Atypical cellular unguioblastic fibroma-A rare case with more atypical histological features than previously reported.

We herein present the clinicopathological features of an atypical cellular unguioblastic fibroma, a rare onychomatrical tumor, in an adult woman of Southeast Asian origin. The tumor displayed both diffuse hypercellularity and atypia in the mesenchymal component and the presence of large multinucleated cells with a ring-/floret-like arrangement of irregular and hyperchromatic nuclei. The mesenchymal cells displayed a patchy weak positive immunereactivity for CD34 (including atypical and wreath-like multinucleated cells) and for CD10 but were negative for low molecular weight cytokeratins, epithelial membrane antigen, CD68, factor XIIIa, smooth muscle actin, desmin, and HMB-45. The proliferative index as measured immunohistochemically (Mib-1/Ki-67) was 5%. The extent of these atypical histological features has not previously been described. One-year follow-up has been uneventful.