False-Negative 68Ga-FAPI PET/CT in Pediatric Thyroid Medullary Carcinoma Seen With 68Ga-DOTATOC PET/CT and 18F-FDG PET/CT.

In adults, 68Ga-FAP inhibitor (68Ga-FAPI) PET/CT outperforms 68Ga-radiolabeled somatostatin analog peptides (68Ga PET/CT) and 18F-FDG PET/CT in detecting thyroid lesions. This is the case of a 13-year-old boy newly diagnosed with medullary thyroid cancer with high calcitonin level. 68Ga PET/CT revealed the presence of only a primary thyroid lesion. Proven to be superior in detecting metastasis, 68Ga-FAPI PET/CT was performed. The results came out negative for primary and potential metastatic lesions. This case sheds shed light on false-negatives reported in 68Ga-FAPI PET/CT scans in pediatric patients, emphasizing the need for alternate radiotracers when a negative study is met.