Seasonal variation in dysplastic naevi.

There is a relationship between sunlight and the development of melanocytic neoplasms. Because the incidence and excision of melanocytic neoplasms varies according to season, we sought to determine if dysplasia and/or intraepidermal melanocytic expression differed in a cohort of dysplastic naevi (DN) removed in January compared with a similar cohort removed in August. The DN were graded based on the degree of dysplasia, and the number of intraepidermal melanocytes were counted after immunohistochemical staining with HMB-45 and Melan-A. There was no seasonal difference in the grading of the dysplastic naevi in either season (P = 0.08). Comparing 85 cases from August and 86 from January, there was a larger number of Melan-A-positive melanocytes in the August samples (P < 0.02), and a larger number of HMB-45-positive melanocytes in January (P < 0.01). This difference may be related to seasonal variations such as exposure to ultraviolet light exposure; however, there was no difference between the two groups in the degree of atypia seen.