Physical activity before and after cancer diagnosis and mortality risk in three large prospective cohorts.

Purpose: Physical activity (PA) can improve cancer survival; however, whether the timing of PA differentially affects mortality risk is unclear. We evaluated the association between PA levels pre- and post-diagnosis and mortality risk in the Women's Health Study (WHS), Physicians' Health Study (PHS)-I, and PHS-II prospective cohorts.

Methods: We categorized PA pre- and post-diagnosis as active (WHS: ≥ 7.5 metabolic equivalent (MET)-h/week; PHS: vigorous PA ≥ 2-4 times/week) or inactive. We analyzed changes in pre- and post-diagnosis PA levels as four joint categories: (1) Inactive → Inactive, (2) Active → Inactive, (3) Inactive → Active, and (4) Active → Active, on mortality risk using multivariable Cox proportional hazards regression.

Results: We identified 10,541 participants with incident cancer and 3,696 deaths during follow-up. Compared to maintaining inactivity in both periods, remaining active pre- and post-diagnosis observed lower all-cause (Hazard Ratio [95% confidence interval]: WHS: 0.55 [0.47-0.64]; PHS-I: 0.77 [0.67-0.88]), cancer (WHS: 0.55 [0.45-0.67]; PHS-I: 0.75; [0.61-0.92]) and non-cancer/cardiovascular disease (CVD) mortality risks (WHS: 0.49 [0.38-0.65]). Similarly, becoming active post-diagnosis was associated with lower all-cause (WHS: 0.60 (0.48-0.75]; PHS-I: 0.72 [0.61-0.88]), cancer (WHS: 0.65 [0.49-0.86]; PHS-I: 0.64 [0.49-0.84]), and non-cancer/CVD mortality risk (WHS: 0.49 [0.33-0.75]). Being active pre- and post-diagnosis was associated with lower mortality risks in separate analyses, although significance differed by cohort and outcome.

Conclusions: Remaining active pre- and post-diagnosis and becoming active post-diagnosis may be associated with improvements in cancer survival, however, research is needed across diverse cancer populations.