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 5 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 5 0.02). We also found significantly increased risks of SCC following indoor tanning at age 40-49 years (RR 5 2.17, 95% CI 1.29-3.67, for 1 time/month versus never) and indoor tanning summarized over ages 10-49 years (P trend 5 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.Cutaneous squamous cell carcinoma (SCC) incidence is increasing worldwide, but population incidence data are scarce in many countries due to registration practices.1 The national cancer registries in Norway and Sweden systematically collect non-melanoma skin cancer incidence (excluding basal cell carcinoma) of which about 95% are SCC.2 Nonmelanoma skin cancer was one of the most rapidly increasing malignant tumors in Sweden in the last decade, with an average annual increase of 4.7% in men and 6.7% in women.
3Norwegian female incidence rates were more than five times higher in 2006-2010 compared to 1956-1960 and the male rates were nearly five times higher. 4 Hair and eye color, the propensity to sunburn, and the ability to tan are generally accepted host risk factors for SCC, 5,6 but pigmentation is less studied as a risk factor for SCC than for cutaneous malignant melanoma (MM). Likewise, nevi count, an important risk factor for MM, has been studied in relation to SCC risk in a few studies but no consistent association has been found.
IJCMost previous studies on the effects of ultraviolet exposure on SCC risk used a case-control design, sometimes nested in a cohort, and more data from prospective studies are needed. 14,19 We have previously studied host characteristics, sun exposure and indoor tanning in a large populationbased cohort study in Scandinavia, and found consistent ...