Domain-specific patterns of physical activity and risk of breast cancer sub-types in the MCC-Spain study.

Purpose: Literature on the separate effects of physical activities (PA) on risk of breast cancer (BC) sub-types is heterogeneous. We investigated domain-specific associations between PA and BC risk by menopausal status and molecular subtype.

Methods: 1389 histologically confirmed invasive BC cases and 1712 controls from the MCC-Spain study were included (age: 20-85 years). Questionnaire information on PA at work, at home, and during leisure time, including recreational PA and sedentary time, and data on reproductive history, anthropometry, family history of BC, diet, and lifestyles were obtained through face-to-face interviews. Information on the expression of oestrogen (ER), progesterone (PR), and HER2 receptors was available for > 95% of the cases. Mixed-effects multivariable logistic regression models were used to estimate odds ratios (OR) of BC sub-types.

Results: Occupational PA (OPA) intensity was associated with higher BC risk. Associations were stronger for pre-menopausal (OR 1.89; 95% confidence interval (CI) 1.22, 2.91) and ER+/PR+, HER2- tumours (OR 1.80; 95% CI 1.28, 2.53). Sedentary time was associated with higher risk of post-menopausal BC (OR 1.69; 95% CI 1.22, 2.32). Moderate-to-high-intensity household (HPA) and recreational PA (RPA) were inversely associated with BC occurrence in pre- and post-menopausal women, with estimated 14-33% lower risks (P for trend < 0.001) above 1000 MET·min/week.

Conclusions: Higher levels of HPA and RPA were associated with lower risk of BC, with heterogeneity by molecular type, whereas sitting time was a consistent independent risk factor of BC risk. The positive association found for OPA with ER+/PR+ BC deserves further investigation.