Finding out the cloak-and-dagger tumor in state of the art

Objectives Tumor-induced osteomalacia (TIO) is a rare disease characterized by hypophosphatemia and osteomalacia. TIO patients suffer from gradually worsening bone pain and muscle weakness and live in a poor quality of life when most of them are still very young. The disease is usually driven by an occult, slow-growing tumour. The only way to cure is to find out the cloak-and-dagger tumor and remove it completely. However, localization of the causative tumor in TIO patients is usually a challenge because most of the lesions are small and stealthy. A novel diagnostic approach, 68Ga-DOTATATE PET/CT, was evaluated for detection of the tumor-induced osteomalacia (TIO) lesions, which was compared with 18F-FDG PET/CT and 99mTc-HYNIC-TOC scintigraphy case by case.

Methods A total of 54 consecutive patients (M 26, F 28, aged 41.5±12.1 years) suffering from osteomalacia underwent PET/CT scans from head to toe 30-45 min after intravenous injection of 111-148 MBq (3-4 mCi) 68Ga-DOTATATE. All 54 patients underwent 99mTc-HYNIC-TOC scintigraphy and 53 patients accepted 18F-FDG PET/CT within 2 weeks for comparison.

Results 68Ga-DOTATATE PET/CT showed positive findings in 44 (81.5%) of the 54 osteomalacia patients, while only 16 (29.6%) were positive on 18F-FDG PET/CT and 15 (27.8%) were detected by 99mTc-HYNIC-TOC scintigraphy. The tumors sized from 1.1 to 6.7 (2.5±1.3) cm was found in the mandible, base of pelvic cavity, caudal vertebrae, and other sites. The SUVmax of 68Ga-DOTA-TATE (11.8±8.9) were significantly higher than those of 18F-FDG (4.4±4.0, P<0.05). To date, 31 of the 44 positive tumors were surgically removed. Among them, 30 were found to be phosphaturic mesenchymal tumors and the other one was diagnosed as odontogenic fibrous tumors. So far, at least in 7 of 10 68Ga-DOTATATE-negative patients, the osteomalacia have been found caused by other reasons such as Fanconi syndrome.

Conclusions 68Ga-DOTATATE PET/CT is a state-of-the-art approach for detection of the causative tumors in patients with osteomalacia.