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Trial Lecture – time and place
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- First opponent: Professor Margaret Karagas, Center for Molecular Epidemiology, Geisel School of Medicine at Dartmouth
- Second opponent: Assistant Professor Sven Sandin, Karolinska Institutet
- Third member and chair of the evaluation committee: Professor Tone K. Omsland, University of Oslo
Chair of the Defence
Professor Nanna Lien, Faculty of Medicine, University of Oslo
Professor Marit B. Veierød, Faculty of Medicine, University of Oslo
Cutaneous squamous cell carcinoma (cSCC) is a common skin cancer and one of the most common types of cancers worldwide, with an incidence that continues to increase in fair-skinned populations.
While cumulative exposure to ultraviolet radiation (UVR) is considered the main environmental cause of cSCC, there is only limited evidence on the relationship between indoor tanning, sunscreen use, sunburns and cSCC risk.
In this thesis, we used data from the Norwegian Women and Cancer (NOWAC) study, to answer important questions on UVR exposure, sunscreen and cSCC risk, by using contemporary epidemiological methods.
We found evidence of a clear dose-response relationship between indoor tanning and cSCC risk, regardless of duration of use or age at initiation. Furthermore, we could not find evidence that sunscreens with higher sun protection factor (SPF) reduced Norwegian women’s cSCC risk more than sunscreens with lower SPF. These results suggest that either there is no difference in their effect long-term, or that the effect is diluted by incorrect application. Finally, by following lifetime patterns of sunburns, we found that high sunburn frequencies throughout life and in particular high exposure in childhood increase skin cancer risk.
Based on this thesis, we conclude that indoor tanning devices should be avoided. Furthermore, the importance of proper use of sunscreen should be emphasized; sunscreen is only a third-line defense after other sun protective measures. Finally, sunburns should be avoided throughout life, in particular in childhood.
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