Invasive and in situ squamous cell carcinoma of the skin: a nationwide study in Iceland

Summary Background The worldwide incidence of cutaneous squamous cell carcinoma (cSCC) is increasing. Objectives To evaluate the tumour burden of in situ and invasive cSCC in Iceland, where the population is exposed to limited ultraviolet radiation. Methods This whole‐population study used the Icelandic Cancer Registry, which contains records of all in situ and invasive cSCC cases from 1981 to 2017. Incidence of cSCC was evaluated according to age, anatomical location, residence and multiplicity, and trends were assessed using joinpoint analysis. Age‐standardized rates (WSR) and age‐specific incidence rates per 100 000 person‐years were calculated, along with cumulative and lifetime risks. Results Between 1981 and 2017, in situ cSCC WSR increased from 1·2 to 19·1 for men and from 2·0 to 22·3 for women. Invasive cSCC WSR rose from 4·6 to 14 for men and from 0·3 to 13·2 for women. The average number of in situ cSCC lesions was 1·71 per woman and 1·39 per man. Women developed more in situ cSCCs than invasive cSCCs in almost all anatomical locations, whereas men developed more invasive cSCCs, mostly on the head and neck. The rates of in situ cSCC were higher in Reykjavik compared with rural areas. Furthermore, women more commonly developed multiple in situ lesions. For lip cSCCs, invasive lesions occurred more frequently than in situ lesions among both sexes. Joinpoint analysis showed that in situ cSCC in women exhibited the most rapid incidence increase. Conclusions cSCC has become an increasingly significant public health problem in Iceland. Tanning bed use and travelling abroad may contribute to skin cancer development. Public health efforts are needed to stem the behaviours leading to this rapid rise in cSCC. What is already known about this topic? Cutaneous squamous cell carcinoma (cSCC) incidence is on the rise worldwide, posing a significant public health threat, especially in light‐skinned populations. What does this study add? Icelandic women were more likely to develop in situ cSCC, and men were more likely to develop invasive cSCC of the head and neck. Women with in situ cSCCs were also at a higher risk of developing more than one cSCC compared with men. cSCC is becoming a significant public health problem in a country with low background ultraviolet radiation. This finding may be due, in part, to increased tanning bed exposure and travel abroad. Linked Comment: Z.C. Venables. Br J Dermatol 2021; 185:477–478.