Background: Consumption of a high-fat diet has been associated with poor survival in breast cancer patients. However, studies examining this association are limited and have not used adjustment of energy in their estimates. Purpose: The effect of usual diet before diagnosis of breast cancer on the risk of dying of breast cancer was examined in a cohort of women with breast cancer from the National Breast Screening Study (NBSS) in Canada. Methods: From a cohort of 89 835 women in the NBSS, a total of 1270 histologically confirmed cases of invasive carcinoma of the breast were identified by active follow-up, supplemented by passive follow-up involving record linkage to provincial cancer registries. Of these, 678 case patients who had completed a diet history and were diagnosed from January 1982 up to June 1992 formed the cohort for this investigation. Diet was ascertained from a self-administered diet-history questionnaire. Mortality data were obtained by linkage to the Canadian Mortality Data Base of Statistics Canada, provincial cancer registries, and annual follow-up of cases through physicians. Risk of dying and survival probabilities were estimated by the Cox proportional hazards method and the actuarial life-table method. Results: There were 83 deaths in this study cohort of 678 women; 76 deaths were due to breast cancer, and the remaining seven resulted from other causes. The 5-year survival rate was 90%. For every 5% increase in energy from saturated fat, the risk of dying of breast cancer increased by 50% (hazard ratio = 1.50; 95% confidence interval [CI]: 1.08-2.08). No significant increase in risk was seen with total fat intake (hazard ratio = 1.21; 95% CI = 0.91-1.61) or oleic acid intake (hazard ratio = 1.25; 95% CI = 0.90-1.74). There was a lower risk of dying of breast cancer in the highest quartiles of beta carotene intake (hazard ratio = 0.48; 95% CI = 0.23-0.99) and vitamin C intake (hazard ratio = 0.43; 95% CI: 0.21-0.86); both vitamins showed a significant dose-response relationship (P for trend, less than or equal to.05). These effects varied with menopausal status at diagnosis and tumor characteristics. Conclusions: These results suggest an increased risk of dying of breast cancer with higher intakes of saturated fat before diagnosis and slightly reduced risk with higher intakes of beta carotene and vitamin C. implications: More attention should be paid to premorbid dietary habits in relation to breast cancer prognosis. Further studies, however, need to be done with ascertainment of dietary changes prior to and subsequent to diagnosis.
