Purpose: The presence of a high number of infiltrating macrophages in uveal melanoma is associated with a bad prognosis. However, there are several known types of macrophages, of which the M2 is considered to be proangiogenic and tumor-promoting. This study was conducted to determine whether the tumor-infiltrating macrophages in uveal melanoma are of this M2 subtype.
Methods: Macrophages were identified in sections from 43 uveal melanomas by immunofluorescence histochemistry, using monoclonal antibodies directed against CD68 and CD163. The immunopositive cell density was measured visually and with a confocal microscope and calculated per square millimeter. Results were compared with clinical and tumor characteristics.
Results: Infiltrating macrophages in uveal melanoma were predominantly CD68(+)CD163(+), thus of the M2 phenotype. The density of CD68(+), CD163(+), and CD68(+)CD163(+) cells was significantly increased in uveal melanomas with monosomy 3 compared with cases with disomy of chromosome 3 and was associated with ciliary body involvement. High CD68(+)CD163(+) staining was associated with an increased microvascular density. Survival was significantly better among patients with low CD68(+) and CD68(+)CD163(+) staining.
Conclusion: The main type of macrophage present in uveal melanoma was the M2 type. Tumors with monosomy of chromosome 3 contained a higher number of M2-macrophages than tumors with disomy of chromosome 3. Infiltration of M2-type macrophages gives a worse prognosis for survival. As M2-type macrophages are proangiogenic, a high density of these cells may contribute to the previously noticed positive association between the density of CD68(+) macrophages and blood vessels.