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.