Analysis of total meat intake and exposure to individual heterocyclic amines in a case-control study of colorectal cancer: contribution of metabolic variation to risk.

A case-control study of colorectal cancer, consisting of 157 cases and 380 controls matched by sex, ethnicity, decade of age and county of residence was performed to explore the associations between environmental exposure, metabolic polymorphisms and cancer risk. Participants were required to provide a blood sample, undergo caffeine phenotyping and complete an in-person interview that evaluated meat consumption, cooking methods and degree of doneness. A color atlas of foods cooked to different degrees of doneness was used to estimate food preparation techniques and food models were used to estimate serving portion sizes. Data was analyzed using a reference database of heterocyclic amine (HCA) exposure based on the food preferences chosen from the atlas. Data regarding individual food items cooked to different levels of doneness, as well as summary variables of foods and of food groups cooked to different degrees of doneness were also evaluated in a univariate analysis for association with colorectal cancer case status. Three measures of metabolic variation, hGSTA1 genotype, SULT1A1 genotype and the phenotype for CYP2A6 were also evaluated for possible association with colon cancer. While higher exposure to HCAs was strongly associated with colorectal cancer risk, increased consumption of five red meats cooked well done or very well done produced comparable odds ratios (OR) for colorectal cancer risk (OR=4.36, 95% CI 2.08-9.60) for the highest quartile of exposure. Similarly, individuals in the most rapid CYP2A6 phenotype quartile showed an odds ratio (OR = 4.18, 95% CI 2.03-8.90). The ORs for the low activity hGSTA1 and low activity SULT1A1 alleles were 2.0, 95% CI 1.0-3.7 and 0.6, 95% CI 0.3-1.1, respectively. Individual measures of specific HCAs provided little improvement in risk assessment over the measure of meat consumption, suggesting that exposure to other environmental or dietary carcinogens such as nitrosamines or undefined HCAs may contribute to colorectal cancer risk.