Tenascin differentiates dermatofibroma from dermatofibrosarcoma protuberans: comparison with CD34 and factor XIIIa

Differentiation of dermatofibroma (DF) from dermatofibrosarcoma protuberans (DFSP) can be difficult. CD34 and Factor XIIIa have been used to differentiate DF from DFSP. However, there is overlap and lack of specificity of their expression. Tenascin is an extracellular matrix glycoprotein that is involved in embryogenesis, carcinogenesis, and wound healing. The aim of the study was to assess the role of tenascin in DF and DFSP and compare the results with those obtained with CD34 and Factor XIIIa. Immunohistochemical staining was performed on 20 cases each of DFSP and DF, using antibodies to tenascin, CD34 and Factor XIIIa, and the streptavidin biotin technique. Positivity for all 3 antibodies was assessed within the tumors. Tenascin expression was also assessed at the dermal-epidermal junction. Strong tenascin positivity was noted at the dermal-epidermal junction overlying the lesion in 20 of 20 cases of DF (100%) and was negative over the lesion in 20 of 20 cases DFSP (100%). Tenascin was noted within the lesion of 80% of both DF and DFSP (16/20 cases). CD34 was strongly expressed in 16 of 20 (80%) DFSP and 5 of 20 (25%) DF, whereas Factor XIIIa was strongly expressed in 19 of 20 (95%) DF and 3 of 15 (15%) DFSP. Although CD34 was expressed in 80% DFSP and Factor XIIIa in 95% of DF, there was overlap in their expression in the 2 types of tumors. The increased expression of tenascin at the dermal-epidermal junction overlying the lesion in DF but not in DFSP, differentiated these 2 tumors. In contrast, tenascin expression within the lesion did not differentiate DF from DFSP.