Prevention of Breast Cancer

Approaches for the primary prevention of breast cancer according to period of life are discussed here briefly and are considered in more detail elsewhere. Although the major reasons for the high rates of breast cancer in affluent Western populations are largely known, this knowledge does not necessarily translate easily into strategies for breast cancer prevention.

Some risk factors (e.g., age at menarche) are well established but are difficult to modify; some (e.g., postmenopausal hormone use) are well established but have other important benefits; and others (e.g., replacement of saturated fat with monounsaturated fat) are unproven although suggested by available data and have other strong benefits that justify the strategy, with reduction in breast cancer being a possible additional benefit.

Also, known risk factors for breast cancer are modest in magnitude; relative risks are usually in the range of 1.3 to 1.8 for attainable changes. Although these relative risks are far less dramatic than those involving smoking and lung cancer, they should still be considered important. To provide perspective, the relative risk of death from breast cancer for women who do not have mammography compared with those who receive regular mammograms is approximately 1.3. Just as great emphasis and resources are given to the provision of mammography, the avoidance of a risk factor with a similar magnitude of effect should have even higher priority, because this prevents both the occurrence and need for treatment of breast cancer as well as death.

When considering primary prevention, one must remember that even small changes at the individual level can produce substantial changes in the population rates of disease.

Some strategies for prevention can be implemented by individuals themselves, but the health system, as well as governments and society as a whole, can take actions that strongly influence rates of breast cancer.

Early onset of menarche in the United States and other affluent countries is largely the result of rapid growth and weight gain of children related to an abundant food supply, excellent sanitation, and low levels of physical activity (including sitting in school). Much of this is desirable for many reasons, and no reasonable expectation exists that one could, or would, want to increase the average age at menarche to 17 years, as has been typical in rural China.

Yet generally desirable increases in physical activity, such as greater recreational activities, have been associated with modest delays in age at menarche and should thus contribute to reductions in breast cancer. The amount of time spent watching television is a major determinant of excessive weight gain by children and is therefore an appropriate focus for reducing risk of breast cancer and future cardiovascular disease. Society, through the provision of daily physical activity in schools and safe environmentsfor recreational activity, must play a major role in these efforts.