Post-diagnosis weight change, body mass index, and breast cancer survival

B95

Weight change and body mass index following a breast cancer diagnosis have potential to impact survival. To explore this relation, we analyzed data from a cohort of 4,021 women who previously participated in consecutive population-based case-control studies of incident breast cancer in Wisconsin, Massachusetts, and New Hampshire. Initially, women age 20-79 with a diagnosis of invasive breast cancer during 1988-2001 were ascertained through the respective state registries. Case-control study participation involved completion of a structured telephone interview with information on height and weight, reproductive and menstrual factors, lifestyle characteristics, family and personal history of breast cancer, and demographics. In 1998-2001, all surviving cases of the original case-control studies were mailed a follow-up questionnaire that addressed post-diagnosis weight, weight gain, physical activity, diet, medication history, alternative therapies, and quality of life. Vital status information was obtained by linkage with the National Death Index through 2005. Hazard ratios (HR) and 95% confidence intervals (CI) were estimated from multivariate Cox proportional hazards models. All final statistical models were adjusted for age, state of enrollment, time from breast cancer diagnosis to completion of the follow-up questionnaire, family history of breast cancer, menopausal status, and stage of disease. To avoid the influence of disease on post-diagnosis body weight, women with metastatic disease at diagnosis were excluded from the analysis. After an average 5.8 years of follow-up, we identified 121 breast cancer deaths and 428 non-breast cancer deaths among the 4,021 breast cancer cases. For every 5 kg weight gain since breast cancer diagnosis, risk of death from breast cancer increased by 14% (HR=1.14; 95% CI: 1.04-1.26). We did not observe effect modification of the weight gain and breast cancer survival association according to age (P-interaction=0.4), menopausal status (P-interaction=0.4), or cigarette smoking (P-interaction=0.3). Risk of breast cancer death was more than twice as high among women classified as obese compared to those classified with normal body mass index (BMI) (HR=2.36; 95% 1.50-3.73 for post-diagnosis BMI >30 kg/m² versus 18.5-24.9 kg/m²). These findings suggest that efforts towards preventing post-diagnosis weight gain may positively affect breast cancer survival.