Andy, I posted the story just after noon today:
techstocks.com
Here's the NY Times version:
October 30, 1997
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 cancer.
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 a link.
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 menopause.
On the other hand, Hunter said, his new results by no means exonerated
all environmental chemicals.
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 postmenopausal."
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." |
