PREMORBID DIET AND THE PROGNOSIS OF WOMEN WITH BREAST-CANCER

Background: Consumption of a high-fat diet has been associated with po or survival in breast cancer patients. However, studies examining this association are limited and have not used adjustment of energy in the ir estimates. Purpose: The effect of usual diet before diagnosis of br east cancer on the risk of dying of breast cancer was examined in a co hort of women with breast cancer from the National Breast Screening St udy (NBSS) in Canada. Methods: From a cohort of 89 835 women in the NB SS, a total of 1270 histologically confirmed cases of invasive carcino ma of the breast were identified by active follow-up, supplemented by passive follow-up involving record linkage to provincial cancer regist ries. Of these, 678 case patients who had completed a diet history and were diagnosed from January 1982 up to June 1992 formed the cohort fo r this investigation. Diet was ascertained from a self-administered di et-history questionnaire. Mortality data were obtained by linkage to t he Canadian Mortality Data Base of Statistics Canada, provincial cance r registries, and annual follow-up of cases through physicians. Risk o f dying and survival probabilities were estimated by the Cox proportio nal 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% (h azard ratio = 1.50; 95% confidence interval [CI]: 1.08-2.08). No signi ficant 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 relatio nship (P for trend, less than or equal to.05). These effects varied wi th menopausal status at diagnosis and tumor characteristics. Conclusio ns: These results suggest an increased risk of dying of breast cancer with higher intakes of saturated fat before diagnosis and slightly red uced risk with higher intakes of beta carotene and vitamin C. implicat ions: More attention should be paid to premorbid dietary habits in rel ation to breast cancer prognosis. Further studies, however, need to be done with ascertainment of dietary changes prior to and subsequent to diagnosis.