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One of the most dramatic features of breast cancer is the disparity in incidence rates between highly westernized and nonwesternized countries. Women born and raised in the United States are at least five times as likely to get breast cancer as women born and raised in Japan. But Japanese women increase their risk if they live in rapidly westernizing Japanese cities or emigrate and live in the United States. As is true with coronary heart disease, differences in diet are thought to be a major underlying factor in the different incidence rates of breast cancer, particularly among postmenopausal women.
Breast cancer is believed to take 3 to 30 years to develop. During this time there are at least three opportunities to interrupt its natural history. The first and most generalizable opportunity is to prevent or limit cancer-causing exposures that would trigger the self-perpetuating replication of damaged breast cells. The second opportunity is to reverse, or at least contain, the growth of cells that have not yet reached a diagnosable precancerous state. The third opportunity is to remove or kill recognizable precancerous or very early cancerous lesions before they cause clinical symptoms.
For the first time in history, healthy women in the United States and several other countries have the opportunity to participate in trials designed to test the success of preventive interventions targeted at each of these three stages in the natural history of breast cancer.
The Women's Health Initiative (WHI), scheduled to enroll the first of its participants in 1993, will test the hypothesis that 10 years of a diet that is very low in fat and high in fruits and vegetables will lower breast cancer incidence in postmenopausal women. The WHI will also investigate whether postmenopausal replacement hormones prevent coronary heart disease and osteoporotic fractures, and it will help to clarify the...