High frequency of K-ras mutations in human colorectal hyperplastic polyps

Molecular characteristics of colorectal hyperplastic polyp subgroups

BACKGROUND/AIMS

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

RESULTS

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

CONCLUSION

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

Molecular Markers for Colorectal Cancer

Colorectal cancers develop through at least 3 major pathways, including chromosomal instability, mismatch repair, and methylator phenotype. These pathways can coexist in a single individual and occur in both sporadic and inherited colorectal cancers. In spite of the unique molecular and genetic signatures of colorectal cancers, nonspecific chemotherapy based on the antineoplastic effects of 5-fluorouracil is the cornerstone of therapy for stage III and some stage II disease. Techniques to recognize colorectal cancer at the molecular level have facilitated development of new signature drugs designed to inhibit the unique pathways of colorectal cancer growth and immunity.

Colorectal cancer: using blood samples and tumor tissue to detect K-ras mutations

We performed a meta-analysis to assess whether blood can be substituted for tumor tissue in K-ras mutation testing. PubMed, EMBASE, MEDLINE, and BIOSIS databases were searched. Twenty-three studies including 1261 patients were included. The pooled overall sensitivity, specificity, and concordance rate were 0.69 (95% CI: 0.59-0.78), 0.96 (95% CI: 0.93-0.97), and 0.86 (95% CI: 0.82-0.89), respectively. Subgroup analysis indicated that plasma (sensitivity: 0.74; mutation rate: 0.34) exhibited superior sensitivity compared with serum (sensitivity: 0.45; mutation rate: 0.24). We conclude that blood is a suitable substitute for tumor tissue in K-ras mutation testing. K-ras mutation positivity in blood can be used to identify patients who should not receive EGFR monoclonal antibody therapy, but the absence of blood positivity does not necessarily imply negativity.

Correlation between Gene Variants, Signaling Pathways, and Efficacy of Chemotherapy Drugs against Colon Cancers

Efficacies, toxicities, and resistance mechanisms of chemotherapy drugs, such as oxaliplatin and 5-fluorouracil (5-FU), vary widely among various categories and subcategories of colon cancers. By understanding the differences in the drug efficacy and resistance at the level of protein–protein networks, we identified the correlation between the drug activity of oxaliplatin/5-FU and gene variations from the US National Cancer Institute-60 human cancer cell lines. The activity of either of these drugs is correlated with specific amino acid variant(s) of KRAS and other genes from the signaling pathways of colon cancer progression. We also discovered that the activity of a non-DNA-binding novel platinum drug, phosphaplatin, is comparable with oxaliplatin and 5-FU when it was tested against colon cancer cell lines. Our strategy that combines the knowledge from pharmacogenomics across cell lines with the molecular information from specific cancer cells is beneficial for predicting the outcome of a possible combination therapy for personalized treatment.

The anti-cancer actions of O6-methylguanine-DNA-methyltransferase in relation to colon polyps

BACKGROUND

Genetic variability in DNA repair genes may contribute to differences in DNA repair capacity and susceptibility to colon polyps and cancer. In this study, we examined the role of MGMT polymorphisms in colon polyps formation.

METHODS

PCR-SSCP analysis was performed included 254 patients with colon polyps and 330 controls.

RESULTS

The homozygous F84F genotype was significantly more prevalent in study group than in controls. The polymorphic allele 84F was more frequent appeared in group of older patients and in group of smoking patients. On the other hand, there were no association between 84F and gender, size of polyps, cancer family history.

CONCLUSIONS

We concluded that high frequency of 84F allele in the group of patients may suggest the role of the MGMT variant in colon polyps etiology.

Molecular features of colorectal polyps presenting Kudo's type II mucosal crypt pattern: are they based on the same mechanism of tumorigenesis?

BACKGROUND AND STUDY AIMS

The molecular features of serrated polyps (SPs) with hyperplastic crypt pattern, also called Kudo's type II observed by chromoendoscopy, were evaluated.

METHODS

The clinicopathological and molecular features of 114 SPs with a hyperplastic pit pattern detected under chromoendoscopy (five dysplastic SPs, 63 sessile serrated adenoma/polyps (SSA/Ps), 36 microvesicular hyperplastic polyps (MVHPs), and 10 goblet cell-rich hyperplastic polyps (GCHPs)) were examined. The frequency of KRAS and BRAF mutations and CpG island methylator phenotype (CIMP) were investigated.

RESULTS

Dysplastic SPs and SSA/Ps were frequently located in the proximal colon compared to others (SSA/Ps vs. MVHPs or GCHPs, P < 0.0001). No significant difference was found in the frequency of BRAF mutation among SPs apart from GCHP (60 % for dysplastic SPs, 44 % for SSA/Ps, 47 % for MVHPs, and 0 % for GCHPs). The frequency of CIMP was higher in dysplastic SPs or SSA/Ps than in MVHPs or GCHPs (60 % for dysplastic SPs, 56 % for SSA/Ps, 32 % for MVHPs, and 10 % for GCHPs) (SSA/Ps vs. GCHP, P = 0.0068). When serrated neoplasias (SNs) and MVHPs were classified into proximal and distal lesions, the frequency of CIMP was significantly higher in the proximal compared to the distal SNs (64 % vs. 11 %, P = 0.0032). Finally, multivariate analysis showed that proximal location and BRAF mutation were significantly associated with an increased risk of CIMP.

CONCLUSIONS

Distinct molecular features were observed between proximal and distal SPs with hyperplastic crypt pattern. Proximal MVHPs may develop more frequently through SSA/Ps to CIMP cancers than distal MVHPs.

KRAS and BRAF mutation analysis in colorectal adenocarcinoma specimens with a low percentage of tumor cells

Background and Objective

The rapid development of molecular biology techniques allows for the introduction of real-time polymerase chain reaction (PCR) methods with a limit of mutation detection at 1 % in a background of wild-type DNA. Analysis of KRAS mutations in codons 12, 13, and 61, together with analysis of BRAF mutations in codon 600, are predictive biomarkers for anti-epidermal growth factor receptor (EGFR) treatment in colorectal cancer. Our aim was to compare PCR methods for KRAS mutations and BRAF mutation analysis using DNA isolated from tissue samples previously evaluated for presence of tumor cells using a quantitative scale and the percentage of tumor cells (PTC) scale. We addressed the question of whether a low number of tumor cells can be qualified for somatic mutation testing.

Results

Our study showed that PTC as low as 10 % was good enough to detect KRAS G12D, G13D, and Q61L mutations in formalin-fixed paraffin-embedded (FFPE) material. Furthermore, our results indicate that up to 20 % of colorectal cancer may carry mutations in the KRAS codon 61 and BRAF codon 600, which suggests the value of these mutation analyses because patients carrying them are unlikely to respond to cetuximab or panitumumab. A low level of KRAS somatic mutation detection has not been studied in depth in the context of clinical outcomes in patients; therefore, we compared new PCR methods, (KRBR-RT 50 Entrogen; ViennaLab StripAssay) and re-evaluated KRAS and BRAF status in patients with relapse after targeted therapy.

Conclusions

The importance of molecular results was confirmed by clinical observation of a patient with relapse who had qualified for targeted therapy with KRAS WT status (but was diagnosed by less sensitive single-stranded conformation polymorphisms method). Interestingly, during anti-EGFR treatment, it came to the selection of cells with KRAS G12C mutation which were present from the beginning in the tumor but at a low level (detected by PCR methods) only and led consequently to the metastasis. Taking into consideration the limit of detection, labor time, and assay cost, the real-time PCR method seems to be very promising especially for FFPE material with the PTC below 15 %.

Sessile serrated adenomas in the proximal colon are likely to be flat, large and occur in smokers

AIM

To examine the epidemiology and the morphology of the proximal sessile serrated adenomas (SSAs).

METHODS

We conducted a retrospective study to identify patients with SSAs using a university-based hospital pathology database query from January 2007 to April 2011. Data collected included: age, gender, ethnicity, body mass index, diabetes, smoking, family history of colorectal cancer, aspirin, and statin use. We collected data on morphology of SSAs including site (proximal or distal), size, and endoscopic appearance (flat or protuberant). We also compared proximal SSAs to proximal tubular adenomas detected during same time period.

RESULTS

One hundred and twenty patients with SSAs were identified: 61% were distal and 39% were proximal SSAs. Proximal SSAs were more likely to be flat than distal (100% vs 78% respectively; P = 0.0001). Proximal SSAs were more likely to occur in smokers (OR = 2.63; 95%CI: 1.17-5.90; P = 0.02) and in patients with family history of colorectal cancer (OR = 4.72; 95%CI: 1.43-15.55; P = 0.01) compared to distal. Proximal SSAs were statistically more likely to be ≥ 6 mm in size (OR = 2.94; P = 0.008), and also more likely to be large (≥ 1 cm) (OR = 4.55; P = 0.0005) compared to the distal lesions. Smokers were more likely to have proximal (P = 0.02), flat (P = 0.01) and large (P = 0.007) SSAs compared to non-smokers. Compared to proximal tubular adenomas, proximal SSAs were more likely to be large and occur in smokers.

CONCLUSION

Proximal SSAs which accounted for two-fifths of all SSAs were more likely to present as flat lesions, larger SSAs, and were more likely to occur in smokers and in patients with family history of colorectal cancer. Our data has implications for colorectal cancer screening.

Simultaneous detection of 19 K-ras mutations by free-solution conjugate electrophoresis of ligase detection reaction products on glass microchips

We demonstrate here the power and flexibility of free-solution conjugate electrophoresis (FSCE) as a method of separating DNA fragments by electrophoresis with no sieving polymer network. Previous work introduced the coupling of FSCE with ligase detection reaction (LDR) to detect point mutations, even at low abundance compared to the wild-type DNA. Here, four large drag-tags are used to achieve free-solution electrophoretic separation of 19 LDR products ranging in size from 42 to 66 nt that correspond to mutations in the K-ras oncogene. LDR-FSCE enabled electrophoretic resolution of these 19 LDR-FSCE products by CE in 13.5 min (E = 310 V/cm) and by microchip electrophoresis in 140 s (E = 350 V/cm). The power of FSCE is demonstrated in the unique characteristic of free-solution separations where the separation resolution is constant no matter the electric field strength. By microchip electrophoresis, the electric field was increased to the maximum of the power supply (E = 700 V/cm), and the 19 LDR-FSCE products were separated in less than 70 s with almost identical resolution to the separation at E = 350 V/cm. These results will aid the goal of screening K-ras mutations on integrated "sample-in/answer-out" devices with amplification, LDR, and detection all on one platform.

Modulatory efficacy of rosmarinic acid on premalignant lesions and antioxidant status in 1,2-dimethylhydrazine induced rat colon carcinogenesis

Colorectal cancer is one of the leading causes of cancer related deaths in Western countries and is becoming increasingly common in Asia. Rosmarinic acid (RA), one of the major components of polyphenol possesses attractive remedial features. The purpose of this study is to investigate the possible chemopreventive mechanism of action of RA against 1,2-dimethylhydrazine (DMH) induced rat colon carcinogenesis by evaluating the circulatory antioxidant status and colonic bacterial enzymes activities. Additionally, we analyzed the aberrant crypt foci (ACF) formation and multiplicity in the colon of experimental groups. Wistar male rats were divided into six groups. Group 1 was control rats, group 2 rats received RA (10 mg/kg b.w., p.o. everyday), rats in groups 3-6 received DMH (20 mg/kg b.w., s.c.) for the first 4 weeks. In addition to DMH, groups 4-6 received 2.5, 5, and 10 mg/kg b.w. RA respectively. The results revealed that supplementation with RA significantly reduced the formation of ACF and ACF multiplicity in DMH treated rats. Moreover RA supplementation prevented the alterations in circulatory antioxidant enzymes and colonic bacterial enzymes activities. Overall, our results showed that all three doses of RA inhibited carcinogenesis, though the effect of the intermediary dose of 5 mg/kg b.w. was more pronounced.

APC and KRAS mutations in distal colorectal polyps are related to smoking habits in men: results of a cross-sectional study

BACKGROUND

The purpose of this study was (a) to evaluate the association between cigarette smoking and the prevalence of distal colorectal polyps and adenocarcinoma and (b) to analyse genetic alterations representing different molecular pathways of the colorectal carcinogenesis.

METHODS

A total of 623 asymptomatic male (mean age: 53 years; 50-65) car factory workers were included. Information on smoking habits and other lifestyle factors were collected followed by a 60 cm colonoscopy. APC and KRAS mutations and microsatellite status were determined in colorectal lesions (colorectal carcinoma (CRC), hyperplastic (HP) and adenomatous polyps (AP)). Data were analysed using unconditional multiple logistic regression models.

RESULTS

Smokers had a higher prevalence of AP (OR 2.1; 95% CI 1.2-3.6; p<0.05) and HP (OR 5.4; 95% CI 2.6- 11.1; p<0.05). No differences in CRC were observed. There was a dose-response relationship with the number of cigarettes smoked. The risk of developing AP or HP decreased after smoking cessation, even among heavy smokers (≥20 packs/year). KRAS mutations were more prevalent among smokers AP (OR 5.6; 95% CI 1.6-20.4; p=0.007). There was a trend of positive association with APC mutations (OR 3.5; 95% CI 0.9-4.4; p=0.096). APC and KRAS mutations were found in 36% and 61% of the HP of smokers, but were absent in non-smokers (p=0.89 and 0.78, respectively). There were no differences in MSI between smokers and non-smokers.

CONCLUSIONS

Cigarette smoking is associated with a higher risk of developing both HP and AP and a higher prevalence of mutations in APC and KRAS.

Clinicopathological and molecular features of colorectal serrated neoplasias with different mucosal crypt patterns

OBJECTIVES

Endoscopic examination shows that serrated neoplasias (SNs), such as serrated adenomas and sessile serrated adenomas, exhibit different mucosal crypt patterns. However, it remains unclear whether advanced serrated polyps with different mucosal crypt patterns have different clinicopathological or molecular features.

METHODS

We classified the mucosal crypt patterns of 86 SNs into three types (hyperplastic, adenomatous, and mixed pattern) and evaluated their clinicopathological and molecular features.

RESULTS

We found significant differences in the proliferative activity status between SNs with mixed/adenomatous patterns and those with the hyperplastic patterns. SNs with the hyperplastic pattern were frequently located in the proximal colon and had a macroscopically superficial appearance, whereas SNs with the adenomatous pattern were often located in the distal colon and had a protruding appearance. Furthermore, a significant difference was observed in the frequency of the CpG island methylator phenotype (CIMP), involving the methylation of two or more CIMP-related genes (MINT1, MINT2, MINT31, p16, and MLH1), between SNs with the hyperplastic pattern and those with the mixed/adenomatous patterns (18/32 (56%) vs. 8/28 (29%) or 7/26 (27%); P=0.0309 or P=0.0249, respectively). Moreover, the prevalence of KRAS mutations was significantly higher in SNs with the adenomatous pattern than in those with the hyperplastic pattern (7/26 (27%) vs. 1/32 (3%); P=0.0173). In comparison with other patterns, the mixed pattern was detected more frequently in mixed serrated polyps (MSPs), which contain separate histological components. Some MSPs exhibited concordant molecular alterations among the different histological components.

CONCLUSIONS

The clinicopathological and molecular features of SNs correlated strongly with their mucosal crypt patterns, which were observed using chromoendoscopy.

[Histopathological diagnosis and differential diagnosis of colorectal serrated polys: findings of a consensus conference of the working group "gastroenterological pathology of the German Society of Pathology"]

Until recently, two major types of colorectal epithelial polyps were distinguished: the adenoma and the hyperplastic polyp. While adenomas - because of their cytological atypia - were recognized as precursor lesions for colorectal carcinoma, hyperplastic polyps were perceived as harmless lesions without any potential for malignant progression, mainly because hyperplastic polyps lack cytological atypia. Meanwhile, it is evident that the lesions formerly classified as hyperplastic represent a heterogeneous group of polyps, some of which exhibit a significant risk of neoplastic progression. These lesions show characteristic epigenetic alterations not commonly seen in colorectal adenomas and progress to colorectal carcinoma via the so-called serrated pathway (CIMP pathway). This group of polyps is comprised not only of hyperplastic polyps, but also of sessile serrated adenomas (SSA), traditional serrated adenomas (TSA) and mixed polyps, showing serrated and "classical" adenomatous features. In a consensus conference of the working group of gastroenterological pathology of the German Society of Pathology, standardization of nomenclature and diagnostic criteria as well as recommendations for clinical management of these serrated polyps were formulated and are presented herein.

Serrated polyposis: an enigmatic model of colorectal cancer predisposition

Serrated polyposis has only recently been accepted as a condition which carries an increased personal and familial risk of colorectal cancer. Described over four decades ago, it remains one of the most underrecognized and poorly understood of all the intestinal polyposes. With a variety of phenotypic presentations, it is likely that serrated polyposis represents a group of diseases rather than a single entity. Further, neoplastic progression in serrated polyposis may be associated with premature aging in the normal mucosa, typified by widespread gene promoter hypermethylation. From this epigenetically altered field, arise diverse polyps and cancers which show a range of molecular features. Despite a high serrated polyp count, only one-third of colorectal cancers demonstrate a BRAF V600E mutation, the molecular hallmark of the canonical serrated pathway, suggesting that though multiple serrated polyps act as a marker of an abnormal mucosa, the majority of CRC in these patients arise within lesions other than BRAF-mutated serrated polyps.

Rapid detection of low-abundance K-ras mutation in stools of colorectal cancer patients using chip-based temperature gradient capillary electrophoresis

Mutant K-ras provides an independent negative predictive marker for epidermal growth factor receptor (EGFR)-targeted therapy in colorectal cancers (CRCs). Rapid, sensitive, and cost-effective screening for K-ras status will overarch rational personalized medicine. Stool-based DNA testing offers unique advantages for CRC screening such as noninvasiveness, high specificity, and patient compliance, whereas complicated procedures and the low sensitivity of the present approaches have hampered its application on a wide scale. In this study, a chip-based temperature gradient capillary electrophoresis (TGCE) technique was applied to detect low-abundance K-ras mutations under a pooled experiment and analyze K-ras mutations in 30 paired stool samples and cancer tissues of CRC patients and 15 stool samples of healthy volunteers. The chip-based TGCE results showed that the successful analysis of K-ras status could be achieved within 6 min with an extremely low sample consumption of 14 nl. Detection is sensitive enough to reliably report 0.2% mutant CRC cells in a wild-type background, and 0.5 ng of template DNA was sufficient for chip-based TGCE. Of the 30 stool samples of CRC patients analyzed, 17 (57%) harbored K-ras mutations, and the lowest percentage of the detectable mutant K-ras in stool samples was 2%. The coincidence rate for K-ras mutations between stools and tissues obtained by the chip-based method reached 97% (29/30). One of the 15 stool samples of normal controls carried K-ras mutations, producing a specificity of 93%. Clone sequencing data entirely confirmed the results obtained by chip-based TGCE. The study demonstrates that chip-based TGCE is capable of rapidly screening low-abundance K-ras mutations with high sensitivity, reproducibility, simplicity, and significant savings of time and sample. Application of this method to genotype the K-ras gene in stools would provide a potential means for predicting the effectiveness of EGFR-targeted therapy in CRC patients using noninvasive approaches.

The clinical significance of serrated polyps

Colorectal cancer (CRC) is a heterogeneous disorder than arises via multiple distinct pathways, such as the serrated pathway, in which serrated polyps (including variants of hyperplastic polyps) are the precursor lesions. Approximately 15-20% of all CRCs arise via the serrated pathway, and these serrated carcinomas are clinically, morphologically, and molecularly distinct from conventional CRCs. The prevention of serrated carcinomas represents an important clinical challenge. Gastroenterologists need to recognize and remove potential precursor lesions and implement a post-polypectomy surveillance program when appropriate. This article focuses on the characteristics and significance of clinically relevant serrated polyps and addresses implications for CRC prevention practices.

Mutant K-ras promotes carcinogen-induced murine colorectal tumourigenesis, but does not alter tumour chromosome stability

K-ras (KRAS) mutations are observed in around 40% of human colorectal adenomas and carcinomas. Previously, we developed and characterized a strain of transgenic mice with inducible intestinal epithelial expression of K-ras{Val12} via a Cre/LoxP system. To evaluate the influence of mutant K-ras on carcinogen-induced colorectal tumourigenesis, we induced neoplastic alterations in the large intestines of wild-type and K-ras{Val12} mice using the colon-selective carcinogen 1,2-dimethylhydrazine (DMH), which has been widely used to induce colorectal tumours that are histopathologically similar to those observed in humans. K-ras{Val12} expression significantly promoted DMH-induced colorectal tumourigenesis: the average lifespan of the mice decreased from 38.52 ± 1.97 weeks for 40 control mice to 32.42 ± 2.17 weeks for 26 K-ras{Val12} mice (mean ± SEM, p < 0.05) and the abundance of large intestinal tumours increased from 2.27 ± 0.15 per control mouse to 3.85 ± 0.20 in K-ras{Val12} mice (mean ± SEM, p < 0.01). Adenomas from DMH-treated K-ras{Val12} mice showed significantly higher proportions of Ki-67-positive proliferating cells (10.9 ± 0.69%) compared with those from DMH-treated wild-type mice (7.77 ± 0.47%) (mean ± SEM, p < 0.01) and a mild increase in apoptotic nuclei staining for cleaved caspase-3 (1.94 ± 0.21% compared with 1.15 ± 0.14%, mean ± SEM, p < 0.01). In the adenomas from DMH-treated K-ras{Val12} mice, K-ras{Val12} transgene recombination and expression were confirmed, with immunohistochemical evidence of strong Erk/MapK and mild PI3K/Akt pathway activation compared with adenomas from DMH-treated wild-type mice. Microarray hybridization and clustering analysis demonstrated different expression profiles in adenomas from DMH-treated wild-type and DMH-treated K-ras{Val12} mice, indicating involvement of different molecular mechanisms including Erk/MapK and PI3K/Akt signalling in K-ras{Val12}-expressing adenomas. Array-comparative genomic hybridization analysis showed chromosome stability in both cohorts, with only a very few tiny alterations observed in one adenoma from a DMH-treated K-ras{Val12} mouse. Taken together, these data show that mutant K-ras significantly promotes DMH-induced colorectal tumourigenesis, resulting in distinct changes in cell signalling and proliferation, but does not alter chromosome stability in the tumours.

The presence of large serrated polyps increases risk for colorectal cancer

BACKGROUND & AIMS

There is evidence that serrated polyps (serrated adenomas and hyperplastic polyps) have different malignant potential than traditional adenomas. We used a colonoscopy database to determine the association between the presence of serrated colorectal polyps and colorectal neoplasia.

METHODS

We performed a multicenter observational study of 10,199 subjects who underwent first-time colonoscopies. Data collected on study subjects included age and sex and the location, size, and histology of polyps or tumors found at colonoscopy. Serrated polyps were defined as those diagnosed by the pathologists in the participating hospitals as a serrated lesion (a lesion given the term of "classical hyperplastic polyp," "traditional serrated adenoma," "sessile serrated adenoma," or "mixed serrated polyp"). Large serrated polyps (LSPs) were defined as those ≥ 10 mm.

RESULTS

There were 1573 patients (15.4%) with advanced neoplasia, 708 patients (6.9%) with colorectal cancer (CRC), and 140 patients (1.4%) with LSPs in our cohort. Multivariate analysis associated the presence of LSPs with advanced neoplasia (odds ratio [OR], 4.01; 95% confidence interval [CI], 2.83-5.69) and CRC (OR, 3.34; 95% CI, 2.16-5.03). The presence of LSPs was the greatest risk factor for CRC, particularly for proximal CRC (OR, 4.79; 95% CI, 2.54-8.42). Proximal and protruded LSPs were the highest risk factors for proximal CRC (OR, 5.36; 95% CI, 2.40-10.8 and OR, 9.00; 95% CI, 2.75-19.2, respectively).

CONCLUSIONS

The presence of LSPs is a risk factor for CRC, particularly CRC of the proximal colon.

Serrated polyps of the colon and rectum (hyperplastic polyps, sessile serrated adenomas, traditional serrated adenomas, and mixed polyps)-proposal for diagnostic criteria

Until recently, two major types of colorectal epithelial polyps were distinguished: the adenoma and the hyperplastic polyp. While adenomas-because of their cytological atypia-were recognized as the precursor lesions for colorectal carcinoma, hyperplastic polyps were perceived as harmless lesions without any potential for malignant progression mainly because hyperplastic polyps are missing cytological atypia. Meanwhile, it is recognized that the lesions, formerly classified as hyperplastic, represent a heterogeneous group of polyps with characteristic serrated morphology some of which exhibit a significant risk of neoplastic progression. These serrated lesions show characteristic epigenetic alterations not commonly seen in colorectal adenomas and progress to colorectal carcinoma via the so-called serrated pathway (CpG-island-methylation-phenotype pathway). This group of polyps is comprised not only of hyperplastic polyps, but also of sessile serrated adenomas, traditional serrated adenomas and mixed polyps, showing serrated and "classical" adenomatous features. Diagnostic criteria and nomenclature for these lesions are not uniform and, therefore, somewhat confusing. In a consensus conference of the Working Group of Gastroenterological Pathology of the German Society of Pathology, standardization of nomenclature and diagnostic criteria as well as recommendations for clinical management of these serrated polyps were formulated and are presented herein.

Serrated adenoma: a distinct form of non-polypoid colorectal neoplasia?

Until recently, 2 major forms of colorectal polyp were recognized: the adenoma and the hyperplastic polyp. Adenomas were known to represent a precursor to colorectal cancer, whereas hyperplastic polyps were viewed as nonneoplastic, having no potential for progression to malignancy. We now recognize, however, that the lesions diagnosed as hyperplastic polyps in the past represent a heterogeneous group of polyps, some of which truly are hyperplastic, and others that truly have a significant risk for transformation to colorectal cancer. These polyps have a characteristic serrated architecture, and include not only hyperplastic polyps but also the recently recognized serrated adenomas. Serrated adenomas occur in 2 forms: the traditional serrated adenoma, which is usually a polypoid lesion endoscopically, and the sessile serrated adenoma, a flat or slightly raised, usually right-sided lesion. Serrated adenomas of both types show characteristic molecular alterations not commonly seen in traditional colorectal adenomas, and probably progress to colorectal cancer by means of a different pathway, the so-called 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.

Clinical relevance of KRAS in human cancers

The KRAS gene (Ki-ras2 Kirsten rat sarcoma viral oncogene homolog) is an oncogene that encodes a small GTPase transductor protein called KRAS. KRAS is involved in the regulation of cell division as a result of its ability to relay external signals to the cell nucleus. Activating mutations in the KRAS gene impair the ability of the KRAS protein to switch between active and inactive states, leading to cell transformation and increased resistance to chemotherapy and biological therapies targeting epidermal growth factor receptors. This review highlights some of the features of the KRAS gene and the KRAS protein and summarizes current knowledge of the mechanism of KRAS gene regulation. It also underlines the importance of activating mutations in the KRAS gene in relation to carcinogenesis and their importance as diagnostic biomarkers, providing clues regarding human cancer patients' prognosis and indicating potential therapeutic approaches.

Mutated K-ras(Asp12) promotes tumourigenesis in Apc(Min) mice more in the large than the small intestines, with synergistic effects between K-ras and Wnt pathways

Summary K-ras mutations are found in 40-50% of human colorectal adenomas and carcinomas, but their functional contribution remains incompletely understood. Here, we show that a conditional mutant K-ras mouse model (K-ras(Asp12)/Cre), with transient intestinal Cre activation by beta-Naphthoflavone (beta-NF) treatment, displayed transgene recombination and K-ras(Asp12) expression in the murine intestines, but developed few intestinal adenomas over 2 years. However, when crossed with Apc(Min/+) mice, the K-ras(Asp12)/Cre/Apc(Min/+) offspring showed acceleration of intestinal tumourigenesis with significantly changed average lifespan (P < 0.05) decreased to 18.4 +/- 5.4 weeks from 20.9 +/- 4.7 weeks (control Apc(Min/+) mice). The numbers of adenomas in the small intestine and large intestine were significantly (P < 0.01) increased by 1.5-fold and 5.7-fold, respectively, in K-ras(Asp12)/Cre/Apc(Min/+) mice compared with Apc(Min/+) mice, with the more marked increase in adenoma prevalence in the large intestine. To explore possible mechanisms for K-ras(Asp12) and Apc(Min) co-operation, the Mitogen-activated protein kinase (Mapk), Akt and Wnt signalling pathways, including selected target gene expression levels, were evaluated in normal large intestine and large intestinal tumours. K-ras(Asp12) increased activation of Mapk and Akt signalling pathway targets phospho-extracellular signal-regulated kinase (pErk) and pAkt, and increased relative expression levels of Wnt pathway targets vascular endothelial growth factor (VEGF), gastrin, cyclo-oxygenase 2 (Cox2) and T-cell lymphoma invasion and metastasis 1 (Tiam1) in K-ras(Asp12)/Cre/Apc(Min/+) adenomas compared with that of Apc(Min/+) adenomas, although other Wnt signalling pathway target genes such as Peroxisome proliferator-activated receptor delta (PPARd), matrix metalloproteinase 7 (MMP7), protein phosphatase 1 alpha (PP1A) and c-myc remained unchanged. In conclusion, intestinal expression of K-ras(Asp12) promotes mutant Apc-initiated intestinal adenoma formation in vivo more in the large intestine than the small intestine, with evidence of synergistic co-operation between mutant K-ras and Apc involving increased expression of some Wnt-pathway target genes.

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.

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.

Pathologic features and biologic importance of colorectal serrated polyps

Serrated polyps of the large intestine comprise a heterogeneous group of mucosal lesions that includes nondysplastic polyps, such as hyperplastic polyps and sessile serrated polyps, and polyps that show overt cytologic dysplasia, namely serrated adenomas and mixed hyperplastic/adenomatous polyps. These polyps have received increased recognition over the past 2 decades, as emerging evidence suggests that a subset may be precursors to colorectal carcinomas that lack chromosomal instability. Several investigators have proposed the concept of the "serrated neoplastic pathway" according to which nondysplastic serrated lesions develop progressively severe dysplasia culminating in the development of microsatellite unstable carcinomas that show DNA hypermethylation and BRAF mutations. A subset of hyperplastic polyps and sessile serrated polyps show mutations in the BRAF gene and abnormal DNA methylation, which can, ultimately, affect the promoter regions of key DNA-repair and tumor suppressor genes, such as MLH1 and MGMT, leading to their decreased transcription and microsatellite instability. On the basis of this hypothesis, many authors have proposed that sessile serrated polyps should be treated and surveilled similar to conventional adenomas, although prospective data are lacking. This review describes the clinicopathologic and molecular features of serrated polyps and discusses the current data regarding their biologic significance.

Association of large serrated polyps with synchronous advanced colorectal neoplasia

OBJECTIVES

Serrated polyps of the colorectum are a histologically and genetically heterogeneous group of lesions, which include classic hyperplasic polyps, sessile serrated adenomas (SSAs), and traditional serrated adenomas. Accumulating evidence suggests that they may have different malignancy potentials. This study sought to determine the association between the presence of large serrated colorectal polyps and synchronous advanced colorectal neoplasia.

METHODS

Among 4,714 asymptomatic subjects who underwent screening colonoscopy, cases of advanced colorectal neoplasia (tubular adenoma > or =1 cm, adenoma with any villous histology, adenoma with carcinoma in situ / high-grade dysplasia, or invasive adenocarcinoma) were compared with controls without advanced neoplasia with respect to candidate predictors, including age, sex, family history of colorectal cancer, body mass index, the presence and number of small tubular adenomas (<1 cm), the presence of multiple small serrated polyps (<1 cm), and the presence of large serrated polyps (> or =1 cm). Independent predictors of advanced neoplasia were determined by multivariate logistic regression analysis.

RESULTS

Among 467 cases and 4,247 controls, independent predictors of advanced colorectal neoplasia were increasing age (odds ratio (OR)=4.51; 95% confidence interval (CI), 1.43-14.3; P=0.01 for subjects > or =80 years vs. 50-54 years of age); non-advanced tubular adenomas (OR=2.33; 95% CI 1.37-3.96, P=0.0017 for 3 or more); and large serrated polyps (OR=3.24; 95% CI 2.05-5.13, P<0.0001). In total, 109 subjects (2.3% of the study population) had large serrated polyps. Right- and left-sided large serrated polyps had a similar association with advanced colorectal neoplasia (OR=3.38 vs. 2.66, P=0.62).

CONCLUSIONS

Large serrated polyps are strongly and independently associated with synchronous advanced colorectal neoplasia. Our results suggest that large serrated polyps may be a marker for advanced colorectal neoplasia. Further studies are needed to determine whether the association with advanced neoplasia differs among subsets of serrated polyps, particularly SSAs and classic hyperplastic polyps.

Ligase detection reaction for the analysis of point mutations using free-solution conjugate electrophoresis in a polymer microfluidic device

We have developed a new method for the analysis of low abundant point mutations in genomic DNA using a combination of an allele-specific ligase detection reaction (LDR) with free-solution conjugate electrophoresis (FSCE) to generate and analyze the genetic products. FSCE eliminates the need for a polymer sieving matrix by conjugating chemically synthesized polyamide "drag-tags" onto the LDR primers. The additional drag of the charge-neutral drag-tag breaks the linear scaling of the charge-to-friction ratio of DNA and enables size-based separations of DNA in free solution using electrophoresis with no sieving matrix. We successfully demonstrate the conjugation of polyamide drag-tags onto a set of four LDR primers designed to probe the K-ras oncogene for mutations highly associated with colorectal cancer, the simultaneous generation of fluorescently labeled LDR/drag-tag conjugate (LDR-dt) products in a multiplexed, single-tube format with mutant:WT ratios as low as 1:100, respectively, and the single-base, high-resolution separation of all four LDR-dt products. Separations were conducted in free solution with no polymer network using both a commercial capillary array electrophoresis (CAE) system and a PMMA microchip replicated via hot-embossing with only a Tris-based running buffer containing additives to suppress the EOF. Typical analysis times for LDR-dt were 11 min using the CAE system and as low as 85 s for the PMMA microchips. With resolution comparable to traditional gel-based CAE, FSCE along with microchip electrophoresis decreased the separation time by more than a factor of 40.

Aberrant crypt foci in colon cancer epidemiology

Colonic carcinogenesis is characterized by progressive accumulations of genetic and epigenetic derangements. These molecular events are accompanied by histological changes that progress from mild cryptal architectural abnormalities in small adenomas to eventual invasive cancers. The transition steps from normal colonic epithelium to small adenomas are little understood. In experimental models of colonic carcinogenesis aberrant crypt foci (ACF), collections of abnormal appearing colonic crypts, are the earliest detectable abnormality and precede adenomas. Whether in fact ACF are precursors of colon cancer, however, remains controversial. Recent advances in magnification chromoendoscopy now allow these lesions to be identified in vivo and their natural history ascertained. While increasing lines of evidence suggest that dysplastic ACF harbor a malignant potential, there are few prospective studies to confirm causal relationships and supporting epidemiological studies are scarce. It would be very useful, for example, to clarify the relationship of ACF incidence to established risks for colon cancer, including age, smoking, sedentary lifestyle, and Western diets. In experimental animal models, carcinogens dose-dependently increase ACF, whereas most chemopreventive agents reduce ACF incidence or growth. In humans, however, few agents have been validated to be chemopreventive of colon cancer. It remains unproven, therefore, whether human ACF could be used as reliable surrogate markers of efficacy of chemopreventive agents. If these lesions could be used as reliable biomarkers of colon cancer risk and their reductions as predictors of effective chemopreventive agents, metrics to quantify ACF could greatly facilitate the study of colonic carcinogenesis and chemoprevention.

Hyperplastic polyps and sessile serrated adenomas as a phenotypic expression of MYH-associated polyposis

BACKGROUND & AIMS

MYH-associated polyposis (MAP) is a disorder caused by a bi-allelic germline MYH mutation, characterized by multiple colorectal adenomas. These adenomas typically harbor G:C-->T:A transversions in the APC and K-ras genes caused by MYH deficiency. Occasional hyperplastic polyps (HPs) have been described in MAP patients but a causal relationship has never been investigated. We examined the presence of HPs and sessile serrated adenomas (SSAs) in 17 MAP patients and studied the occurrence of G:C-->T:A transversions in the APC and K-ras gene in these polyps.

METHODS

MAP patients were analyzed for the presence of HPs/SSAs. APC-mutation cluster region and K-ras codon 12 mutation analysis was performed in adenomas (n = 22), HPs (n = 63), and SSAs (n = 10) from these patients and from a control group of sporadic adenomas (n = 17), HPs (n = 24), and SSAs (n = 17).

RESULTS

HPs/SSAs were detected in 8 of 17 (47%) MAP patients, of whom 3 (18%) met the criteria for hyperplastic polyposis syndrome. APC mutations were detected only in adenomas and comprised exclusively G:C-->T:A transversions. K-ras mutations were detected in 51 of 73 (70%) HPs/SSAs in MAP patients, compared with 7 of 41 (17%) sporadic HPs/SSAs in the control group (P < .0001). In HPs/SSAs, 48 of 51 (94%) K-ras mutations showed G:C-->T:A transversions, compared with 2 of 7 (29%) sporadic HPs/SSAs in the control group (P < .0001).

CONCLUSIONS

HPs and SSAs are a common finding in MAP patients. The detection of almost exclusively G:C-->T:A transversions in the K-ras gene of HPs/SSAs strongly suggests that these polyps are related causally to MYH deficiency. This implies that distinct pathways, that is, APC-gene related in adenomas and nonrelated in HPS/SSAs, appear to be operational in MAP.

Detection of mutated K-ras DNA in urine, plasma, and serum of patients with colorectal carcinoma or adenomatous polyps

Our previous studies demonstrated that urine contains DNA derived from the circulation and that this DNA originated, in part, from organ sites and tumors distal to the urinary tract. To explore the potential use of DNA from urine as compared to other body fluids as a source for circulating DNA for cancer detection, the DNA concentration and the frequency of detection of mutated Kristin-ras (K-ras) DNA in serum, plasma, and urine were examined. The concentration of DNA in the urine was similar to that in the serum, but the DNA concentration in plasma was significantly lower than in either urine or serum (P < 0.05). When DNA derived from 10 muL of body fluid was used in each mutation assay, the detection frequency of mutated K-ras DNA was comparable among serum, plasma, and urine. However, when DNA derived from 200 muL of body fluid was used, the incidence of detecting mutated K-ras DNA in urine was significant higher (95%) than in either serum (35%) or plasma (40%) (P < 0.0005), suggesting that inhibitory factors in serum/plasma may be more limiting than in urine. The use and practicality of urine as a source of circulating DNA for cancer detection are discussed.

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.

Genetic and epigenetic changes in aberrant crypt foci and serrated polyps

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

COX-2 expression in sporadic colorectal adenomatous polyps is linked to adenoma characteristics

AIMS

To assess cyclooxygenase-2 (COX-2) expression in sporadic colonic adenomas and to explore the association of COX-2 positivity with adenoma characteristics linked to increased risk of malignant transformation.

METHODS AND RESULTS

COX-2 expression and localization were assessed in 64 colorectal adenomas and 35 paired adjacent normal colonic mucosal biopsy specimens. The number of adenoma specimens was then extended to include polyps exhibiting an increasing degree of epithelial dysplasia. Forty colonic hyperplastic polyps were also identified from the pathology diagnostic database and included in the analysis. Immunohistochemistry was performed with the Envision+ peroxidase-linked biotin-free system incorporating a signal amplification step. There was a statistically significant increase in COX-2 expression in colonic polyps compared with paired adjacent normal mucosa, chi(2) = 40.1, P = 0.001. The probability of COX-2 expression increased along with increasing adenoma size and increasing degree of epithelial dysplasia. Fifty-five per cent of the hyperplastic polyp specimens expressed COX-2.

CONCLUSIONS

This study associates COX-2 epithelial expression with a number of adenoma characteristics that convey an increased risk of malignant transformation. This is in keeping with a positive role for COX-2 in early colorectal carcinogenesis.

Nomenclature, molecular genetics and clinical significance of the precursor lesions in the serrated polyp pathway of colorectal carcinoma

Serrated adenomas (SAs) are part of the distinct serrated polyp pathway of colorectal carcinogenesis characterized by microsatellite instability and deficiency in DNA mismatch repair. Sessile SA is a recently recognized lesion that typically presents as a large sessile polyp, but lacks the conventional dysplasia. It is more frequently found on the right side than on the left side of the colon, and is thought to represent an intermediate form in the hyperplastic polyp to sessile SA, traditional SA, and colon cancer sequence. Many terms have been used and are still in use in the literature to describe this lesion, such as "hyperplastic polyposis", "giant hyperplastic polyposis," "large hyperplastic polyps," "hyperplastic-adenomatous polyposis syndrome," "giant hyperplastic polyp," and "mixed epithelial polyp." The purpose of this paper is to review and clarify the confusing nomenclature, and to provide a framework for understanding the genetic alterations and clinical significance of these precursor lesions in the serrated polyp pathway of colorectal caner.

Molecular classification and genetic pathways in hyperplastic polyposis syndrome

Hyperplastic Polyposis (HPPS) is a poorly characterized syndrome that increases colorectal cancer (CRC) risk. We aimed to provide a molecular classification of HPPS. We obtained 282 tumours from 32 putative HPPS patients with >or= 10 hyperplastic polyps (HPs); some patients also had adenomas and CRCs. We found no good evidence of microsatellite instability (MSI) in our samples. The epithelium of HPs was monoclonal. Somatic BRAF mutations occurred in two-thirds of our patients' HPs, and KRAS2 mutations in 10%; both mutations were more common in younger cases. The respective mutation frequencies in a set of 'sporadic' HPs were 18% and 10%. Importantly, the putative HPPS patients generally fell into two readily defined groups, one set whose polyps had BRAF mutations, and another set whose polyps had KRAS2 mutations. The most plausible explanation for this observation is that there exist different forms of inherited predisposition to HPPS, and that these determine whether polyps follow a BRAF or KRAS2 pathway. Most adenomas and CRCs from our putative HPPS patients had 'classical' morphology and few of these lesions had BRAF or KRAS2 mutations. These findings suggest that tumourigenesis in HPPS does not necessarily follow the 'serrated' pathway. Although current definitions of HPPS are sub-optimal, we suggest that diagnosis could benefit from molecular analysis. Specifically, testing BRAF and KRAS2 mutations, and perhaps MSI, in multiple polyps could help to distinguish HPPS from sporadic HPs. We propose a specific model which would have diagnosed five more of our cases as HPPS compared with the WHO clinical criteria.

The role of chemotherapy in microsatellite unstable (MSI-H) colorectal cancer

INTRODUCTION

High-frequency microsatellite instability (MSI-H) is an alternate pathway of colorectal carcinogenesis, which accounts for 15% of all sporadic colorectal cancers. These tumours arise from mutations in the DNA mismatch repair system and thus have different responses to chemotherapeutic agents compared to microsatellite stable (MSS) cancers.

OBJECTIVE

This review aims to summarise the available literature on the responses to chemotherapy in MSI-H colorectal cancer (CRC).

RESULTS AND DISCUSSION

5 Fluorouracil (5FU) is commonly used as a chemotherapeutic agent in colon cancer and in vitro evidence shows reduced response to 5FU in MSI-H CRC. The clinical evidence is conflicting but favours a reduced response to 5FU in MSI-H CRC. Several newer agents such as COX-2 inhibitors and irinotecan are also reviewed.

CONCLUSION

Available evidence suggests that MSI-H CRC have different behaviour patterns and response to chemotherapy compared with MSS CRC.

[Emerging concepts in colorectal serrated polyps]

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

Ligase detection reaction/hybridization assays using three-dimensional microfluidic networks for the detection of low-abundant DNA point mutations

We have fabricated a flow-through biochip assembly that consisted of two different microchips: (1) a polycarbonate (PC) chip for performing an allele-specific ligation detection reaction (LDR) and (2) a poly(methyl methacrylate) (PMMA) chip for the detection of the LDR products using an universal array platform. The operation of the device was demonstrated by detecting low-abundant DNA mutations in gene fragments (K-ras) that carry point mutations with high diagnostic value for colorectal cancers. The PC microchip was used for the LDR in a continuous-flow format, in which two primers (discriminating primer that carried the complement base to the mutation being interrogated and a common primer) that flanked the point mutation and were ligated only when the particular mutation was present in the genomic DNA. The miniaturized reactor architecture allowed enhanced reaction speed due to its high surface-to-volume ratio and efficient thermal management capabilities. A PMMA chip was employed as the microarray device, where zip code sequences (24-mers), which were complementary to sequences present on the target, were microprinted into fluidic channels embossed into the PMMA substrate. Microfluidic addressing of the array reduced the hybridization time significantly through enhanced mass transport to the surface-tethered zip code probes. The two microchips were assembled as a single integrated unit with a novel interconnect concept to produce the flow-through microfluidic biochip. A microgasket, fabricated from an elastomer poly(dimethylsiloxane) with a total volume of the interconnecting assembly of <200 nL, was used as the interconnect between the two chips to produce the three-dimensional microfluidic network. We successfully demonstrated the ability to detect one mutant DNA in 100 normal sequences with the biochip assembly. The LDR/hybridization assay using the assembly performed the entire assay at a relatively fast processing speed: 6.5 min for on-chip LDR, 10 min for washing, and 2.6 min for fluorescence scanning (total processing time 19.1 min) and could screen multiple mutations simultaneously.

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.

Conditional expression of mutated K-ras accelerates intestinal tumorigenesis in Msh2-deficient mice

K-ras mutation occurs in 40-50% of human colorectal adenomas and carcinomas, but its contribution to intestinal tumorigenesis in vivo is unclear. We developed K-ras(V12) transgenic mice that were crossed with Ah-Cre mice to generate K-ras(V12)/Cre mice, which showed beta-naphthoflavone-induction of Cre-mediated LoxP recombination that activated intestinal expression of K-ras(V12) 4A and 4B transcripts and proteins. Only very occasional intestinal adenomas were observed in beta-naphthoflavone-treated K-ras(V12)/Cre mice aged up to 2 years, suggesting that mutated K-ras expression alone does not significantly initiate intestinal tumourigenesis. To investigate the effects of mutated K-ras on DNA mismatch repair (MMR)-deficient intestinal tumour formation, these mice were crossed with Msh2(-/-) mice to generate K-ras(V12)/Cre/Msh2(-/-) offspring. After beta-naphthoflavone treatment, K-ras(V12)/Cre/Msh2(-/-) mice showed reduced average lifespan of 17.3+/-5.0 weeks from 26.9+/-6.8 (control Msh2(-/-) mice) (P<0.01). They demonstrated increased adenomas in the small intestine from 1.41 (Msh2(-/-) controls) to 7.75 per mouse (increased fivefold, P<0.01). In the large intestine, very few adenomas were found in Msh2(-/-) mice (0.13 per mouse) whereas K-ras(V12)/Cre/Msh2(-/-) mice produced 2.70 adenomas per mouse (increased 20-fold, P<0.01). Over 80% adenomas from K-ras(V12)/Cre/Msh2(-/-) mice showed transgene recombination with expression of K-ras(V12) 4A and 4B transcripts and proteins. Sequencing of endogenous murine K-ras showed mutations in two out of 10 tumours examined from Msh2(-/-) mice, but no mutations in 17 tumours from K-ras(V12)/Cre/Msh2(-/-) mice. Expression of K-ras(V12) in tumours caused activation of the mitogen-activated protein kinase and Akt/protein kinase B signaling pathways, demonstrated by phosphorylation of p44MAPK, Akt and GSK3beta, as well as transcriptional upregulation of Pem, Tcl-1 and Trap1a genes (known targets of K-ras(V12) expression in stem cells). Thus, mutated K-ras cooperates synergistically with MMR deficiency to accelerate intestinal tumorigenesis, particularly in the large intestine.

Tobacco smoking and colorectal hyperplastic and adenomatous polyps

Colorectal adenomas and possibly some hyperplastic polyps are precursors of colorectal cancer. Tobacco use is associated in epidemiologic studies with these polyps, although links between smoking and colorectal cancer are less consistent. To characterize the role of tobacco in early colorectal carcinogenesis, we compared tobacco use among 4,383 subjects with histologically verified benign (hyperplastic or adenomatous) polyps of the distal colon (descending colon, sigmoid, and rectum) with tobacco use among 33,667 subjects who were endoscopy negative for distal colon tumors, in the screening arm of the Prostate, Lung, Colorectal, and Ovarian Trial, a randomized trial of flexible sigmoidoscopy. Risks, estimated by the odds ratio (OR), associated with current cigarette use were OR = 4.4 [95% confidence interval (95% CI), 3.7-5.2] for hyperplastic polyps only, OR = 1.8 (95% CI, 1.5-2.1) for adenomas only, and OR = 6.2 (95% CI, 4.7-8.3) for subjects with both hyperplastic and adenomatous polyps concurrently. Effects were weaker among ex smokers; the smoking-associated ORs remained consistently higher for hyperplastic polyps. This pattern was also seen in relation to cigarettes smoked per day, smoking duration, and pack-years. Tobacco-associated risks for multiple polyps were also stronger when hyperplastic disease was involved. In conclusion, tobacco use, particularly recent use, increases risk for both adenomatous and hyperplastic polyps, but the risks are substantially greater for hyperplastic lesions.

Advanced colorectal polyps with the molecular and morphological features of serrated polyps and adenomas: concept of a 'fusion' pathway to colorectal cancer

AIM

To establish and explain the pattern of molecular signatures across colorectal polyps.

METHODS AND RESULTS

Thirty-two sessile serrated adenomas (SSA), 10 mixed polyps (MP), 15 traditional serrated adenomas (SA), 49 hyperplastic polyps (HP) and 84 adenomas were assessed for mutation of KRAS and BRAF and aberrant expression of p53. The findings were correlated with loss of expression of O-6-methylguanine DNA methyltransferase (MGMT). KRAS mutation occurred more frequently (26.5%) than BRAF mutation (4.8%) in adenomas (P < 0.001) and particularly in adenomas with villous architecture (50%). Loss of expression of MGMT correlated with KRAS mutation in small tubular adenomas (P < 0.04). BRAF mutation was frequent in HPs (67%) and SSAs (81%), while KRAS mutation was infrequent (4% and 3%, respectively). Of MPs and SAs, 72% had either BRAF or KRAS mutation. Aberrant expression of p53 was uncommon overall, but occurred more frequently in MPs and SAs (12%) than adenomas (1%) (P < 0.04) and there was concordant loss of expression of MGMT.

CONCLUSIONS

Molecular alterations that are characteristic of the serrated pathway and adenoma-carcinoma sequence can co-occur in a minority of advanced colorectal polyps that then show morphological features of both pathways. These lesions account for only 2% of colorectal polyps, but may be relatively aggressive.

Serrated mucosal lesions of the colorectum

PURPOSE OF REVIEW

To examine and clarify the nomenclature and histologic lesions identified as serrated mucosal lesions of the colorectum, including serrated adenomas, sessile serrated polyps (also known as sessile serrated adenomas) and hyperplastic polyps. This is timely given the significant confusion in ascribing a microscopic diagnosis and clinical utility of such a diagnosis.

RECENT FINDINGS

The emergence of sessile serrated polyps (or adenomas) as distinct histomorphologic lesions from serrated adenomas, as well as the appreciation of the possibility of different modes of dysplasia exhibited in serrated lesions.

SUMMARY

Clarification of the microscopic features, nomenclature and biology of serrated lesions are important for accurate histologic diagnosis, and in clinical terms for useful outcomes assessment, recommendations for follow-up and risk stratification.

Colonic chicken-skin mucosa in children with polyps is not a preneoplastic lesion

Colonic polyps are common both in adults and children; however, the malignant potential varies according to the type of polyp. Most childhood polyps are solitary juvenile polyps, which have negligible malignant potential. Chicken-skin mucosa (CSM) is an endoscopic finding initially described associated with adenomatous polyps and adenocarcinoma, suggesting a preneoplastic lesion. Subsequently, CSM was described in association with juvenile polyps, suggesting that this mucosal finding is not a precursor to dysplasia. To determine whether CSM represents a preneoplastic lesion, we studied endoscopic colonic mucosal biopsies for markers of cell replication (Ki-67) and malignant transformation (p53) in mucosal biopsies of CSM, normal colonic tissue, tubular adenomas, and adenocarcinomas. Samples were subjected to immunostaining for the presence of Ki-67 and p53. The degree of Ki-67-positive staining cells was similar for CSM and normal colonic tissue, whereas there was significantly increased staining for both tubular adenomas and adenocarcinomas. There was no evidence of p53 staining in CSM and normal colonic mucosa, whereas there was varying degrees of staining in tubular adenomas and adenocarcinomas. The association of CSM with benign juvenile polyps and the absence of histologic markers for increased replication and malignant transformation support the notion that this endoscopic finding is not preneoplastic. Rather, CSM arises in proximity to polyps of all histologic types because of local mucosal damage.

Serrated adenoma of the colorectum and the DNA-methylator phenotype

Serrated adenomas (SA) of the colorectum show features intermediate between hyperplastic polyps (HP) and adenomas. HP and SA are related lesions and there is now strong evidence for a 'serrated-polyp pathway' to colorectal cancer (CRC) that is largely independent of the classic adenoma-to-carcinoma sequence. A recently recognized lesion in this pathway is a HP variant characterized by relatively large size, atypical histology and proximal location in the colorectum. This HP variant has been given a variety of names in the literature including 'sessile SA' and 'type I SA'. Because this lesion lacks the traditional cytology of colorectal adenoma and in order to avoid confusion with SA, it is referred to in this review as sessile serrated polyp. SA are characterized by a heterogeneous group of changes at the molecular level, but a high proportion have BRAFmutations and DNA methylation. They may develop in HP or sessile serrated polyps, or may arise de novo. In the serratedpolyp pathway, the advent of genetic instability is likely to be an important rate-limiting step that drives rapid neoplastic evolution. Methylation and inactivation of the DNA repair genes MLH1 and MGMT (O-6-methylguanine-DNA methyltransferase) have been proposed as critical steps leading to genetic instability. Stretches of DNA rich in the bases guanine and cytosine (CpG islands; where p represents a phosphodiester bond linking adjacent cytosine and guanine bases) that are normally unmethylated may become methylated in malignant human colorectal tumors. Subsets of colorectal cancers with an unusually high number of methylated CpG islands have been described as having the 'CpG-island-methylator phenotype' It is possible that many, if not all, CRCs with the CpG-island-methylator phenotype evolve through the serrated-polyp pathway that would, therefore, explain approximately 20% of all CRCs. The current lack of guidelines for managing serrated polyps may explain the static incidence of proximal CRC, despite the falling incidence rates for left-sided CRC during the same time period.

K-ras as a target for cancer therapy

The central role K-, H- and N-Ras play in regulating diverse cellular pathways important for cell growth, differentiation and survival is well established. Dysregulation of Ras proteins by activating mutations, overexpression or upstream activation is common in human tumors. Of the Ras proteins, K-ras is the most frequently mutated and is therefore an attractive target for cancer therapy. The complexity of K-ras signaling presents many opportunities for therapeutic targeting. A number of different approaches aimed at abrogating K-ras activity have been explored in clinical trials. Several of the therapeutic agents tested have demonstrated clinical activity, supporting ongoing development of K-ras targeted therapies. However, many of the agents currently being evaluated have multiple targets and their antitumor effects may not be due to K-Ras inhibition. To date, no selective, specific inhibitor of K-ras is available for routine clinical use. In this review, we will summarize the structure and function of K-ras with attention to its role in tumorigenesis and discuss the successes and failures of the various strategies designed to therapeutically target this important oncogene.