DERMATOFIBROSARCOMA PROTUBERANS - A CRITICAL REAPPRAISAL OF THE ROLE OF IMMUNOHISTOCHEMICAL STAINS FOR DIAGNOSIS

An immunohistochemical study of 14 cases of dermatofibrosarcoma protub erans in routinely processed formalin-fixed, paraffin-embedded tissues was performed using a panel of antibodies, including muscle-specific actin (HHF35), alpha-smooth-muscle actin, desmin, vimentin, cytokerati n cocktail, myelin basic protein, epithelial membrane antigen, KP-1 (C D68), anti-melanoma-specific antigen (HMB-45), S-100 protein, collagen type IV, and the anti-HPCA-1 hematopoietic progenitor cell antibody ( CD34). Staining for actin and collagen type IV expression was limited to perivascular areas, but no staining could be observed in the prolif erating spindle cells. Myelin basic protein reactivity was limited to the perineurium of entrapped nerves; some faint focal positivity was a lso observed in many of the spindle cells forming the tumor, but this was interpreted as nonspecific reactivity. S-100 protein stains were n egative throughout the lesion; however, focal scattered S-100 protein- positive dendritic cells were observed in one case. Stains for epithel ial membrane antigen, desmin, cytokeratin, KP-1, and HMB-45 were unifo rmly negative in all cases studied. Vimentin showed strong immunoreact ivity in the spindle cells in all cases. Seven of the 14 cases showed strong immunoreactivity with anti-HPCA-1 (CD34); however, this antibod y also stained scattered fibroblastic cells outside the tumor, and foc al positivity could also be obtained in dermal fibroblasts in the cont rols. The findings support the fibroblastic nature of these tumors and provide no convincing evidence to support neural or myofibroblastic d ifferentiation. Contrary to recent claims in the literature, the CD34 immunoreactivity observed in these neoplasms is most likely nonspecifi c rather than representing a sensitive or specific marker for dermatof ibrosarcoma protuberans. The diagnosis of DFSP remains largely depende nt on the recognition of its characteristic light microscopic features and the role of immunostains is still limited, for the time being, to ruling out alternate diagnoses.