No differences in the long-term prognosis of iris and choroidal melanomas when adjusting for tumor thickness and diameter

OBJECTIVE: To assess the long-term prognosis for patients with iris melanomas and compare it with the prognosis for small choroidal melanomas. DESIGN: Retrospective observational case series. METHODS: All patients treated for iris melanomas at a single referral institution between January 1st 1986 and January 1st 2016 were included. Patients treated for small choroidal melanomas during the same period were included for comparison. The cumulative incidence of melanoma-related mortality was calculated. Patient and tumor characteristics and size-adjusted hazard ratio (HR) for melanoma-related mortality were compared between iris and small choroidal melanomas. RESULTS: Forty-five iris melanomas and 268 small choroidal melanomas were included. Twenty-four iris melanomas (53%) had been treated with local resection, 12 (27%) with Ruthenium-106 brachytherapy, 7 (16%) with enucleation and 2 (4%) with proton beam irradiation. Twenty-one (68%), 7 (16%) and 2 (4%) of the iris melanomas were of the spindle, mixed and epithelioid cell types, respectively. Twenty-three patients had deceased before the end of follow-up. Median follow-up for the 22 survivors was 13.3 years (SD 9.4). Patients with iris melanomas were more often asymptomatic at presentation and had a trend towards significantly lower age (59 versus 63 years, Student’s T-tests p = 0.057). Further, iris melanomas had significantly smaller basal diameter (5.8 versus 8.0 mm, p < 0.0001) and tumor volume (79 mm(3) versus 93 mm mm(3), p < 0.0001) but greater thickness (3.0 versus 2.5 mm, p < 0.0001). The cumulative incidence of iris melanoma-related mortality was 5% at 5 years after diagnosis, and 8% at 10, 15 and 20 years. The incidence was not significantly different to small choroidal melanomas (Wilcoxon p = 0.46). In multivariate Cox regression with tumor diameter and thickness as covariates, patients with choroidal melanomas did not have increased HR for melanoma-related mortality (HR 2.2, 95% CI 0.5–9.6, p = 0.29). Similarly, there were no significant survival differences in matched subgroups (Wilcoxon p = 0.82). CONCLUSIONS: There are no survival differences between iris and choroidal melanomas when adjusting for tumor size. The reason for the relatively favorable prognosis of iris melanomas compared to melanomas of the choroid and ciliary body is likely that they are diagnosed at a smaller size.