Metastatic Malignant Phosphaturic Mesenchymal Tumor of Mandibular Alveolus: a Rare Case Report and Review of Literature.

Malignant phosphaturic mesenchymal tumors (PMT) of the head and neck region are extremely rare, which cause paraneoplastic syndrome characterized by hypophosphatemia and osteomalacia. We report a 48-year-old gentleman who had persistent knee and calf pain associated with weakness in lower limbs on presentation. He had hypophosphatemia and elevated FGF-23 and 68 Ga-DOTANOC PET scan showed soft tissue density mass with increased peripheral radiotracer uptake in the left mandibular alveolus and adjoining floor of the mouth, revealing the primary tumor. It also showed a non-avid, histological inconclusive nodule of 17 × 12 mm in size in the lower lobe of the right lung. The patient was treated with composite resection and bilateral level I-III neck dissection with microvascular free fibula osteocutaneous flap mandibular reconstruction. Histopathological examination showed malignant PMT with positive soft tissue margins and bilateral metastatic cervical lymphadenopathy. The patient received adjuvant radiation therapy and sequential post therapy scans showed no evidence of locoregional disease, however showed progressive functional pulmonary metastatic disease which did not respond to chemotherapy. We also made a brief review of literature of head and neck malignant PMT focusing on presentation, primary and adjuvant treatment, and response to treatment. © Indian Association of Surgical Oncology 2021.