P4-10-03: Association between BMI, Physical Activity and Breast Cancer Histologic Types.

Abstract

Abstract Background: Previous research indicates that certain breast cancer risk factor associations vary by histologic tumor type. However, most studies have been too small to examine risk factors for uncommon histologic types. We examined the association between body mass index (BMI), physical activity, and the relative risk of breast cancer histologic types in a large prospective cohort study to determine whether associations for these risk factors varied by histology. Methods: This analysis included women in the NIH-AARP Diet and Health Cohort Study who were 50 to 71 years old, postmenopausal at baseline, and not previously diagnosed with cancer (N=190,348). The study cohort was established in 1995–1996 when participants completed a baseline questionnaire regarding health and nutritional information. BMI (kg/m2) was calculated from self-reported height and weight. Daily routine physical activity at work or home was derived from a question asking women what best described their daily routine at work, or throughout the day if they did not work at a job. Choices were mostly sitting with little walking, sitting with a fair amount of walking, mostly standing or walking, light lifting or climbing stairs/hills, or heavy work/carrying heavy loads. Cancer diagnosis and histology were obtained from state cancer registries. This analysis includes participant follow-up through December 31, 2006. After a median 11.2 years of follow-up, 7,631 invasive breast cancers were diagnosed: 5,278 ductal, 831 lobular, 640 mixed ductal-lobular, 214 mucinous, 132 tubular, and 536 other types. Multivariable-adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using Cox proportional hazards regression. Results: Compared to women with a BMI of 18.5 to 24.9, obese women had increased risks of ductal (HR and 95% CI for BMI 30 to 34.9: 1.24, 1.14 — 1.36; BMI ≥ 35: 1.45, 1.30 — 1.62) and mucinous (HR and 95% CI for BMI 30 to 34.9: 1.58, 1.04 — 2.39; BMI ≥ 35: 1.93, 1.16 — 3.20) cancers. For both histologic types, the relative risk increased with increasing BMI (P-trend: ductal P<0.01; mucinous P<0.01). Women whose daily activity at work or home consisted of mostly standing or walking were at reduced risk of ductal and mixed ductal-lobular cancers compared with women who reported mostly sitting (HR and 95% CI for ductal: 0.86, 77 — 0.96; mixed-ductal lobular: 0.64, 0.48 — 0.86). Women who performed heavy work or carried heavy loads were also at a decreased risk of ductal and mixed ductal-lobular cancers compared with women reporting mostly sitting (HR and 95% CI for ductal: 0.68, 0.52−0.91; mixed ductal-lobular: 0.18, 0.04−0.72), though there were few mixed ductal-lobular cases who reported heavy activity. Conclusions: High BMI was associated with increased risk of ductal and mucinous breast cancers. Women who spent their daily routine activity mostly standing or walking or doing heavy work had a reduced risk of ductal and mixed ductal-lobular cancers. These differences suggest that associations of BMI and physical activity vary by breast cancer histologic type in postmenopausal women and may have different roles in the etiology of these cancers. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P4-10-03.