Background: Body mass index (BMI) and physical activity and their relation to breast cancer-specific survival have not been well-studied in older survivors (≥65 years of age at diagnosis), despite their comprising nearly half of today’s 3.5 million breast cancer survivors. Additional data are needed to determine if specific guidelines for older survivors are warranted.

Objective: To examine the associations of pre- and post-diagnosis BMI and recreational physical activity with breast cancer-specific and all-cause mortality among women with non-metastatic breast cancer, overall and stratified by age 65 years at diagnosis.

Methods: In the Cancer Prevention Study-II Nutrition Cohort, 4,927 women diagnosed with breast cancer between 1992 and 2011 completed biennial surveys and were followed for cause-specific mortality. Pre-diagnosis exposures were assessed at the questionnaire completed ≥6 months before diagnosis, and post-diagnosis exposures were assessed at the first questionnaire completed ≥2 years after diagnosis to avoid capturing short-term changes due to treatment. BMI was computed as weight (kg) divided by height squared (m2). Physical activity was based on the summary MET-hours/week of recreational activity. Multivariable Cox proportional hazards models were used to calculate hazard ratios (HR) and 95% confidence intervals (CI).

Results: Over a mean follow-up time of 9.8 years after diagnosis, 1,394 deaths, including 452 from breast cancer, occurred. The median age at diagnosis was 70 years (77% ≥65 years). Compared with normal weight (BMI 18.5-<25 kg/m2), class II-III obesity (BMI ≥35 kg/m2) was associated with higher risk of breast cancer-specific mortality in pre-diagnosis (HR: 2.2; 95% CI: 1.5-3.2) and post-diagnosis analyses (HR: 1.6; 95% CI: 1.0, 2.5), although the association was limited to women ≥65 years of age at diagnosis. Pre-diagnosis but not post-diagnosis BMI was positively associated with all-cause mortality among both age groups (P-trend <0.0001). Pre-diagnosis physical activity was not associated with breast cancer-specific mortality overall or in either age group. There was a significant inverse trend for post-diagnosis physical activity and breast cancer-specific mortality overall (P-trend=0.03) and among women <65 years of age at diagnosis (P-trend=0.01) but not among women ≥65 years of age at diagnosis (P-trend=0.21). Pre- and post-diagnosis physical activity were significantly associated with reduced all-cause mortality in both age strata.

Conclusion: Our results suggest that pre- and post-diagnostic morbid obesity is associated with increased risk of death from breast cancer in older, but not younger, breast cancer survivors. Conversely, physical activity may reduce risk of breast cancer death in survivors <65 years of age at diagnosis. However, both were associated with overall longevity, regardless of age.

Citation Format: Maret L. Maliniak, Alpa V. Patel, Marjorie L. McCullough, Peter T. Campbell, Corinne R. Leach, Susan M. Gapstur, Mia M. Gaudet. Obesity, physical activity, and breast cancer survival among older breast cancer survivors in the CPS-II Nutrition Cohort [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3008. doi:10.1158/1538-7445.AM2017-3008