Comparison of microcirculation patterns and MIB-1 immunoreactivity in iris and posterior uveal melanoma

Abstract

Purpose To compare melanomas confined to the iris and those involving either the ciliary body or choroid for the histologic features of microcirculation patterns and tumor cell proliferation indices. Design Retrospective comparative human tissue study. Participants Ninety-eight uveal melanomas were studied, including 18 tumors confined to the iris, 30 tumors involving the ciliary body, and 50 tumors confined to the choroid. Methods Formalin-fixed, paraffin-embedded sections from each tumor were stained with hematoxylin–eosin and with periodic acid–Schiff. Adjacent histologic sections were stained with the MIB-1 antibody that reacts with the Ki-67 antigen. Main outcome measures Microcirculation patterns were assessed in the periodic acid–Schiff-stained sections. Proliferative activity was assessed in the MIB-1–stained sections. The mean MIB-1 positive cell count per high-power field (HPF) was calculated in 10 HPF (× 40) in the area of maximal immunoreactivity. Two observers evaluated each MIB-1–stained section, and the interobserver reproducibility was assessed. Results Histologic microcirculation patterns associated with death from metastatic disease in ciliary body and choroidal melanomas (parallel vessels with cross-linking and networks of back-to-back loops) were not found in any of the iris melanomas. By contrast, 34% and 63% of the choroidal and ciliary body melanomas, respectively, showed at least one of these patterns. The mean positive cell count per HPF ± standard error was 19.9 ± 3.5, 27 ± 5.3, and 1.9 ± 0.4 in choroidal, ciliary body, and iris melanoma, respectively ( P = 0.003, Kruskal-Wallis test). Conclusions Melanoma confined to the iris is characterized by a low rate of proliferation and the histologic absence of microcirculation patterns associated with metastatic posterior uveal melanoma. Both features are consistent with the relatively benign nature of iris lesions compared with melanomas involving the ciliary body or choroid.