Physical activity during adolescence and young adulthood and the risk of breast cancer in BRCA1 and BRCA2 mutation carriers

Background: Physical activity is inversely associated with the risk of breast cancer among women in the general population. It is not clear whether or not physical activity is associated with the risk of BRCA-associated breast cancer. Methods: We conducted a case–control study of 443 matched pairs of BRCA mutation carriers to evaluate the association between physical activity and breast cancer risk. Moderate and vigorous physical activities at ages 12–13, ages 14–17, ages 18–22, ages 23–29 and ages 30–34 were determined using the Nurses’ Health Study II Physical Activity Questionnaire. We estimated mean metabolic equivalent task hours/week for moderate, vigorous and total physical activities overall (ages 12–34), during adolescence (ages 12–17) and during early adulthood (ages 18–34). Logistic regression analysis was used to estimate the odds ratios (OR) and 95% confidence intervals (CI) for total, moderate and strenuous recreational physical activities and breast cancer risk, by menopausal status. Results: Overall, there was no significant association between total physical activity and subsequent breast cancer risk (OR _{Q4 vs. Q1}  = 1.01, 95% CI 0.69–1.47; P-trend = 0.72). Moderate physical activity between ages 12–17 was associated with a 38% decreased risk of premenopausal breast cancer (OR _{Q4 vs. Q1}  = 0.62; 95% CI 0.40–0.96; P-trend = 0.01). We found no association between exercise and breast cancer diagnosed after menopause. Conclusions: These findings suggest that early-life physical activity is associated with a reduced risk of premenopausal breast cancer among BRCA mutation carriers. Impact: Future prospective analyses, complemented by mechanistic evidence, are warranted in this high-risk population.