Letter to the Editor: Comparison of Alternative Tumor Size Classifications for Posterior Uveal Melanomas

We would like to congratulate Skinner and colleagues on their recent article, in which they perform a thorough statistical comparison of multiple uveal melanoma classification systems that are based on anatomic features, including the TNM staging system. Although the TNM system can work well as a prognostication tool in some cancer types, its prognostic value in uveal melanoma has been disappointing as a result of limited predictive value for individual patients, lack of uniformity and reproducibility in the measurement of clinicopathologic features, and the cumbersome methodology required to calculate tumor stage using the current version. These limitations have resulted in poor acceptance of the system by many leading ocular oncology centers. The authors demonstrate that simply measuring the tumor largest basal diameter (LBD) provides virtually the same prognostic information as the unwieldy TNM staging system. Interestingly, LBD is the only clinicopathologic feature that provides additional (albeit modest) prognostic information to the prospectively validated gene expression profiling (GEP) prognostic assay used in many ocular oncology centers. We believe that LBD provides additional prognostic information, at least in part, because it is related to the length of time the tumor has been growing in the eye, whereas the prognostic information contained in the other clinicopathologic features of the TNM staging system appears to be subsumed under the tumor’s GEP. These findings raise questions about the role of the TNM system for prognostic purposes in uveal melanoma. Nevertheless, the TNM system is of great value for grouping patients with uveal melanoma into ‘‘bins’’ based on similar clinicopathologic features for purposes of clinical and epidemiologic research. The authors have performed a very important, thoughtful, and well-executed study that is likely to have an important impact on the field going forward.