Podoplanin expression in fibrous histiocytomas and cellular neurothekeomas

Podoplanin, also recognized by the monoclonal antibody D2-40, is a mucin-type transmembrane glycoprotein that is highly expressed in lymphatics and in a range of vascular and nonvascular proliferations. Recently, podoplanin has been detected in fibrous histiocytomas (FHs) and proposed to represent a potentially useful marker in the diagnostic evaluation of this lesion. There is, however, limited data concerning podoplanin expression in FH and its morphological mimics. Cellular neurothekeomas (CNs) are rare cutaneous neoplasms of uncertain histogenesis that often morphologically mimic FH. In this study, we reviewed our experience with podoplanin expression in FH (n = 30), especially in comparison to CN (n = 15). In addition, we also immunostained a selected group of other mesenchymal lesions that may fall within the differential diagnosis of FH for podoplanin, including dermal nerve sheath myxoma (n = 2), dermatofibrosarcoma protuberans (N = 8), and plexiform fibrohistiocytic tumor (n = 2). Podoplanin expression was observed in a significant subset of FHs (26/30, 86.6%) and in all CNs (15/15, 100%), whereas DFSPs, dermal nerve sheath myxomas, and plexiform fibrohistiocytic tumors were all negative. To the best of our knowledge, this is the first report demonstrating podoplanin expression in CN. Expression of podoplanin in CN represents a potential pitfall in the use of this antibody for diagnostic evaluation of FH. However, podoplanin may be of value as an adjunct to morphological examination in assessment of problematic lesions falling within the differential diagnosis of FH and CN.