VS38 IMMUNOSTAINING IN MELANOCYTIC LESIONS

Aims-To investigate the immunoreactivity of a range of melanocytic les ions, both benign and malignant, with the monoclonal antibody VS38. Th is was recently described as a marker of reactive/neoplastic plasma ce lls and, therefore, is useful in the diagnosis of plasmacytoma/myeloma and lymphomas with plasmacytic differentiation. This study was prompt ed by the recent observation that a plasmacytoid melanoma arising in t he nasal cavity was strongly immunoreactive with VS38, which was there fore a potential source of major diagnostic error. Methods-The Strepta vidin-peroxidase complex technique was used on paraffin wax embedded s ections of 167 melanocytic lesions. Diaminobenzidine (DAB) was used as chromogen for non-pigmented or lightly pigmented lesions and nickel/D AB for more heavily pigmented lesions. Results-Positive immunostaining for VS38 was seen in 14.5% (10/69) of benign naevi (including 40% (fo ur of 10) of Spitz naevi), 10.5% (two of 19) of dysplastic naevi/in si tu melanomas, 92% (35/38) of primary cutaneous melanomas, 100% (four o f four) of primary mucosal melanomas, 91.7% (33/36) of recurrent/metas tatic melanomas, and 100% (one of one) of clear cell sarcomas of soft tissues. Conclusions-VS38 immunostaining is frequently positive in pri mary and recurrent/metastatic malignant melanoma and is also reactive less commonly with benign naevi. These results should be borne in mind when this recently described marker of normal/neoplastic plasma cells is used to identify tumour lineage, particularly in tumours arising a t unusual sites, such as in the nasal cavity. The possibility of malig nant melanoma should be actively considered and excluded in any undiff erentiated tumour which shows VS38 immunoreactivity.