HMB45: a specific marker for melanoma metastases in the central nervous system?

The monoclonal antibody HMB45 is used to detect an epitope specific for melanocytes, malignant melanomas and melanoma metastases. Using the PAP method, we observed consistent expression of HMB45 in 19 metastases of melanotic and amelanotic malignant melanomas of the central nervous system, while metastases of 32 adenocarcinomas, 10 squamous cell and 8 small cell carcinomas were negative except for 2 cases of breast cancer. Differential diagnosis between cancer and melanoma metastases can be made using cytokeratins as an additional immunocytochemical marker protein. Ten meningeomas and 5 pineocytomas were also negative. Even though it is not absolutely specific, we consider the HMB45 immunoreaction diagnostic for a metastasis of a malignant melanoma if the tumour is cytokeratin negative and HMB45 positive in a large number of tumour cells.