International validation of a staging system for ciliary body and choroidal melanomas using estimated tumour volume

To validate a newly proposed anatomic staging system for choroidal and ciliary body melanoma, based on tumour volume estimated from routine clinical measurements, and compare its prognostic performance with the American Joint Committee on Cancer (AJCC) 8th edition classification.

A retrospective, multicentre cohort study.

A total of 5 410 consecutive patients diagnosed with choroidal and/or ciliary body melanoma at 6 European ocular oncology centres.

Tumours were staged according to both classifications. Prognostic performance was evaluated using competing risk regression, Cox regression, Kaplan-Meier survival analyses, and net reclassification improvement.

The new classification showed better prognostic discrimination than the AJCC system, with a net reclassification improvement of 23%. In competing risk regression, it produced a higher Wald statistic (761 vs 628) and a subdistribution hazard ratio of 1.42 versus 1.22. Cox regression for melanoma-related mortality demonstrated higher hazard ratios, peaking at 24 for the new model compared with 13 for the AJCC classification. Cumulative incidence analyses revealed 15-year metastatic death rates ranging from 7% to 76% with the new system versus 11% to 69% with AJCC, widening the absolute range by 11 percentage points.

This large international validation study demonstrates that the new volume-based classification provides more accurate prognostic stratification for choroidal and ciliary body melanoma. Its improved risk discrimination, using readily available clinical measurements, supports its applicability in clinical practice and potential utility for guiding follow-up and resource allocation.