Physical activity and risk of testicular cancer: a systematic review

BACKGROUND: Physical activity has been implicated as a risk factor in the development of testicular cancer (TC), but the relationship remains controversial. This systematic review pooled available evidence regarding this association. METHODS: Using Boolean search terms and following PRISMA guidelines, we examined the risk of TC across three categories of exposure: intensity (i.e. comparison of risk between those previously exposed to high, moderate and low levels of physical activity); dose-response (i.e. whether risk of TC increases or decreases with increasing exposure to physical activity); and the role of timing of physical activity (i.e. during early childhood or adolescence). RESULTS: Thirteen studies (11 case-control studies, 2 cohort studies) were included in the review. While some studies have reported a strong protective effect of high levels of physical activity on risk of TC, others have reported either no relationship or a weak direct association; and while a dose-response relationship has been identified across several studies, this relationship has been observed in both directions. Similarly conflicting results exist in terms of individual types of activity and the lifecourse timing of the physical activity. Reasons for this inconsistency may include the absence of any association, heterogeneous assessment of physical activity, misclassification bias and difference in sample sizes. CONCLUSIONS: On balance, there is presently no strong evidence of an association between physical activity and risk of subsequent TC. This review highlights key areas for future investigation that may clarify any association between physical activity and risk of testicular cancer. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12885-018-4093-3) contains supplementary material, which is available to authorized users.