Phosphaturic mesenchymal tumor: a report of 6 patients treated at a single institution and comparison with reported series.

Osteogenic osteomalacia (OO)-associated phosphaturic mesenchymal tumors (PMTs) might represent a single histopathologic paraneoplastic entity. These tumors are largely misunderstood, ignored, or unknown by pathologists and clinicians. To elucidate the characteristics of OO-associated PMTs, we retrospectively analyzed the clinicopathologic features of PMTs from 6 patients, with either known OO or features suggestive of PMT-mixed connective tissue variant, who were studied and managed at a single center during the period from 1993 to 2011. Histologically, the tumor showed proliferation of spindle cells with focal areas of matrix production that showed distinct calcification, ossification, and osteoid-like matrix. Two patients had no evidence of disease and normal biochemical values; the other 2 patients each had multiple surgeries for multiple recurrences. In conclusion, PMT is histologically a benign lesion, with the malignant and metastatic variant being extremely rare. Infiltration of surrounding tissue is a frequent feature that is best managed with complete surgical removal of all involved tissue, which dramatically resolves the tumor-associated osteomalacia.