Significant 99mTc-FAPI-46 Uptake in 2 Cases of TENIS Syndrome With Negative Tc-OCTREOTIDE Scan, a New Hope in Theranostic Applications

The role of fibroblast activation protein inhibitor (FAPI) as a novel radiopharmaceutical in the field of cancer diagnosis and treatment (theranostic) is still under investigation. We present 2 patients of differentiated thyroid cancer with thyroglobulin elevation and negative iodine scintigraphy (TENIS syndrome) who underwent 99mTc-OCTREOTIDE scan and 99mTc-FAPI SPECT/CT to evaluate possible sites for metastasis. 99mTc-OCTREOTIDE scan showed no remarkable uptake in these patients. On the other hand, foci of metastatic disease were found, with intense 99mTc-FAPI-46 uptake. Malignant FAPI uptake was evident in the lungs, liver, adrenal, and abdominal lymph nodes in a patient and in the lungs of another one. Due to proper uptake in diagnostic scans, these patients were recognized as a suitable candidate for treatment with 177Lu-FAPI-46.