Threshold analysis of mortality outcomes in the collaborative ocular melanoma study (COMS)

The collaborative ocular melanoma study (COMS) reported similar survival between plaque brachytherapy (a type of interventional radiotherapy) and enucleation for medium-sized choroidal melanomas. We aimed to quantify the mortality differences required to achieve statistical significance and assess the robustness of these thresholds.

We reanalyzed 12-year mortality data from COMS using threshold analysis to determine how many additional or fewer deaths in either treatment arm would shift the lower bound of the 95% confidence interval (CI) for the risk ratio above 1.

At 12 years, there were 105 melanoma-related deaths in the brachytherapy arm and 98 in the enucleation arm (risk ratio 1.08, 95% CI 0.82-1.42). Achieving statistical significance would have required 31 additional deaths in the brachytherapy arm or 23 fewer in the enucleation arm; conversely, favoring brachytherapy would have necessitated 34 additional deaths in the enucleation arm or 27 fewer in the brachytherapy arm. These thresholds remained consistent across power levels and sensitivity scenarios.

The COMS trial did not reveal a clinically meaningful survival difference. Our findings underscore the substantial mortality shifts required for statistical significance and highlight the challenges in detecting modest treatment effects in uveal melanoma trials.