Toronto Globe and Mail, October 12, 2006
SCIENTISTS FIND FARM LINK TO BREAST CANCER
[Rachel's introduction: A new study from Canada links farm life to an increased likelihood of breast cancer.]
By Martin Mittelstaedt
A team of researchers who studied the occupations of nearly all the Windsor, Ontario women who developed breast cancer in a period from 2000 to 2002 found they were about three times more likely to have worked on farms than women who didn't have the disease.
What's more, those who farmed and then later worked in the automotive industry were four times more likely to have the disease, according to a paper about the research being published Thursday in the Annals of the New York Academy of Sciences.
The new study is one of the most detailed investigations undertaken in Canada into the occupations of women who developed breast cancer, and it indicates that something about farming increases the risk of the disease, the most common cancer to afflict females in the country.
Although the researchers didn't determine what these risks were, they speculated about pesticides, many of which are able to mimic or block the normal functioning of estrogen and other hormones.
"If you were going to hypothesize about the No. 1 most likely cause of this elevated risk, I think you'd have to look at the whole chemical exposure that exists on farms," said Jim Brophy, head of the Occupational Health Clinics for Ontario Workers in Sarnia, and lead author of the paper.
A staggering 99 per cent of all those treated for the disease at Windsor's cancer centre during the period of the research agreed to participate. Dr. Brophy said there was an enormous desire among women, who typically are not asked about the role their jobs may have played in their illness, to be part of a study that might help explain their cancer.
That desire has a resonance with Tricia Pletsch, who worked on her parent's farm near Chatham as a teenager and developed breast cancer two years ago, at 39. Her family doesn't have a history of the cancer, but she worries about the heavy chemical use on the farm while growing up.
"Pesticides were really popular in the seventies," she said.
Like most women with breast cancer, her doctors never asked about her occupation when trying to explain her illness and were at a total loss to explain why she was afflicted.
"No one asked me what I did, and when I asked them why I got it, no one had a clue," she said.
Scientists around the world are struggling to explain the recent epidemic of breast cancer in industrialized countries because fewer than 10 per cent of those with the disease have a known genetic predisposition for it.
Rates for the cancer in Canada are among the highest in the world, with the lifetime risk of about one in nine. During the past 30 years, there has been a largely unexplained 25-per-cent increase in the country's age-adjusted incidence rate.
Previous research has found an association between breast cancer and a woman's socioeconomic status, diet, age of first pregnancy, and several other factors, but the majority of cases have no known risk factor.
It is also not known why women with higher socioeconomic status are more at risk, but Dr. Brophy says occupation should be investigated more closely because it might provide clues on cancer-causing substances and new prevention strategies.
"If you would capture the lifetime [work] histories of people with cancer, it might be very revealing in terms of risk factors that we're not currently addressing. That could have an enormous preventative effect," Dr. Brophy said.
He said there has to be a major risk in farming to cause the research results. "It's very dramatic, in the most common cancer among women where 50 per cent of the cases are unexplained, to have a three-fold excess," Dr. Brophy said.
In Canada, none of the provincial registries track cancers by occupation. About 22,000 women in Canada will develop breast cancer this year and an estimated 5,300 will die from it.
Up until now, little research on occupation and breast-cancer risk has been done in Canada, although researchers at the British Columbia Cancer Agency looked at work histories and the disease in 2000. They also found an association with agriculture, although they looked at far fewer women farmers than the current study, whose results were considered statistically significant.
An official with Canada's largest cancer registry says he thinks it would be a good idea to study the occupations of those with the disease, although he said this effort would require millions in funding and a political will to implement.
"I certainly don't dispute that it's a neglected area, particularly with women coming into the work force and the nature of work changing," said Eric Holowaty, an epidemiologist at Cancer Care Ontario.
In Windsor, the researchers compared the work histories of 564 woman treated for breast cancer over a 21/2-year period ending in 2002 against a similarly sized random control group of women who didn't have the cancer.
Those with the disease were 2.8 times more likely to have worked on farms. This rate jumped to four times more likely if the women worked in agriculture and then the automotive industry and fell to 2.3 times if they worked on farms and then in health care.
There was no extra risk of breast cancer for women who never worked on farms and then went into the auto industry or into health care, suggesting that agriculture somehow primes women to get the disease.
The Windsor area has large numbers of women employed in agriculture because it is one of the most intensively farmed regions in Canada, with major fruit and vegetable crops. The area also has one of the largest car-making sectors in the country.
About 300 women in the study worked in agriculture.
The researchers found little difference between the women who got breast cancer and the control group with respect to hormone replacement therapy, breast-feeding history, smoking, oral contraceptive use, having a mother with the cancer and previous pregnancies.
Copyright 2006 Bell Globemedia Publishing Inc.