S-100 protein expressing spindle cells in spindle cell lipoma: a diagnostic pitfall

Spindle cell lipoma represents a distinct clinicopathological entity and is related to cellular angiofibroma and mammary-type myofibroblastoma. Spindle cell lipomas are composed of mature lipogenic cells and a variable number of CD34-positive spindle cells that show loss of retinoblastoma protein expression. Spindle cell lipomas occasionally express S-100 protein. We studied one case of purely dermal spindle cell lipoma and four cases of classical subcutaneous spindle cell lipoma arising in one female and four male patients (age ranged from 55 to 69 years). The neoplasms arose on the nose, the chin, the neck, the forehead and retroauricular, and all lesions had been marginally or incompletely excised. The studied cases showed classical histological and immunohistochemical features of spindle cell lipoma and, in addition, strong expression of S-100 protein by spindle-shaped tumour cells. S-100-expression in spindle cell lipoma may cause problems in the differential diagnosis with neural and melanocytic neoplasms and emphasizes the plasticity of the spindle cells in spindle cell lipoma.