Trends in incidence of ocular malignant melanoma in Denmark 1943-1982.

All records of ocular malignant melanoma notified to the Danish Cancer Registry between 1943 and 1982 were re-coded, and 1,624 out of 1,650 cases were verified and included in this investigation. The annual number of incident cases increased from about 30 to 50, but the age-standardized incidence rate remained stable at 0.75 per 100,000 in males and 0.60 in females. There was no predilection for one or the other eye in either sex. About 80% of the tumours were located in the choroid, 10% in the ciliary body and iris, 5% in the conjunctiva, and 5% in "multiple regions". The histopathology of the tumours was: epithelioid cell type in 12%, spindle-cell type in 36%, and mixed-cell type in 51%. The stable incidence rates of ocular malignant melanomas were in marked contrast to the 5- and 6-fold increase observed for cutaneous melanomas during the same time period. Possible differences in risk factors are discussed. Similarities and differences between the present data and results from other countries are highlighted.