Clavicular Osteoradionecrosis With 99mTc-FAPI-46 Uptake in a Patient With Breast Cancer

A 65-year-old woman with a 10-year history of right breast cancer underwent mastectomy and chemoradiotherapy. Five years later, left supraclavicular lymph node metastases prompted further chemoradiotherapy. She recently developed new right cervical lymph node metastases and left supraclavicular ulcer, referred for 99mTc-FAPI-46 imaging in a clinical trial. The whole body imaging demonstrated a focal uptake at the left thoracic inlet corresponded on CT to geographic osteolysis with irregular sclerotic margins at the medial end of the left clavicle, consistent with postradiotherapy osteonecrosis. This case emphasizes recognizing nonmalignant 99mTc-FAPI uptake, to avoid misinterpretation as metastatic disease.