Melan-A/Mart-1 expression in various melanocytic lesions and in non-melanocytic soft tissue tumours

Aims: The purpose of this study was to test different malignant non-melanoc ytic tumours with the commercially available antibody Melan-A to examine it s diagnostic specificity and to compare the S100, Melan-A and HMB-45 reacti vity in various melanocytic lesions. Methods and results: Seventy-three benign and malignant melanocytic lesions and 31 cases of non-melanocytic tumours, sarcomas, carcinomas and carcinoi ds, were selected. Immunohistochemical staining of paraffin sections, follo wing a high temperature antigen unmasking technique, was performed. Melan-A stains junctional and dermal melanocytes in all benign melanocytic lesions with the exception of neuro-naevoid areas, The epithelioid and the spindle cells in malignant melanomas did not show considerable difference in their Melan-A reactivity. The predominantly spindle cell type mucosal melanomas contained more Melan-A-positive cells than HMB-45-positive cells and simila r results were observed in metastatic malignant melanomas. In desmoplastic melanomas the positivity of Meran-A was not consistent. None of the sarcoma s, carcinomas and carcinoids expressed Melan-A. Almost all soft tissue tumo urs, except for two malignant gastrointestinal stromal tumours, were unreac tive for HMB-45. These two cases did not react with hilelan-A antibody. Conclusions: Melan-A is a useful additional marker to differentiate non-mel anocytic tumours from primary or metastatic melanoma, In melanocytic lesion s the Melan-A staining pattern is similar to S100, but seems to be more spe cific. In desmoplastic melanomas, however, the variable Melan-A staining fu rther necessitated detailed histological examination and the use of the S10 0 reaction.