A new report by the Institute of Medicine found that some environmental exposures play a well-established role in raising breast cancer risk, while others -- such as certain chemicals -- have no impact at all, drawing its conclusions from previous research.
IOM researchers, who presented their findings at the San Antonio Breast Cancer Symposium, evaluated the impact of numerous environmental factors on the risk of developing breast cancer and found women could take a few preventive steps to possibly lower their risk. Women could, for example, avoid unnecessary medical tests that involve radiation, skip certain types of post-menopausal hormone replacement therapies, drink alcohol in moderation, exercise and maintain a healthy weight and not smoke.
Ionizing radiation from medical diagnostic tests, estrogen-progestin hormone replacement therapy and being overweight are well-established risk factors uncovered in previous studies, the authors found. For the purposes of their research, they determined environmental factors can be anything not determined by DNA.
But scientific evidence is less conclusive about other environmental factors, such as exposure to the chemicals benzene, 1,3-butadiene and ethylene oxide, found in such common substances as tobacco smoke and gasoline fumes.
"The epidemiologic evidence is more limited, contradictory or absent," they wrote. "Evidence from animal or mechanistic studies sometimes adds support to the epidemiologic evidence or suggests biologic plausibility when human evidence is lacking for a particular factor."
Studies on animals also suggest that chemicals such as bisphenol A (BPA) "suggest biological plausibility as a hazard," but findings from some other studies are contrdictory.
The researchers also found that hair dyes and ionizing radiation from cell phones and other devices did not impact a woman's risk for breast cancer.
Despite their findings, the authors said since exposure varies from woman to woman, so does potential risk. Since much of the data on some of these substances are inconclusive, and exposure does vary so widely, the breast cancer community needs to develop better ways to study the impact of some environmental factors, according to the report.
Experts said while the IOM findings aren't new, they helped highlight how difficult it can be to determine breast cancer risk, since so many factors may play a role. The report, they say, also serves as further evidence that for breast cancer, the environment plays a much bigger role than genetics.
"The report highlights the true complexities of the various risk factors for breast cancer, including our own genetic profiles, our risks of individual exposure to potential cancer-causing factors in the environment and other risk factors that we can and cannot reasonably control," said Robert J. Schneider, co-director of the Breast Cancer Research Program at NYU Langone Medical Center.
"The focus of much of the breast cancer research is on something other than the environment," said Dr. Stefan Gluck, professor of medicine at the University of Miami's Miller School of Medicine. "People are trying to find molecular pathways or individual genes, and environmemt plays a much bigger role."
Dr. Marc Lippman, deputy director of the University of Miami's Sylvester Cancer Center, said the majority of breast cancer risk is related to hormones.
s "Ninety percent of breast cancer risk is clearly related to differences in the hormone environments for women, either their own hormones or the hormones they take," he said. Exposure to hormones starts early in life at puberty, and adds up over time, he explained. Differences in risk can vary depending on the age of onset of puberty, for example.
Lippman said he didn't expect the findings to lead to any new recommendations for screening or treatment but said information about risk factors clearly linked to breast cancer, such as weight, have led him to encourage his patients to eat healthier diets and follow the other advice given in the report.
The authors hope their report leads research into a new direction, including a closer look at certain chemical exposures.
"[There is a need for] research on the etiology of breast cancer to do more to incorporate new understanding of breast development over the life course, recent advances in elucidating the molecular biology of tumorigenesis, and the challenges of assessing the potential impact of a multitude of low level chemical exposures."
Susan G. Komen for the Cure, the breast cancer advocacy group that funded the IOM research, said in a press release it hopes other agencies will join the research effort.
"We would like to issue a challenge to other agencies working in the environmental area to join with Susan G. Komen to create a fund to begin work on these very important initiatives," the group said.