Publications from the Carcinogenic Potency Project

Ames, B. N., and Gold, L. S. The Causes and Prevention of Cancer: The Role of Environment. In: The True State of the Planet (ed. R. Bailey), Washington, D.C.: Free Press, 1995, pp. 141-175.

The idea that there is an epidemic of human cancer caused by synthetic industrial chemicals is false.

If lung cancer (which is primarily due to smoking) is excluded, cancer death rates are decreasing in the United States for all other cancers combined. In addition, there is a steady rise in life expectancy in the developed countries.

Pollution appears to account for less than 1 percent of human cancer, yet public concern and resource allocation for chemical pollution are very high, in good part because of the use of animal cancer tests in cancer risk assessment.

About half of the chemicals tested, whether synthetic or natural, are carcinogenic to rodents at the high doses tested in rodents.

Linear extrapolation from near-toxic doses in rodents to low-level exposure in humans has led to grossly exaggerated mortality forecasts. Such extrapolations cannot be verified by epidemiology. Furthermore, relying on such extrapolations for synthetic chemicals while ignoring the enormous natural background leads to an imbalanced perception of hazard and allocation of resources.

Zero exposure to rodent carcinogens cannot be achieved. Low levels of rodent carcinogens of natural origin are ubiquitous in the environment. It is thus impossible to obtain conditions totally free of exposure to rodent carcinogens or to background radiation.

Risks compete with risks: society must distinguish between significant and trivial risks. Regulating trivial risks or exposure to substances erroneously inferred to cause cancer at low doses can harm health by diverting resources from programs that could be effective in protecting the health of the public.

Epidemiological evidence in humans is sufficient to identify several broad categories of cancer causation for which the evidence is strong and plausible. Since many of these are avoidable, it is possible to reduce incidence rates of many types of cancer.

Tobacco is the most important global cause of cancer and is preventable. Smoking contributes to about one-third of U.S. cancer, about one-quarter of U.S. heart disease, and about 400,000 premature deaths per year in the United States.

The quarter of the population with the lowest dietary intake of fruits and vegetables compared to the quarter with the highest intake has roughly twice the cancer rate for most types of cancer (lung, larynx, oral cavity, esophagus, stomach, colon and rectum, bladder, pancreas, cervix, and ovary).

Decreases in physical activity and increases in smoking, obesity, and recreational sun exposure have contributed to increases in some cancers in the modern industrial world, whereas improvements in hygiene have reduced other cancers related to infection.

Chronic infections contribute to about one-third of the world's cancer.

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Last updated: November 10, 1995

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