Case Report: Phosphaturic mesenchymal tumor of the scapula without calcification: a potential diagnostic pitfall.

Introduction: Phosphaturic mesenchymal tumor (PMT) is extremely rare, yet it is the most common cause of tumor-induced hypophosphatemic osteomalacia (TIO). Accurate histopathological diagnosis is critical for treatment. Nevertheless, its rarity and variable histomorphology make the diagnosis highly challenging. Notably, grungy calcification serves as a key morphological diagnostic clue for PMT. Case description: Herein, we report a case of a 57-year-old female patient who presented with a three-year history of recurrent bone pain. Laboratory investigations revealed hypophosphatemia. Whole-body positron emission tomography/computed tomography (PET/CT) showed an osteolytic lesion in the scapula. Biopsy demonstrated tumor cells arranged in a patchy pattern around the bone trabeculae and intermingled with mature adipose tissue. Myxoid degeneraty -30ion was observed in the stroma, but no calcification was identified. Immunohistochemically, the tumor cells expressed SATB2, SSTR2A, ERG, and CD56. The diagnosis of scapular PMT was ultimately established based on histopathological, clinical, and laboratory correlations, and the postoperative course showed substantial relief of bone pain and a progressive increase in serum phosphorus, which strongly reinforced this diagnosis. Conclusions: We report an unusual case of PMT arising in the scapula, characterized by the absence of calcification, which initially made the histopathological diagnosis elusive. This case highlights that pathologists must integrate clinical and laboratory findings, as these often provide greater diagnostic value than morphology alone, underscoring the importance of a multidisciplinary approach in diagnosing rare tumors.