Iris melanomas: are they more frequent in New Zealand?

Melanomas are the most common primary neoplasms of the iris with an incidence reported to range between 0.019–0.08/100 000 inhabitants/year.Jensen, in Denmark, has observed a recent increase in the incidence of these tumours and suggested that the increase in ultraviolet solar radiation might be responsible. In New Zealand solar ultraviolet radiation is high and levels are increasing as a result of depletion of the ozone layer over Antarctica. New Zealanders tend to spend large amounts of time out of doors, their predominant ethnicity is white, and they have a high frequency of solar related tumours. If a cause and effect relation exists between sunlight exposure and iris melanomas an increased number of these tumours might be anticipated. To explore this relation we reviewed data of patients with iris melanomas to determine the incidence of these tumours in the South Island of New Zealand and to compare it with countries for which this information is available. All iris tumour surgery is likely to be undertaken in two university affiliated hospitals (Christchurch and Dunedin) whose catchment population is the entire South Island of New Zealand. Files of all patients from these centres who had surgery for presumed iris melanoma in the years 1984–98 (15 year period) were reviewed. For inclusion in the analysis, patients had to be permanent residents of the South Island, have comprehensive clinical records, and a histological specimen available for review. Histology slides were obtained from all lesions and they were examined in masked fashion by two experienced ocular pathologists. For analysis, the malignant category consisted of spindle B, epithelioid, …