Meat consumption, cigarette smoking, and genetic susceptibility in the etiology of colorectal cancer: results from a Dutch prospective study

Gene-diet interaction on cancer risk in epidemiological studies

Genetic factors clearly play a role in carcinogenesis, but migrant studies provide unequivocal evidence that environmental factors are critical in defining cancer risk. Therefore, one may expect that the lower availability of substrate for biochemical reactions leads to more genetic changes in enzyme function; for example, most studies have indicated the variant MTHFR genotype 677TT is related to biomarkers, such as homocysteine concentrations or global DNA methylation particularly in a low folate diet. The modification of a phenotype related to a genotype, particularly by dietary habits, could support the notion that some of inconsistencies in findings from molecular epidemiologic studies could be due to differences in the populations studied and unaccounted underlying characteristics mediating the relationship between genetic polymorphisms and the actual phenotypes. Given the evidence that diet can modify cancer risk, gene-diet interactions in cancer etiology would be anticipated. However, much of the evidence in this area comes from observational epidemiology, which limits the causal inference. Thus, the investigation of these interactions is essential to gain a full understanding of the impact of genetic variation on health outcomes. This report reviews current approaches to gene-diet interactions in epidemiological studies. Characteristics of gene and dietary factors are divided into four categories: one carbon metabolism-related gene polymorphisms and dietary factors including folate, vitamin B group and methionines; oxidative stress-related gene polymorphisms and antioxidant nutrients including vegetable and fruit intake; carcinogen-metabolizing gene polymorphisms and meat intake including heterocyclic amins and polycyclic aromatic hydrocarbon; and other gene-diet interactive effect on cancer.

Evidence-based nutrition: Does it differ from evidence-based medicine?

Clearly defined processes exist for developing evidence-based guidelines in clinical medicine. Approaches such as the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) where recommendations are made on the basis of quality of evidence gathered in a systematic literature review are also appropriate for recommendations relating to nutritional management of disease. Strong recommendations are based on high-quality evidence derived from randomized controlled trials (RCTs). In nutritional studies, RCTs often examine risk factors and occasionally other surrogates of disease rather than clinical end-points. Criteria are suggested as to when such surrogates may be used. GRADE and similar approaches are less appropriate when considering recommendations regarding chronic disease prevention. Cancer develops over many years, and RCTs exploring nutritional measures to reduce risk are inappropriate. The World Cancer Research Fund (WCRF) has developed an approach in which recommendations are based on clearly defined 'convincing' or 'probable' relationships between nutritional variables and disease outcomes. The WCRF criteria have been adapted for developing a wide range of policy recommendations which provide opportunities for those responsible for implementing policy to select options best suited to their purpose. Recommendations related to nutrition policy tend to evolve as a delicate balance between political wisdom and judgement of the scientific evidence. However, policy recommendations are important since they have the potential to create environments which are conducive to the behavioural changes required for improved nutrition.

Risk of colorectal cancer in relation to frequency and total amount of red meat consumption. Systematic review and meta-analysis

INTRODUCTION

The colon and rectum are common sites of food-related cancer in developed countries. Recent studies strongly suggest that red meat intake is associated with colon cancer, whereas for rectal cancer such an association still needs to be proved. The aim of the study was to assess the role of total amount and frequency of red meat intake in colorectal carcinogenesis based on published data using meta-analysis methods.

MATERIAL AND METHODS

The literature published until 2009 was selected from: MEDLINE, PubMed, Scopus, Embase, CancerLit, Google Scholar and Cochrane Library databases. The used search terms were: colorectal cancer, colon cancer, rectal cancer, meat intake, red meat intake, red meat consumption, meat consumption, colorectal cancer risk, colon cancer risk, rectal cancer risk and lifestyle. Articles investigating red meat intake of more often than once a day or 50 g per day were reviewed and selected for further analysis.

RESULTS

Twenty-two studies fulfilled the established criteria. A meta-analysis confirmed the carcinogenic effect of the consumption of over 50 g of red meat per day for the colon (relative risk 1.21, 1.07-1.37) but not for the rectum (relative risk 1.30, 0.90-1.89). Red meat intake more frequently than once a day can induce both colonic (relative risk 1.37, 1.09-1.71) and rectal cancer (relative risk 1.43, 1.24-1.64).

CONCLUSIONS

Red meat intake is associated with elevated risk of developing colorectal cancer. The frequency of red meat consumption rather than total amount of consumed meat is associated with a higher risk of colorectal carcinogenesis.

Advances in understanding the relationship between dietary factors and risk of colorectal cancer

The purpose of this paper is to summarize the relationship between dietary factors and risk of colorectal cancer. There is evidence that meat, high-fat diet and drinking increase the chance of developing colorectal cancer, while whole grains, dietary fiber, folacin, selenium, zinc and calcium reduce the risk of colorectal cancer. Therefore, an inadequate diet may contribute to the development of colorectal cancer. These viewpoints provide a basis for prevention of colorectal cancer in terms of diet control.

Glutathione S-transferase M1 polymorphism and sporadic colorectal cancer risk: An updating meta-analysis and HuGE review of 36 case-control studies

PURPOSE

Sporadic colorectal cancer (CRC) is considered to be a multifactorial disease, in which multiple exposures to endogenous factors interact with individual genetic background in a complex manner, resulting in modulation of the risk. The glutathione S-transferase M1 gene (GSTM1) is a particularly attractive candidate for CRC susceptibility because it codes an enzyme involved in the metabolism of environmental carcinogens. However, the epidemiological findings have been inconsistent.

METHODS

To evaluate this association, we performed an extensive meta-analysis of 36 case-control studies (including 10,009 cases and 15,070 controls).

RESULTS

Overall, the combined data showed that GSTM1 deficiency is associated with a marginal effect on CRC risk (odds ratio [OR] = 1.13; 95% confidence interval [CI]: 1.03-1.23; P for heterogeneity <0.001). When stratified by race and tumor site, significant results were only observed in Caucasians (OR = 1.14, 95% CI: 1.01-1.27; P for heterogeneity <0.001), whereas no increased risk was detected in other subgroups.

CONCLUSIONS

The findings of our study support the suggestion that GSTM1 polymorphism is associated with an increased risk of CRC, especially in the Caucasian population. Further investigation into the association between GSTM1 polymorphism and the risk of CRC is warranted and should include larger sample sizes and other genetic polymorphisms in metabolism of environmental carcinogens.

GSTM1, GSTT1, GSTP1, GSTA1 and colorectal cancer risk: a comprehensive meta-analysis

Glutathione S-transferases (GSTs) catalyse reactions between glutathione and lipophilic compounds with electrophilic centres, leading to neutralisation of toxic compounds, xenobiotics and products of oxidative stress. Controversy exists about whether GST polymorphisms (GSTM1 null/present genotype, GSTT1 null/present genotype, GSTP1 Ile105Val and GSTA1 *A/*B) represent risk factors for colorectal cancer. This meta-analysis aims to examine the associations between the above-mentioned polymorphisms and colorectal cancer risk. Forty-four studies were eligible for GSTM1 (11,998 colorectal cancer cases, 17,552 controls), 34 studies for GSTT1 (8596 cases, 13,589 controls), 19 studies for GSTP1 (5421 cases, 7671 controls) and four studies for GSTA1 polymorphism (1648 cases, 2039 controls). Pooled odds ratios (ORs) were appropriately derived from fixed-effects or random-effects models. Separate analyses were conducted on Caucasian and Chinese populations. Where appropriate, sensitivity analysis concerning the deviation of genotype frequencies in controls from the Hardy-Weinberg equilibrium was performed. GSTM1 null allele carriers exhibited increased colorectal cancer risk in Caucasian populations (pooled OR=1.150, 95% confidence interval (CI): 1.060-1.248, random effects); no significant association was detected for Chinese subjects (pooled OR=1.025, 95% CI: 0.903-1.163, fixed effects). Similarly, GSTT1 null allele carriers exhibited increased colorectal cancer risk in Caucasian populations (pooled OR=1.312, 95% CI: 1.119-1.538, random effects); the association in Chinese subjects was not significant (pooled OR=1.068, 95% CI: 0.788-1.449, random effects). Concerning GSTP1 Ile105Val no significant associations were demonstrated in either race. GSTA1 *A/*B polymorphism was not associated with colorectal cancer risk. GSTM1 and GSTT1 null genotypes confer additional risk for colorectal cancer in Caucasian populations.

Integration of risk and benefit analysis-the window of benefit as a new tool?

Foods and food components can have positive and/or negative effects on our health, resulting in benefits and risks. At present these are evaluated in largely separated trajectories. In view of assessment, management, and communication, we here propose and argue for an integrated evaluation of risk and benefit of food components and foods. The window of benefit assessment concept is described as a framework to combine thresholds and scores. The recommended dietary allowance (RDA) and the tolerable upper intake level (UL) delimit the range of intakes that should be considered sufficient to prevent deficiency, while avoiding toxicity. Within these thresholds, two additional thresholds, the lower and upper level of additional benefit (LLAB and ULAB), define the range of intakes that constitute an additional benefit. Intake within these limits should thus be protective against a specified health or nutritional risk of public health relevance. To faithfully predict outcomes and to obtain the tools that are necessary to support scientific valid evaluations, a mechanism based systems biology understanding of the effects of foods and nutrients is seen as the way forward. Ultimately this should lead to an integrated risk-benefit assessment, which will allow better management and, especially, communication, to the benefit of the consumer.

Fish consumption and the risk of colorectal cancer: the Ohsaki Cohort Study

BACKGROUND

Evidence from laboratory and animal studies suggests that high fish consumption may reduce the risk of colorectal cancer, but the results of studies in humans have been inconsistent. The objective of this study was to prospectively examine the association between fish consumption and the risk of colorectal cancer incidence in Japan, where fish is widely consumed.

METHODS

We analysed data from 39 498 men and women registered in the Ohsaki National Health Insurance Cohort Study who were 40-79 years old and free of cancer at the baseline. Fish consumption was assessed at the baseline using a self-administered food frequency questionnaire.

RESULTS

During 9 years of follow-up, we identified 566 incident cases of colorectal cancer (379 men and 187 women). The hazard ratios and 95% confidence intervals (CIs) for colorectal cancer incidence in the highest quartile of fish consumption compared with the lowest quartile were 1.07 (95% CIs; 0.78-1.46, P-trend=0.43) for men, and 0.96 (95% CIs; 0.61-1.53, P-trend=0.69) for women.

CONCLUSION

The results of this prospective cohort study revealed no association between fish consumption and the risk of colorectal cancer.

Meat and heterocyclic amine intake, smoking, NAT1 and NAT2 polymorphisms, and colorectal cancer risk in the multiethnic cohort study

BACKGROUND

N-acetyltransferases (NAT) 1 and 2 are polymorphic enzymes catalyzing the metabolic activation of heterocyclic amines. We investigated the modifying effects of NAT1 and NAT2 polymorphisms on the association of meat consumption, heterocyclic amine intake, and smoking with colorectal cancer risk.

METHOD

In the Multiethnic Cohort study, participants completed a smoking history and a food-frequency questionnaire at recruitment and a cooked meat module 5 years later to estimate heterocyclic amine intake (2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine, 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline, 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline). Blood samples were collected from incident cases and age-, sex-, ethnicity-, frequency-matched controls to determine genotypes. For analysis of meat intake and smoking, data were available for 1,009 cases and 1,522 controls; for heterocyclic amine intake analyses, 398 cases and 1,444 controls were available. Multivariate logistic regression models were used to estimate odds ratios.

RESULTS

Smoking was associated with an increased colorectal cancer risk (odds ratio, 1.51; 95% confidence interval, 1.17-1.95) for > or =30 pack-years compared with never smokers (P trend = 0.0004). The association was stronger with presence of the "rapid" compared with the "slow/intermediate" NAT2 genotype (P interaction = 0.003). No significant associations were observed for intakes of red meat, processed meat, and heterocyclic amine, or meat doneness preference, but a dietary pattern high in meat showed a weak positive interaction with the NAT2 genotype (P interaction = 0.05).

CONCLUSION

The enhanced association between smoking and colorectal cancer risk in subjects with the NAT2 rapid genotype supports a role for NAT2 and tobacco smoke heterocyclic amines in the etiology of colorectal cancer. This study only provides weak support for a similar association with meat heterocyclic amines.

The impact of dietary and lifestyle risk factors on risk of colorectal cancer: a quantitative overview of the epidemiological evidence

Colorectal cancer is a major cause of cancer mortality and is considered to be largely attributable to inappropriate lifestyle and behavior patterns. The purpose of this review was to undertake a comparison of the strength of the associations between known and putative risk factors for colorectal cancer by conducting 10 independent meta-analyses of prospective cohort studies. Studies published between 1966 and January 2008 were identified through EMBASE and MEDLINE, using a combined text word and MESH heading search strategy. Studies were eligible if they reported estimates of the relative risk for colorectal cancer with any of the following: alcohol, smoking, diabetes, physical activity, meat, fish, poultry, fruits and vegetables. Studies were excluded if the estimates were not adjusted at least for age. Overall, data from 103 cohort studies were included. The risk of colorectal cancer was significantly associated with alcohol: individuals consuming the most alcohol had 60% greater risk of colorectal cancer compared with non- or light drinkers (relative risk 1.56, 95% CI 1.42-1.70). Smoking, diabetes, obesity and high meat intakes were each associated with a significant 20% increased risk of colorectal cancer (compared with individuals in the lowest categories for each) with little evidence of between-study heterogeneity or publication bias. Physical activity was protective against colorectal cancer. Public-health strategies that promote modest alcohol consumption, smoking cessation, weight loss, increased physical activity and moderate consumption of red and processed meat are likely to have significant benefits at the population level for reducing the incidence of colorectal cancer.

Cigarette smoking and colorectal cancer incidence and mortality: systematic review and meta-analysis

The association between cigarette smoking and colorectal cancer (CRC) has been controversial. To synthesize the available data, we conducted a comprehensive meta-analysis of all prospective studies. A total of 36 studies were included in our meta-analysis. We examined the association between smoking and CRC, colon cancer and rectal cancer in terms of incidence and mortality. Separate analyses were conducted for smoking status, daily cigarette consumption, duration, pack-years and age of initiation. Relative to nonsmokers, current and former smokers had a significantly increased risk of CRC incidence and mortality, respectively. When CRC data were combined with colon/rectal cancer data, current smokers had a significantly increased risk of CRC incidence. All 4 dose-response variables examined-daily cigarette consumption (RR = 1.38 for an increase of 40 cigarettes/day), duration (RR = 1.20 for an increase of 40 years of duration), pack-years (RR = 1.51 for an increase of 60 pack-years) and age of initiation (RR = 0.96 for a delay of 10 years in smoking initiation)-were significantly associated with CRC incidence (all p-values < 0.0001). The relationship between duration of smoking and rectal cancer incidence was also significant. Among the subset of studies that distinguished cancer by site, a higher risk was seen for rectal cancer than for colon cancer for all analyses. Among prospective studies, a consistent association exists between smoking and CRC. The association is stronger for rectal cancer than for colon cancer in the subset of studies that differentiated cancer by site.

Animal origin foods and colorectal cancer risk: a report from the Shanghai Women's Health Study

The association of animal-origin food consumption and cooking patterns with colorectal cancer (CRC) risk was evaluated in a cohort of 73,224 participants of the Shanghai Women's Health Study. After a mean follow-up time of 7.4 yr, 394 incident cases of CRC (colon = 236; rectal = 158) were diagnosed. Overall, no association was found between the risk of CRC and intake of total meat and total fish. Eel (P(trend) = 0.01), shrimp (P(trend) = 0.06), and shellfish (P(trend) = 0.04) consumption were positively associated with CRC risk. High egg intake and high intake of total cholesterol were also related to risk of CRC (RR for the highest vs. lowest quintiles of intake were 1.4 (95% CI = 1.1-2.0) for eggs and 1.6 (95% CI = 1.1-2.3) for cholesterol). Milk intake was inversely associated with the risk of colon cancer (P(trend) = 0.05). Common Chinese cooking practices except the smoking method of cooking were not related to CRC risk. The latter was positively associated with colon cancer (RR = 1.4 for ever vs. never, 95% CI = 1.1-1.9). A possible role of cholesterol and environmental pollution in the etiology of CRC was suggested.

ArylamineN-Acetyltransferases: What We Learn from Genes and Genomes

Arylamine N-acetyltransferases (NATs) are phase II xenobiotic metabolizing enzymes, catalyzing acetyl-CoA-dependent N- and O-acetylation reactions. All NATs have a conserved cysteine protease-like Cys-His-Asp catalytic triad inside their active site cleft. Other residues determine substrate specificity, while the C-terminus may control hydrolysis of acetyl-CoA during acetyltransfer. Prokaryotic NAT-like coding sequences are found in >30 bacterial genomes, including representatives of Actinobacteria, Firmicutes and Proteobacteria. Of special interest are the nat genes of TB-causing Mycobacteria, since their protein products inactivate the anti-tubercular drug isoniazid. Targeted inactivation of mycobacterial nat leads to impaired mycolic acid synthesis, cell wall damage and growth retardation. In eukaryotes, genes for NAT are found in the genomes of certain fungi and all examined vertebrates, with the exception of canids. Humans have two NAT isoenzymes, encoded by highly polymorphic genes on chromosome 8p22. Syntenic regions in rodent genomes harbour two Nat loci, which are functionally equivalent to the human NAT genes, as well as an adjacent third locus with no known function. Vertebrate genes for NAT invariably have a complex structure, with one or more non-coding exons located upstream of a single, intronless coding region. Ubiquitously expressed transcripts of human NAT1 and its orthologue, murine Nat2, are initiated from promoters with conserved Sp1 elements. However, in humans, additional tissue-specific NAT transcripts may be expressed from alternative promoters and subjected to differential splicing. Laboratory animals have been widely used as models to study the effects of NAT polymorphism. Recently generated knockout mice have normal phenotypes, suggesting no crucial endogenous role for NAT. However, these strains will be useful for understanding the involvement of NAT in carcinogenesis, an area extensively investigated by epidemiologists, often with ambiguous results.

A 22-year prospective study of fish, n-3 fatty acid intake, and colorectal cancer risk in men

BACKGROUND

Fish is the main dietary source of long-chain n-3 fatty acids, which have been suggested to play a protective role in colorectal cancer development in laboratory and animal studies. Human studies have not shown consistent results. We examined the association between intakes of fish and n-3 fatty acids from fish and colorectal cancer risk in men enrolled in the Physicians' Health Study.

METHODS

The Physicians' Health Study began as a randomized trial to examine the effect of aspirin and beta-carotene supplementation on cancer and cardiovascular disease. Fish intake was assessed at the 12-month follow-up with an abbreviated food-frequency questionnaire. Cox proportional hazards models were used to estimate multivariate relative risks for colorectal cancer for the categories of fish intake and quartiles of n-3 fatty acid intake.

RESULTS

During 22 years of follow-up, 500 men had a confirmed diagnosis of colorectal cancer. Fish intake was inversely associated with colorectal cancer risk [multivariate relative risk (95% confidence interval) for highest versus lowest category, 0.63 (0.42-0.95); P trend = 0.02] [corrected] The inverse association was observed for both colon and rectal cancers. Our findings for n-3 fatty acids were similar to those for fish; the multivariate relative risk (95% confidence interval) of total colorectal cancer for the highest versus lowest quartile of n-3 fatty acids was 0.74 (0.57-0.95; P trend = 0.01).

CONCLUSIONS

Our results from this long-term prospective study suggest that intakes of fish and long-chain n-3 fatty acids from fish may decrease the risk for colorectal cancer.

Prospective study of NAT1 and NAT2 polymorphisms, tobacco smoking and meat consumption and risk of colorectal cancer

Heterocyclic amines in tobacco smoke and fried meat are activated or detoxified by N-acetyltransferases (NAT1 and NAT2). We identified 379 cases with colorectal cancer (CRC) and 769 sub-cohort members among a cohort of 57,000 members. There were no statistically significant associations between tobacco smoking, consumption of meat (red, processed and fried) and CRC risk. Preference for brown-dark pan-fried meat increased the CRC risk. NAT1 fast acetylators had a significantly higher risk of CRC than NAT1 slow acetylators, whereas NAT2 acetylator status did not affect the CRC risk. There were no statistically significant interactions between tobacco smoking and either NAT1 or NAT2 acetylator status in relation to CRC risk. However, smoking intensity increased CRC risk among carriers of both NAT1 and NAT2 fast. This indicates that N-acetylator status affects the relationship between smoking and CRC risk.

Modification by N-acetyltransferase 1 genotype on the association between dietary heterocyclic amines and colon cancer in a multiethnic study

OBJECTIVE

Colorectal cancer incidence is greater among African Americans, compared to whites in the U.S., and may be due in part to differences in diet, genetic variation at metabolic loci, and/or the joint effect of diet and genetic susceptibility. We examined whether our previously reported associations between meat-derived heterocyclic amine (HCA) intake and colon cancer were modified by N-acetyltransferase 1 (NAT1) or 2 (NAT2) genotypes and whether there were differences by race.

METHODS

In a population-based, case-control study of colon cancer, exposure to HCAs was assessed using a food-frequency questionnaire with a meat-cooking and doneness module, among African Americans (217 cases and 315 controls) and whites (290 cases and 534 controls).

RESULTS

There was no association with NAT1*10 versus NAT1-non*10 genotypes for colon cancer. Among whites, there was a positive association for NAT2-"rapid/intermediate" genotype [odds ratio (OR)=1.4; 95% confidence interval (CI)=1.0, 1.8], compared to the NAT2-"slow" that was not observed among African Americans. Colon cancer associations with HCA intake were modified by NAT1, but not NAT2, regardless of race. However, the "at-risk" NAT1 genotype differed by race. For example, among African Americans, the positive association with 2-amino-1-methyl-6-phenyl-imidazo[4,5-b]pyridine (PhIP) was confined to those with NAT1*10 genotype (OR=1.8; 95% CI=1.0, 3.3; P for interaction=0.02, comparing highest to lowest intake), but among whites, an association with 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) was confined to those with NAT1-non*10 genotype (OR=1.9; 95% CI=1.1, 3.1; P for interaction=0.03).

CONCLUSIONS

Our data indicate modification by NAT1 for HCA and colon cancer associations, regardless of race. Although the at-risk NAT1 genotype differs by race, the magnitude of the individual HCA-related associations in both race groups are similar. Therefore, our data do not support the hypothesis that NAT1 by HCA interactions contribute to differences in colorectal cancer incidence between African Americans and whites.

Diet, gender, and colorectal neoplasia

The association between diet and colorectal cancer has been studied in depth for many decades, with equivocal results. It has been hypothesized that cancers arising in the distal and proximal colon have different pathologies, and therefore different risk factors. As such, it is possible that diet-related factors might influence colorectal neoplasia differently depending on the subsite. Recent evidence indicates that women may be more likely to develop proximal cancers than men. Additionally, the link between certain dietary factors and colorectal neoplasia in women seems to vary by menopausal status. Given these observations, women may be affected differently than men by diet-related factors. The objective of this article was therefore to review the data for diet and colorectal adenomas and cancer, and then attempt to address the potential differences in the association of diet-related factors and colorectal neoplasia in men and women. For total energy intake, selenium, and fiber, it seems that there may be slightly stronger effects in men as compared with women, whereas calcium and folate seem to affect both sexes similarly. With regard to vitamin D and colorectal cancer, women may exhibit stronger associations than men. Perhaps the most evidence for a sex-specific effect is observed for obesity, where more substantial direct relationships between body size and colorectal neoplasia have been reported for men than for women. However, this observation may be influenced by the differential effects in women by menopausal status. Further research on sex-specific dietary effects is warranted.

NAT2 fast acetylator genotype is associated with an increased risk of colorectal cancer in Taiwan

In Taiwan, colorectal cancer has one of the highest rates of increased incidence in the past two decades. Heterocyclic amines from dietary cooked meats are metabolically activated by NAT2 (N-acetyltransferase 2), which are associated with colorectal cancer incidence. Thus, the NAT2 fast acetylator genotype may be associated with colorectal cancer risk. However, the association between the NAT2 genotype and colorectal cancer risk is not clearly understood. We conducted a study with 244 primary colorectal cancer cases and 299 cancer-free healthy control subjects to verify the association of NAT2 polymorphisms with the risk of Taiwanese colorectal cancer. Our data showed that subjects with the NAT2 W/W homozygous genotype had a 1.63-fold increased risk of colorectal cancer compared with those with the Mx/Mx slow acetylator genotype (95 percent confidence interval, 1.03-2.58); however, no risk was found in the W/Mx heterozygous and Mx/W+W/W fast acetylator genotypes. Being stratified by gender factors, the colorectal cancer risk in females with homozygous W/W or Mx/W+W/W fast acetylators increased 2.47-fold and 2.13-fold compared with those with the Mx/Mx slow acetylator genotype (95 percent confidence interval, 1.27-4.82 for W/W genotype; 95 percent confidence interval, 1.17-3.89 for Mx/W+W/W genotype); however, the risk of the NAT2 genotype and colorectal cancer was not observed in males. Collectively, patients with the NAT2 fast acetylator genotype were more prone to colorectal cancer and reflected the possibility that exposure to heterocyclic amines may contribute to colorectal cancer development in Taiwan, especially in Taiwanese females.

Meat and meat-mutagen intake, doneness preference and the risk of colorectal polyps: the Tennessee Colorectal Polyp Study

Although meat intake has been fairly consistently linked to the risk of colorectal cancer, only a few studies have evaluated meat intake by doneness level and the heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs) produced by high temperature cooking of meat in relation to colorectal adenomatous and hyperplastic polyps. We evaluated these associations in a large colonoscopy-based case-control study. Included in this study were participants with adenomatous polyp only (n = 573), hyperplastic polyp only (n = 256), or both adenomatous and hyperplastic polyps (n = 199), and 1,544 polyp-free controls. In addition to information related to demographic and other lifestyle factors, meat intake by cooking method and doneness preference were obtained through telephone interviews. Polytomous logistic regression models were used to estimate odds ratios (OR) and 95% confidence intervals for the association between exposures and colorectal polyp risks. Presence of hyperplastic polyp was found to be positively associated with high consumption of total meat (p(trend) = 0.076) or red meat (p(trend) = 0.060), with an approximate 50-60% elevated risk observed in the highest vs. the lowest intake group. High intake of 2-amino-I-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and 2-amino-3,4,8-trimethylimidazo [4,5]quinoxaline (DiMeIQx) were associated with increased risk for hyperplastic polyp (p(trend) = 0.036 and 0.038, respectively). With a possible exception of the intake of total well-done meats (p(trend) = 0.055) or well-done red meats (p(trend) = 0.074) with the risk of large adenomas, no other positive association was found specifically for the risk of adenomas with any of the exposure variables aforementioned. This study provides additional support for a positive association of high intake of red meat with colorectal adenomas, and suggests that high intake of meats and meat carcinogens may also be associated with hyperplastic polyps.

Blood levels of long-chain polyunsaturated fatty acids, aspirin, and the risk of colorectal cancer

BACKGROUND

N-3 fatty acids may decrease risk of colorectal cancer by inhibiting the cyclooxygenase-2 enzyme and production of proinflammatory eicosanoids derived from arachidonic acid (20:4n-6). Aspirin also inhibits the cyclooxygenase-2 enzyme and may share with n-3 fatty acids a potential mechanism to decrease the risk of colorectal cancer.

METHODS

We conducted a nested case-control analysis using blood samples collected from the Physicians' Health Study participants in 1982 to 1984. N-3 and n-6 fatty acid levels were measured using gas-liquid chromatography for 178 men who developed colorectal cancer through December 31, 1995 and 282 age- and smoking-matched controls. We used conditional logistic regression to examine associations. All statistical tests were two-sided.

RESULTS

Total long-chain n-3 fatty acids were nonsignificantly inversely associated with colorectal cancer risk [relative risk (RR) for highest versus lowest quartile, 0.60; 95% confidence interval (95% CI), 0.32 to 1.11; P(trend) = 0.10], after adjustment for possible confounders. We observed potential interaction between randomized aspirin assignment and long-chain n-3 fatty acid levels (P(interaction) = 0.04). Among men not on aspirin, RRs (95% CI) for increasing quartiles of long-chain n-3 fatty acids were 1.00 (reference), 0.60 (0.28-1.28), 0.51 (0.22-1.17), and 0.34 (0.15-0.82), P(trend) = 0.006. For participants taking aspirin, there was no additional benefit of increasing n-3 fatty acid levels. The RR (95% CI) for the highest versus lowest quartile of n-6 fatty acids was 0.64 (0.35-1.17).

CONCLUSIONS

Blood levels of long-chain n-3 fatty acids were associated with decreased risk of colorectal cancer among men not using aspirin. N-6 fatty acids were nonsignificantly inversely associated with colorectal cancer risk.

Meat consumption and risk of colorectal cancer: a meta-analysis of prospective studies

Accumulating epidemiologic evidence indicates that high consumption of red meat and of processed meat may increase the risk of colorectal cancer. We quantitatively assessed the association between red meat and processed meat consumption and the risk of colorectal cancer in a meta-analysis of prospective studies published through March 2006. Random-effects models were used to pool study results and to assess dose-response relationships. We identified 15 prospective studies on red meat (involving 7,367 cases) and 14 prospective studies on processed meat consumption (7,903 cases). The summary relative risks (RRs) of colorectal cancer for the highest vs. the lowest intake categories were 1.28 (95% confidence interval (CI) = 1.15-1.42) for red meat and 1.20 (95% CI = 1.11-1.31) for processed meat. The estimated summary RRs were 1.28 (95% CI = 1.18-1.39) for an increase of 120 g/day of red meat and 1.09 (95% CI = 1.05-1.13) for an increase of 30 g/day of processed meat. Consumption of red meat and processed meat was positively associated with risk of both colon and rectal cancer, although the association with red meat appeared to be stronger for rectal cancer. In 3 studies that reported results for subsites in the colon, high consumption of processed meat was associated with an increased risk of distal colon cancer but not of proximal colon cancer. The results of this meta-analysis of prospective studies support the hypothesis that high consumption of red meat and of processed meat is associated with an increased risk of colorectal cancer.

Glutathione S-transferases mu 1, theta 1, pi 1, alpha 1 and mu 3 genetic polymorphisms and the risk of colorectal and gastric cancers in humans

INTRODUCTION

Glutathione S-transferases (GSTs) are considered to be cancer susceptibility genes as they play a role in the detoxification of carcinogenic species. This study aimed to elucidate the influence of several GST polymorphisms on colorectal and gastric cancer risk.

PATIENTS AND METHODS

GST mu1 (GSTM1), theta1 (GSTT1), pi1 (GSTP1), alpha1 (GSTA1) and mu3 (GSTM3) genotypes were determined in 144 colorectal cancer patients, 98 gastric cancer patients and 329 healthy control individuals.

RESULTS

Colorectal cancer: the risk is greater for carriers of the GSTM1 null genotype (odds ratio [OR] = 1.91, 95% confidence interval [CI] = 1.25-2.91), for carriers of the GSTT1 null genotype (OR = 3.62, 95% CI = 2.34-5.62), and for simultaneous carriers of both GSTM1 and GSTT1 null genotypes (OR = 4.98, 95% CI = 2.77-9.00). Carriers of the GSTP1 104 Val/Val genotype are at a lower risk (OR = 0.31, 95% CI = 0.09-0.88). Among carriers of the GSTP1 Ile/Ile genotype, smoking increases the risk compared with nonsmoking (OR = 2.35, 95% CI = 1.11-4.99). Gastric cancer: the risk is greater for carriers of the GSTT1 null genotype (OR = 2.58, 95% CI = 1.53-4.36) and for simultaneous carriers of both GSTM1 and GSTT1 null genotypes (OR = 3.32, 95% CI = 1.62-6.77). Carriers of the GSTP1 104 Val/Val genotype are at a lower risk (OR = 0.20, 95% CI = 0.02-0.86).

DISCUSSION

The GSTT1 null genotype, particularly if it is associated with the GSTM1 null genotype, greatly increases the risk for colorectal and gastric cancers. The GSTP1 104 Val/Val genotype may protect from both malignant tumors.

CONCLUSION

This study indicates that GST polymorphisms, in particular the GSTM1/GSTT1 double-null haplotype, can be considered low-penetrance genes for gastrointestinal cancer.

GSTM1 and GSTT1 Polymorphisms, Cigarette Smoking, and Risk of Colon Cancer: A Population-based Case-control Study in North Carolina (United States)

Cigarette smoke is a risk factor for colon cancer, but the importance of dose and interaction with genetic susceptibility remain poorly understood. We used data from a population-based case control study, to examine the association between cigarette smoking and colon cancer in African Americans and whites, and colon cancer and polymorphisms in GSTM1 and GSTT1. A total of 554 cases of primary colon cancer and 874 controls were included in this analysis. We found no association between cigarette smoking (ever versus never) and colon cancer in African Americans (odds ratio (OR)=0.93, 95% confidence interval (CI)=0.65-1.33). In contrast, there was an increased risk of cigarette smoking in whites (OR=1.43, CI=1.05-1.94). There was a small increased risk of colon cancer for individuals with GSTM1 null (African Americans, OR=1.43, CI, 0.98-2.09; whites, OR=1.19, CI, 0.90-1.58) and a decreased risk of colon cancer for individuals with GSTT1 null (African Americans, OR=0.59, CI: 0.40-0.86; whites, OR=0.72, CI: 0.53-1.00). There were weak interactions between GSTT1 null and cigarette smoking in whites, and GSTM1 null genotype and cigarette smoking in African Americans. GSTT1 and GSTM1 polymorphisms may be weakly related to colon cancer risk and there may be racial differences in gene-smoking interactions.

Effect of NAT1 and NAT2 genetic polymorphisms on colorectal cancer risk associated with exposure to tobacco smoke and meat consumption

N-Acetyltransferases 1 and 2 (NAT1 and NAT2), both being highly polymorphic, are involved in the metabolism of aromatic and heterocyclic aromatic amines present in cigarette smoke and red meat cooked by high-temperature cooking techniques. We investigated the effect of differences in acetylation capacity, determined by NAT1 and NAT2 genotypes, on colorectal cancer risk associated with exposure to tobacco smoke or red meat consumption. In this population-based case-control study in Germany, 505 patients with incident colorectal cancer and 604 age- and sex-matched control individuals with genotyping data and detailed risk factor information were included. Genotyping of NAT1 and NAT2 genetic polymorphisms was done using a fluorescence-based melting curve analysis method. The association between genotypes, environmental exposures, and colorectal cancer risk was estimated using multivariate logistic regression. Colorectal cancer risk associated with active smoking was elevated after accumulation of 30(+) pack-years of smoking [odds ratio (OR), 1.4; 95% confidence interval (95% CI), 0.9-2.2] but not significantly modified by either NAT1 or NAT2 genotype. Exposure to environmental tobacco smoke was associated with an increased risk for colorectal cancer only among NAT2 fast acetylators (OR, 2.6; 95% CI, 1.1-5.9 for exposure in childhood and adulthood). Frequent consumption of red meat significantly increased colorectal cancer risk for the group comprising all NAT2 fast acetylators or carriers of the NAT1*10 allele (OR, 2.6; 95% CI, 1.1-6.1) but not among those with "slow" NAT1 and NAT2 genotypes. Our findings indicate that NAT1 and NAT2 genotypes may contribute jointly to individual susceptibility and that heterocyclic aromatic amines may play an important role in colorectal cancer associated with red meat and possibly also exposure to environmental tobacco smoke.

Gene-gene, gene-environment & multiple interactions in colorectal cancer

This review comprehensively evaluates the influence of gene-gene, gene-environment and multiple interactions on the risk of colorectal cancer (CRC). Methods of studying these interactions and their limitations have been discussed herein. There is a need to develop biomarkers of exposure and of risk that are sensitive, specific, present in the pathway of the disease, and that have been clinically tested for routine use. The influence of inherited variation (polymorphism) in several genes has been discussed in this review; however, due to study limitations and confounders, it is difficult to conclude which ones are associated with the highest risk (either individually or in combination with environmental factors) to CRC. The majority of the sporadic cancer is believed to be due to modification of mutation risk by other genetic and/or environmental factors. Micronutrient deficiency may explain the association between low consumption of fruit/vegetables and CRC in human studies. Mitochondrial modulation by dietary factors influences the balance between cell renewal and death critical in colon mucosal homeostasis. Both genetic and epigenetic interactions are intricately dependent on each other, and collectively influence the process of colorectal tumorigenesis. The genetic and environmental interactions present a good prospect and a challenge for prevention strategies for CRC because they support the view that this highly prevalent cancer is preventable.

The association of the DNA repair gene XRCC3 Thr241Met polymorphism with susceptibility to colorectal cancer in a Chinese population

Growing evidence suggests that the Thr241Met (T241M) polymorphism in the homologous recombination repair gene XRCC3 may alter DNA repair capacity and subsequent susceptibility to carcinogens. In a few studies of colorectal cancer (CRC), however, the results have been discrepant. A population-based nested case-control study including 140 cases and 280 cancer-free controls was conducted to evaluate the effect of XRCC3 polymorphism, environmental exposure, and family history (FH) on the risk of CRC. The variant allele frequency was low among the ethnic Han Chinese, but we observed a significant difference between cases (6.07%) and controls (2.32%). The analytic results of the unconditional logistic regression model adjusted by age, sex, alcohol intake, cigarette smoking, and FH of cancer in first-degree relatives showed a significantly increased risk of CRC (adjusted odds ratio [OR] = 3.13, 95% confidence interval [CI]: 1.41-6.95, P = 0.005) as the T/M and M/M genotypes compared with the T/T genotype, which changed weakly in consideration of the subsite (adjusted OR = 4.80, 95%CI: 1.77-12.98, P = 0.002 in colon cancer, adjusted OR = 2.41, 95%CI: 0.93-6.25, P = 0.071 in rectal cancer, respectively). Combined with environmental factors such as alcohol intake and cigarette smoking, no significant interaction could be found. However, the results revealed a significant association between FH of cancer in first-degree relatives and the risk of CRC (adjusted OR = 2.24, 95%CI: 1.18-4.25, P = 0.014). These results also suggest that XRCC3 T241M polymorphism and FH of cancer may be risk factors for CRC, and the XRCC3 241Met allele may be an effective biomarker for genetic susceptibility to CRC. Larger studies are needed to confirm our findings and identify the underlying mechanisms.

N-acetyltransferase (NAT) 2 acetylator status and age of onset in patients with hereditary nonpolyposis colorectal cancer (HNPCC)

N-acetyltransferase (NAT) 2 is an essential polymorphic enzyme involved in the metabolism of various xenobiotics, including potential carcinogens. The individual differences in the NAT2 metabolic capacity are caused by allelic variants of the NAT2 gene which are determined by a pattern of single nucleotide polymorphisms (SNPs) resulting in slow (SA), intermediate (IA) or rapid acetylator (RA) phenotypes. Highly penetrant germline mutations in mismatch repair (MMR) genes are the cause of the disease in hereditary nonpolyposis colorectal cancer (HNPCC). There is no strict correlation between the type of germline mutation in MMR genes and the HNPCC phenotype, but age of tumor onset (AO) in HNPCC has been associated at least in part with different variants in apoptosis-related genes. To clarify the potential modifying role of the NAT2 acetylator status in HNPCC, we performed a multicenter study in 226 individuals with colorectal cancer carrying exclusively pathogenic germline mutations in MSH2 or MLH1. We did not observe any significant difference in the NAT2 acetylator status frequency between HNPCC patients and 107 healthy controls (P=0.156), and between MLH1 and MSH2 mutation carriers (P=0.198). Multivariate Cox regression analysis revealed that male patients had a significantly increased risk to develop CRC compared to females during any interval (P=0.043), while the NAT2 acetylator status (P=0.447) and the mutated gene (MLH1 or MSH2) (P=0.236) were not risk factors for AO. The median AO in HNPCC patients was 39 years in patients with RA as well as with SA status (P=0.347). In MLH1 mutation carriers, the median AO was 38 years in RA and 36 years in SA status patients (P=0.901), whereas in MSH2 mutation carriers, the median AO was 39 years in RA and 42 years in SA status patients (P=0.163). Log-rank test revealed a significantly lower age of CRC onset in male compared to female HNPCC patients (P=0.0442). These data do not support the hypothesis that the NAT2 acetylatorship acts as a modifying factor on AO in HNPCC-associated CRC.

Increased risk of colorectal cancer due to interactions between meat consumption and the CD36 gene A52C polymorphism among Japanese

A previous study showed expression of CD36, recently reported to play important roles in metabolism of oxidized low-density lipoprotein and long-chain fatty acids and to be positively correlated with colon cancer prognosis. To examine relationships between colorectal cancer and the CD36 gene A52C polymorphism according to meat consumption as a surrogate for saturated fatty acid intake, we conducted the present hospital-based, case-control study of 128 cases and 238 non-cancer controls. Consumption of meat and vegetables/fruit was divided into three (low, moderate, and high) and two (low and high) groups, respectively. Regarding the risk of colorectal cancer on cross-classifying subjects for the CD36 genotype and meat consumption, the odds ratio (OR) for the C/C genotype with moderate meat consumption relative to the A/A genotype with low meat consumption was 8.30 (95% confidence interval, CI=2.15-32.00). None of individuals with the C/C genotype was in the high meat consumption group. In the low vegetables/fruit consumption group, the OR for the C/C genotype relative to the A/A genotype was 3.03 (95% CI=1.12-7.90). Our findings suggest that interactions between moderate-high meat consumption and the CD36 gene A52C polymorphism may increase the risk of colorectal cancer.

Prospective study of N-acetyltransferase-2 genotypes, meat intake, smoking and risk of colorectal cancer

Consumption of red meat has been associated with elevated risk of colorectal cancer; however, mechanisms underlying this relationship are not well established. N-acetyltransferase 2 (NAT2) appears to activate carcinogenic heterocyclic amines found in meat as well as cigarette smoke. Genetic variation in this enzyme, associated with rapid acetylation, may modulate the influence of meat intake on cancer risk. We examined the risk of incident colorectal cancer according to NAT2 genotypes, meat intake and smoking in a prospective, nested case-control study among 32,826 women enrolled in the Nurses' Health Study who provided prediagnostic blood specimens. We matched 183 women with colorectal cancer to 443 controls. Although acetylator genotype alone was not associated with the risk of colorectal cancer, women with rapid acetylator genotypes experienced a greater risk associated with intake of > or = 0.5 serving of beef, pork or lamb as a main dish per day compared to intake of less meat (multivariate OR = 3.01; 95% CI = 1.10-8.18). In contrast, among slow acetylators, intake of beef, pork or lamb was not associated with risk of colorectal cancer (multivariate OR = 0.87; 95% CI = 0.35-2.17). The interaction between acetylator genotype and meat intake approached statistical significance (P interaction = 0.07). Moreover, compared to slow acetylators who smoked < or = 35 pack-years and ate < 0.5 serving/day of red meat, the OR for rapid acetylators who smoked > 35 pack-years and ate > or = 0.5 serving/day was 17.6 (95% CI 2.0-158.3). These prospective data suggest that red meat may increase the risk of colorectal cancer, particularly among genetically susceptible individuals. The influence of NAT2 genotype on this association supports a role for heterocyclic amines in mediating the effect of red meat on colorectal carcinogenesis.

Meat, fish, and colorectal cancer risk: the European Prospective Investigation into cancer and nutrition

BACKGROUND

Current evidence suggests that high red meat intake is associated with increased colorectal cancer risk. High fish intake may be associated with a decreased risk, but the existing evidence is less convincing.

METHODS

We prospectively followed 478 040 men and women from 10 European countries who were free of cancer at enrollment between 1992 and 1998. Information on diet and lifestyle was collected at baseline. After a mean follow-up of 4.8 years, 1329 incident colorectal cancers were documented. We examined the relationship between intakes of red and processed meat, poultry, and fish and colorectal cancer risk using a proportional hazards model adjusted for age, sex, energy (nonfat and fat sources), height, weight, work-related physical activity, smoking status, dietary fiber and folate, and alcohol consumption, stratified by center. A calibration substudy based on 36 994 subjects was used to correct hazard ratios (HRs) and 95% confidence intervals (CIs) for diet measurement errors. All statistical tests were two-sided.

RESULTS

Colorectal cancer risk was positively associated with intake of red and processed meat (highest [>160 g/day] versus lowest [<20 g/day] intake, HR = 1.35, 95% CI = 0.96 to 1.88; Ptrend = .03) and inversely associated with intake of fish (>80 g/day versus <10 g/day, HR = 0.69, 95 % CI = 0.54 to 0.88; Ptrend<.001), but was not related to poultry intake. Correcting for measurement error strengthened the associations between colorectal cancer and red and processed meat intake (per 100-g increase HR = 1.25, 95% CI =1.09 to 1.41, Ptrend = .001 and HR = 1.55, 95% CI = 1.19 to 2.02, Ptrend = .001 before and after calibration, respectively) and for fish (per 100 g increase HR = 0.70, 95% CI = 0.57 to 0.87, Ptrend<.001 and HR = 0.46, 95% CI = 0.27 to 0.77, Ptrend = .003; before and after correction, respectively). In this study population, the absolute risk of development of colorectal cancer within 10 years for a study subject aged 50 years was 1.71% for the highest category of red and processed meat intake and 1.28% for the lowest category of intake and was 1.86% for subjects in the lowest category of fish intake and 1.28% for subjects in the highest category of fish intake.

CONCLUSIONS

Our data confirm that colorectal cancer risk is positively associated with high consumption of red and processed meat and support an inverse association with fish intake.

Fish, long-chain n-3 polyunsaturated fatty acids, and risk of colorectal cancer in middle-aged Japanese: the JPHC study

Although long-chain n-3 polyunsaturated fatty acids (Ln-3 PUFA), which are abundant in fish, have shown protective effects on colorectal cancer in laboratory studies, epidemiological studies to date have not been consistent. We evaluated the relationship of consumption of fish and Ln-3 PUFA to the colon and rectal cancer risk in the two cohorts of the Japan Public Health Center-based prospective study of 42,525 men and 46,133 women. Dietary and other exposure data were obtained between 1990 and 1994. Through December 1999, 705 cases of colon and rectal cancer were documented. When data from the two cohorts were pooled, multivariable relative risks (RRs) for the highest quartile compared with the lowest quartile of fish consumption were 1.07 (95% confidence interval, CI = 0.77-1.48) for colon cancer and 0.95 (95% CI = 0.63-1.43) for rectal cancer with no dose-risk trend. RRs for the highest quartile compared with the lowest quartile of eicosapentaenoic acid consumption were 1.05 (95% CI = 0.76-1.46) for colon cancer and 0.91 (95% CI = 0.60-1.38) for rectal cancer with no dose-risk trend. This study does not support the role of fish and Ln-3 PUFA in the etiology of colon and rectal cancer in this population whose fish consumption was high and the variation in Ln-3 PUFA consumption was large.

Vegetable/fruit, smoking, glutathione S-transferase polymorphisms and risk for colorectal cancer in Taiwan

AIM: To investigate the colorectal cancer risk associated with polymorphic GSTM1, GSTT1 and GSTP1 and the effect of diet and smoking.

METHODS: With consents, genotypes of the genes were determined using PCR methods for 727 cases and 736 sex and age-matched healthy controls recruited at a medical center in the Northern Taiwan. Nurses who were blind to the study hypothesis conducted interviews with study participants for the information of socio-demographic variables, diet and smoking.

RESULTS: There was no significant association between GSTM1 genotypes and the disease. Men, not women, with GSTT1 null genotype were at significant risk of colorectal cancer, but limited to rectal tumor, and in men aged 60 years and less. The corresponding association with the GSTP1 with G allele compared to GSTP1 A/A genotype was at borderline significance. Compared to men with GSTT1 present and GSTP1 A/A combined, men with both GSTT1 null and GSTP1 with G allele genotypes were at significant risk (odds ratio (OR) = 1.91, 95% confidence interval (CI) = 1.21-3.02), also limited to the rectal tumor and younger men. The beneficial effects of vegetable/fruit intake on colorectal cancer were much higher for men with GSTT1 present (OR = 0.32, 95%CI = 0.20-0.50) or GSTP1 A/A genotypes (OR = 0.40, 95%CI = 0.25-0.64). These effects remained significant for women. But, the greatest protective effect from vegetable/fruit intake for women was observed in those with GSTT1 null or GSTP1 with G allele genotypes. In addition, non-smoking men benefitted significantly from combined effect of higher vegetable/fruit intake and GSTT1 present or GSTP1 A/A genotypes with OR = 0.17 and 0.21 respectively.

CONCLUSION: This study suggests that the GSTT1 gene can modulate the colorectal cancer risk and vegetable/fruit-related colorectal cancer risk, particularly in men of no smoking history.

The CYP1A1 genotype may alter the association of meat consumption patterns and preparation with the risk of colorectal cancer in men and women

We hypothesized that the risk of colorectal cancer associated with meat preparation methods producing heterocyclic amines or polycyclic aromatic hydrocarbons is modified by the CYP1A1 genotype alone or in combination with the GSTM1 genotype or the NAT2 imputed phenotype. A total of 952 rectal cancer cases and 1205 controls (between September 1997 and February 2002) and 1346 colon cancer cases and 1544 controls (between October 1991 and September 1994) from Utah and Northern California were recruited from a population-based case-control study. Detailed interviews ascertained lifestyle, medical history, and diet and we extracted DNA from whole blood. Risk of colorectal cancer decreased among men with the CYP1A1 *2 any variant genotype and the lowest intake of poultry and men and women with high use of white meat drippings. Risk increased among men with the CYP1A1 *1 (no variant) allele and high white meat mutagen index, but decreased among those with the CYP1A1 *2 genotype. Risk increased with a high white meat mutagen index among women with the CYP1A1 *2 genotype and the GSTM1 present genotype. Risk of colorectal cancer decreased with the CYP1A1 *2 genotype, the NAT2 slow phenotype, and the use of white meat or its drippings. The association of risk for colorectal cancer and selected red and white meat mutagen indices and the use of white meat drippings, or fried white meat variables was more evident within select combinations of the CYP1A1 genotype and either the GSTM1 genotype or NAT2 than with the CYP1A1 alone. Genetic susceptibility may modify the associations of some meat or meat preparation factors with the risk of colorectal cancer.

Nutrition and cancer: a review of the evidence for an anti-cancer diet

It has been estimated that 30–40 percent of all cancers can be prevented by lifestyle and dietary measures alone. Obesity, nutrient sparse foods such as concentrated sugars and refined flour products that contribute to impaired glucose metabolism (which leads to diabetes), low fiber intake, consumption of red meat, and imbalance of omega 3 and omega 6 fats all contribute to excess cancer risk. Intake of flax seed, especially its lignan fraction, and abundant portions of fruits and vegetables will lower cancer risk. Allium and cruciferous vegetables are especially beneficial, with broccoli sprouts being the densest source of sulforophane. Protective elements in a cancer prevention diet include selenium, folic acid, vitamin B-12, vitamin D, chlorophyll, and antioxidants such as the carotenoids (α-carotene, β-carotene, lycopene, lutein, cryptoxanthin). Ascorbic acid has limited benefits orally, but could be very beneficial intravenously. Supplementary use of oral digestive enzymes and probiotics also has merit as anticancer dietary measures. When a diet is compiled according to the guidelines here it is likely that there would be at least a 60–70 percent decrease in breast, colorectal, and prostate cancers, and even a 40–50 percent decrease in lung cancer, along with similar reductions in cancers at other sites. Such a diet would be conducive to preventing cancer and would favor recovery from cancer as well.

Diet and cancer prevention

Dietary effects are presumed to underlie many of the large international differences in incidence seen for most cancers. Apart from alcohol and a few micronutrients, however, the role of specific nutritional factors remains ill-defined. The evidence for a role of energy balance, physical inactivity, and obesity has strengthened, while for dietary fat it has weakened. Phytochemicals such as folate, lycopene and flavonoids are still the subject of active research. As the mechanisms underlying human carcinogenesis are better understood, dietary research will focus increasingly on intermediate markers such as the insulin-like growth factors and potentially carcinogenic metabolites.

Red Meat, Chicken, and Fish Consumption and Risk of Colorectal Cancer

Background: Red meat and processed meat consumption have been associated with increased risk of colorectal cancer in some, but not all, relevant cohort studies. Evidence on the relationship between risk of colorectal cancer and poultry and fish consumption is inconsistent. Methods: We conducted a prospective cohort study of 37,112 residents of Melbourne, Australia recruited from 1990 to 1994. Diet was measured with a food frequency questionnaire. We categorized the frequency of fresh red meat, processed meat, chicken, and fish consumption into approximate quartiles. Adenocarcinomas of the colon or rectum were ascertained via the Victorian Cancer Registry. Results: We identified 283 colon cancers and 169 rectal cancers in an average of 9 years of follow-up. For rectal cancer, the hazard ratios [95% confidence intervals (95% CI)] in the highest quartile of consumption of fresh red meat and processed meat were 2.3 (1.2–4.2; P for trend = 0.07) and 2.0 (1.1–3.4; P for trend = 0.09), respectively. The corresponding hazard ratios (95% CIs) for colon cancer were 1.1 (0.7–1.6; P for trend = 0.9) and 1.3 (0.9–1.9; P for trend = 0.06). However, for neither type of meat was the heterogeneity between subsites significant. Chicken consumption was weakly negatively associated with colorectal cancer (hazard ratio highest quartile, 0.7; 95% CI, 0.6–1.0; P for trend = 0.03), whereas hazard ratios for fish consumption were close to unity. Conclusion: Consumption of fresh red meat and processed meat seemed to be associated with an increased risk of rectal cancer. Consumption of chicken and fish did not increase risk.

Meat consumption patterns and preparation, genetic variants of metabolic enzymes, and their association with rectal cancer in men and women

Meat consumption, particularly of red and processed meat, is one of the most thoroughly studied dietary factors in relation to colon cancer. However, it is not clear whether meat, red meat, heterocyclic amines (HCA), or polycyclic aromatic hydrocarbons (PAH) are associated with the risk for rectal cancer. Rectal cancer cases (n = 952) and controls (n = 1205) from Utah and Northern California were recruited from a population-based case-control study between September 1997 and February 2002. Detailed in-person interviews regarding lifestyle, medical history, and diet were conducted. DNA was extracted from peripheral lymphocytes obtained from whole-blood samples, and glutathione S-transferase (GST)M1 enzyme and N-acetyl transferase (NAT)2 enzyme genotypes were assessed. Although energy and cholesterol intakes were higher among cases than controls, adjustment for confounders accounted for the differences. Increased consumption of well-done red meat [odds ratio (OR) 1.33 95% CI 0.98, 1.79] was associated with an (P = 0.04) increase in risk for rectal cancer among men. The mutagen index, calculated on the bases of reported amount, doneness, and method of cooking meat, was also positively but not significantly (P = 0.24) associated with risk of rectal cancer for men (OR 1.37 95% CI 0.98, 1.92). NAT2-imputed phenotype and GSTM1 did not consistently modify rectal cancer risk associated with meat intake. These data suggest that mutagens such as HCA that form when meat is cooked may be culpable substances in rectal cancer risk, not red meat itself.

Risk factors for colorectal cancer

Colorectal cancer is one of the most common cancers in human population. It causes significant morbidity and mortality in our country. The incidence of colorectal cancer increases in the fifth decade of life. The aim of this study was to evaluate the association between colorectal cancer and potential risk factors. A case-control study of colorectal cancer was carried out between 1998 and 1999 in Clinical Center of Serbia, Center for Digestive Surgery. A total of 100 cases of newly diagnosed patients with colorectal cancer confirmed by histopathology and an equal number of controls, individually matched by gender and age (+/-5 years), were chosen from patients from the same hospital with no history of cancer at all. McNemar test and conditional logistic regression were used in the analysis. According to logistic regression analysis the following risk factors were independently related with the occurrence of colorectal cancer: cigarette smoking, alcohol consumption, and diet rich in red meat and fat promote the carcinogenic process; food rich in vegetables, fruits, grains, vitamin C, physical activity, and oral contraceptive use inhibit the same process. A family history of cancer and long standing inflammatory bowel diseases also have significant role. There is convincing evidence that nutrition affects colorectal carcinogenesis in a complex fashion.

Pancreatic cancer mortality in China (1991-2000)

AIM: To describe the mortality rate of pancreatic cancer and its distribution in China during the period of 1991-2000.

METHODS: Based on the data of demography and death collected through China’s Disease Surveillance Point System (DSPS) over the period of 1991-2000, the distribution of death rate of pancreatic cancer was described in terms of age group, gender, calendar year, rural/urban residence and administrative district.

RESULTS: A total of 1619 death cases attributed to pancreatic cancer (975 men and 644 women) were reported by DSPS during 1991-2000. The reported, adjusted and age-standardized mortality rates increased from 1.46, 1.75, and 2.18 per 100000 populations in 1991 to 2.38, 3.06, and 3.26 per 100000 populations in 2000. The majority (69.62%) of the deaths of pancreatic cancer were seen in the age group of 60 years and older. The mortality rate was higher in men than in women, but the male to female death rate ratios decreased during the 10 years. Our data also showed that the death rate of pancreatic cancer in urban areas was about 2-4 fold higher than that in rural areas, and in Northeast and East China, the death rates were higher than those in the other 5 administrative districts.

CONCLUSION: The death rate due to pancreatic cancer was rising during the period of 1991-2000 and the peak mortality of pancreatic cancer might arrive in China.

Comments on the history and importance of aromatic and heterocyclic amines in public health

The carcinogenic risk of aromatic amines in humans was first discovered when a physician related the occurrence of urinary bladder cancer to the occupation of his patients. They were employed in the dyestuff industry, chronically exposed to large amounts of intermediate arylamines. Laboratory investigations disclosed that rats and mice administered specific azo dyes arylamines or derivatives developed cancer, primarily in the liver. Also, at that time, a possible pesticide, 2-aminofluorene, was tested for chronic toxicity, revealing that it rapidly induced cancers in several organs of rodents. This led to investigations on the mode of action of this class of chemicals, including their metabolic conversion. Biochemical activation to more reactive N-hydroxy compounds was found to occur, mostly in the liver, through what is now known as the cytochrome p450 enzyme systems, and also through prostaglandin synthetases. There were species differences. Guinea pigs were resistant to carcinogenesis because of the low titer of the necessary activating enzymes. In target tissues, a second essential reaction was necessary, namely acylation or sulfate ester formation. The reactive compounds produced display attributes of genotoxicity in appropriate test systems. Interest in this class of compounds increased when of Sugimura and colleagues discovered the formation of mutagens at the surface of cooked meat or fish, that were identified as heterocyclic amines (HCAs). These compounds undergo the same type of activation reactions, as do other arylamines. Epidemiological data suggest that meat eaters may have a higher risk of breast and colon cancer. HCAs induced cancer in rats in these organs and also in the prostate and the pancreas. In addition, there is some evidence that they affect the vascular system. The formation of HCAs during cooking can be decreased by natural and synthetic antioxidants, by tryptophan or proline, or by removing the essential creatine through brief microwave cooking prior to frying or broiling. The amounts of HCAs in cooked foods are small, but other components in diet such as omega-6-polyunsaturated oils have powerful promoting effects in target organs of HCAs. On the other hand, the action of HCAs may be decreased by foods containing antioxidants, such as vegetables, soy, and tea. Some constituents in foods also induce phase II enzymes that detoxify reactive HCA metabolites. Additional mechanisms involved decreased growth of neoplasms by intake of protective foods. Possibly, the carcinogenic effect of HCAs is accompanied by the presence of reactive oxygen species (ROS), which are also inhibited by antioxidants. World-wide, there have been many contributors to knowledge in this field. Adequate information may permit now to adjust lifestyle and lower the risk of human disease stemming from this entire class of aryl and HCA.