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full NYTs: Exposure to DDT Doesn't Increase Risk of Breast Cancer
Subject: ARTICLE: DDT and Breast Cancer - New Study
Study: Exposure to DDT Doesn't Increase Risk of Breast Cancer
By GINA KOLATA
Challenging the convictions of many advocates for patients, a large study
has found no evidence that exposure to the chemicals DDT and PCB's increases
the risk of breast cancer.
There has long been concern that certain chemicals, notably the pesticide
DDT, which was banned in 1972, and the industrial chemicals known as
polychlorinated biphenyls, or PCBs, banned in 1977, might have contributed to
the slow rise in the incidence of breast cancer in this country.
The chemicals, which accumulate in body fat, can act like weak estrogens in
the body. And the more estrogen a woman is exposed to, the greater her risk
of breast cancer.
Previous, smaller studies led to contradictory results, and some had design
flaws that made them less than definitive.
The new study, by Dr. David Hunter, an epidemiologist at the Harvard School
of Public Health, and his colleagues, was larger and better designed than any
before it. It involved nurses who agreed in 1976 to participate in the
long-term study, in which their health would be monitored. In 1989 and 1990,
32,826 of them sent in samples of their blood, which was stored.
Hunter and his colleagues examined the levels of DDT and PCB's in the blood
of 240 of those women who subsequently developed breast cancer and compared
them with the levels in the blood of other study participants who were
similar in every way but did not develop breast cancer.
The investigators found no relationship between the level of DDT and PCB's
in women's blood and their likelihood of subsequently developing breast
The results, to be published on Thursday in The New England Journal of
Medicine, came as a shock to some advocates for patients.
"I just find it very difficult to believe," said Geri Barish, president of
1 in 9: The Long Island Breast Cancer Action Coalition, based in East Meadow,
N.Y. "I can't accept it at all."
A co-author of the study, Dr. Mary Wolff, a chemist at Mount Sinai School
of Medicine in New York , said it was too soon to rule out the possibility of
But some leading scientists who were not involved in the study said the
results, along with those of several other studies, made it extremely
unlikely that there was any merit to the notion that DDT and PCB's were
linked to breast cancer.
Hunter's study was "pretty definitive," said Dr. Virginia Ernster,
professor of epidemiology at Stanford University.
Dr. Shelia Zahm, deputy chief of the occupational epidemiology branch at
the National Cancer Institute, said the new study was "certainly a strong
piece of evidence against the hypothesis."
The hypothesis had been fueled by a small study in 1994 by Dr. Wolff. She
measured levels of DDE, a metabolite of DDT, and of PCB's in the blood of 58
women with breast cancer and compared them with levels of the chemicals in
the blood of women without cancer. The higher the level of DDE in her blood,
the greater a woman's risk of breast cancer, Dr. Wolff found.
Her study was soon followed by larger studies, in Europe, Mexico and the
United States, that failed to find such correlations. In the European study,
the researchers even found that the higher the level of DDE in a woman's
body, the lower her risk of breast cancer.
But, Dr. Zahm said, there were design problems in those studies. They were
small, had too many subjects drop out or the researchers did not insist that
the levels of DDT and PCB's be measured in the same year in all of the women,
an important consideration since the levels of these chemicals fall every
year as the body slowly rids itself of them.
And so, Dr. Zahm said, it remained possible that the negative results were
spurious. Hunter, she added, had "a strong study design." And now, she
concluded, the body of evidence that DDT and PCB's can cause breast cancer
"is not very compelling."
Some scientists, like Dr. Bruce Ames, a biochemist who is director of
environmental health science at the University of California at Berkeley, and
Dr. Stephen Safe, a toxicologist at Texas A&M University in College Station,
have been skeptical of the hypothesis from the beginning.
They noted that DDT and PCB's are very weak estrogens present in minuscule
amounts in the body. Studies in which laboratory animals were given high
doses of such compounds led to contradictory results: in some the compounds
were found to caused breast cancer, in others they protected against it.
Moreover, plants have so many naturally occurring estrogens and
anti-estrogens that they might overwhelm any conceivable effects of
environmental chemicals like DDT and PCB's.
For example, Safe said, the amount of biologically active plant estrogens
in a single glass of red wine is 1,000 times greater than that of all the
environmental chemicals that a person gets from pesticides in a day's food.
"And that's just in glass of wine, never mind beans, carrots, and all the
other vegetables," he said.
Hunter said that perhaps it was time to question the assumption that much
breast cancer is caused by unknown environmental agents. A recent study, for
example, found that the high rate of breast cancer in the San Francisco Bay
area can be completely attributed to known risk factors like a woman's age
when she starts to menstruate, has a first child and when she begins
On the other hand, Hunter said, his new results by no means exonerated all
Dr. Zahm agreed. "Even if we suspect one chemical and the evidence doesn't
bear it out, that doesn't negate the entire argument," she said.
In fact, said Dr. Wolff, who did the chemical analyses for Hunter's study,
it does not even negate the DDT and PCB argument.
"I think it's premature" to abandon the DDT and PCB hypothesis, Dr. Wolff
said. "It may be important in some groups of women and it may be not only how
high the levels are but the time of life in which they occur. Maybe it's even
different for different kinds of breast cancer, like premenopausal and
Julia Brody, the executive director of the Silent Spring Institute in
Newton, Mass., an advocacy group studying links between women's health and
the environment, said the new study was "definitely not the last chapter."
After all, Ms. Brody said, "this is a study of two chemicals out of
80,000," in the environment.
Safe said those who believed in the hypothesis would always want "another
study, another study."
"For advocates, it's never-ending," he said. "But for other people, there
may be times when we want to spend our money on other things."
The New England Journal of Medicine
Copyright 1997 The New York Times