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 <20 years at first pregnancy (0.79 (0.72,0.86)); >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.