Influence of aetiological factors for breast cancer on outcome after diagnosis

Abstract

762 Background: Risk factors which influence the incidence of breast cancer may also affect survival after diagnosis. Methods: We studied the prognostic effects of reproductive history, height, weight, body mass index (BMI), smoking history, alcohol intake and prior use of the combined oral contraceptive pill (COC) and hormonal replacement therapy (HRT) in 4816 women who had taken part in the population-based SEARCH-breast cancer study. Hazard ratios (HRs) for death (all causes) were estimated using Cox proportional hazards survival model for each risk factor. Multivariate analysis was performed adjusting for grade, stage and age at diagnosis. Results: Median follow up was 5.27 years. On univariate analysis, reproductive history, age at menarche and menopause, menopause status at diagnosis, smoking history, prior use of HRT and COC were not seen to influence prognosis. Tumour grade and stage had a highly significant impact on overall survival (p<0.0001). Increasing height and decreasing weight were associated with a decreased risk of death. BMI was associated with a HR for death of 1.03 (95%CI 1.02–1.05; p=0.0002) per unit increase. Women who were in the highest quartile of BMI were 1.6 times more likely to die (95%CI 1.2–2.0) than those in the lowest quartile. Improved prognosis was seen with increasing current alcohol consumption. The HR for death was 0.98 per unit alcohol consumed per week (95%CI 0.96–0.99; p=0.0043); intake of 14 or more units was associated with a HR of 0.69 (95%CI 0.49–0.96). Previous alcohol intake did not significantly affect outcome. The effects of BMI and current alcohol consumption were not attenuated after adjusting for grade and stage. However, the effect of alcohol intake was marginally significant at the 5% level after adjusting for multiple comparisons. Conclusions: Our finding that an increase in BMI is associated with a negative impact on survival supports previously published data. The apparent benefit of alcohol intake has not been described before. Other studies have either shown no effect or poorer outcome in heavy drinkers. Our findings are preliminary and may simply be due to chance or confounding; or may reflect a true biological effect. Further work is needed to clarify these alternatives. No significant financial relationships to disclose.