Cancer and the Role of Environment
UPdate Fall 2001

The role of the environment in human health is generally a subject only briefly touched upon in medical school training.  It wasn't until I attended the World Breast Cancer Conference in July 1997 that I first heard discussion amongst a number of prominent scientists, physicians and other health professionals about the growing body of evidence linking environmental contamination and cancer.  I became very interested in this subject since I developed breast cancer at the age of 37, with no risk factors and having breast fed three children.

When I was doing my literature search on the link between cancer and pesticides, the librarian helping me stated: "I don't have to worry about exposure to pesticides.  I hate gardening!"  Another interested person felt she was not at risk because she did not live in farm country where all the spraying was taking place.  Not many people realize that they are being exposed to minute quantities of pesticide residues, not to mention a host of other chemicals used in food preparation, every time they eat.

An obvious place to start looking for the root causes of cancer is with substances that are known to cause cancer in animal models, that is carcinogens.  One such class of carcinogenic substances, the organochlorines (OCs) are found all around us.  They're in our drinking water, in much of our pesticide-treated food, and in many of our laundry detergents and cleaning products as well.  DDT, a well-known OC, is so persistent that although its use has been banned in North America for more than 25 years, it is still found in detectable levels in the tissue and blood of people living from Florida to the high Arctic.  This ban notwithstanding, OCs are still produced in North America and exported abroad, particularly to developing countries.  As a consequence, imported fruits and vegetables which end up back on our dinner tables often have detectable levels of substances we know to be human carcinogens.

Aside from being potentially carcinogenic, some of these chemicals also behave like a much weaker version of our body's own estrogen.  Because these estrogen-like chemicals are outside the body, they are classified as xenoestrogens, "xeno" meaning "foreign" in Greek. 

We know that the more estrogen a woman is exposed to during her life, the greater her risk of breast cancer.  Estrogen, essential for sexual development and reproduction, stimulates breast cells to grow, divide and spread.  Similar to "bad" and "good" cholesterol, it's believed our body produces "bad" and "good" estrogens.  Certain xenoestrogens, like OCs, act like bad estrogens, which in turn stimulate uncontrolled growth of breast cells.  Other xenoestrogens such as those found in plant foods like soy products, cauliflower and broccoli, may act like good estrogens because they prevent cancer.  (They are also called phytoestrogens.)
Devra Lee Davis, an epidemiologist and toxicologist from the World Resources Institute in New York, believes the increased incidence in breast cancer over the past several decades is due, at least in part, to increased exposure to estrogen-like chemicals in the environment and in the foods we eat.  In 1940, one billion pounds of these chemicals were produced in the U.S.  By 1950 this increased to 50 billion pounds, and by the late 1980s climbed to 500 billion pounds.  At least 600 of these estrogen-like chemicals are known to cause cancer in animals and 25 are proven to cause cancer in humans up to one and three decades after exposure.  Davis says it's not isolated exposure to these contaminants but rather a lifetime of being exposed to hundreds of chemicals, some of which become more potent when combined, that may heighten one's risk.

The proposed link between chemical xenoestrogens and breast cancer came about by accident in 1991 when Tufts University researchers noticed that breast cancer cells, which need estrogen to reproduce, were growing rapidly in plastic dishes.  They discovered that nonylphenol, a chemical added to plastic to prevent cracking, was leaching out of the plastic and triggering the growth of the breast cancer cells.  In other words, it was acting like estrogen.  The researchers then exposed other cancer cells to common pesticides, detergents and plastics, and observed the same results.  The implications are disturbing, considering how common these products are in our lives.

Since then, other researchers have studied the role of xenoestrogens (particularly the pesticide DDT and potentially carcinogenic chemicals known as PCBs) in the development of breast cancer.  As with many such lines of inquiry, the results are not clear.  Some studies have indicated a link between exposure and breast cancer, but other studies have found no connection.  Some researchers say the evidence may be conflicting because these studies only give you a snapshot of the current levels of contaminants in a woman's body.  This approach doesn't consider what the level of exposure might have been in the womb or during childhood, possibly the most risky times for exposure to these chemicals.

In 1962, the renowned biologist, Rachel Carson, in her book Silent Spring alerted us to the poisoning of the earth with toxic chemicals.  Because of her concern about pesticides, she was ridiculed by some in the chemical industry as an ignorant, hysterical woman who wanted to turn the world over to insects, and considerable resources were spent trying to discredit her.  Rachel Carson died in 1964 of breast cancer.

Thus far, I have discussed mainly the link between pesticides and breast cancer because that is my special interest.  But also consider the following:
- Farmers exposed to herbicides for more than 20 days per year have been found to have a six-fold increase in non-Hodgkin's lymphoma.
- There is a significant association between yard treatment with pesticides and pediatric soft tissue sarcomas, leukemias and brain cancers.
- The provincial and federal health departments report that there are instances where maximum allowable levels of DDT intake may be exceeded in breast-fed infants.
- In the last 30 years, the global average human sperm count has decreased by 50%.  Some argue this is a result of higher exposure to xenoestrogens.
I could go on and on.

There will always be those with vested interests to argue that we do not yet have sufficient proof of a relationship between environmental contaminants and cancer and other diseases, and from a strictly scientific point of view they are correct.  We can always do more research, and we will never have proof, only more evidence.  How much evidence is enough?

More than 50 years ago, the Surgeon General in the U.S. warned that cigarette smoking was harmful to human health.  It wasn't until dozens of studies in more than 20 different countries, all showing that smoking increased the risk of lung cancer and other diseases, that governments finally took action.  It took almost 25 years for warnings to appear on cigarette packages, and only in 1997 was the tobacco industry actually held legally accountable.

There seems to be sufficient evidence now linking pesticides to cancer and other diseases to justify adopting a precautionary principle regarding the use of these chemicals.  For too long, industry and government have been minimizing the role that environmental contaminants may play in human health.  Let us learn from our experience with smoking.  Let us no longer allow others to poison our planet while we remain silent.  To quote Abraham Lincoln, "to sin by silence when they should protest, makes cowards out of men."

Reprinted from Eco Farm and Garden

Nicole Bruinsma lives with her husband and three young daughters in Chelsea, Quebec and works as a family physician in a nearby rural hospital.  She is vice-president of CAPE, the Canadian Association of Physicians for the Environment, and is very active in her community on environmental issues.

Related Resources:
Exposure, Environmental Links to Breast Cancer, a 54 minute video hosted by Olivia Newton-John can be borrowed from the Canadian Cancer Society, N.S. Division for a one week period without charge by N.S. and N.B. residents.  Call Myrna Drake at 902-423-618 or 1-800-639-0222

Living Downstream: An Ecologist Looks at Cancer and the Environment, by Sandra Steingraber, Addison Wesley, 1997.

The Nova Scotia Breast Cancer Action Group can be reached through their website

See also: Prevention is the Cure, UPdate Fall 2001