Diagnostic performance of ⁶⁸Ga-DOTATOC PET/CT in tumor-induced osteomalacia

Objective: Tumor-induced osteomalacia (TIO) is caused by typically small tumors that secrete fibroblast growth factor 23 (FGF23). As tumor resection is the only effective treatment for TIO, it is important to detect the culprit tumor. We aimed to assess the utility of ⁶⁸Gallium-DOTA-D-Phe(1)-Tyr(3)-octreotide (⁶⁸Ga-DOTATOC) PET/CT in TIO and the correlation between biochemical parameters and the PET/CT results. Methods: Thirty-five patients with clinically suspected TIO who had undergone ⁶⁸Ga-DOTATOC PET/CT were retrospectively analyzed. ⁶⁸Ga-DOTATOC PET/CT results were compared with biochemical parameters and the final diagnosis, including histopathology. Results: ⁶⁸Ga-DOTATOC PET/CT detected focal uptake consistent with TIO in 21/35 patients, one of which was considered false positive. In 16 patients, the cause of osteomalacia was confirmed histologically as phosphaturic mesenchymal tumor (n = 15) or fibrous dysplasia (n = 1). The other four patients were judged clinically as true positive by subsequent MRI and the clinical course. Overall, the detection rate of ⁶⁸Ga-DOTATOC PET/CT was 57% (20/35). Median tumor maximum standardized uptake value (SUVmax) was 6.9 (range 1.5–37.7). There was no significant difference in serum intact FGF23 level between DOTATOC-positive and DOTATOC-negative cases, and no significant correlation was observed between intact FGF23 level and tumor SUVmax. Conclusions: ⁶⁸Ga-DOTATOC PET/CT was clinically useful in detecting culprit tumors and subsequent patient management in TIO.