(68)Ga DOTA-TATE PET/CT allows tumor localization in patients with tumor-induced osteomalacia but negative (111)In-octreotide SPECT/CT

Tumor-induced osteomalacia (TIO) is a paraneoplastic syndrome characterized by renal phosphate wasting, hypophosphatemia and low calcitriol levels as well as clinical symptoms like diffuse bone and muscle pain, fatigue fractures or increased fracture risk. Conventional imaging methods, however, often fail to detect the small tumors. Lately, tumor localization clearly improved by somatostatin-receptor (SSTR) imaging, such as octreotide scintigraphy or octreotide SPECT/CT. However, recent studies revealed that still a large number of tumors remained undetected by octreotide imaging. Hence, studies focused on different SSTR imaging methods such as (68)Ga DOTA-NOC, (68)Ga DOTA-TOC and (68)Ga DOTA-TATE PET/CT with promising first results. Studies comparing different SSTR imaging methods for tumor localization in TIO are rare and thus little is known about diagnostic alternatives once a particular method failed to detect a tumor in patients with TIO. Here, we report the data of 5 consecutive patients suffering from TIO, who underwent both (111)Indium-octreotide scintigraphy ((111)In-OCT) SPECT/CT as well as (68)Ga DOTA-TATE PET/CT for tumor detection. While (111)In-OCT SPECT/CT allowed tumor detection in only 1 of 5 patients, (68)Ga DOTA-TATE PET/CT was able to localize the tumor in all patients. Afterwards, anatomical imaging of the region of interest was performed with CT and MRI. Thus, successful surgical resection of the tumor was achieved in all patients. Serum phosphate levels returned to normal and all patients reported relief of symptoms within weeks. Moreover, an iliac crest biopsy was obtained from every patient and revealed marked osteomalacia in all cases. Follow-up DXA revealed an increase in BMD of up to 34.5% 1-year postoperative, indicating remineralization. No recurrence was observed. In conclusion our data indicates that (68)Ga DOTA-TATE PET/CT is an effective and promising diagnostic tool in the diagnosis of TIO, even in patients in whom (111)In-OCT prior failed to detect a tumor.