A comparison of some methods for identifying amelanotic and oligomelanotic melanoma metastases in paraffin sections

Four methods were compared for identifying amelanotic and oligomelanotic melanomas in paraffin sections of formalin-fixed metastases from subjects with primary cutaneous melanomas. Of the amelanotic and oligomelanotic metastases a characteristic pattern of fluorescence was seen with an incident-light fluorescence microscope in 11 of 25 (44%); the Warthin-Starry stain at pH 3.2 was positive in 14 of 25 (56%); these two procedures together were a little more effective, 63% positive; S100 protein was revealed by immunoperoxidase staining in 26 of 28 (93%); the monoclonal antibody NKI/C-3 against a human melanoma antigen gave positive immunoperoxidase staining in 24 of 27 cases (89%). Of the pigmented metastases S100 protein was demonstrated in 18 of 21 (86%) and NKI/C-3 gave positive staining in all 20 tested. These antibodies are not specific for melanoma but a metastasis which does not react with either antibody is unlikely to be melanoma.