A smear preparation showed few multinucleated giant cells. Sections revealed a cellular lesion that was infiltrating and destroying bone in some areas while in others a more discrete interface was appreciated. The lesion consisted of numerous multinucleated giant cells arranged diffusely and in clusters in a background of stromal cells. The nuclei of the giant cells had small round to oval nuclei with distinct nucleoli; hemosiderin deposition was prominent. Bone uninvolved by tumor showed prominent "tunneling" resorption and marrow fibrosis.