Functional imaging in primary tumour-induced osteomalacia: relative performance of FDG PET/CT vs somatostatin receptor-based functional scans: a series of nine patients

Context Localization of phosphatonin-producing mesenchymal tumours in patients with primary tumour-induced osteomalacia (pTIO) is challenging. Functional imaging plays an important role in the localization of these tumours. Objective We studied the relative performance of different functional imaging modalities (F-18-FDG PET/CT, Tc-99-HYNIC-TOC SPECT/CT and Ga-68-DOTATATE PET/CT) in tumour localization in cases of pTIO. Design and Methods Retrospective chart evaluation of 16 patients with confirmed TIO treated from 2006 to 2013 was conducted in a tertiary care referral centre. Results Of 16, nine patients had pTIO. In these nine, the positivity rates of different functional imaging modalities were 50% for F-18-FDG PET/CT (four of eight patients), 100% for Tc-99-HYNIC-TOC SPECT/CT (six of six patients) and 100% for Ga-68-DOTATATE PET/CT (seven of seven patients). Of nine patients, six were subjected to both the Tc-99-HYNIC-TOC SPECT/CT and Ga-68-DOTATATE PET/CT and all of them showed coregistration on the two scans. Conclusions In patients with pTIO, the somatostatin receptor-based functional scans performed better than F-18-FDG PET/CT in tumour localization. Amongst the somatostatin receptor-based scans, Tc-99-HYNIC-TOC SPECT/CT and Ga-68-DOTATATE PET/CT performed equally well for localization of tumours.