[Clinical and immunohistopathologic study of phosphaturic mesenchymal tumor]

Objective: To study the clinicopathological characteristics and immunohistochemical phenotype of phosphaturic mesenchymal tumor (PMT) . Methods: The clinicopathological data and immunohistochemical profiles were obtained retrospectively from 206 patients diagnosed with PMT at Peking Union Medical College Hospital (PUMCH) during July 2008 to September 2017, with a review of literature. Results: The mean age of PMT patients was 42 years (range 13 to 70 years), with a male to female ratio of 1.1∶1.0. All patients presented with different degree of bone pain, muscle weakness, shorten of stature, thoracic deformity and pathological fractures, with hypophosphatemia and high serum ALP. Phosphatemia returned to normal within 1 week after operation in all cases underwent complete tumor resection. The duration of osteomalacia before resection (documented in 197 cases) ranged from 20 days to 40 years (average 5.7 years). The average blood phosphorus concentration raised from 0.49 mmol/L to 0.92 mmol/L before and after tumor resection (P<0.01), with 147 cases (84.0%, 147/175) returned to normal range within 2 weeks. The rate or blood phosphorus concentration recovery in 15 days after operation was 79.6% in average, displayed significant differences between patients with complete resection and those with partial resection (85.4% vs. 21.1%, P<0.01). PMT lesions mainly involved lower extremities (55.8%), followed by head and neck (29.1%). In immunohistochemical study, all cases were positive for vimentin (100.0%), while most cases were positive for NSE (96.3%), CD56 (94.2%), FGF23(88.4%), CD68 (88.3%), D2-40 (70.9%), CD34 (23.1%), SMA (55.5%), bcl-2 (59.8%) and CD99 (47.1%). The Ki-67 positive index of tumor varied from less than 2% (51.4%), 3% to 10% (41.3%) to >10% (7.2%). Conclusions: PMT mainly occurs in lower limbs or head and neck, with unique clinical characteristics and blood biochemical indexes. The tumor expresses a variety of immunohistochemical markers, indicating the potential of multi-directional differentiation. Clinical profile, blood biochemistry testing and immunohistochemical phenotype is helpful for diagnosis of PMT.