Association between pre-diagnosis recreational physical activity and risk of breast cancer recurrence: the California Teachers Study

Purpose: Studies have reported inverse associations of pre-diagnosis recreational physical activity (RPA) level with all-cause and breast cancer (BCa)-specific mortality among BCa patients. However, the association between pre-diagnosis RPA level and BCa recurrence is unclear. We investigated the association between pre-diagnosis RPA level and risk of BCa recurrence in the California Teachers Study (CTS). Methods: Stage I–IIIb BCa survivors (n = 6,479) were followed with median of 7.4 years, and 474 BCa recurrence cases were identified. Long-term (from high school to age at baseline questionnaire, or, age 55 years, whichever was younger) and baseline (past 3 years reported at baseline questionnaire) pre-diagnosis RPA levels were converted to metabolic equivalent of task-hours per week (MET-hrs/wk). Multivariable Cox proportional hazards models estimated hazard ratios (HRs) and 95% confidence intervals (CIs) for risk of BCa recurrence overall and by estrogen receptor (ER)/progesterone receptor (PR) status. Results: Long-term RPA was not associated with BCa recurrence risk (p_trend = 0.99). The inverse association between baseline pre-diagnosis RPA level and BCa recurrence risk was marginally significant (≥26.0 vs. <3.4 MET-hrs/wk: HR = 0.79, 95% CI = 0.60–1.03; p_trend = 0.07). However, the association became non-significant after adjusting for post-diagnosis RPA (p_trend = 0.65). An inverse association between baseline pre-diagnosis RPA level and BCa recurrence risk was observed in ER−PR− cases (≥26.0 vs. <3.4 MET-hrs/wk: HR = 0.31, 95% CI = 0.13–0.72; p_trend = 0.04), but not in ER+ or PR+ cases (p_trend = 0.97). Conclusions: Our data indicates that the benefit of baseline RPA on BCa recurrence may differ by tumor characteristics. This information may be particularly important for populations at higher risk of ER−PR− BCa.