Locally aggressive and multifocal phosphaturic mesenchymal tumors: two unusual cases of tumor-induced osteomalacia

Tumor-induced osteomalacia (TIO) has long been recognized as a clinical paraneoplastic syndrome. The identification of a unique histopathologic entity, the phosphaturic mesenchymal tumor (PMT), as a distinct etiology for TIO has been a more recent discovery. The majority of published cases describe a solitary, non-aggressive appearing soft tissue or osseous lesions in patients with osteomalacia; aggressive appearing or multifocal lesions appear to be exceedingly rare. These tumors characteristically secrete fibroblast growth factor 23 (FGF23). Elevated serum levels of FGF23 result in phosphate wasting and osteomalacia. In the majority of cases, laboratory abnormalities and clinical signs and symptoms of osteomalacia precede identification of the causative lesion by years. Following diagnosis, complete resection with wide margins to prevent local recurrence is most often curative. Imaging characteristics of PMT are diverse and remain incompletely defined, as the majority of previous publications are outside of the radiologic literature. We present multiple imaging modalities in two cases of patients with debilitating osteomalacia and unusual appearing PMTs: one with a locally aggressive lesion leading to pathologic fracture, the second presenting with exceedingly rare multifocal PMT.