Tenascin expression in cutaneous fibrohistiocytic tumors. Immunohistochemical investigation of 24 cases.

We studied the immunolocalization of the extracellular matrix glycoprotein tenascin in a series of 24 cutaneous fibrohistiocytic tumors, including seven benign lesions (benign fibrous histiocytoma/dermatofibroma), six intermediate malignancy lesions (dermatofibrosarcoma protuberans), and 11 malignant lesions (three atypical fibroxantomas and eight malignant fibrous histiocytomas). The results of the immunohistochemical staining were evaluated semiquantitatively. All lesions expressed tenascin in the extracellular matrix, with some differences in the distribution of the immunoreactivity. In benign fibrous histiocytoma and in dermatofibrosarcoma protuberans, there was a homogeneous, intense, and diffuse staining of the extracellular matrix (++); the only exception was the homogenized, sclerotic collagen present in late, regressing benign fibrous histiocytoma, which showed a weak and patchy reactivity (+). In atypical fibroxantomas and in malignant fibrous histiocytomas, there was an irregular distribution of the positivity within the tumor matrix (+). Prominent staining of the cytoplasm of several neoplastic cells was observed in atypical fibroxantoma and malignant fibrous histiocytoma (++), focal cytoplasmic staining of scattered cells was found in dermatofibrosarcoma protuberans (+), and cytoplasmic staining was absent from benign fibrous histiocytoma (-). These findings indicate a relationship between cytoplasmic and extracellular matrix expression of tenascin in these lesions, with an increase in cytoplasmic staining and a decrease in extracellular matrix staining in the malignant forms. Based on these different staining patterns, tenascin immunolocalization could furnish some help in the differential diagnosis among benign, intermediate malignancy, and malignant cutaneous fibrohistiocytic tumors. Moreover, the intense tenascin staining at the edge of the lesion could be helpful in defining its extent and therefore provide an additional criterion to evaluate the radicality of the surgical procedure.