Phosphaturic mesenchymal tumor: two contrasting cases

Excerpt

The term phosphaturic mesenchymal tumor (PMT) is a rare tumor that has been linked to oncogenic osteomalacia for some time [1, 2]. This tumor, which has often been described by other histological terms depicting the cell type of the tumor, for example, some have been reported with a descriptive diagnosis, “benign vascular tumor containing numerous giant cells,” or else labeled with a miscellaneous diagnosis such as hemangiopericytoma, before being recognized as a distinct entity [1]. However, combined with the proper histological features, such as osteoclast-like giant cells, with spindle cells, microcysts, and prominent blood vessels, as well as the clinical setting of oncogenic osteomalacia and the presence of fibroblast growth factor-23 (FGF-23), the correct diagnosis of PMT can be made [1]. Resection of the tumor cures patients of the symptoms of oncogenic osteomalacia and reverses the biochemical abnormalities. We present two contrasting cases. The first was that of a patient with a tumor that showed the typical microscopic features of a PMT. However, there was no clinical or biochemical evidence of oncogenic osteomalacia. The second was a patient with a tumor that did not show the histological features of a PMT, but had unequivocal clinical and biochemical features of oncogenic osteomalacia that resolved as expected with the identification and resection of a soft tissue lesion. These two contrasting cases demonstrate several key features. The tumor may have the histology of a PMT without the associated osteomalacia. Second, a patient may present with oncogenic osteomalacia, but may have a variant histology. Third, a PMT may be small and difficult to diagnose on imaging studies. Thus, radiologists and other clinicians need to be aware of the entity of oncogenic osteomalacia, be familiar with the clinical, imaging, and biochemical features, and perform the appropriate investigations to confirm the diagnosis and localize the tumor. Furthermore, in the United States, as the serum phosphorus is routinely provided in neither the results of a basic metabolic panel (BMP) nor a comprehensive metabolic panel (CMP) and instead must be specifically ordered as a separate test, this further highlights the need for the clinician to be aware of this entity as part of an appropriate investigation. …