Associations between Pre-Diagnostic Physical Activity with Breast Cancer Characteristics and Survival.

Physical activity (PA) is known to reduce breast cancer (BC) risk and improve patient prognosis. However, the association between pre-diagnostic PA and the aggressiveness of BC is unclear. We investigated the associations between PA, BC tumour characteristics, and survival. This retrospective observational study included 7688 BC patients from the Singapore Breast Cancer Cohort (2010-2016). PA information from the questionnaire included intensity (light/moderate/vigorous) and duration (<1 h/1-2 h/>2 h per week). A PA score (1-5) incorporating intensity and duration was calculated. Associations between PA score and tumour characteristics such as stage, histological grade, nodal and hormone receptor status were examined using multinomial regression. Moreover, 10-year overall survival was estimated using Cox regression analysis in 6572 patients after excluding patients with invalid survival data and stage IV disease. Breast tumours associated with higher PA score were more likely to be non-invasive (OR invasive   vs.   non-invasive(reference) [95% CI]: 0.71 [0.58-0.87], p -trend = 0.001), of lower grade (OR poorly   vs.   well differentiated(reference) : 0.69 [0.52-0.93], p = 0.014), ER-positive (OR ER-negative   vs.   ER-positive(reference) : 0.94 [0.89-1.00], p -trend = 0.049), PR-positive (OR PR-negative   vs.   PR-positive(reference) : 0.82 [0.67-0.99], p = 0.041), HER2-negative (OR HER2-negative   vs.   HER2-positive(reference) : 1.29 [1.02-1.62], p -trend = 0.002), and less likely to be of HER2-overexpressed subtype (OR HER2-overexpressed   vs.   Luminal A(reference) : 0.89 [0.81-0.98], p -trend = 0.018). These associations (odds ratios) were more pronounced among post-menopausal patients. A higher PA score did not improve survival. Higher levels of pre-diagnostic PA were associated with less aggressive tumours in BC patients. This illustrated another benefit of PA in addition to its known role in BC risk reduction.