By DENISE GRADY
An exhaustive new report meant to address public fears
about possible links between breast cancer and the environment findsevidence strong enough to make only a few firm recommendations, most already well known and none with a large proven benefit.
The most consistent data suggest that women can reduce their risk by avoiding unnecessary medical radiation, forgoing hormone treatments for menopause that combine estrogen and progestin, limiting alcohol intake and minimizing weight gain, the report found. (Controlling weight appears helpful only in preventing postmenopausal breast cancers, not those in younger women.) Overuse of CT scans, which deliver a relatively high dose of radiation, was a particular concern, but the report stated that women should not be deterred from having routine mammograms, which use a much smaller dose.
The report, 364 pages long and two years in the making, was issued on Wednesday by the Institute of Medicine, an independent group that is part of the National Academy of Sciences and advises the government and public. The work was done by a committee of 15 outside experts, mostly from universities, and nine institute staff members. The sole sponsor was a breast cancer advocacy group, Susan G. Komen for the Cure, which requested the report and spent $1 million on it.
For women who were hoping for definitive safety information about the huge number of chemicals to which people are exposed — from air pollution and cosmetics to cleaning products, food and drinking water — the report may come as a disappointment. It is based largely on a review of existing research, and its limited advice reflects the lack of solid scientific information in many areas of concern to the public.
“In the last 20 years, the National Institutes of Health and private foundations have put a lot of money into trying to identify what are the risk factors for breast cancer,” said Irva Hertz-Picciotto, chairwoman of the expert committee and chief of environmental and occupational health at the University of California, Davis. “It’s a bit disappointing that so little has been learned with the amounts of money that have gone into it.”
The committee could not “identify a bunch of environmental factors” that might contribute to breast cancer, Dr. Hertz-Picciotto said.
The problem is difficult to study for a number of reasons. Suspect chemicals cannot ethically be given to people to see if they cause cancer. People exposed in the past can be studied, but information about the dose and timing may be sketchy. Animal studies can provide useful information, but do not always apply to humans. And people are often exposed to mixtures of chemicals that may interact in complex ways, with effects that may also vary depending on an individual’s genetic makeup.
Even for women who follow every bit of advice that the panel did offer, there are no guarantees. The report carefully states: “The potential risk reductions from any of these actions for any individual woman will vary and may be modest.”
The recommended choices may involve tradeoffs. Moderate drinking may help prevent heart disease, and women who give it up lose that benefit, the report acknowledged. Similarly, deciding whether a CT scan is really needed may not be so simple; a woman who turns down the test may forfeit important diagnostic information.
About 230,000 new cases of breast cancer, and about 40,000 deaths from the disease, are expected this year in the United States. In the next ten years, an estimated 24 of every 1,000 white women aged 50, or 2.4 percent, will be found to have breast cancer, compared to 2.2 percent of black women, 2 percent of Asian women and 1.7 percent of Hispanic women.
Additional recommendations in the report, based on somewhat weaker evidence than those regarding medical radiation and hormone treatments, include increasing exercise and avoiding smoking. The panel also found “possible associations” between breast cancer and secondhand smoke, nighttime shift work and exposures to the chemicals benzene, ethylene oxide and 1,3-butadiene, which are found in some workplaces, car exhaust, gasoline fumes and tobacco smoke.
A still lower level of evidence was “biological plausibility,” meaning that scientists can see a mechanism in animals by which certain substances might cause breast cancer, but that there is not enough information to assess the risk in humans. One such chemical is bisphenol A, or BPA, which is used in some plastic containers, can liners, food packaging and other products. It can mimic estrogen, which can feed the growth of some breast cancers.
Dr. Hertz-Piccioto said that women could try to avoid BPA, but must choose substitutes carefully to make sure they do not wind up exposed to something worse.
The scientists let hair dyes off the hook, at least so far: they found no evidence that personal use of hair dye increases risk. But they made no determination about possible risks to hairdressers, who may have regular, heavy exposure to the dyes. The report said more information was also needed about nail salon workers and consumers exposed to various manicure products, which contain multiple hazardous chemicals.
The panel said much more research was needed on the effects of various environmental exposures at different stages of life, because the vulnerability of breast tissue may vary during childhood, adolescence, adulthood, before and after pregnancy and even in the womb. Dr. Hertz-Picciotto said studies in women exposed to radiation during childhood found an increased risk of breast cancer and suggested that young girls may be particularly susceptible.
The scientists mapped out many other topics for further study, including the role night-shift work may play in breast cancer and the effects of chemicals that may act like hormones.
Elizabeth Thompson, president of Susan G. Komen for the Cure, said her organization was pleased with the report. She said her group had sought out the Institute of Medicine because its work is highly respected and rigorous, and her group wanted an unbiased report that stuck strictly to the science and did not go beyond the data.