International uveal melanoma incidence trends in view of a decreasing proportion of morphological verification

The introduction of eye-preserving therapies for uveal melanoma in the 1970s complicates time trend analyses of the uveal melanoma incidence because the proportion of morphologically verified uveal melanoma has been decreasing over the decades. We carried out incidence trend analyses, based on data from internationally accredited population-based cancer registries throughout the world that take missing data on topography, morphology and basis of diagnosis of eye tumours into account. We selected incidence data of cancer registries that were included in Cancer Incidence In 5 Continents, Volumes VI-VIII covering a registration period of at least 15 years (usually 1983 to 1997) and classified each eye cancer as morphologically verified uveal melanoma, clinically diagnosed uveal melanoma, uveal melanoma identified as DCO case (Death certificate only), possibly uveal melanoma, other eye tumour or unclassifiable eye tumour and calculated age-standardized incidence rates by 3-year calendar periods using the World Standard Population as the reference. The uveal melanoma incidence decline in the United States SEER Caucasian population is due mainly to an incidence decline in the early registration period (from 1974-76 to 1986-88). The data from France and Italy suggest a recent increase in incidence. Uveal melanoma diagnosed clinically increasingly contribute to the overall uveal melanoma incidence over time. Combining all registries, the proportion of morphologically verified uveal melanoma decreased from 82% in 1983-87 to 75% in 1993-97. Uveal melanoma incidence rates remained quite stable during the period 1983-97. The interpretation of uveal melanoma incidence trends is complicated by missing data on topography within the eye, morphology and basis of diagnosis.