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

Background: 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. Methods: 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. Results: 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. Conclusions: 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.