Usefulness of 68Ga-DOTATOC PET/CT to localize the culprit tumor inducing osteomalacia

Abstract

Tumor-induced osteomalacia (TIO) is an uncommon paraneoplastic syndrome presenting with sustained hypophosphatemia. Treatment of choice is removal of the tumor causing the TIO, but identification of the culprit tumor by routine imaging is challenging. This study aimed to assess the usefulness of somatostatin receptor imaging, called 68Ga-DOTATOC PET/CT, in the management of patients with TIO. Twelve patients who were suspected of having TIO underwent 68Ga-DOTATOC PET/CT. Lesion detectability and maximum standardized uptake value (SUVmax) were determined and retrospectively compared with the clinical/imaging surveillance and histopathologic diagnosis. The median duration of suspected TIO with hypophosphatemia was 7.8 years (range 2.1–21.0). Conventional radiologic and/or nuclear medicine images failed to identify the culprit tumors. However, 68Ga-DOTATOC PET/CT scans showed that 8 of the 12 patients had positive lesions, suggesting the presence of focal culprit tumors. The SUVmax of positive tumors was 1.9–45.7 (median: 11.5). Six skeletal lesions and two extra-skeletal lesions were identified. Seven of the lesions were pathologically confirmed as potential culprits of TIO. Hypophosphatemia was resolved in five patients who underwent lesion excision. The 68Ga-DOTATOC PET/CT is a useful whole-body imaging modality for the detection of causative tumors in patients with suspected TIO.