Clinical utility of 68Ga-FAPI PET/CT in breast cancer: Highlight on subtypes with diagnostic limitations on 18F-FDG PET/CT

Background 18 F-FDG PET/CT is established in breast cancer imaging but underperforms in invasive lobular carcinoma (ILC), low-proliferative luminal A tumors, and invasive ductal carcinoma (IDC) with lobular features. 68 Ga-FAPI PET/CT targets cancer-associated fibroblasts (CAFs) within the tumor microenvironment and demonstrates superior lesion detection in 18 F-FDG -low subtypes. The aim of this study is to illustrate, in hypothesis-generating fashion, the potential clinical utility of 68 Ga-FAPI PET/CT across six breast cancer cases where 18 F-FDG PET/CT demonstrates diagnostic limitations. Methods Retrospective single-centre case series (January 2025–March 2026). Seven cases were selected representing distinct clinical scenarios. Both modalities were performed within 10 days with no intervening treatment. Images were reviewed by two nuclear medicine physicians; clinical impact was assessed by two medical oncologists using predefined categories. Results 68 Ga-FAPI PET/CT demonstrated additive clinical information in all six cases including detection of occult nodal disease, unusual metastatic sites, multicentric disease, and upstaging from curative to palliative intent. Median FAPI SUVmax (19.6; range 13.6–24.2) substantially exceeded median 18 F-FDG SUVmax (3.75; range 2.2–4.5) across all cases. Median FAPI-to-FDG SUVmax ratio was 5.2 (range 3.6–8.4). Conclusions 68 Ga-FAPI PET/CT is a clinically valuable complementary or alternative imaging modality. These six cases suggest a potential role for 68 Ga-FAPI PET/CT in FDG-limited breast cancer subtypes. Findings are hypothesis-generating and require prospective validation in adequately powered cohort studies.