The prognostic implication of latitude in uveal melanoma: a nationwide observational cohort study of all patients born in Sweden between 1947 and 1989.

ABSTRACT

BACKGROUND: The incidence of uveal melanoma increases with latitude. In this study, we examine the importance of latitude for uveal melanoma prognosis. METHODS: All uveal melanoma patients born in Sweden between 1947 and 1990 were included (n = 745). The latitude of patients' birthplaces and home counties at the time of uveal melanoma diagnosis were collected. For all latitudes, data on sunlight and UV intensity parameters, temperature, daytime length variations, and socioeconomic factors were added. The prognostic implication of birthplace latitude and of moving > 1 degree of latitude was examined with multivariate Cox regressions and competing risk analyses. FINDINGS: There were no significant differences in patient sex, age, tumor size, T-category, or BAP-1 immunoexpression between patients born in the south, central or northern regions of Sweden. Decreasing birthplace latitude was a predictor of uveal melanoma-related mortality in multivariate Cox regression. Patients that were born in southern regions or moved > 1 degree south between birth and diagnosis had higher incidence of uveal melanoma-related mortality in competing risk analysis. The sum of yearly sunshine hours, global sunlight radiation, average daily ultraviolet light intensity, average annual temperature, or net wealth were not predictors of uveal melanoma-related mortality. INTERPRETATION: Latitude is a prognostic factor in uveal melanoma. This does not seem to be related to variations in patient or tumor characteristics at presentation, in management, in sunlight intensity, in ultraviolet light irradiance, in temperature, or in wealth. Future studies should examine if periodical changes in daylight hours or other factors could explain the prognostic implication.