Weight, weight gain, and survival after breast cancer diagnosis.

PURPOSE: To determine whether weight prior to diagnosis and weight gain after diagnosis are predictive of breast cancer survival.
METHODS: Patients included 5,204 Nurses' Health Study participants diagnosed with incident, invasive, nonmetastatic breast cancer between 1976 and 2000; 860 total deaths, 533 breast cancer deaths, and 681 recurrences (defined as secondary lung, brain, bone, or liver cancer, and death from breast cancer) accrued to 2002. We computed the change in body mass index (BMI) from before to the first BMI reported > or = 12 months after the date of diagnosis. Cox proportional hazards models were used to evaluate associations of categories of BMI before diagnosis and of BMI change with time to event. We stratified by smoking, menopausal status, and breast cancer-related variables.
RESULTS: In multivariate-adjusted analyses, weight before diagnosis was positively associated with breast cancer recurrence and death, but this was apparent only in never smokers. Similarly, among never-smoking women, those who gained between 0.5 and 2.0 kg/m(2) (median gain, 6.0 lb; relative risk [RR], 1.35; 95% CI, 0.93 to 1.95) or more than 2.0 kg/m(2) (median gain, 17.0 lb; RR, 1.64; 95% CI, 1.07 to 2.51) after diagnosis had an elevated risk of breast cancer death during follow-up (median, 9 years), compared with women who maintained their weight (test for linear trend, P = .03). Associations with weight were stronger in premenopausal than in postmenopausal women. Similar findings were noted for breast cancer recurrence and all-cause mortality.
CONCLUSION: Weight and weight gain were related to higher rates of breast cancer recurrence and mortality, but associations were most apparent in never-smoking women.