Increasing Incidence of Posterior Uveal Melanoma in Scandinavia 1960-2022: A Tri-National Study.

Purpose: To investigate temporal trends in the incidence of posterior uveal melanoma in Scandinavia (Sweden, Denmark, and Norway) between 1960 and 2022 and explore potential associations with changes in tumor size and patient age at diagnosis.

Design: Retrospective, registry-based cohort study utilizing nationwide data from the three Scandinavian countries.

Participants: All patients diagnosed with posterior uveal melanoma (choroid or ciliary body) in Sweden (1960-2022), Denmark (1960-2022), and Norway (1993-2022), totaling 10,154 cases. Iris melanomas were excluded.

Methods: Crude, age-standardized, and log-transformed age-standardized incidence rates were calculated using direct standardization (1970-1974 population). Linear regression was applied to assess trends in incidence, largest basal diameter (LBD), tumor thickness, and patient age at diagnosis. A multivariate linear regression model tested whether tumor size or patient age accounted for the time-dependent increase in incidence. P values were Bonferroni-adjusted for multiple comparisons.

Main Outcome Measures: Crude, age-standardized, and log-transformed age-standardized incidence rates of posterior uveal melanoma.

Results: Crude, age-standardized, and log-transformed age-standardized incidence rates increased significantly in all three countries. Combined Scandinavian age-standardized rates rose from 5.2-6.8 per million inhabitants and year in the 1960s to 6.1-8.7 in the 2010s (slope 0.033; 95% CI 0.022-0.044; P<0.001). Log-transformed rates showed a similar upward trend (slope 0.002; 95% CI 0.002-0.003; P<0.001). Tumor size (diameter and thickness) decreased, while patient age at diagnosis increased over time. Multivariate analysis confirmed a time-dependent increase in incidence (P<0.001), independent of tumor size or patient age.

Conclusions: Posterior uveal melanoma incidence in Scandinavia has increased since 1960. The linear trend is independent of changes in tumor size or patient age.