EXPRESSION OF BASEMENT-MEMBRANE ANTIGENS IN SPINDLE-CELL MELANOMA

Spindle cell melanoma (SCM) is an uncommon form of melanoma that may b e confused histologically with other tumors, including malignant perip heral nerve sheath tumors (MPNST). Tumors with neural differentiation and melanocytic nevi may both show basement membrane immunohistochemic ally and at the ultrastructural level. However, most ultrastructural s tudies of melanoma have failed to demonstrate well formed basement mem brane around tumor cells. The presence of basement membrane has been u sed by some authors as evidence favoring MPNST, as opposed to SCM. To evaluate this distinction immunohistochemically, 22 primary and metast atic cutaneous melanomas having a spindle cell component (SCM) were st udied using monoclonal antibodies against laminin and Type TV collagen . S100 protein and HMB45 antigen expression were also studied. All but one of the SCM were reactive for S100 protein in at least 25% of the cells. Thirteen of 20 tumors (65%) were focally reactive with HMB45. L aminin was expressed in 42% of the tumors (only membranous pattern in 3; cytoplasmic and membranous in 5). Seventeen tumors (77%) expressed type TV collagen (only membranous pattern in 7; cytoplasmic and membra nous pattern in 10). Laminin and type TV collagen, known components of basement membrane, are often found in SCM. Therefore, their detection cannot be used to distinguish SCM from MPNST.