent resection for sporadic stage C CRC were studied. No patient received chemotherapy. Minimum follow up was five years.

METHODS

DNA extracted from archival malignant and non-malignant tissue was amplified by polymerase chain reaction using a panel of 11 microsatellites. MSI-H was defined as instability at > or =40% of markers, MSS as no instability, and MSI-L as instability at >0% but <40% of markers. Patients with MSI-H CRC were excluded from analysis as they have previously been shown to have better survival.

RESULTS

Thirty three MSI-L and 176 MSS CRCs were identified. There was no difference in biological characteristics or overall survival of MSI-L compared with MSS CRC but MSI-L was associated with poorer cancer specific survival (hazard ratio 2.0 (95% confidence interval 1.1-3.6)).

CONCLUSIONS

Sporadic MSI-L and MSS CRCs have comparable clinicopathological features. Further studies are required to assess the impact of MSI-L on prognosis.

Prognostic implications of hMLH1 and p53 immunohistochemical status in right-sided colon cancer

PURPOSE

Extensive research into the molecular biology of colorectal cancer has identified a plethora of molecular markers reputed to provide independent prognostic information. p53 mutational status has been associated with both improved and reduced survival; however, tumors expressing a particular phenotype associated with defective mismatch repair consistently do better. This study was designed to examine site-specific survival implications of p53 and mismatch repair status.

METHODS

Mismatch repair (hMLH1 and hMSH2) and p53 status was investigated immunohistochemically in 111 proximal colon cancers along with tumor TNM stage, grade, and extramural vascular invasion. Fisher's exact test was used to assess categoric data; univariate and multivariate models compared survival between the respective tumor phenotypes.

RESULTS

Thirty-two percent of tumors showed loss of expression of hMLH1 and in a multivariate analysis were associated with a significant survival advantage after adjustment for tumor stage, p53 status, and extramural vascular invasion (hazard ratio, 0.29; 95 percent confidence interval, 0.1-0.87; P = 0.027). Only two tumors showed loss of expression of hMSH2, which was not related further to survival. Aberrant p53 expression was detected in 39 percent of tumors. Such expression was found to be associated with a significantly reduced survival in univariate analysis (P = 0.037, log-rank test) but not in a multivariate model. Subgroup analysis showed no association between survival and p53 expression in mismatch repair proficient tumors.

CONCLUSIONS

Loss of hMLH1 expression is an independent predicator of improved survival in this series and perhaps the underlying cause of the observed survival difference associated with p53 expression.

Hyperplastic polyposis and the risk of colorectal cancer

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Promoter hypermethylation frequency and BRAF mutations distinguish hereditary non-polyposis colon cancer from sporadic MSI-H colon cancer

BACKGROUND

Colorectal cancers resulting from defective DNA mismatch repair can occur in both hereditary non-polyposis colon cancer (HNPCC) and in the sporadic setting. They are characterised by a high level of microsatellite instability (MSI-H) and superficially resemble each other in that they are frequently located in the proximal colon and share features such as circumscribed tumour margins and tumour-infiltrating lymphocytes. However, significant differences can be demonstrated at the molecular level including widespread promoter hypermethylation and BRAF -activating mutations which occur significantly less often in HNPCC.

AIMS

In this study, we sought to determine whether the presence of widespread promoter hypermethylation and BRAF mutations would exclude HNPCC.

MATERIALS AND METHODS

We investigated the methylation status of four methylated in tumour markers (MINTs 1,2,12 and 31), and the promoter regions of 5 genes hMLH1, HPP1, MGMT, p16INK4A and p14ARF, in 21 sporadic MSI-H colorectal cancers and compared these with 18 cancers from HNPCC patients. The methylation status of CpG islands were determined by either methylation specific PCR (MSP) or combined bisulfite restricton analysis (COBRA). In addition we considered the BRAF mutation status of 18 HNPCC tumours and 19 sporadic MSI-H cancers which had been previously determined by RFLP analysis and confirmatory sequencing.

RESULTS

Methylation of the promoter regions in target genes occurred less frequently within the HNPCC tumours (27% of analyses), compared with the sporadic MSI-H tumours (59% of analyses) (P < 0.001). Methylation of MINTs 1, 2, 12 and 31 occurred in 4% of analyses for HNPCC tumours contrasted with 73% for sporadic MSI-H tumours (P < 0.001). BRAF mutations were detected in 74% of sporadic tumours but none of the HNPCC cancers tested.

CONCLUSIONS

The total number of genes and MINTs methylated in HNPCC was lower than in MSI-H colorectal tumours. No HNPCC tumour showed evidence of widespread promoter hypermethylation or BRAF mutation suggesting this feature could be used as a discriminator between familial and sporadic cases.

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.