Estimating the long-term probability of developing breast cancer.

Public awareness of breast cancer risk has increased during the 1980s, in part because of publicity highlighting recent increases in incidence rates and the occurrence of breast cancer in numerous public figures. This publicity, coupled with a trend toward increased patient participation in medical decision making, has led many women to seek information about their individual risks of developing breast cancer. Relative risk estimates for various individual risk factors are readily available from epidemiologic studies (7), but few authors have reported risks for combinations of factors. Even fewer have reported results in terms of the probability of disease occurrence, a form more easily interpretable by most patients. Geneticists have estimated the probability that a first-degree relative of a patient with breast cancer will also develop breast cancer (2,3). While a family history of breast cancer is a major risk factor, a recent genetic analysis of more than 200 families with bilateral breast cancer suggested the presence of important nongenetic risk factors as well (4), consistent with previous epidemiologic results. Obesity and the use of exogenous hormones are examples of modifiable factors that may affect lifetime breast cancer risk beyond an inherited predisposition.