Robert Hiatt (UCSFB Site Director) Health News
Expert Panel Pinpoints Environmental Culprits in Breast Cancer
Unneeded radiation, hormone therapy, alcohol raise risk but hair dye, cellphones appear safe, report says
Women can lower their risk of developing breast cancer by avoiding unnecessary medical radiation, forgoing menopausal hormone therapy and limiting alcohol use, but they don't need to worry about using hair dyes or cellphones, a broad new national report says.
Reviewing the body of research on environmental factors that may affect breast cancer risk, the nonprofit, independent Institute of Medicine (IOM) also said that the scientific jury is still out on whether exposure to some chemicals -- including bisphenol A (BPA), pesticides and ingredients in cosmetics and dietary supplements -- alter women's odds of the disease.
"There's been so much concern about the environment, and I think the report is a comprehensive look at what we really know, based on human evidence," said Dr. Robert Hiatt, a member of the 15-member IOM committee that compiled the 364-page analysis.
"It does a number of things: identifies elements of the environment we think are important in breast cancer causation, tells researchers and public health people what we can do to move forward on the issue, and provides opportunities for individual women to modify their lifestyle or behavior to diminish the impact," added Hiatt, also a professor and chair of epidemiology and biostatistics at the University of California, San Francisco.
The report, funded by Susan G. Komen for the Cure, was unveiled Wednesday at the San Antonio Breast Cancer Symposium.
The committee, interpreting "environment" to include all factors not inherited through DNA, noted that many breast cancer risk factors can't be modified, including age, family history, and age at first menstruation and menopause. Another barrier is that breast cancer research cannot center on the strongest types of studies -- randomized controlled clinical trials -- because of the ethical challenges of intentionally exposing women to potentially harmful substances.
Of the environmental factors reviewed, those with the most consistent evidence of a link to higher breast cancer risk are:
· Use of hormone therapy combining estrogen and progestin.
· Exposure to ionizing radiation, which occurs during diagnostic tests such as CT scans.
· Excess weight among postmenopausal women.
· Alcohol consumption.
"Obviously some risk factors are outside of our influence, but some are under our control," said Dr. Iuliana Shapira, director of the cancer genetics service at Monter Cancer Center in Lake Success, N.Y. "The more CT scans we have, the more likely we are to get cancer. This is a wake-up call."
The connection between smoking and breast cancer is more nebulous, the report said, because of mixed evidence. For several other factors -- including secondhand smoke exposure, nighttime shift work and exposure to the workplace chemicals benzene, ethylene oxide or 1,3-butadiene -- the evidence is less persuasive but suggests a possible link to higher risks.
A breast cancer association with bisphenol A (BPA), which is widely used in plastic containers and food packaging, is biologically plausible, the committee said, but research assessing the risk in humans is lacking. The same is true of pesticides and ingredients in cosmetics and dietary supplements, most of which aren't tested before going to market.
However, research doesn't support a link between the use of hair dyes and non-ionizing radiation -- which is emitted from electronic devices such as cellphones and microwaves -- and breast cancer, the study said.
"I'm impressed that they have taken certain positions that may have not actually been supported by public awareness or understanding, such as cigarette smoking or hair dyes," said Robert Schneider, co-director of the Breast Cancer Research Program and associate director of translational cancer research at NYU Langone Medical Center, in New York City. "In public, there's a widespread view that these are all related to breast cancer. I think the report did an excellent job demystifying what the risks are."
Advocating a "life-course approach," the report called for future research to focus on the many stages of breast development, which begins in utero and undergoes substantial changes through puberty, pregnancy, breast-feeding and menopause. Most research has concentrated on the several years before women develop breast cancer, but environmental exposures during their other life stages may have a profound influence on chances of developing the malignancy, which is diagnosed in about 230,000 American women each year.
"The most interesting thing the committee does a little differently, and is certainly useful, is explicitly recommending that we have to think about a life-course approach and the difficulties that come with that," said IOM committee member Dr. David Hunter, dean for academic affairs and a professor of cancer prevention at Harvard School of Public Health. "We're really calling for attention to developing methods that would give us information about exposures that would have happened in the distant past . . . and inevitably, that's going to take quite some time to develop and to come up with newer information. We don't really say we have the answers here, but we're calling on people to be more creative and look harder."
Along with the report, the committee released a brochure offering women information gleaned from the review in a simple question-and-answer format, which Dr. Stephanie Bernik said will help increase public understanding of the environmental issues surrounding breast cancer.
"They're putting it together in a way that's easy for women to access and understand," said Bernik, chief of surgical oncology at Lenox Hill Hospital in New York City. "I think a lot of women want to understand what they can do, and this is something physicians can easily give to their patients."