Long-term follow-up of circumscribed iris melanomas treated by proton beam therapy

Iris melanomas are a rare entity accounting for 2-5% of uveal melanomas. The most frequent primary treatment for circumscribed iris melanomas is irradiation, particularly by proton beam therapy (PBT). Short-term efficacy is encouraging but there is little data on long-term tumour control and side effects.

To describe the long-term results in terms of local and systemic control, eye preservation and side-effects after PBT for circumscribed iris melanomas.

Retrospective chart review of patients treated by PBT between 1998 and 2022. Diffuse iris melanomas, ciliary body melanomas with iris involvement or tumours with extrascleral invasion were excluded.

Of 143 patients treated by PBT, n = 91 were treated five years or more before data update and were included. Median follow-up was 10.7 years (range 1.7-22.7 years). Documented growth was present for 74% of patients. The median clinical largest diameter was 5 mm, and the median ultrasound thickness was 2.1 mm. The tumour invaded the iridocorneal angle in 68% of patients. Overall survival was 94%. Three patients presented with metastatic disease, of which one died of metastasis. Seven deaths were unrelated to iris melanoma. Five (3.5%) patients experienced ocular relapse. The most frequent complications were cataract and raised intraocular pressure (no neovascular glaucoma). Four patients (4.3%) required secondary enucleation.

Long-term follow-up confirms that PBT is an excellent treatment option for localized iris melanomas, with very favourable local tumour control, eye preservation, and overall survival. Relapses are very rare but can occur several years after treatment, warranting a prolonged follow-up.