Environmental risks of breast cancer remain uncertain

Women may be able to reduce their risk of breast cancer by minimising exposure to environmental risk factors, but incomplete data and interactions with genetic susceptibility make it difficult to quantify the effect for individual women, concludes a new report from the US Institute of Medicine.

The 364 page review of the evidence was commissioned by the breast cancer charity Susan G Komen for the Cure and released on 7 December at the San Antonio Breast Cancer Symposium.

The strongest evidence for reducing environmental risks is for women to:

• Avoid inappropriate exposure to medical radiation

• Avoid combination menopausal hormone therapy unless it is medically appropriate

• End active smoking and exposure to secondhand smoke

• Limit or eliminate alcohol consumption

• Maintain or increase physical activity

• Maintain healthy weight or reduce overweight and obesity

• Limit or eliminate exposure to chemicals that are plausible contributors to breast cancer, and

• Consider use of chemoprevention if their risk of breast cancer is high.

The Institute of Medicine’s committee concluded, on the basis of animal or mechanistic data, that bisphenol A, found in some plastics, and some other chemicals were “plausible” hazards. The committee found no strong evidence that non-ionising radiation and personal use of hair dyes were associated with an increased risk of breast cancer.

The committee cautioned that there is little quantitative evidence to indicate what difference avoiding the known hazards will make.

“The breast undergoes substantial changes from the time it begins developing in the fetus through old age, especially in response to hormonal changes during puberty, pregnancy, lactation, and menopause,” the committee wrote.

“The timing of a variety of environmental exposures may be important in directly increasing or reducing breast cancer risks or in acting indirectly by influencing the developmental events. There may be critical windows of susceptibility (eg, periods of rapid cell proliferation or maturation) when specific mechanisms that increase the likelihood of a breast cancer developing may be more likely to come into play.”

Among its recommendations for future research are calls for integrated and transdisciplinary studies across the life course; a better understanding of the mechanisms of action of environmental risk factors; a focus on high risk individuals; and comparative effectiveness research on imaging procedures and diagnostics that takes the potential negative effects of those tools into account.

The American Cancer Society estimates that breast cancer will be diagnosed in 230 480 women and 2140 men in the US in 2011, while 39 520 women and 450 men are projected to die from the disease. The incidence of the cancer peaked in the US in 1999 and has fallen over the past decade.