Objective To synthesise the literature on indoor tanning and non-melanoma skin cancer.,Design Systematic review and meta-analysis.,Data sources PubMed (1966 to present), Embase (1974 to present), and Web of Science (1898 to present).,Study selection All articles that reported an original effect statistic for indoor tanning and non-melanoma skin cancer were included.,Articles that presented no data, such as review articles and editorials, were excluded, as were articles in languages other than English.,Data extraction Two investigators independently extracted data.,Random effects meta-analysis was used to summarise the relative risk of ever use versus never use of indoor tanning.,Dose-response effects and exposure to indoor tanning during early life were also examined.,The population attributable risk fraction for the United States population was calculated.,Results 12 studies with 9328 cases of non-melanoma skin cancer were included.,Among people who reported ever using indoor tanning compared with those who never used indoor tanning, the summary relative risk for squamous cell carcinoma was 1.67 (95% confidence interval 1.29 to 2.17) and that for basal cell carcinoma was 1.29 (1.08 to 1.53).,No significant heterogeneity existed between studies.,The population attributable risk fraction for the United States was estimated to be 8.2% for squamous cell carcinoma and 3.7% for basal cell carcinoma.,This corresponds to more than 170 000 cases of non-melanoma skin cancer each year attributable to indoor tanning.,On the basis of data from three studies, use of indoor tanning before age 25 was more strongly associated with both squamous cell carcinoma (relative risk 2.02, 0.70 to 5.86) and basal cell carcinoma (1.40, 1.29 to 1.52).,Conclusions Indoor tanning is associated with a significantly increased risk of both basal and squamous cell skin cancer.,The risk is higher with use in early life (<25 years).,This modifiable risk factor may account for hundreds of thousands of cases of non-melanoma skin cancer each year in the United States alone and many more worldwide.,These findings contribute to the growing body of evidence on the harms of indoor tanning and support public health campaigns and regulation to reduce exposure to this carcinogen.
Xeroderma pigmentosum (XP) is a rare, autosomal recessive disorder of DNA repair characterized by sun sensitivity and ultraviolet (UV) induced skin and mucous membrane cancers.,Described in 1874 by Moriz Kaposi in Vienna, nearly 100 years later James Cleaver in San Francisco reported defective DNA repair in XP cells.,This eventually provided the basis for a mechanistic link between sun exposure, DNA damage, somatic mutations and skin cancer.,XP cells were found to have defects in 7 of the proteins of the nucleotide excision repair pathway and in DNA polymerase eta.,XP cells are hypersensitive to killing by UV and XP cancers have characteristic “UV signature” mutations.,Clinical studies at NIH found a nearly 10,000-fold increase in skin cancer in XP patients under age 20 years demonstrating the substantial importance of DNA repair in cancer prevention in the general population.,About 25 % of XP patients have progressive neurological degeneration with progressive loss of neurons, probably from DNA damage induced by oxidative metabolism which kills non-dividing cells in the nervous system.,Interestingly, patients with another disorder, trichothiodystrophy have defects in some of the same genes as XP but they have primary developmental abnormalities without an increase in skin cancer.