January 17, 2007

Environmental causes of avoidable forms of cancer

The National Cancer association has listed the percentage of avoidable cancers with different environmental causes.

Proportion of cancer deaths caused by different avoidable cancers

Causes Percent 1981(US)* Percent 1998(UK)**

Tobacco 25-40 29-31
Diet 10-70 20-50
Medicines 0.3-1.5 <1
Infection: parasites, bacteria, viruses
10 best estimate 10-20
Ionizing and UV light 2-4 5-7
Occupation 2-8 2-4
Pollution: air, water, food <1-5 1-5
Physical inactivity 1-2

*Doll R and Peto R. The causes of cancer: quantitative estimates of avoidable risks of cancer in the United States today. Journal of the National Cancer Institute 1981;66:1191-1308.

**Doll R. Epidemiological evidence of the effects of behavior and the environment on the risk of human cancer. Recent Results in Cancer Research 1998;154:3-21.

Aaron Blair, Ph.D., the chief of the Occupational Epidemiology Branch in NCI's Division of Cancer Epidemiology and Genetics, was interviewed and he said:

This includes radiation from many sources - cosmic rays, radon, X-rays, atomic bombs, and above ground nuclear bomb tests. So, the estimates for tobacco and ionizing radiation are very solid. However, the total contribution from all the other causes of cancer, such as diet, occupational exposures, or air and water pollution, may be correct, but we are less certain. For these categories, we never know if we have really identified all the potential factors that contribute to the cancer risk in the population.

There is very solid evidence that environmental factors are the major cause of cancer, although the specific environmental factors involved differ by tumor. Tobacco smoke is the major cause of lung cancer. But there is a long list of other chemicals that cause lung cancer - arsenic, asbestos, PAHs (polyaromatic hydrocarbons), and chromium, to name a few. For breast cancer, hormone use is one of the major factors affecting risk. Prostate cancer has nothing that reaches the level of evidence of lung or breast cancer, although there are a number of strong leads. Physical inactivity is strongly linked to colorectal cancer, as well as a number of dietary factors -- low fiber is probably implicated.

My hunch is that general environmental exposures (pollutants in air and water) will be understood to be more important in the future decades. These won't account for as large a percentage of cancers as tobacco, although they could rise above the 2-5 percent range because of the large numbers of people exposed. They were on Doll and Peto's list, but there was very little information to back up their estimates (see table below). Doll and Peto assumed that several environmental exposures in the industrial arena were the same as in the general population. Researchers are beginning to focus on potentially hazardous substances in the water and air. This is a difficult research area and is every bit as hard to study as diet. My suspicion is that we will have much more solid information in the next couple of decades about how these things may contribute to cancer

The Cancer Prevention Coalition is more firm:

A 2000 publication on a large-scale study of identical twins in Sweden, Denmark, and Finland; this showed that cancer risk in adopted children parallels that of their adoptive, rather than biological, parents. "The overwhelming contribution to the causation of cancer in the population of (90,000) twins that we studied was the environment" (20). The critical significance of these findings has been recently stressed. "Thus the conclusion from twin studies is consistent with the conclusion from migrant studies: the majority, probably the large majority, of important cancers in western populations are due to environmental rather than genetic factors. Overly enthusiastic expectations regarding genetic research for disease prevention have the potential to distort research priorities for spending and health.

The cancer establishment has ignored the June 2002 admission by Doll that most non-smoking cancers "are caused by exposure to chemicals, often environmental ones"

Another discussion of coal health risks

Coal plants are the primary human activity responsible for the release of cancer-causing radioactive substances known as radionuclides. The International Agency for Research on Cancer (IARC) has classified radium-226, radium-228, thorium-232, and their decay products, as promoting cancer in human beings. All of these radionuclides are present in coal. They become more concentrated when they are burned and emitted as gases and particles.

19 coal plants emit 4,415 pounds of toxic mercury - contaminates fish and leads to permanent brain damage in exposed children.

Studies show people living near coal plants have a higher risk of cancer and asthma, and the children are at risk of brain disorders that result in learning and behavioral disorders. Particle pollution that can get into the lungs and bloodstream, as well as acid gases and mercury, are just a few of the concerns of residents living near coal plants.

A recent study shows that 240 more deaths a year will result from the 19 proposed plants (in Texas)- 12,000 deaths over their 50-year life.

Coal usage and production in the united states. Over 1000 plants.

A PBS debate on coal versus nuclear