Beyond FDG: Serial 68 Ga-FAPI PET/CT for Staging and Treatment Response Assessment in Metastatic Pleomorphic Lobular Breast Cancer.

68 Ga-FAPI PET/CT has demonstrated higher sensitivity than 18 F-FDG PET/CT in breast cancer, particularly in invasive lobular carcinoma. However, its role in treatment response assessment remains limited. We report a case of recurrent metastatic pleomorphic lobular breast cancer in which baseline 68 Ga-FAPI PET/CT revealed extensive regional and distant disease underestimated by 18 F-FDG PET/CT. Serial follow-up FAPI PET/CT after initiation of olaparib demonstrated marked response with near complete resolution of disease, highlighting the potential utility of FAPI PET/CT for response assessment in lobular breast cancer.