KP1 (CD 68) staining of malignant melanomas.

The monoclonal antibody KP1, which recognizes the CD 68 antigen on macrophages and myeloid precursors, was tested on 28 malignant (primary and metastatic) melanomas, 28 naevi, and 17 skin biopsies showing either normal (10) or hyperplastic melanocytes (7). Sixteen of 20 primary melanomas and six of eight metastatic melanomas showed variable numbers of KP1 positive tumour cells. All but five benign melanocytic proliferations (two Spitz naevi and three intradermal naevi), as well as normal and hyperplastic melanocytes were negative. These results indicate that difficulties may occur with the use of KP1 in the differential diagnosis between melanomas and neoplasms derived from histiocytes-macrophages, and that the expression of CD 68 antigen might be related to tumour progression in melanocytic cells.