Antigenic and cellular heterogeneity of primary uveal malignant melanomas

Monoclonal antibody (MAb) MAb8-1H, which identifies an ocular melanoma-associated antigen, and computer-assisted cytomorphometric analysis were used to investigate antigenic and cellular heterogeneity in four atypical cases of choroidal or ciliary body melanoma. The presence of one or more well-localized, morphologically distinct areas within each uveal melanoma, suggestive of multiple tumor cell populations, was observed by conventional light microscopy. In one choroidal melanoma with an unusual bilobed configuration, MAb8-1H bound only to the anterior lobe composed of spindle melanoma cells. In the other three cases, MAb8-1H bound selectively to discrete regions within the uveal melanoma corresponding to the well-localized, morphologically distinct areas seen by light microscopy. In each case, a computer was used to calculate the nuclear area of 50 tumor cells corresponding to the areas binding or not binding MAb8-1H. In three of the four cases examined, the differences in mean nuclear area between the discrete populations of tumor cells were statistically significant. Our results suggest that some uveal melanomas are composed of two or more discrete populations of tumor cells with regard to both expression of melanoma-associated antigens and cytomorphologic features.