Prognostic Value of Positive Presurgical FDG PET/CT in the Evaluation of Tumor-Induced Osteomalacia

Objectives Tumor-induced osteomalacia (TIO), a rare paraneoplastic syndrome, is curable by excision or destruction of the causative tumor. However, occasionally, TIO may relapse after surgical intervention. We aimed to investigate the roles of F-18-FDG PET/CT in the prognosis of TIOs. Methods Seventy-six patients who had surgically removed tumors that caused osteomalacia were included in this retrospective investigation. All patients underwent both F-18-FDG and Ga-68-DOTATATE PET/CT prior to surgery. The prognostic value of presurgical FDG PET/CT study was determined with 5-year follow-up. Results In the presurgical evaluation, Ga-68-DOTATATE detected lesions in all 76 patients. However, FDG PET/CT was positive in only 25 among all 76 patients. Following surgical removal of the causative tumor, all 76 patients had symptomatic relief and normalization of the serum phosphate level initially. However, 15 of 76 cases (19.7%) had recurrent hypophosphatemia and became symptomatic again during the follow-up. Among these 15 patients with recurrence, 11 (73.3%) had recurrent lesions at the original location of the resected causative tumors, whereas 4 were in other locations due to malignant nature of the primary tumor. Interestingly, 14 of these 15 patients with recurrent disease had positive presurgical FDG PET/CT findings with an incident ratio of 56.0% (14 of 25). In contrast, only 1 patient with recurrent disease had negative presurgical FDG PET/CT scan with an incident ratio of 1.9% (1 of 51), significantly less than the positive presurgical FDG PET/CT group (P < 0.05). Conclusions A positive presurgical FDG PET/CT suggests increased likelihood for possible recurrence of TIO after surgical resection. In contrast, when a causative tumor detected by Ga-68-DOTATATE PET/CT does not have elevated activity on FDG PET/CT, the chance of recurrence is very small.

Automated summary

This study found that a positive presurgical FDG PET/CT suggests an increased likelihood of TIO recurrence after surgical resection, while the chance of recurrence is very small when a causative tumor detected by Ga-68-DOTATATE PET/CT does not show elevated activity on FDG PET/CT.