PLENARY:

ADDRESSING THE ENVIRONMENTAL CAUSES OF CANCER

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Devra Lee Davis, Ph.D., M.P.H.
June 11, 1999

I. Abstract

This lecture addressed health and cancer related to the environment. Although environmental agents are not a causative factor for all cancers, there is significant scientific information that shows alteration of the chemical and physical environment by technology, pollution, industry, and personal habits impact the rates and types of various cancers. Dr. Davis explores some of these links and their effects on cancer with an emphasis on breast cancer.

II. The Cancer-Related Issues Addressed

Cancer has a strong environmental component as evidenced by its varying rate worldwide. There is a ten-fold difference in cancer rates among various countries. This large variation suggests that a certain proportion of cancers can be attributed to the environment, are controllable, and should serve as a focus for prevention efforts. The largest modifiable cause of cancer in the modern world today is cigarette smoking. Alcohol is also another known risk factor. The longer in life and more one consumes alcohol, the greater the risk for a variety of diseases. Currently, young people are consuming alcohol more frequently and heavily, placing them at greater risk.

Other correlated environmental causes of cancer include jobs in certain occupations. Workers in farming and industry have had increased rates of cancers. Workers exposed to solvents and cutting oils, certain types of dust and fumes are also more likely to develop certain types of cancers.

III. The Program

A. Philosophical Background

People with cancer have been voting with their wallets, with their hearts and minds in saying that conventional treatment is not enough. Remarkable change is taking place in medicine. The world is catching up in bringing complementary and alternative therapies to the treatment of cancers. Technology today can be both part of the problem and the solution for treatment.

B. Details

C. Research

Science requires a certain level of evidence, but in cancer and prevention we must look at the downside risk of doing something verses the risk of doing nothing. It is important to understand that risks are relative. It is better to be approximately right than precisely wrong!

The evidence linking environment and health is of three types: laboratory studies, wildlife studies, and human studies. The laboratory studies are well controlled with petri dishes and laboratory animals. Wildlife studies are more difficult to gather data from and are less precise. Also, animal histories are often unknown, but information gathered is useful in predicting environmental effects on humans. Human studies are the hardest to complete in clinical trials. Examining environment in human studies is even more difficult because we do not have standardized information. No country has invested the resources to develop the capacity to answer the questions of environment and health effects. Because of the lack of resources, we have to rely on animal and wildlife studies to predict environmental effects on people.

The environment is crucially important in breast cancer. We know that fewer than 1 in 10 cases of cancer arise in women born with genetic defects. This means that the one person who got the disease was born with the genetic defect, but the other 9 out of 10 who developed cancer did not have risk factors and did not inherit the gene responsible for breast cancer. Defects in genes cause cancer, but those defects are acquired over time. Risk factor means that there is a risk for breast cancer in those with certain exposures compared with those who do not have those exposures.

There are known risk factors for breast cancer. One is exposure to radiation, particularly to the young breast or in the embryo and early radiation is much more toxic. Routine mammography for women over 50 who do not have a genetic susceptibility does not convey a risk of breast cancer. Radiation to young people does convey a risk, particularly chest radiation. A familial history of a mother or sister with breast cancer prior to menopause is important. Early menses prior to age 12 is a risk factor for breast cancer. Lack of exercise, sex, age, and late menopause (after the age of 55) are also risk factors.

What we know of these risk factors implies that they impact the total amount of hormones circulating in the body. For example, the earlier a woman starts her period, the longer her exposure to hormones. If a woman has no children, the more hormonal cycles she will be exposed to. If a woman drinks a lot of alcohol or does not exercise she has a greater level of circulating hormones. We theorize that environmental factors contribute to increased hormone levels and concurrently, increased rates of breast cancer.

Protective factors that reduce breast cancer risk include soy in the diet, certain vegetables, exercise before or after menopause. Women who engage in vigorous exercise additionally have reduced risks of recurrence of breast cancer. Exercise reduces the total amount of circulating hormones in the body.

Fiber, fish and olive oil have been suggested to be protective against breast cancer. A high fiber diet may absorb and decrease circulating hormone levels leading to a decreased risk of breast cancer. Melatonin may also have protective effects. A study of blind women in Sweden found that they had higher melatonin levels and lower rates of breast cancer.

A brief review of the experimental evidence outlines tumor progression of breast cancer cells that acquired a genetic alteration. The cell develops hyperplasia (hyper growth), dysplasia (dysfunctional growth), after which it becomes invasive and enters the blood stream. The good news is that there is treatment at each of these three stages.

Reviewing the research on animal studies reveals interesting findings. The alligators of Lake Apopka in Florida are an example. Lake Apopka is a large fresh water lake that supplies drinking water for parts of the local community. A massive chemical spill into the lake in the 1980’s included inert DDT, a common ingredient in pesticides at the time. Alligators born in the lake within five years after the spill were predominantly female. The few males born had small penises making mating difficult. Estrogen levels of these alligators were four times that of the estrogen levels of alligators from non-contaminated lakes. This suggests that exposures to DDT caused increased hormone levels and resultant genetic defects. There is evidence in laboratory experiments where breast cancer cells were exposed to DDT and proliferated at a much greater rate than those not exposed. Similar results were found using red dye # 3.

Some studies on humans and organochlorides are not as clear as the experiments with DDT and red dye mentioned above. One study in Europe examined the blood of over 1000 women diagnosed with breast cancer (with an average stage II or stage III breast cancer). These women had lower amounts of DDT in their blood compared to those women who did not have breast cancer. It is suspected that the women with cancer had metabolized DDT and hence their levels were lower. Another study done at Harvard had similar results. A Denmark study published in The Lancet found that women who had higher levels of some organochlorines in their blood 10 years before the diagnosis of breast cancer had a two-fold increase in breast cancer.

IV. Comments

Utilizing precautionary principles, we must err on the side of protecting public health. We cannot wait for the scientific evidence to be 100% decisive. We have studies of more than 100 different compounds known to cause cancer in laboratory animals. Some of these compounds even cause breast tumors to develop in male animals. We should take action now on those chemicals, as some of them are not regulated or controlled.

A study to be released in the Annals of Public Health revealed that young men today are developing three to four times more non-smoking related cancer than their grandfathers did. The causes are unclear but of concern is that testicular cancer and non-hodgkins lymphoma is on the rise in Generation X males. Non-hodgkins lymphoma has increased in women as well. By the time we are certain of the evidence of why these cancers are increased in humans, it will be too late to do anything for these people. It becomes apparent that we cannot wait for the research to identify the specific causes. It makes good sense now to err on the side of reducing suspect risks.

A review of the suspect risks and ways to reduce them do not involve a discussion of controllable factors such as diet or exercise. The environment is key to identifying suspect risks. You can say no to dangerous sex and you can say no to drugs, but you cannot say no to a belching factory in your hometown, a power plant that is leaking, or a polluted water supply.

The United States is one of the cleanest environments in the world. We have reduced our blood levels of DDT ten-fold since the 1970’s and now breast cancer rates are starting to come down. Yet we still cannot explain why most cancers occur and we do know that some cancers derive from environmental factors.

One method of controlling environmental factors is through integrated pest management. This proposal reduces the use of pesticides in the homes and environments of young children. We have banned smoking in public places because of the risks to children and others. Studies from the National Cancer Institute and others imply that the risk of illness from pesticides is as high as it is from second hand smoke.

Integrated pest management implies smart use of pesticides. During epidemics of infectious diseases, there may be a need for pesticides. Smart use will keep populations safe while effectively utilizing pesticides only when needed. We must work with industry and the private sector to find greener and more energy efficient ways of using products that are less toxic.

Dr. Davis is the director of the Health, Environment, and Development Program at the World Resources Institute. More information about this organization and the work of Dr. Davis can be obtained on the internet at: http://www.wri.org.