Elevated FAPI Activity in Lung Metastases in a Pediatric Thyroid Cancer Patient With Thyroglobulin Elevation and Negative Iodine Scintigraphy.

In adults, fibroblast activation protein inhibitor (FAPI) PET/CT scan has been employed for detecting recurrent and metastatic thyroid cancer in patients with thyroglobulin elevation and negative iodine scintigraphy (TENIS) syndrome. A 7-year-old boy with TENIS syndrome underwent 18 F-FAPI PET/CT scan, which showed intense 18 F-FAPI activity in metastatic lymph node in the right neck and pulmonary metastases. Meanwhile, intense uptake was noted on the region of the right ischiopubic synchondrosis. This case sheds light on the use of FAPI PET/CT scan in pediatric patients with TENIS. The need for caution is also highlighted for false-positive FAPI PET/CT findings in pediatric patients.