Age at first indoor tanning use and melanoma risk: a prospective, population-based cohort study

Ghiasvand REZA, University of Oslo, Norway

1 Oslo Centre for Biostatistics and Epidemiology, Institute of Basic Medical Sciences, University of Oslo, Norway
2 Department of Community Medicine, Faculty of Health Sciences, University of Tromsų, The Arctic University of Norway, Tromsų, Norway
3 Department of Research, Cancer Registry of Norway, Oslo, Norway
4 Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden
5 Genetic Epidemiology Group, Folkhälsan Research Center, Helsinki, Finland
6 Cancer and Population Studies Group, QIMR Berghofer Medical Research Institute, Australia
7 CRUK Manchester Institute, University of Manchester, United Kingdom

Purpose: We assessed melanoma risk and age at melanoma diagnosis in relation to age at initiation of indoor tanning.
Methods: We used data from the Norwegian Women and Cancer study, a large, prospective, population-based cohort study established in 1991. Host characteristics and history of UV exposure (sunburns, sunbathing, and indoor tanning) were recorded by questionnaire at inclusion and updated with follow-up questionnaires every 4-6 years. Multivariable relative risks (RRs) and 95% confidence intervals (CIs) were estimated by Poison regression. Multivariable linear regression analysis was used to study age at diagnosis in relation to age at initiation of indoor tanning. Models were adjusted for birth-cohort, year at inclusion, ambient UV of residence, hair colour, skin colour, cumulative sunburns, and sunbathing.
Results: During follow-up of 141 045 women through December 2012 (mean follow-up 13.7 years), 861 incident melanoma were diagnosed. We found an increased risk of melanoma for women with age at initiation <30 years compared to never-users (adjusted RR=1.34, CI 1.05-1.66). Moreover, a significant interaction between cumulative exposure of indoor tanning and age at initiation was found (PInteraction=0.01), with a higher risk of melanoma among women initiating <30 years than those initiating ≥30 years. Compared to never-users of indoor tanning, mean age at diagnosis was 2.15 years (CI 0.87-3.37) lower among women with age at initiation<30 years and 1.18 year (CI 0.21-2.07) lower among women with initiation at ≥30 years of age.
Conclusions: This study provides strong support for the declaration by the IARC that indoor tanning increases melanoma risk with greater increase in risk among women starting indoor tanning before age 30 years. Furthermore, indoor tanning leads to melanoma at a younger age.
Funding sources: The Norwegian Extra Foundation for Health and Rehabilitation through Extra funds and the Norwegian Cancer Society.