Dietary factors and truncating APC mutations in sporadic colorectal adenomas

Inactivating mutations in APC are thought to be early, initiating events in colorectal carcinogenesis. To gain insight into the relationship between diet and inactivating APC mutations, we evaluated associations between dietary factors and the occurrence of these mutations in a Dutch case-control study of sporadic colorectal adenomas (278 cases; 414 polyp-free controls). Direct-sequencing was used to screen adenomas for mutations in the mutation cluster region of APC; truncating mutations were detected in 161 (58%) of the adenomas. Red meat consumption was significantly differently related to polyps with truncating APC mutation (APC(+) polyps) compared to polyps without truncating APC mutation (APC(-) polyps) (highest vs. lowest tertile, odds ratio [OR] = 0.5, 95% confidence interval [CI] = 0.3-1.0). High intake of red meat and fat seemed to increase the risk of APC(-) polyps only (APC(+) vs. controls: red meat, OR = 1.0, 95% CI = 0.6-1.6; fat, OR = 1.1, 95% CI = 0.6-1.9; APC(-) vs. controls: red meat, OR = 1.8, 95% CI = 1.0-3.1; fat, OR = 1.9, 95% CI = 1.0-3.7). Intake of carbohydrates was inversely associated with both polyp groups, most noticeably with APC(-) polyps. Most other evaluated dietary factors were not distinctively associated with a specific APC status. None of the dietary factors was specifically associated with a particular type of truncating APC mutation. Our data suggest that red meat and fat may increase the risk of APC(-) polyps in particular, whereas carbohydrates may especially decrease the risk of APC(-) polyps. However, most examined dietary factors do not appear to be specifically associated with the occurrence of truncating APC mutations in colorectal adenomas but seem to affect both pathways equally.     

K-ras oncogene mutations in sporadic colorectal cancer in The Netherlands Cohort Study

Activation of K-ras oncogene has been implicated in colorectal carcinogenesis, being mutated in 30-60% of the adenocarcinomas. In this study, 737 incident colorectal cancer (CRC) patients, originating from 120 852 men and women (55-69 years at baseline) participating in the Netherlands Cohort Study (NLCS), were studied in order to evaluate subgroups with respect to K-ras mutation status. Mutation analysis of the exon 1 fragment of the K-ras oncogene, spanning codons 8-29, was performed on archival colorectal adenocarcinoma samples of all patients using macrodissection, nested PCR and direct sequencing of purified fragments. The method of mutation detection was validated by the confirmation of reported K-ras status in CRC cell lines, a good correlation between fresh-frozen and routinely fixed, paraffin-embedded tissue, a detection limit of 5% mutated DNA and a good reproducibility. Various types of K-ras mutations were evaluated with respect to tumour sub-localization, Dukes' stage and tumour differentiation. In 37% (271/737) of the patients, the exon 1 fragment of K-ras gene was found to be mutated. The predominant mutations are G>A transitions and G>T transversions, and codons 12 and 13 are the most frequently affected codons. Patients with a rectal tumour were found to have the highest frequency of G>T transversions as compared with patients with a colon or rectosigmoid tumour. This difference appeared to be confined to women with a rectal tumour harbouring G>T transversions. No significant differences were observed for Dukes' stage with respect to types of K-ras mutation, which does not support direct involvement of the K-ras oncogene in adenocarcinoma progression. The equal distribution of K-ras mutations among cases with or without a family history of colorectal cancer argues against an important role for this mutation in familial colorectal cancer, and could imply that K-ras mutations are more probably involved in environmental mechanisms of colorectal carcinogenesis.     

Fat and K-ras mutations in sporadic colorectal cancer in The Netherlands Cohort Study

Associations between dietary intake of various fats and specific K-ras mutations in colorectal cancer (CRC) were investigated within the framework of The Netherlands Cohort Study on diet and cancer (NLCS). After 7.3 years of follow-up and with exclusion of the first 2.3 years, 448 colon and 160 rectal cancer patients and 2948 subcohort members (55-69 years at baseline) were available for data-analyses. Mutation analysis of the K-ras gene was performed on all archival colon and rectal adenocarcinoma specimens. Case-cohort analyses were used to compute adjusted incidence rate ratios (RR) and 95% confidence intervals (CI) for colon and rectal cancer cases and for K-ras mutation subgroups. The intake of total, saturated and monounsaturated fat was not significantly associated with colon or rectal cancer. High intake of dietary polyunsaturated fat and, specifically, linoleic acid is associated with an increased risk of mutated K-ras colon tumours. The RRs for 1 SD of increase of polyunsaturated fat and linoleic acid were 1.21 (95% CI 1.05-1.41) and 1.22 (95% CI 1.05-1.42), respectively, and similar associations were observed for both G > A transitions and G > T or G > C transversions in the colon. In contrast, no significant associations were observed with rectal cancer risk, overall nor with specific K-ras mutation status. A high intake of polyunsaturated fat, in particular linoleic acid, may be an important dietary risk factor for K-ras mutated colon tumours, possibly by generating G > A transitions or G > T or G > C transversions in the K-ras oncogene.     

The frequency and spectrum of K-ras mutations among Iraqi patients with sporadic colorectal carcinoma

Background: The epidemiology of colorectal cancers (CRC) is well known to differ in different geographical regions. K-ras mutations have been implicated in CRC carcinogenesis and they were extensively studied in developed countries; however, such studies are scarce from developing countries, like Iraq. Aim: To determine the frequency and spectrum of K-ras mutations among CRC Iraqi patients, and their clinico-pathological associations, if any. Materials and Methods: Fifty consecutive surgically resected sporadic CRC were evaluated. The evaluation included screening for ten K-ras mutations in codon 12 and 13 by mutant enriched polymerase chain reaction followed by reverse hybridization to oligospecific probes. Results: Out of the 50 enrolled patients, 24 (48%) had K-ras mutations. A total of 29 mutations were identified in the tumors of the latter 24 patients (20/24 tumors had single mutations, 3/24 had double mutations and 1/24 had triple mutations). The most frequently encountered mutations were the G>T transversions and G>A transitions (41.4% each). Codon 12 mutations constituted 89.7%, while codon 13 the remaining 10.3%. The most frequent mutation was GGT>GTT (Gly>Val) of codon 12 documented in 31%. No significant clinico-pathological correlations with K-ras mutational status were identified. Conclusion : The K-ras mutations are frequently encountered among Iraqi sporadic CRC patients, with relative higher frequencies of G>T transversions and Gly>Val codon 12 substitutions than encountered in their counterparts in developed countries. The latter is most likely to be related to differences in local carcinogens exposure, an aspect which requires further scrutiny.     

Simultaneous mutations in K-ras and TP53 are indicative of poor prognosis in sporadic colorectal cancer

Despite the fact that the mutations in K-ras codon 12 and TP53 are common abnormalities in colorectal cancer, the determination of K-ras mutation combined with TP53 gene mutation, with diagnostic and prognostic purposes is still controversial. We have analyzed K-ras and TP53 mutations in 77 sporadic colorectal adenocarcinomas by means of polymerase chain reaction and sequencing. We observed a negative correlation between both K-ras and TP53 mutations. Patients with mutations in K-ras but not in TP53 exhibited worse survival rates than those with mutations in TP53 and not in K-ras. Moreover, we found the worst outcome in patients with mutations in both K-ras and TP53. These results may relate to the previously published data about primary human and rodent cells, in which transformation by Ras require either a cooperating oncogene or the inactivation of tumor suppressors such as p53 or p16. In conclusion, simultaneous mutations in K-ras and TP53 are indicative of a worse prognosis in sporadic colorectal cancer.     

The PPAR{gamma} Pro12Ala polymorphism and risk for incident sporadic colorectal adenomas

Peroxisome proliferator-activated receptor gamma (PPARgamma), a member of the nuclear hormone receptor superfamily initially shown to be a key regulator of fat cell differentiation, can inhibit cell growth and induce apoptosis in colon cell lines. There are heterozygous loss of function mutations in the gene encoding PPARgamma in tumors from approximately 10% of human colon cancer patients. A common structural polymorphism has been detected in the PPARgamma gene at codon 12 (Pro12Ala). We investigated the hypothesis that the PPARgamma Pro12Ala polymorphism is associated with colorectal adenoma risk in a recently concluded case-control study of incident sporadic colorectal adenomas (163 cases and 212 controls). The multivariate-adjusted odds ratio (OR) for incident sporadic colorectal adenoma was 0.65 (95% CI 0.39-1.09) for those with the Pro12Ala or Ala12Ala genotype compared with those with the Pro12Pro genotype. Multivariate-adjusted inverse associations with the Ala12 variant were more pronounced among those who were female (OR 0.36, 95% CI 0.18-0.75) or did not take non-steroidal anti-inflammatory drugs (OR 0.38, 95% CI 0.14-1.00). Marginally significant results were observed among those with a lower waist:hip ratio (OR 0.52, 95% CI 0.24-1.12) or a lower body mass index (OR 0.46, 95% 0.20-1.05). Smoking was a very strong risk factor (OR 2.34, 95%CI 1.37-4.02) for colorectal adenoma among those with the wild-type (Pro12Ala) genotype, but not those with the Ala12 variant (OR 0.86, 95%CI 0.35-2.09). Larger studies are needed to validate these results, which suggest that the PPARgamma Pro12Ala polymorphism may interact with other factors to protect against colorectal adenoma.     

K-ras mutations and HLA-DR expression in large bowel adenomas.

A total of 72 sporadic colorectal adenomas in 56 patients were studied for the presence of point mutations in codons 12 and 13 of the K-ras gene and for HLA-DR antigen expression related to clinicopathological variables. Forty K-ras mutations in 39 adenomas were found (54%): 31 (77%) in codon 12 and nine (23%) in codon 13. There was a strong relationship between the incidence of K-ras mutations and adenoma type, degree of dysplasia and sex. The highest frequency of K-ras mutations was seen in large adenomas of the villous type with high-grade dysplasia. Fourteen out of 15 adenomas obtained from 14 women above 65 years of age carried mutations. HLA-DR positivity was found in 38% of the adenomas, large tumours and those with high-grade dysplasia having the strongest staining. Coexpression of K-ras mutations and HLA-DR was found significantly more frequently in large and highly dysplastic adenomas, although two-way analysis of variance showing size and grade of dysplasia to be the most important variable. None of the adenomas with low-grade dysplasia showed both K-ras mutation and HLA-DR positivity (P = 0.004). K-ras mutation is recognised as an early event in colorectal carcinogenesis. The mutation might give rise to peptides that may be presented on the tumour cell surface by class II molecules, and thereby induce immune responses against neoplastic cells.     

结直肠癌不同病变阶段K-ras基因突变的研究

目的:研究结直肠癌不同病变阶段K-ras基因变化及其对结直肠癌演变的影响.方法:提取20例结直肠癌患者的原发灶、淋巴结转移灶、远处转移灶、结直肠腺瘤和相应正常结直肠组织的DNA各20 份,经PCR扩增,对产物进行基因序列分析.结果: 正常结直肠组织均表达野生型K-ras基因,结直肠腺瘤、原发灶、淋巴结转移灶和远处转移灶的K-ras突变率分别为20.0%(4/20)、30.0%(6/20)、25.0%(5/20)和30.0%(6/20),有3例远处转移灶出现复合突变.在发生K-ras突变的标本中,结直肠腺瘤、淋巴结转移灶、远处转移灶的突变类型与原发灶的一致性分别为0%(0/4)、40.0%(2/5)和50.0%(3/6).结论:结直肠腺瘤、淋巴结转移灶和远处转移灶不宜作为临床检测K-ras突变的常规标本,但在无法获得原发灶标本时,淋巴结转移灶和远处转移灶的检测结果也有一定的参考价值;结直肠癌发生、发展的过程中,K-ras基因可能在多阶段发生多次不同的突变.     

A summary measure of pro- and anti-oxidant exposures and risk of incident,sporadic, colorectal adenomas

Despite compelling basic science evidence, the search for causal associations linking specific pro- and anti-oxidants to presumably oxidative stress-related neoplasms, such as colorectal adenoma, has produced inconsistent results. We developed an oxidative balance score (OBS) to characterize the pro-oxidant and anti-oxidant exposures of 2,305 participants in a case–control study of colorectal adenoma that used both endoscopy-confirmed and community controls. Twelve lifestyle medical and dietary factors with known pro- or anti-oxidant properties were considered. Each high anti-oxidant exposure and low pro-oxidant exposure was awarded one or two points depending on the level of exposure, and the points for each OBS component were summed. We observed a significant inverse association between OBS (continuous variable) and colorectal adenoma in the analyses with either community, or endoscopy controls (each p-trend < 0.01). When the OBS was treated as an ordinal variable and a score of ≤3 points was used as the referent category, in the analyses with the endoscopy controls the adjusted odds ratios for scores of 4–6, 7–9, 10–12, 13–15, and 16+, were 0.42, 0.32, 0.22, 0.20, and 0.19, respectively, with all 95% confidence intervals excluding 1.0. The corresponding analysis for community controls showed a similar trend. Our findings are in line with the basic science evidence supporting the role of oxidative stress in colorectal neoplasia.     

Matrilysin gene expression in sporadic and familial colorectal adenomas

We examined the expression of matrilysin mRNA in sporadic and hereditary colorectal adenomas to clarify the role of matrilysin in tumorigenesis. Matrilysin mRNA was not detected in normal colorectal mucosa from patients with either sporadic or familial adenomas. Matrilysin mRNA expression in sporadic adenomas correlated with the degree of dysplasia and the size of the mass, whereas most of the adenomas in patients with familial adenomatous polyposis coli expressed matrilysin mRNA irrespective of adenoma size or degree of dysplasia. Because matrilysin is more likely to be expressed in adenomas with a potential for malignancy, this enzyme may play a role in the malignant conversion of colorectal adenomas. Mol. Carcinog. 19:225–229, 1997. © 1997 Wiley-Liss, Inc.     

K-ras gene mutations in adenomas and carcinomas of the colon.

DNA extracted from 29 colorectal carcinomas and 40 sporadic adenomas was amplified by the polymerase chain reaction (PCR) and analysed for the presence of K-ras gene mutations at codon 12 using a panel of synthetic oligonucleotide probes specific for normal and mutated sequences. The presence of mutations was correlated with various histopathological and clinical data. Ten carcinomas (34.5%) and 14 sporadic adenomas (35%) showed K-ras mutations at codon 12. In the carcinoma group, no apparent correlation was found between the presence of mutant oncogenes and the degree of histological differentiation, Dukes' staging or the development of distant metastasis. In the adenoma group, the frequency of mutations increased with the size of the adenoma and the severity of the dysplastic changes. This study confirms that ras gene mutations are common and early events in colon carcinogenesis. They appear to give a selective growth advantage to those polyps with mutations which leads to their increase in size and thus possibly prepare the ground for malignant transformation.     

K-ras mutations in colorectal adenocarcinomas and neighbouring transitional mucosa

The K-ras gene in codons 12 and 13 was investigated using allele-specific polymerase chain reaction in matched normal mucosa (n = 106), transitional mucosa (n = 69) and tumours (n = 149) from 149 patients with colorectal adenocarcinomas. K-ras mutations in codon 12 were detected in 41/149 (28%) of tumours and 4/69 (6%) of transitional mucosa samples, but not in the normal mucosa. Further, mutation rates were increased in younger patients (P = 0.001) and in mucinous carcinomas (50%) compared with well differentiated (17%), moderately differentiated (26%) or poorly differentiated (24%) tumours. Our findings indicate that mucinous carcinoma may represent a distinct genetic entity.     

Polymorphism of the cyclin D1 gene, CCND1, and risk for incident sporadic colorectal adenomas

Cyclin D1, encoded by the CCND1 gene and activated by the adenomatous polyposis coli-beta-catenin-T-cell factor/lymphoid enhancing factor pathway, induces G(1) to S-phase cell cycle transition, promoting cell proliferation. A recently described codon 242, exon 4, G to A single nucleotide polymorphism (A870G) produces a longer half-life cyclin D1. To investigate whether CCND1 genotype influences risk for colorectal adenoma, we genotyped CCND1 by PCR/RFLP on 161 incident sporadic adenoma cases and 213 controls ages 30-74 years in a North Carolina colonoscopy-based case-control study. At least one polymorphic A allele was found in 68% of cases and 60% of controls. Having an A allele was associated with increased risk for adenoma: the age- and sex-adjusted odds ratio (OR) was 1.5 [95% confidence interval (CI) 1.0-2.4], a finding that was stronger for those whose adenomas were multiple (OR 2.9, 95% CI 1.4-6.0), larger (>or=1 cm; OR 2.4, 95% CI 1.2-4.8), had moderate to severe dysplasia (OR 2.1, 95% CI 1.1-3.8), or were in the right side of the colon (OR 3.6, 95% CI 1.3-10.0). Joint risk factor multivariate analyses revealed stronger positive associations among those who were older (>57 years; OR 2.8, 95% CI 1.4-5.5), male (OR 2.8, 95% CI 1.3-5.7), currently smoked (OR 2.7, 95% CI 1.3-5.7), or currently drank alcohol (OR 2.2, 95% CI 1.2-4.2) if they had an A allele and stronger inverse associations among those who used nonsteroidal anti-inflammatory drugs (OR 0.4, 95% CI 0.2-0.9) or had higher calcium intakes (OR 0.4, 95% CI 0.2-0.9) if they had no A allele. These data support the hypothesis that the CCND1 A870G polymorphism may increase risk for colorectal neoplasms.     

Chromosome 5 allele loss in familial and sporadic colorectal adenomas

DNA extracted from familial and sporadic colorectal neoplasms was compared with constitutional DNA using a range of hypervariable locus specific probes to assess the extent of allele loss during conversion to malignancy. Chromosome 5 allele loss was observed in 23% of carcinoma samples, as previously found by others. However, we have been able to show for the first time loss of the D5S43 locus on chromosome 5 in adenomas from three patients, two of whom had the precancerous condition adenomatous polyposis coli (APC). These results suggest significant genetic changes involving chromosome 5 are occurring in benign adenomas. Probes for chromosome 1 (loci D1S7 and D1S8) and for chromosome 7 (loci D7S21 and D7S22) revealed no notable alterations in the adenoma samples. Complete loss of alleles for loci on chromosome 7 was not observed in carcinomas but reduced intensity of one parental allele was found in three specimens one of which was known to have multiple copies of this chromosome. Results using probes for chromosome 1 suggest that deletion of the D1S7 or D1S8 loci is not a common event in colorectal carcinogenesis. Loss of chromosome 5 alleles in adenomas from APC patients provides evidence in support of Knudson's hypothesis.     

K-ras and p53 mutations in hereditary non-polyposis colorectal cancers

Genetic instability related to defective DNA mismatch repair genes may be involved in the pathogenesis of carcinoma in Hereditary Non-Polyposis Colorectal Cancer (HNPCC). To test that the targets of genetic instability could include critical transforming genes involved in colon tumor progression, we examined 23 colorectal carcinomas in patients with HNPCC in order to detect somatic mutations in K-ras and p53 genes. Using single strand conformation polymorphism followed by direct DNA sequencing, we detected 4 mutations in K-ras gene (17%) and 3 in p53 gene (13%) which change the aminoacid sequence of the protein p53. This is significantly lower than in sporadic cancer. Our data suggest that colon cancer in HNPCC might partly involve a distinct pathogenetic mechanism that involves other genes than those altered in sporadic tumors. Int. J. Cancer 74:94–96. © 1997 Wiley-Liss, Inc.     

Deletion analysis of chromosome 8p in sporadic colorectal adenomas.

In order to assess the stage of colorectal tumorigenesis at which chromosome 8p loss of heterozygosity (LOH) occurs, 56 sporadic adenomas were examined for LOH at four polymorphic loci which show frequent LOH in carcinomas. LOH was found in only 5 out of 51 (9.8%) informative adenomas, whereas studies with the same markers in 85 informative carcinomas showed a LOH of 45%. The adenomas showing LOH were all in the ''high-risk'' clinicopathological category, being 10 mm or more in diameter and showing tubulovillous architecture. It is concluded that the chromosome 8p locus is involved preferentially in the development of carcinomas rather than adenomas.     

Risk factors for Ki-ras protooncogene mutation in sporadic colorectal adenomas.

The Ki-ras protooncogene frequently is mutated in colorectal adenocarcinomas, but the etiology of this molecular event is uncertain. We investigated the association between variables known or suspected to be related to risk for colorectal cancer and the occurrence of Ki-ras mutations in colorectal adenomas. This study was conducted among 678 male and female participants, 40-80 years of age, enrolled in a phase III trial testing the effects of a wheat bran fiber supplement on adenoma recurrence. Exposure information on the risk factors of interest was assessed through self-administered questionnaires. Mutations in codons 12 and 13 of the Ki-ras protooncogene were analyzed in baseline adenomas 0.5 cm or larger by PCR amplification followed by direct sequencing. Eighteen percent (120 of 678) of the participants had one or more adenoma(s) with Ki-ras mutations. A higher risk of Ki-ras mutations was associated with increasing age and a lower intake of total folate. The odds ratio (OR) for Ki-ras mutations for individuals >72 years of age was 1.98 [95% confidence interval (CI) = 1.19-3.27; P for trend = 0.008] compared with those less than 65 years of age. Compared with individuals in the lower tertile of total folate, those in the upper tertile had an approximately 50% lower risk of having Ki-ras mutation-positive adenomas (OR = 0.52; 95% CI = 0.30-0.88; P for trend = 0.02). There was a suggestion of a stronger inverse association of total folate with G-->T transversions (OR = 0.41; 95% CI = 0.20-0.87) than G-->A transitions (OR = 0.61; 95% CI = 0.31-1.21), although the CIs for the associations overlap. The results of these analyses suggest that the protective effect of folate in colon cancer observed in published studies may be mediated through folate's effect on Ki-ras mutations.     

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.     

Diet, lifestyle and risk of K-ras mutation-positive and -negative colorectal adenomas

K-ras mutation-positive (K-ras+) and -negative (K-ras-) colorectal adenomas may differ clinically and pathologically. As environmental compounds may cause mutations in the growth-related K-ras oncogene or affect clonal selection depending on mutational status, we evaluated whether the aetiology of K-ras+ and K-ras- adenomas differs. K-ras mutations in codons 12 and 13 were assessed in colorectal adenoma tissue (K-ras+: n = 81, K-ras-: n = 453). Dietary and lifestyle data were collected through questionnaires that were also administered to 709 polyp-free controls. Multiple logistic regression analyses showed that intake of vitamin B2 and monounsaturated fat were differently associated with risk of K-ras+ and K-ras- adenomas; vitamin B2 was inversely associated with K-ras- (highest vs. lowest tertile: odds ratio (OR) = 0.70, 95% confidence interval (CI) = 0.50-0.97, p trend = 0.020), but not with K-ras+ adenomas, and a positive association with monounsaturated fat was confined to K-ras- adenomas (OR = 1.57, 95% CI = 1.06-2.34, p trend = 0.029). Besides, potential, not statistically significant, differences in risk arose because red meat was distinctly positively associated with K-ras+ adenomas (OR = 1.70, 95% CI = 0.94-3.09, p trend = 0.061); total dietary and polyunsaturated fat tended to be inversely associated with risk of K-ras+ but not of K-ras- adenomas; inverse associations with dairy products, calcium, protein and tea were confined to K-ras- adenomas, and smoking was more markedly positively associated with K-ras- adenomas. No differences in risk of K-ras+ and K-ras- adenomas could be detected for other factors. In conclusion, dietary and lifestyle factors may influence risk of K-ras+ and K-ras- adenomas differently. However, epidemiological literature on diet, lifestyle and colorectal K-ras mutations is inconsistent.     

K-ras mutations and RASSF1A promoter methylation in colorectal cancer

Human cancer is characterized by genetic and epigenetic alterations. In this study we provide evidence for the interruption of Ras signaling in sporadic colorectal cancer (CRC) by either genetic activation of the K-ras oncogene or epigenetic silencing of the putative tumor suppressor gene RASSF1A. Paraffin embedded tumor tissue samples from 222 sporadic CRC patients were analysed for K-ras codon 12 and codon 13 activating mutations and RASSF1A promoter hypermethylation. Overall, K-ras mutations were observed in 87 of 222 (39%) and RASSF1A methylation was observed in 45 of 222 (20%) of CRCs. Mutation of K-ras alone was detected in 76 of 222 (34%) CRCs. RASSF1A promoter methylation with wild-type K-ras was observed in 34 of 222 (15%) CRCs. In 101 of 222 (46%) CRCs neither K-ras mutations nor RASSF1A methylation was observed and 11 of 222 (5%) CRCs showed both K-ras mutations and RASSF1A methylation. These data show that the majority of the studied CRCs with K-ras mutations lack RASSF1A promoter methylation, an event which occurs predominantly in K-ras wild-type CRCs (P=0.023, Chi-square test).