Both sexes, all ages and ethnic groups, and people from every country in the world are affected by cancer. However, different groups may be affected by different cancers. For example, breast cancer is most common among females (Lewis & Elvin-Lewis, 1977, pp. 105-126).
At the cellular level, the kinds of cells damaged and the damage that occurs varies with the type of cancer. In colon cancer, carcinogenesis may start with undifferentiated stem cells migrating to the mucosal surface of the colon. Undifferentiated stem cells have the ability to proliferate, and can bud and proliferate (Grundman, 1985). Genetic factors may be involved in production of colon cancers - e.g. a preformed intraluminal substance converts homozygote polypoid cells into adenomas that become carcinomas. Another substance, believed to be a primary bile acid, may be converted into a carcinogenic substance that triggers growth of the adenoma when gut microflora shifts from aerobic lactobacilli and peptostreptococci to anaerobic Bacteroides species (Freed, 1984). Units of DNA coding for cell characteristics may be behind many cancers. These genes, known as oncogenes, may be created in tissue by mutation. The Rous oncogene was shown to be a gene of viral origin that was picked up by chicken chromosomes; it remains latent until it becomes activated and causes cancer. Similar protooncogenes are associated with human cancers, though these genes are probably not of