Some Steps Are Proven, Others May Be Recommended but Still Need Research
By Rita Rubin
WebMD Health News
Reviewed by Laura J. Martin, MD
Dec. 7, 2011 -- Women can reduce their risk of breast cancer by not taking combination estrogen/progestin hormone therapy, not smoking, minimizing their exposure to radiation during CT scans and the like, avoiding weight gain after menopause, cutting back on alcohol, and staying active, a new report says.
"The potential risk reductions from any of these actions for any individual woman will vary and may be modest," according to a brief summary of the nearly 400-page Institute of Medicine report, presented at the San Antonio Breast Cancer Symposium. "Because much of the evidence on breast cancer risk factors has come from studies of postmenopausal breast cancer in white women, it is hard to judge the potential benefit for younger women or women of other races."
The report, requested by Susan G. Komen for the Cure, examines what's known about the link between breast cancer and any factors other than those directly inherited through genes, which it refers to as "environmental factors."
"Such factors include how a woman grows and develops during her lifetime; what she eats and drinks; the physical, chemical, and microbial agents she encounters; how much physical activity she engages in; medical treatments and interventions she undergoes; and social and cultural practices that she experiences," according to the summary brief.
The Institute of Medicine (IOM), part of the National Academies, provides independent advice to policy makers, the private sector, and the public.
Much Left to Learn
More than 230,000 U.S. women are expected to be diagnosed with breast cancer this year. Despite decades of research costing millions of dollars, much about how environmental factors contribute to breast cancer risk remains unknown, Irva Hertz-Picciotto, PhD, chair of the IOM's Committee on Breast Cancer and the Environment, said at a news conference.
"The evidence is less than persuasive but suggests a possible association with increased risk" for such factors as secondhand smoke, nighttime shift work, and exposure to such chemicals as benzene and ethylene oxide, chemicals found in some vehicle and workplace fumes and tobacco smoke, according to the committee.
Animal studies have shown that that some environmental agents, such as the chemical bisphenol A (BPA) -- widely used in plastic containers -- are at least biologically plausible risk factors, but studies in humans are lacking, the panelists say.
Ideal Study Hard to Do
Part of the problem is that environmental exposures begin in the womb and continue throughout life, so tracking them is virtually impossible, committee member Robert Hiatt says.
The ideal study would follow individuals for that entire span, he says, but that would be prohibitively expensive and time-consuming.
"The breast undergoes substantial changes over a woman's lifetime," the committee members note. "Future research should emphasize a 'life course' model."
Testing of chemicals in animals often occurs too late in their life span to provide clues about the impact of early exposures in humans, says panel member David Eaton, PhD, professor of environmental and occupational health sciences at the University of Washington.
"Also," says Hertz-Picciotto, professor of public health sciences at the UC Davis Health System, "we need to consider possible combined effects of many low-level exposures."
Still, Hiatt says, "I actually think the time is very exciting for getting some place in this area."
For example, he says, some studies are now looking at what determines the age at which girls enter puberty. Previous research has shown that the earlier the onset of puberty, the greater the breast cancer risk in adulthood.
And sophisticated molecular approaches can now uncover "fingerprints" left behind by exposures long ago, says Cheryl Lyn Walker, PhD, director of the Institute of Biosciences and Technology at the Texas A&M Health Science Center.
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