Epidemiological Study On The Environmental And Host Factors Of Colorectal Cancer

[ Background ] Colorectal cancer is one of the most common malignant tumors that do harm to people's health. In Europe and America countries, the incidence rate of colorectal cancer is the second of the total malignant tumors in male, and the third in female. In China, the mortality rate of colorectal cancer is the fifth or sixth of the total malignant tumors with an increasing trend, the adjusted mortality rate is about 5.29/100,000 in male and 3.86/100,000 in female.The incidence of colorectal cancer may result from the both of environmental and host factors. High fatty and low fiber diet, fried, smoked or baked meat or fish, fewer vegetable and fruit diet and unclean drink waters et al were the common risk factors of colorectal cancer in the epidemiological reports of foreign countries. The relationship of pesticide pollution and human malignant tumors were also reported in some articles. The relationship between organochloride pollution and the incidence of colorectal cancer need further evidence, but no ecological study based on the total population existed by this time. The Meta-analysis on the risk factors of colorectal cancer from fourteen case-control studies in China, 1988-2000, showed that chronic diarrhea, mucous and blood stool, polyp in large intestine, constipation and appendicitis were the risk factors of colorectal cancer; fry-cooked fish, fatty food, smoking, psychic attack and family history of cancer were also the risk factors, but dietary fiber and light physical activities were the protective factors. There is no cohort study about risk factors of colorectal cancer in China by now.The response of individuals to the environment mutagen may be not completely alike. Hereditary susceptibility of tumor takes an important role in the incidence of colorectalcancer. The classic epidemiological study have shown the family aggregation of this cancer, and the family history of cancer and the hereditary trend of polyp were important risk factors of colorectal cancer. The recent literature suggests the highly attention should be paid on the interaction of environmental factors and hereditary susceptibility. Glutathione-S-Transferases (GSTs) is a common family of metabolism enzymes. GSTs have the function of detoxification for polycyclic aromatic hydrocarbon and mixed cyclic chemical carcinogen or cocarcinogen of organochloride and from the fried, smoked or baked food. It was reported that the GSTM1 null and GSTT1 null genotypes could decrease the activity of the corresponding enzyme. There were several studies about the relationship between the genotypes of GSTM1 and GSTT1 and colorectal cancer, with quite different results. There was no such study report based on population in China so far.[Objective and Significance] With a wide view on the epidemiological studies of colorectal cancer, the results of the reports were not completely similar because of the difference in selection of subjects and research methods, so further analysis and study with different method are wanted. This study is to reveal the relationship between the extent of organochloride pollution and the incidence rate of colorectal cancer, and to verify the influence of remain pollution of pesticide in environment on the incidence of colorectal cancer, and to offer the basic epidemiological data for further study on the mechanism of colorectal cancer occurrence. It was also wanted to reveal the risk factors of colorectal cancer by cohort analysis of exposure factors in a 10-year followed cohort, which could overcome the shortcomings of that all results of risk factors of colorectal cancer in China were only from case-control studies. The screening power for colorectal cancer by FOBT was evaluated by discussing the relationship between the outcomes of FOBT and the cumulated incidence rates of colorectal cancer during short-term, medium-term and long-term. Because there was no effective method in curing colorectal cancer, it is important to carry out the primary prevention focused to the environmental factors from furthe...