ABSTRACT
From studies of migrants moving from areas of low colorectal cancer incidence to westernized countries having a high incidence, it became apparent that within one or two generations, these immigrants developed cancer rates similar to those of the indigenous populations of the host countries. This pointed to the environment as providing the main risk factors for colorectal neoplasia, the most logical conclusions being that diet and lifestyle are the main etiologies in at least 30% of the cases. This does not negate the importance of genetic risk factors in dominant highpenetrance disorders such as familial adenomatous polyposis, hereditary non-polyposis colorectal cancer, or chronic and extensive inflammatory bowel disease. However, these can only contribute to about 3-5% of colorectal cancer cases. The remainder are probably explained by the widespread presence of inherited low-penetrance genetic perturbations that interact with environmental factors and lead to adenoma and/or cancer of the large bowel.1,2 So, even though diet has a very important role in the etiology of large-bowel cancer, we must also take into consideration interaction with race, gender, genetic make-up, and lifestyle.3 These are discussed in Chapter 2.
