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

SIMPLE SUMMARY: Physical activity is known to reduce breast cancer risk and improve patient prognosis. However, the association between pre-diagnostic physical activity and the aggressiveness of breast cancer is unclear. Here, we assessed the effects of pre-diagnostic physical activity on breast cancer aggressiveness among breast cancer patients. Despite not improving overall survival, higher levels of pre-diagnostic physical activity contributed to less aggressive forms of breast tumours. These results underline the importance of physical activity in improving patient prognosis. ABSTRACT: 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.