Neoplastic pathology of oncogenic osteomalacia/rickets

Reported are two cases of oncogenic osteomalacia, each caused by a small mesenchymal tumor, with detailed assessment of the tumors by light microscopy, electron microscopy, and immunohistochemistry. One tumor was a primitive mesenchymal tumor with prominent giant cell and vascular components, and the second resembled the giant cell variant of soft parts chondroma. Osteoclast-like, multinucleated giant cells and vascularity were prominent features in both tumors. Although the literature documents a histologically heterogeneous group of tumors as causing this syndrome, most have multinucleated giant cells and/or extensive vascularity. The high incidence of these two histologic features in this group of tumors suggests that either or both may be related to the pathogenesis and/or metabolic consequences of oncogenic osteomalacia/rickets.