Case 1 in Table 1:
Here, we present a representative patient with a residual tumor. A 38-year-old male was referred to the evaluation of worsening pain in his knee, hips, and lower back without an injury history. The medical history of the patient was unremarkable. On laboratory results, low serum phosphate (1.3 mg/dL), high ALP (524 U/L), intact parathyroid hormone (117 pg/mL), and FGF23 (660 pg/ml) levels were observed. Functional imaging with somatostatin receptor scintigraphy showed increased uptake in the nasal region (Fig. 2a). A contrast-enhanced maxillofacial area CT revealed a mass in the nasal cavity (Fig. 2b and c). An incisional biopsy was performed, and microscopic examination revealed a vascular-rich tumor composed of FGF23-positive bland spindle cells (Fig. 2d). A PMT diagnosis was made. Two weeks after the initial biopsy, endoscopic resection of the tumor was performed. However, low serum phosphate and high FGF23 levels persisted, and MRI revealed a residual tumor at the left cribriform plate one year after resection (Fig. 2e and f). After the patient underwent re-excision under the endoscopic endonasal technique, the serum phosphate levels returned to normal. The last follow-up was negative for tumor recurrence or residual tumor.