Risk factors for breast cancer mortality among the National Breast Screening Study of Canada participants.

We studied the relationship between risk factor information and breast cancer mortality by means of a case control study, nested within the population of the National Breast Screening Study of Canada (NBSS). The characteristics of women aged 40-59 years, identified at the initial screen, who subsequently died of breast cancer up to 7 years from the initial screen, were compared with those of controls drawn from the same population. Among the factors evaluated in this study, number of live births and presence of symptoms in the breast revealed on direct questioning were found to be significantly related to breast cancer mortality. The results suggest a decrease in risk of dying of breast cancer associated with one or more live births (OR: 0.79, 95% CI: 0.68, 0.93), and an increase in risk of dying of breast cancer associated with symptoms in the breast revealed on direct questioning at the initial screen (OR: 2.01, 95% CI: 1.20, 3.37).