Breast cancer risk can be reduced through lifestyle changes

Molly A. Brewer, MD, talks to all of her patients about the importance of exercise and weight loss in preventing breast cancer and other cancers. Many patients, however, do not follow her recommendations to eat healthier and be more physically active.

"The hardest thing for someone to do is change their lifestyle. ... It's much easier to take a pill than to go out every morning and exercise," said Dr. Brewer, a gynecologist and oncologist in Farmington, Conn.

She hopes a new Institute of Medicine finding that life choices such as poor nutrition might be linked to the development of breast cancer will help persuade her patients to lead healthier lives.

"I will talk to patients about this" report, said Dr. Brewer, a professor in the division of gynecology oncology at the Carole and Ray Neag Comprehensive Cancer Center at the University of Connecticut Health Center. "I will tell them, 'It's been reinforced by the IOM that lifestyle changes probably are the most important prevention [against breast cancer] you can take.' "

On Dec. 7, the IOM issued a report that identifies environmental factors that might increase women's risk of developing breast cancer. The 15-member expert committee, which included environmental health scientists, epidemiologists, oncologists and toxicologists, defined "environmental" as all factors not directly inherited through DNA. Such factors include what a woman eats and drinks; physical, chemical and microbial agents she encounters; how much physical activity she engages in; and medical treatments she undergoes.

Susan G. Komen for the Cure, the world's largest breast cancer organization, commissioned the study. The IOM panel spent more than a year reviewing published literature on breast cancer and the environment and recommended areas where more research is needed.

Panel members found evidence that women might be able to reduce their risk of breast cancer by avoiding unnecessary medical radiation, menopausal hormone therapy and tobacco smoke; limiting alcohol consumption; maintaining a healthy weight; and exercising regularly.

"The potential risk reductions for any individual woman will vary and may be modest, but the impact of these actions could be important at a population level," the report said.

Studies indicate a possible, though less clear, link between cancer and exposure to the chemicals benzene, 1,3-butadiene and ethylene oxide, the IOM report said. Those chemicals commonly are found in gasoline fumes, vehicle exhaust and tobacco smoke.

Due to insufficient or contradictory evidence, the committee was unable to determine whether some environmental agents of public concern, such as bisphenol A and ingredients in cosmetics, alter women's risk of breast cancer.

The committee said BPA, which is widely used in plastic containers and food packaging, is a biologically plausible hazard. That means scientists can see a clear mechanism in animals by which the agent might cause breast cancer. But studies to assess the chemical's risk in humans are lacking or inadequate, the report said.

The panel said there is no evidence that personal use of hair dyes and nonionizing radiation emitted by mobile devices and other technologies increase women's risk.

"Women may choose to minimize their exposure to some chemicals, but the committee found the research inadequate to draw conclusions about the potential benefit of such actions," the IOM said.

Research challenges

Breast cancer is the second-most common cancer among U.S. women, after skin cancer, according to the Centers for Disease Control and Prevention.

In 2011, an estimated 288,130 new cases of breast cancer will be diagnosed among women, and 39,520 women are expected to die of the disease, the American Cancer Society said. Only lung cancer accounts for more cancer deaths in women.

Risk factors of developing breast cancer include a family history of the disease, old age, having no biological children or having a first child after age 30.

Though researchers have spent the past two decades trying to determine which environmental factors may influence breast cancer risk, limited progress has been made. Among the challenges is that many studies focus on women's exposure to environmental factors during adulthood and they do not assess exposure earlier in life.

Another issue is that the impact of many chemicals on developing breast cancer never has been studied in humans, because it would be unethical to intentionally expose women to potentially harmful substances, the IOM said. The committee said more needs to be learned about how to interpret animal studies so the findings can be relevant for humans.

The IOM panel recommends that researchers learn more about the biologic significance of the life stages at which environmental risk factors are encountered.

"I'm actually quite hopeful that the research we outlined will give us a path forward," said committee member Robert A. Hiatt, MD, PhD. He is professor and chair of the Dept. of Epidemiology and Biostatistics at the University of California, San Francisco. "Many of the [report's findings] will likely come up in discussion in clinical settings. ... Doctors need to be prepared to respond to these questions about [breast cancer risk factors] in an educated way. Hopefully, the report will provide them the information they need to respond to the questions accurately."