Relationship between season and diagnoses of melanocytic tumours

The frequency of various diagnoses of pigmented lesions, their distribution on various body sites and the seasonal variations in their diagnoses were studied according to the specimen of pigmented lesions sent to a laboratory for histopathological examination. From the total number of 18,402 investigated lesions, 7,682 were excised from males and 10,720 from females. Melanoma was diagnosed in 2.5% of all excised tumours more often during the summer months. Lighter clothing and greater awareness during summer may explain this finding. Additional factors such as a sun-induced melanocytic activation in naevi cannot be ruled out. Dysplastic naevi, which represented 26% of all naevi in this study, were excised less often during summer. Presuming that the majority of the north German population acquires the highest ultraviolet (UV) doses of the year during summer, it seems unlikely that the histological features of dysplasia in naevi are related to short-term UV activation. The localization of dysplastic naevi did not correspond to the body-site distribution of melanoma according to sex. This finding does not indicate the dysplastic naevus as a possible precursor lesion of malignant melanoma.