Is season important for the diagnosis of cutaneous melanoma in southern Brazil? A 10-year hospital-based study.

Background: Exposure to sunlight is an important etiologic factor in cutaneous melanoma (CM). In several countries, more cases of CM are diagnosed in summer than in winter.

Aim: To analyze whether there is seasonal variation in the diagnosis of CM in southern Brazil.

Methods: Data were collected from a hospital-based registry, including all cases of CM diagnosed between 1996 and 2005. Summer to winter and spring to fall ratios were used for the analysis, and a 95% confidence interval (CI) was calculated using Poisson regression.

Results: Two hundred and eighty-one patients were diagnosed in this period. Although some months were shown to have higher absolute numbers of diagnosed melanomas (April, July, and January), there was no statistically significant seasonal variation in most of the melanomas in terms of either the summer to winter ratio [odds ratio (OR) = 1.09; 95% CI, 0.77-1.44] or spring to autumn ratio (OR = 1.01; 95% CI, 0.71-1.43). Only the number of lentigo maligna melanomas (LMMs) diagnosed in summer was higher than that in winter (OR = 2.83; 95% CI, 1.07-8.78).

Conclusions: In southern Brazil, CMs do not seem to be more frequently diagnosed in summer than in winter. Darkening of melanocytic lesions and increased awareness of skin lesions during the summer could be possible explanations for LMMs being more frequently diagnosed in summer than in winter in this sample.