Obesity, physical activity, and breast cancer survival among older breast cancer survivors in the Cancer Prevention Study-II Nutrition Cohort

Abstract

Purpose: Nearly half of the 3.5 million female breast cancer survivors in the US are aged 65 years or older at diagnosis, yet little is known about associations of obesity and physical activity with breast cancer-specific mortality (BCSM) among older survivors.

Methods: Between 1992 and 2013, 5254 women in the Cancer Prevention Study-II Nutrition Cohort were diagnosed with local or regional breast cancer among whom 1771 deaths (505 breast cancer deaths) occurred. Multivariable Cox proportional hazards regression models were used to examine associations of pre- and post-diagnosis body mass index (BMI) and moderate-vigorous physical activity (MET-hours/week) with mortality outcomes stratified by age at diagnosis (<65, ≥65 years).

Results: Among women ≥65 years of age at diagnosis (n = 4226), pre- and post-diagnosis BMI (per 5 kg/m²) were associated with a higher risk of BCSM (pre-diagnosis, HR 1.27, 95% CI 1.14-1.41; post-diagnosis, HR 1.19, 95% CI 1.04, 1.36); neither pre- nor post-diagnosis physical activity was associated with BCSM. Among women <65 years of age at diagnosis (n = 1028), BMI at both time points were not significantly associated with BCSM; however, there was a significant inverse trend of post-diagnosis physical activity with BCSM (P-trend = 0.01). Among both age groups, BMI and physical activity, regardless of when assessed, were significantly associated with all-cause mortality.

Conclusions: Higher BMI, pre- or post-diagnosis, was associated with a higher risk of BCSM in older patients, independent of comorbidities and stage at diagnosis. Weight management should be discussed even with women aged 65 years or older to lower rates of BCSM.

Keywords: Aged; Breast cancer; Obesity; Older survivors; Physical activity; Survival.