An exploration of the role of exercise in modulating breast cancer progression in vitro: a systematic review and meta-analysis

Background: Breast cancer is the most prevalent cancer in women worldwide. In the UK, approximately 5% of all breast cancers are already metastatic at the time of diagnosis. An abundance of literature shows exercise can have beneficial effects on the outcome and prognosis of breast cancer patients, yet the molecular mechanisms remain poorly understood. There are several in vitro models that aim to recapitulate the response of breast cancer to exercise in vivo: this systematic review and meta-analysis summarises the existing literature. Methods: The following search terms were used to conduct a systematic literature search using a collection of databases (last search performed May 2020): 'in vitro' and 'exercise' and 'breast cancer'. Only studies that investigated the effects of exercise on breast cancer in vitro were included. Standardised mean differences (SMD) were calculated to determine pooled effect sizes. Results: This meta-analysis has successfully demonstrated that various identified exercise interventions on breast cancer cells in vitro significantly reduced breast cancer cell viability, proliferation, and tumourigenic potential (SMD: -1.76, p = 0.004, SMD: -2.85, p = 0.003 and SMD: -3.15, p = 0.0008, respectively). A clear direction of effect was found with exercise on breast cancer cell migration in vitro, however this effect was not significant (SMD: -0.62, p = 0.317). Conclusion: To our knowledge, this is the first meta-analysis and systematic review investigating and summarising literature on exercise and breast cancer in vitro, highlighting models used and priority areas for future research focus.