Host characteristics, sun exposure, indoor tanning and risk of squamous cell carcinoma of the skin

Use of indoor tanning devices increases risk of cutaneous malignant melanoma, but the association with risk of squamous cell carcinoma (SCC) of the skin is unclear. Cohort studies of SCC risk are rare and we aimed to assess the association between SCC risk and host characteristics, sun exposure, and indoor tanning in a population-based cohort of Norwegian and Swedish women conjunctly with SCC incidence data from national cancer registries. Host characteristics and exposure to sun and indoor tanning devices before 50-years old were recorded by questionnaire at inclusion (30-50 years) in 1991/92. Multivariable relative risks (RRs) and 95% confidence intervals (CIs) were estimated by Poisson regression. During follow-up of 106,548 women through December 2009, SCC was diagnosed in 141 women. Skin sensitivity to acute sun exposure was the most important pigmentation characteristic (RR=2.73, 95% CI 1.47-5.05, for red with pain/red with pain and blisters versus brown). We found no consistent associations with sunburns and bathing vacations in the first five age decades, but a significant positive trend for bathing vacations summarized over ages 10-49 years (P-trend=0.02). We also found significantly increased risks of SCC following indoor tanning at age 40-49 years (RR=2.17, 95% CI 1.29-3.67, for1 time/month versus never) and indoor tanning summarized over ages 10-49 years (P-trend=0.001). RR for ever versus never use of indoor tanning over ages 10-49 years was 1.93 (95% CI 1.27-2.95). Propensity to burn was an important host characteristic, and bathing vacations and indoor tanning summarized over ages 10-49 years increased SCC risk. What's new? Indoor tanning devices are known to increase the risk of malignant melanoma, but their impact on the risk of squamous cell carcinoma (SCC) of the skin is unclear. In this large, population-based, prospective cohort study, the authors found that skin sensitivity to acute sun exposure was the most important host risk factor for SCC, and that the use of indoor tanning devices was indeed associated with an increased risk of SCC. They conclude that the use of indoor tanning devices should therefore be discouraged.