FAPI-Negative FDG-Avid Metastatic Relapse of Breast Cancer on PET/CT

A 69-year-old woman with breast cancer underwent F-18-FDG PET/CT because of the increased CA-15-3 level. F-18-FDG PET/CT showed multiple hypermetabolic lymph nodes (LNs) in the neck and mediastinum. The patient was also referred for Ga-68-fibroblast activation protein inhibitor (FAPI) 04 PET/CT for further evaluation. However, F-18-FDG-avid LNs were FAPI-negative on Ga-68-FAPI-04 PET/CT. Supraclavicular LN biopsy confirmed the metastasis of breast cancer. Recent reports have focused on the potential of FAPI PET imaging in breast cancer; however, this case highlights that false-negative Ga-68-FAPI-04-PET/CT findings should also be considered while evaluating metastatic spread.

Automated summary

A 69-year-old woman with breast cancer had F-18-FDG PET/CT and Ga-68-FAPI-04 PET/CT for evaluation. F-18-FDG PET/CT showed hypermetabolic lymph nodes, while Ga-68-FAPI-04 PET/CT showed negative results for these nodes. Biopsy confirmed metastasis of breast cancer. This case highlights the possibility of false-negative Ga-68-FAPI-04 PET/CT findings in evaluating metastatic spread in breast cancer.