Recognition of malignant melanoma by monoclonal antibody HMB‐45. An immunohistochemical study of 200 paraffin‐embedded cutaneous tumors

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Abstract
Antibodies to S‐100 protein have been used widely as markers of malignant melanoma, despite abundant evidence that they are non‐specific for this neoplasm. Hence, alternatives to these reagents are desirable in diagnostic dermatopathology. We evaluated the characteristics of a new monoclonal antibody (HMB‐45) which does have putative specificity for melanoma, and compared it with a polyclonal anti‐S‐100 reagent in immunohistochemical staining of 67 melanomas of the skin and 133 non‐melanomatous cutaneous neoplasms. All specimens were formalin‐fixed and paraffin‐embedded, and were studied with the avidin‐biotin‐peroxidase complex technique. HMB‐45 labelled 62 of 67 melanomas, while anti‐S‐100 recognized all tumors of this type. On the other hand, S‐100 also was expressed by 15 of the non‐melanocytic neoplasms, all 133 of which were HMB‐45‐negative. The only cases of melanoma that were missed by the latter reagent were of the spindle‐cell type. Hence, HBM‐45 was 100% specific and 93% sensitive, relative to a diagnosis of malignant melanoma in paraffin sections. Epithelioid and small‐cell neoplasms are reliably recognized by this antibody, but it would appear that spindle‐cell melanomas must be detected by other immunohistochemical means.