Spotlight: Is there a Link between Environment and Cancer?
When you hear that someone has cancer, you might ask
yourself, “Why did it happen? Was it because of chemicals?” We often try to
pinpoint a reason for cancer. If a person is a house painter and develops
cancer, you think to yourself, “It must have been something in the paint.” If a
person who gets cancer works in a hair salon, you ask yourself, “Was it because
of all the chemicals in the salon?” The wondering is endless—was a cancer caused
by lawn chemicals? By chemicals that farmers use on crops? By living near a
Researchers have been hard at work for years trying to
determine links between cancer and environmental causes. It’s an extremely
complex job. They can question cancer patients comprehensively, but it’s almost
impossible to know exactly what people have come in contact with throughout
their lives, when they came in contact with it and how much of the substance
they came in contact with.
Currently, researchers from the National Cancer Institute,
the National Institute of Environmental Health Sciences and the Environmental
Protection Agency are studying farmers and their spouses in Iowa and North
Carolina. The investigators ask what pesticides and herbicides the farmers use,
when they use them and how much they use. They also ask about other factors that
contribute to cancer risk, such as smoking. They then look at the medical
records from tumor registries, identifying who developed cancer and what type of
cancer it was. They’ve been collecting this data since 1993.
So far, researchers have seen only a slight increase in
lung cancer and leukemia among farmers who have used the pesticide diazinon.
There’s also a slight increase in prostate cancer in farmers who use
methylbromide, which fumigates the soil.
But even if future evidence proves that these pesticides
have caused an increase in cancer in farmers, researchers still don’t know what
that means for the general population. Farmers are exposed to much higher levels
of these chemicals than people in the general population.
A complex interplay: potential cancer-causing agent, additional risk factors present and genetic makeup
There are chemicals that have been shown to cause cancer in
rats. For example, aflatoxin, which is produced by a mold on peanuts, causes
liver cancer in rats.
In fact, aflatoxin causes liver cancer in humans as well. A
study of men in Shanghai showed that men who ate foods containing high doses of
aflatoxin were at a four times higher risk of liver cancer. Hepatitis B is also
a risk factor for liver cancer; it raises the risk by a factor of seven. But the
risk of liver cancer in men who consumed high levels of aflatoxin and who had
hepatitis B was 70 times higher.
This points out that even if researchers could identify how
much one chemical increases the risk of cancer, there are too many other
variables among humans that make risk levels nearly impossible to predict. One
person who consumes higher than usual levels of a chemical and who has a healthy
diet and doesn’t smoke may have a lower likelihood of developing cancer than a
person who consumes even higher levels of that same chemical but who also
smokes. And yet another person may have a genetic predisposition to develop
cancer, so that even a small amount of exposure could cause cancer in that
Human behavior is extremely individualized and
unpredictable. This is what makes it difficult for researchers to make solid
pronouncements about the effects of environment on cancer risk. The best bet for
each of us is to create as a healthy a lifestyle as possible and to get routine
cancer screenings at the appropriate time. This is likely to be protective
against possible exposure to carcinogens and genetic predisposition.
The National Cancer
Institute; The New York Times, Science Times Section, “Environment and Cancer:
The Links are Elusive.” 13 December 2005.