Breast cancer risk factors and survival by tumor subtype: pooled analyses from the Breast Cancer Association Consortium.

BACKGROUND It is not known if modifiable lifestyle factors that predict survival after invasive breast cancer differ by subtype. METHODS We analyzed data for 121,435 women diagnosed with breast cancer from 67 studies in the Breast Cancer Association Consortium with 16,890 deaths (8,554 breast cancer-specific) over 10 years. Cox regression was used to estimate associations between risk factors and 10-year all-cause mortality and breast cancer-specific mortality overall, by estrogen receptor (ER) status, and by intrinsic-like subtype. RESULTS There was no evidence of heterogeneous associations between risk factors and mortality by subtype (adjusted p>0.30). The strongest associations were between all-cause mortality and BMI {greater than or equal to}30 vs 18.5-25 kg/m2 (HR (95%CI): 1.19 (1.06,1.34)); current vs never smoking (1.37 (1.27,1.47)), high vs low physical activity (0.43 (0.21,0.86)), age {greater than or equal to}30 years vs 0 to <5 years vs {greater than or equal to}10 years since last full term birth (1.31 (1.11,1.55)); ever vs never use of oral contraceptives (0.91 (0.87,0.96)); ever vs never use of menopausal hormone therapy, including current estrogen-progestin therapy (0.61 (0.54,0.69)). Similar associations with breast cancer mortality were weaker; e.g. 1.11 (1.02,1.21) for current vs never smoking. CONCLUSIONS We confirm associations between modifiable lifestyle factors and 10-year all-cause mortality. There was no strong evidence that associations differed by ER status or intrinsic-like subtype. IMPACT Given the large dataset and lack of evidence that associations between modifiable risk factors and 10-year mortality differed by subtype, these associations could be cautiously used in prognostication models to inform patient-centered care.