Long-term Recreational Physical Activity and Risk of Invasive and In Situ Breast Cancer
The California Teachers Study
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Results: Invasive breast cancer risk was inversely associated with long-term strenuous activity (>5 vs 0.5 h/wk per year: relative risk, 0.80; 95% confidence interval, 0.69-0.94; P trend = .02), as was in situ breast cancer risk (>5 vs 0.5 h/wk per year: relative risk, 0.69; 95% confidence interval, 0.48-0.98; P trend = .04). Strenuous and moderate long-term activities were associated with reduced risk of ER-negative (strenuous: P trend = .003; moderate: P trend = .003) but not ER-positive (strenuous: P trend = .23; moderate: P trend = .53) invasive breast cancer.
Conclusion: These results support a protective role of strenuous long-term exercise activity against invasive and in situ breast cancer and suggest differing effects by hormone receptor status.