Colorectal cancer as a disease of the environment.

Colorectal cancer is common in North America and Europe but is virtually unknown among the native population of sub-Saharal Africa. Within the continent of Europe, colon cancer incidence varies fourfold between cancer registry regions. Within the United Kingdom, colon cancer is, and has been for 70 years, commoner in Scotland than in England and Wales. In Scotland, the disease is one-third commoner in the north of the country than in the south. Colorectal cancer risk is determined by local environmental conditions within the bowel: these are determined to a large extent by diet which in its turn is dictated by environmental conditions, both geographic and economic. Cancer as a group of diseases which causes 40% of all deaths, is a disease of the environment, with colorectal cancer the best example of this in a common tumour.