The Development of Cancer

Multistage Carcinogenesis

The elderly are more susceptible to cancer than other groups because it is a multistage process that may take 15-45 years before clinical signs are evident. Cancerous growth forms as the result of a sequence of events over a period of time. The events are associated with the exposure of DNA to harmful molecules originating from within or outside of the body. Researchers suggest that an average of five or six chemical insults to susceptable genes will lead to cancer. Some people are genetically susceptible to cancer because enzymes which help to prevent cancer growth are not efficient or enzymes that may contribute to cancer formation are very active.

There are three phases of development involved in the formation of cancerous growth.

The first stage consists of a mutation of DNA which does not undergo DNA repair (by enzymes) or undergoes faulty DNA repair.

The second step is promotion which involves an action promoting the uncontrolled growth and proliferation of mutated cells. In time these cells loose their normal abilities and just reproduce.

The third step is metastasis. This is the invasion of cancerous cells into nearby tissues as well as the migration of cancerous cells to other tissues via circulatory or transport systems.

Substances introduced to the body can cause mutation, promotion , or both. A carcinogen which causes both is called a 'complete carcinogen'. Physical damage to tissues can cause cell proliferation. Some mutagens can damage surrounding tissues, leading to cell proliferation. This may also lead to cancer.

These events invariably occur naturally over time as we are exposed to man-made environmental contaminants and toxins that occur naturally in our food, in minerals, and in our bodies as oxidative by-products of metabolism.

Examples of naturally occurring carcinogens include aflatoxin, a by-product of mold found in peanut butter; isocyanate, found in brown mustard; estragole from basil; nitrosamines from cooked bacon; and benzo(a)pyrenes found in charred or barbecued foods.

Excess consumption of fat or salt, tobacco use, and alcohol consumption can raise susceptibility to chemical insult resulting in disease. Please see our Extoxnet FAQ page on Diet and Cancer.

Please see The Institute for Environmental Toxicology's site on Carcinogenicity.

Also see Misconceptions About Environmental Pollution, Pesticides and the Causes of Cancer, by Bruce N. Ames and Lois S. Gold


This page was prepared by Theresa L. Pedersen, UCD EXTOXNET FAQ Team. August 1997.