Diagnostic Performance of Somatostatin Receptor-directed PET/CT for Tumor-induced Osteomalacia

To evaluate the efficacy of somatostatin receptor (SSTR)-directed PET/CT in localizing phosphaturic mesenchymal tumors (PMT) in patients with suspected tumor-induced osteomalacia (TIO) and to explore relationships between imaging parameters and biochemical markers.

This retrospective analysis included 20 patients with suspected TIO, undergoing SSTR-directed PET/CT. Imaging findings and laboratory markers were assessed. SSTR-positive tumors were resected, while patients without detectable tumor, but persistent renal phosphate wasting, continued on medical treatment. Follow-up assessments included laboratory values and clinical examinations.

PMT were detected on PET in 12 patients (60%), were resected, and confirmed immunohistochemically. Phosphorus levels (r = 0.26; p = 0.03), tubular reabsorption of phosphate (TRP; r = 0.77; p < 0.01) and tubular maximum of phosphate reabsorption over GFR (TmP/GFR; r = 0.44; p = 0.07) were lower in patients with detected PMT compared to those without. Elevation of fibroblast growth factor 23 (FGF23) was not significantly higher in PMT positive vs negative patients (253% vs 134% above the upper limit of normal; p = 0.97). Total lesion uptake (TLU) negatively correlated with TmP/GFR (r = -0.71; p = 0.03). A maximum standardized uptake value (SUVmax) threshold of 7.6 differentiated PMT from bone fractures (83% sensitivity; 100% specificity). Post-resection follow-up confirmed clinical cure in all cases.

In SSTR-directed PET/CT, a distinction between PMT and bone fracture may be possible with a SUVmax threshold of 7.6. The integration of PET derived TLU, along with TmP/GFR may improve diagnosis and treatment planning for TIO.