Overview of the epidemiology of colorectal cancer.

INTRODUCTION: The epidemiology of colorectal cancer has generated more interest recently, because recent developments in genetics, molecular biology, and genetic epidemiology have increased our understanding of the role of genes in the etiology of colorectal cancer. Interactions between genetic susceptibility and environmental factors in the etiology of cancer may be easier to define. EPIDEMIOLOGY: Colorectal cancer is common in the Western world and is rare in developing countries. A sharp increase is seen in Eastern Europe and Japan. ETIOLOGY: Molecular genetics has shown that accumulation of genetic changes is important in the development of colorectal cancer. Mutations in at least four to five genes are required for the formation of a malignant tumor. Environmental mutagenic factors may determine which susceptible individuals grow carcinomas. Environmental risk factors for colorectal cancer are found in a western diet, rich in fat, meat, and animal protein and low in fiber, fruit, and vegetables. The complex interrelations between food components make it difficult to define the precise role of specific food factors. PREVENTION: Conclusive evidence of the effectiveness of primary prevention of colorectal cancer via dietary measures or nonsteroidal anti-inflammatory drugs is lacking. Secondary prevention by interrupting the adenoma carcinoma sequence is an actual possibility, its effectiveness, however, needs to be determined. Molecular genetics holds a promise for identifying populations at high risk for colorectal cancer, therefore, targeting the screening to make it more cost-effective.