Diffuse versus nondiffuse small (≤ 3 MM thickness) choroidal melanoma: comparative analysis in 1,751 cases. The 2012 F. Phinizy Calhoun lecture.

OBJECTIVE: To determine prognosis of small choroidal melanoma (≤ 3 mm thickness) comparing diffuse versus nondiffuse variants.

METHODS: Retrospective chart review of 1,751 patients with small choroidal melanoma classified as diffuse (thickness/base ≤ 20%) versus nondiffuse (thickness/base >20%).

RESULTS: Of 1,751 patients with small choroidal melanoma, 297 (17%) were diffuse and 1,454 (83%) nondiffuse. Features with statistical differences (diffuse vs. nondiffuse) included mean distance to optic disk (3 vs. 4 mm), mean tumor base (12 vs. 8 mm), and mean tumor thickness (1.9 vs. 2.5 mm). Using Kaplan-Meier estimates, melanoma-related metastasis (diffuse vs. nondiffuse) was 8% versus 4% at 5 years, 16% versus 10% at 10 years, and 19% versus 16% at 15 years (P = 0.0344). Melanoma-related death was 6% versus 2% at 5 years, 11% versus 4% at 10 years, and 16% versus 6% at 15 years (P < 0.0001). In the subgroup of thin melanoma 2 mm or less in thickness, melanoma-related death was 7% versus 2% at 5 years, 10% versus 2% at 10 years, and 16% versus 4% at 15 years (P = 0.0077). By multivariate analysis, factors predictive of metastasis from diffuse melanoma included larger tumor basal dimension (P = 0.0027) and plateau/flat tumor configuration (P = 0.0257).

CONCLUSION: Of 1751 patients with small (≤ 3 mm thickness) choroidal melanoma, those with diffuse tumor show higher probability of metastasis and death than those with nondiffuse tumor. This finding is evident even in the thinnest melanomas (≤ 2 mm thickness).