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Many risk factors for breast cancer are known, but each makes a relatively small contribution to individual risk. Nearly a dozen risk factors taken together accounted for only about 25% of total risk in a population of 570,000 women enrolled in the American Cancer Society's Cancer Prevention Study I (1959-66). This study was considered path-breaking in 1982. Nevertheless, breast cancer remains the leading cause of cancer in US women three decades later.
Seidman et al. (Wed,) studied this question.