Seasonal variation in diagnosis of cutaneous invasive melanoma and cutaneous squamous cell carcinoma: A nationwide study in the Netherlands

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Introduction

Skin cancer is the most frequently diagnosed form of cancer in the Netherlands [1] . After basal cell carcinoma (BCC), cutaneous squamous cell carcinoma (cSCC) is the most common skin cancer type (20 % of all skin cancers), followed by cutaneous melanoma (CM) (10 % of all skin cancers) [1] . Unlike cSCCs and melanomas, BCCs are considered non-lethal since they do not have the tendency to metastasize [2] .

The overall incidence rate of melanoma has increased substantially in the Netherlands between 2003 and 2018 [3] . A nearly three-fold increase in the age-standardized rate (ESR) was observed in 1989–2019, from 11.51 to 30.81 per 100.000 person-years, respectively [4] . Furthermore, an ever-increasing trend is also seen for the incidence of cSCCs [5] as a nearly fourfold increase in the ESR of cSCCs was noted between 1989 and 2019, from 12.89 to 48.85 per 100.000 person-years [4] . An increase in the occurrence of multiple cSCCs per patient was also reported [5] .

A large part of the increase in skin cancer incidence is due to more and excessive exposure to ultraviolet radiation. Melanoma risk is associated with intermittent or non-occupational exposure to sunlight and sunburn history (for example increased sunbed use, frequent holidays abroad and partaking in outdoor sports) [67] . SCCs, in contrast, are associated with chronic and occupational sunlight exposure [89] . Other important causes of the increasing incidence are better registration of new diagnoses, improved surveillance and increased awareness [10] .