Invasive and In‐Situ Squamous Cell Carcinoma of the Skin: A Nationwide Study in Iceland

BACKGROUND Squamous cell carcinoma (cSCC) incidence is increasing. OBJECTIVES To evaluate the tumor burden of in-situ and invasive cSCC in Iceland, whose population is exposed to limited UV radiation. METHODS This whole population study used the Icelandic Cancer Registry, which contains records of all in-situ and invasive cSCC cases from 1981-2017. cSCC incidence according to age, anatomic location, residence and multiplicity was evaluated, and trends assessed using joinpoint analysis. Age-standardized rates (WSR) and age-specific incidence rates per 100,000 were calculated, along with cumulative and lifetime-risks. RESULTS Between 1981 and 2017, in-situ cSCC WSR increased from 1.2 to 19.1 in men and from 2.0 to 22.3 for women. Invasive cSCC WSR rose from 4.6 to 14 in men, and from 0.3 to 13.2 in women. The average number of in-situ cSCC lesions per woman was 1.71, and 1.39 per man. Women developed more in-situ than invasive cSCC in almost all anatomical locations while men developed more invasive cSCCs, mostly on the head and neck. The rates of in-situ cSCC were higher in Reykjavik compared to rural areas. Women also developed multiple in-situ lesions more commonly. For lip cSCCs, invasive lesions occurred more frequently than in-situ lesions among both genders. Joinpoint analysis showed that cSCC in-situ in women exhibited the most rapid incidence increase. CONCLUSION cSCC has become an increasingly significant public health problem in Iceland. Tanning bed use and traveling abroad might contribute to skin cancer development. Public health efforts are needed to stem the behaviors leading to this rapid rise in cSCC.