Estimation of breast cancer risk by women aged 40 and over: a population-based study.

Identify factors associated with knowledge of breast cancer and estimation of risk.Telephone survey of 412 women aged 40 and over, living in Montreal and selected by random digit dialing.The majority of the respondents had recently been exposed to some information on breast cancer, but only a third quoted the average lifetime probability estimate of about 1 in 10. Older individuals systematically considered themselves at low risk (odds ratio (OR) of perceiving risk as lower than average for women aged 50 or over versus under 50: 2.6, 95% confidence interval: (1.5, 4.6)). In addition, both a first-degree family history of breast cancer (OR: 5.3 (1.7, 17.0)) and a recent mammogram (OR: 3.0 (1.4, 6.2)) were strongly associated with a woman's probability of perceiving herself at high risk.Information campaigns should emphasize the frequency of breast cancer in different age groups and the strength of the established associations with specific risk factors. Better knowledge of risk could promote sustained participation in breast screening programs.