Uveal melanoma cell staining for CD34 and assessment of tumor vascularity.

Purpose: Aggressive melanoma cells may express endothelial markers that can be used to calculate microvascular density (MVD). High MVD has been associated with adverse outcome in uveal melanoma. If tumor cells label with endothelial cell markers, then MVD may not accurately reflect a tumor's vascularity. This study was designed to study the influence of melanoma cell labeling by endothelial cell markers on MVD.

Methods: Tissue sections of 200 ciliary body or choroidal melanomas were stained with CD34 alone, and the MVD was calculated by counting discrete foci of CD34 labeling in hot spots, as described previously. From adjacent sections double labeled by fluorescent immunohistochemical stains for S100 protein and CD34, tumor cells labeling with both markers were identified. The relationship between marker coexpression and MVD was tested. Tissue sections were also double labeled for Melan-A and CD34.

Results: MVD was found to be associated with death from metastatic melanoma as reported previously. However, colocalization of both Melan-A and S100 protein with CD34 was demonstrated. The labeling of tumor cells by CD34 was associated with an elevated calculation of MVD (P < 0.0001) but not with cell type, mitotic figures, tumor-infiltrating lymphocytes, or PAS-positive patterns.

Conclusions: CD34 may label uveal melanoma cells and may contribute to computation of MVD. Although MVD is prognostically significant in uveal melanoma, this feature is not an exclusive measure of tumor vascularity.