Indoor tanning and the risk of developing non-cutaneous cancers: a systematic review and meta-analysis

Purpose Despite a strong association between indoor tanning and the risk of cutaneous cancers, the relationship between indoor tanning and non-cutaneous cancers is unknown. Our objective was to estimate the association of indoor tanning with developing non-cutaneous cancers. Methods We conducted a systematic literature review and meta-analysis of the association between indoor tanning and non-cutaneous cancer sites. Associations were estimated using random effects models. Heterogeneity was investigated through subgroup analyses and the Q -test and I 2 statistics. Results From 15 identified studies, 33 effect estimates for 12 cancer sites were included in the review. Adjustment for sun exposure was a significant source of heterogeneity in the association of indoor tanning and non-cutaneous cancer risk (meta-regression p = 0.0043). When restricting to studies that adjusted for solar ultraviolet radiation (7 studies and 19 effect estimates) a potential increased risk was observed among ever users of indoor tanning devices with the risk of hematologic malignancies (pooled relative risk = 1.11; 95% CI 0.96–1.28), with differing effects observed by hematologic types and subtypes of non-Hodgkin lymphoma. No association was observed among solid non-cutaneous cancers (pooled relative risk = 0.98; 95% CI 0.94–1.19). Neither study design nor geographical region was significant sources of heterogeneity in these associations. Conclusion When controlling for sun exposure, indoor tanning does not protect against solid non-cutaneous cancers and may increase the risk of some hematologic malignancies. Given the well-established relationship with skin cancer and potential relationship with hematologic malignancies, efforts to reduce the use of indoor tanning devices should continue.