Comparison of Alternative Tumor Size Classifications for Posterior Uveal Melanomas.

Purpose: Determine which posterior uveal melanoma (PUM) size classification with three categories has the best prognostic discrimination.

Methods: Single-institution study of 424 consecutive patients with PUM. The tumor's largest basal diameter (LBD), smallest basal diameter (SBD), and thickness (TH) were estimated by fundus mapping and ultrasonography. Tumors were assigned to "small," "medium," or "large" size categories defined by 11 different classifications (Linear LBD, Rectangular LBD × TH, Cubic LBD × SBD × TH, Warren Original, Warren Modified, Augsburger, COMS Original, COMS Revised, TNM 2002, and modified TNM 2010 classification [a,b]). Prognostic significance of classifications was evaluated by Kaplan-Meier event curves with computation of log rank test for trend statistic.

Results: In six classification systems (Warren Original, Warren Modified, COMS Revised, TNM 2002, TNM 2010a, TNM 2010b) >50% of tumors fell within one subgroup. In the Warren Original classification <5% of tumors fell within one subgroup. Separation of Kaplan-Meier curves among three size categories was judged "excellent" in four classifications (Linear LBD, Cubic Volume, TNM 2010a, and TNM 2010b) and "very poor" in the Warren Original. Linear LBD classification was associated with highest log rank statistic value. TNM 2010a, TNM 2010b, TNM 2002, Augsburger, and Cubic Volume classifications were also determined to be quite good.

Conclusions: Linear LBD classification was the best three-size category discriminator among low-, intermediate-, and high-risk subgroups. Considering our findings, it seems possible that the arduous work required to apply complex classifications, especially for three-category systems, for PUM may not be justified in routine clinical practice.