Effects of exercise-conditioned serum on cancer cell behaviour in vitro: a systematic review and meta-analysis

Abstract

BackgroundPhysical activity reduces cancer risk but the underlying mechanisms remain unclear. We meta-analysed the effects of acute exercise and exercise training on serum-stimulated cancer cell behaviours in vitro.MethodsSystematic searches of PubMed, Scopus and SPORTDiscus up to February 2021 revealed 8 studies reporting 61 effect sizes eligible for meta-analysis. Standardised mean differences (SMDs) between exercise-conditioned serum and resting serum were pooled using random-effects models.ResultsAcute exercise-conditioned serum significantly reduced cancer cell growth (SMD -1.31, 95% CI -1.77 to -0.86, p<0.0001) and colony formation (SMD -2.33, 95% CI -2.66 to -2.00, p<0.0001) in vitro. These growth-inhibitory effects were sustained at 1 to 4 h (growth: SMD -1.56, 95% CI -2.47 to -0.64, p=0.0008; colony formation: -2.57, 95% CI -3.05 to -2.09, p<0.0001) and 24 h post-exercise (growth: SMD -2.62, 95% CI -4.18 to -1.05, p<0.001; colony formation: SMD -2.80, 95% CI -3.42 to -2.18, p<0.0001). In contrast, exercise training-conditioned serum had no effect on cancer cell growth in vitro (SMD -0.14, 95% CI -0.47 to 0.19, p=0.41). ConclusionAcute exercise promotes transient serological changes that suppress cancer cell growth and clonogenicity in vitro. Repetitive exposure to these factors may play an important role in reducing cancer risk.