Diagnostic performance and impact on patient management of ⁶⁸Ga-DOTA-TOC PET/CT for detecting osteomalacia-associated tumours

Purpose: Oncogenic osteomalacia is an endocrine disorder induced by small benign tumours (TIO) producing excessive fibroblast growth factor-23 (FGF23). The only way of curing oncogenic osteomalacia is surgical resection of the culprit TIO, which is extremely difficult to detect using conventional imaging modalities due to its small size and variable location in the body. Since TIO frequently overexpress somatostatin receptors, a clinical utility of SPECT or PET with radiolabelled somatostatin analogues has been reported. Among them, ⁶⁸Ga-DOTA-TOC has recently been granted a marketing authorization, facilitating its routine application. We report here the results of the first series evaluating the diagnostic performance of ⁶⁸Ga-DOTA-TOC PET/CT in detecting TIO and its impact on patient management.

Methods: ⁶⁸Ga-DOTA-TOC PET/CT and clinical and imaging data from 15 patients with clinical and biochemical signs of oncogenic osteomalacia were retrospectively reviewed. The ⁶⁸Ga-DOTA-TOC PET/CT findings were compared with the results of post-surgical pathology and clinical and biochemical follow-up.

Results: ⁶⁸Ga-DOTA-TOC PET/CT resulted in the detection of one focus suspicious for TIO in nine of 15 patients (60%), and a tumour was surgically removed in eight. Post-operative pathology confirmed a TIO in those eight patients whose symptoms diminished promptly and biochemical anomalies resolved. ⁶⁸Ga-DOTA-TOC PET/CT sensitivity, specificity and accuracy were 73%, 67% and 71%, respectively. ⁶⁸Ga-DOTA-TOC PET/CT findings affected patient management in 67% of cases. In particular, ⁶⁸Ga-DOTA-TOC PET/CT was able to detect the TIO with a negative or a false-positive result of a previous ¹¹¹In-pentetreotide SPECT/CT in 5/8 patients (63%) or a previous FDG PET/CT in 7/11 patients (64%). No close relationship was found between the positivity of ⁶⁸Ga-DOTA-TOC PET/CT and the serum level of a biochemical marker. However, a true-positive result of ⁶⁸Ga-DOTA-TOC PET/CT was obtained in only one patient with a non-elevated serum level of FGF23.

Conclusion: ⁶⁸Ga-DOTA-TOC PET/CT is an accurate imaging modality in the detection of TIO; in particular, it is worthwhile after failure of somatostatin receptor SPECT(/CT) or FDG PET/CT.