Intense FAP Expression of Ovarian Metastatic Breast Cancer Detected by [ 68 Ga]RTX-1363 PET/CT.

PET/CT targeting fibroblast activation protein α (FAP) in cancer-associated fibroblasts shows promise in theranostics. Here, we report the case of a 31-year-old woman with hormone receptor-positive/human epidermal growth factor receptor 2-negative breast cancer who presented with rising CA15-3 for further diagnostic workup. Whereas [ 18 F]FDG PET/CT was unremarkable, novel [ 68 Ga]RTX-1363 PET/CT revealed intense tracer accumulation in thoracoabdominal lymph nodes and both ovaries. Follow-up imaging confirmed tumor progression, and diagnostic laparoscopy verified metastatic disease in the ovaries with high FAP expression in the tumor stroma. This case underscores the superior sensitivity of [ 68 Ga]RTX-1363 PET/CT over [ 18 F]FDG PET/CT, enhancing breast cancer diagnostic and therapeutic strategies.