Atypical fibroxanthoma. An unusual variant with osteoclast-like giant cells.

We report three cases of an unusual variant of atypical fibroxanthoma with numerous multinucleated osteoclast-like giant cells. Histologically, the lesions were composed of uniformly dispersed multinucleated osteoclast-like giant cells within a pleomorphic cellular proliferation with microscopic and histochemical features of atypical fibroxanthoma. Multinucleated osteoclast-like giant cells, however, stained with KP-1, a macrophage-associated antigen only. These cells are not necessarily an integral part of the tumor and may represent a reactive histiocytic component.