Phosphaturic mesenchymal tumors. Survey of 8 cases from a single Mexican medical institution.

Phosphaturic mesenchymal tumor (PMT) is a morphologically heterogeneous soft tissue and bone neoplasm, producing a paraneoplastic syndrome due to phosphate wasting. These tumors produce fibroblast growth factor 23, which is implicated in renal tubule phosphate loss. Medical records of patients seen from 1999 to 2013 with osteomalacia associated or not with a tumor were reviewed. Clinical and laboratory data, radiographic studies, and follow-up of 8 patients were tabulated. Histologic features and the immunoprofile of the tumors were analyzed. There were 208 patients with osteomalacia, but only 8 (3.84%) had osteomalacia associated with a tumor. The median age of the patients was 40 years. The tumor size ranged from 1.5 to 4 cm. Five were located in soft tissues and skin; and 3, in bones. Osteomalacia symptoms lasted from 2 to 14 years with a median of 6 years. Laboratory data showed hypophosphatemia and phosphaturia in all patients. All tumors were histologically benign. Histologically, the salient features were a hemangiopericytoid pattern, chronic hemorrhage, and microcystic areas. All neoplasms were diffusely positive for vimentin and focally positive for epithelial membrane antigen, CD34, and S-100 protein. Ki-67 was positive in approximately 10% of neoplastic cells in 2 cases and less than 1% in the remainder. We report 8 cases of PMTs producing osteomalacia, from a single third-level Mexican medical institution. These tumors occurred in soft tissues, skin, and bones. All tumors were benign, small, not easily detected by physical examination and diagnosed due to the metabolic abnormalities.