Physical activity and breast cancer risk by pathological subtype.

Abstract Objective To examine the influence of physical activity on breast cancer risk and evaluate whether adherence to international recommendations is associated with a decreased risk. Methods This is a multicenter matched case-control study where 698 pairs completed a physical activity questionnaire. Recreational physical activity during the last year was quantified in metabolic equivalent hours per week (MET-h/week) and categorized in activities of moderate (3.0–5.9 MET) and vigorous (>6 MET) intensity. The adherence to World Cancer Research Fund and the American Institute for Cancer Research recommendation was also assessed. The association with breast cancer risk, overall and by pathologic subtype, was evaluated using conditional and multinomial logistic regression models. Results Mean MET-h/week was 16.6 among cases and 20.4 among controls. Premenopausal breast cancer risk decreased by 5% ( P =0.007) for every 6 MET-h/week increase in energy expenditure. By contrast, postmenopausal women needed to do more intense exercise to observe benefits. The protection was more pronounced for nulliparous women, as well as for hormone receptor positive and HER2+ tumors. Physically inactive women displayed a 71% increased risk when compared with those who met the international recommendation ( P =0.001). Finally, women who were inactive during the previous year, regardless of the overall physical activity reported in previous periods, showed an increased risk when compared to always active women. Conclusions Women who report adherence to international physical activity recommendations entail a significant decrease in risk for all pathologic breast cancer subtypes. This is of particular interest in Spain, where a significant increase in overweight and obesity in recent decades is observed.