Currently, there is no study that has reported on the seasonal trends of skin cancer in the Netherlands. This study aimed to investigate seasonal variation in diagnosis of cutaneous melanoma (CM) and cutaneous squamous cell carcinoma (cSCC) focusing on different subgroups.
CM diagnosed from 2001 till 2019 and cSCCs from 2001 till 2015 were selected from the Netherlands Cancer Registry. The monthly distribution of CM and cSCC diagnoses were evaluated. Summer-to-winter ratios (SWRs) were calculated overall and stratified by patient and tumour characteristics.
Significant increases in melanoma incidence were noted over the summer months (SWR 1.39 (CI 1.37–1.40)). This increase was less apparent for cSCCs, as higher incidence rates were observed in the months September-November (SWR 1.13 (CI 1.12–1.14)). The seasonal variation of CM was greater in women and younger people, in superficial spreading melanoma and lentigo maligna melanoma, for the extremities, in thinner lesions, and for stage I at diagnosis. The seasonal variation of cSCC was similar for both sexes, most marked in patients 45‐69 and ≥ 70, and for the extremities.
Our findings showed a pronounced seasonal variation in the diagnosis of CM with a peak in the summer months. For cSCC, no evident peak was observed, but an increase in diagnosis was noted in fall. Both CM and cSCC showed strong seasonal effects for the extremities.
Skin cancer is the most frequently diagnosed form of cancer in the Netherlands . 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) . Unlike cSCCs and melanomas, BCCs are considered non-lethal since they do not have the tendency to metastasize .
The overall incidence rate of melanoma has increased substantially in the Netherlands between 2003 and 2018 . 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 . Furthermore, an ever-increasing trend is also seen for the incidence of cSCCs 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 . An increase in the occurrence of multiple cSCCs per patient was also reported .
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) . SCCs, in contrast, are associated with chronic and occupational sunlight exposure . Other important causes of the increasing incidence are better registration of new diagnoses, improved surveillance and increased awareness .