Immunohistochemical diagnosis of malignant melanoma of the conjunctiva and uvea: comparison of the novel antibody against melan-A with S100 protein and HMB-45

A novel antibody A103, which recognizes melan-A/MART-1, has been found to be more sensitive than the antibody HMB-45, which recognizes gp100, in melanocytic lesions of the skin and might therefore also be useful in the diagnosis of uveal and conjunctival melanocytic lesions. In this study we compared the staining characteristics of anti-melan-A, anti-S100 protein and HMB-45 in 13 conjunctival, 11 iris and 37 ciliary and choroidal malignant melanomas. The ciliary and choroidal melanomas comprised 13 spindle cell (10 spindle B and three spindle A), 14 mixed cell and 10 epithelioid cell tumours. In the conjunctival melanomas the diagnostic sensitivity was 100% for anti-S100 and anti-melan-A and 85% for HMB-45. In the iris melanomas the sensitivity was 100% for anti-S100 and anti-melan-A and 55% for HMB-45. A high staining intensity of anti-melan-A was particularly noticed in iris melanomas. In the choroidal malignant melanomas, the spindle cell and mixed cell types showed a sensitivity of only 69-79% with all three antibodies. In the epithelioid cell type the sensitivity was 80% for anti-S100 and 100% for HMB-45 and anti-melan-A. In conclusion, anti-melan-A was found to be a useful addition to antibody panels for ocular melanocytic lesions. Anti-melan-A has a higher sensitivity than HMB-45 in conjunctival and iris melanomas, but the sensitivity is similar to HMB-45 in choroidal melanomas. Anti-melan-A stains in a very similar pattern to anti-S100, but the staining intensity of anti-melan-A is higher than that of anti-S100 in iris melanoma.