Diagnostic performance of Ga-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 Gallium-DOTA-D-Phe(1)-Tyr(3)-octreotide (Ga-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 Ga-DOTATOC PET/CT were retrospectively analyzed. Ga-DOTATOC PET/CT results were compared with biochemical parameters and the final diagnosis, including histopathology.

Results: Ga-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 Ga-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: Ga-DOTATOC PET/CT was clinically useful in detecting culprit tumors and subsequent patient management in TIO.