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A 54-year-old woman suspected of lung cancer underwent [18F]FDG and [18F]FAPI-74 PET scans. CT revealed a 7-cm lesion in the left upper lobe. Despite detecting only necrotic cells on biopsy during bronchoscopy, malignancy was strongly suspected, leading to a planned lobectomy.
[18F]FDG PET-CT showed a highly avid mass (SUVmax: 14.2) in the left upper lung lobe, along with suspicious lymph node metastases with mild uptake in the left hilar, thoracic para-aortic, and left supraclavicular regions (A: MIP; B: PET/CT fusion, left). Similarly, [18F]FAPI-74 PET-CT also showed intense uptake (SUVmax: 9.02) with heterogeneous distribution in the same lesion, but with slightly larger extent (A and B, right), and no significant uptake was observed in the lymph nodes. Some areas displayed faint to mild FAPI uptake mismatched with FDG.
Histopathology revealed epithelioid granuloma (C: arrows indicate Langhans giant cells in H&E staining), but results for Grocott stain, PAS stain, and Ziehl–Neelsen stain were all negative. Immunohistochemical staining for FAP showed some areas with FAP expression surrounding the necrotic tissue in heterogenous uptake on [18F]FAPI-74 PET (D).
FAPI, an emerging pan-tumour tracer, also accumulates in chronic infections, leading to false positives [1]. Literature supports FAPI PET/CT’s use in granulomatous conditions like tuberculosis [2,3,4]. The mismatch between FAPI and FDG accumulation may represent varying lesion stages. The FDG-avid lesion might represent an inflammatory-proliferative stage, while the FAPI-positive lesion could represent a fibrotic phase [5]. Evaluation of FAPI uptake in non-malignant tumours will expand the clinical utility of FAPI-PET across diverse scenarios.
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Conceptualisation: TW, ID, and FLG; data collection: TW, TK, TH, MT, SN, TK, EF, TK, NO, SF, and HK; original draft preparation: TW and ID; review and editing: YM, JC, and FLG; supervision: EM, YS, and FLG. All authors have read and agreed to the submitted version of the manuscript.
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FLG is an advisor at ABX Radiopharmaceuticals, SOFIE Biosciences, Telix Pharma, and Alpha Fusion. FLG has shares in a consultancy group for iTheranostics. The other authors declare no potential conflicts of interest relevant to this study.
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Watabe, T., David, I.R., Kimura, T. et al. Epithelioid granuloma mimicking lung cancer showed intense uptake on [18F]FAPI-74 PET. Eur J Nucl Med Mol Imaging 51, 930–931 (2024). https://doi.org/10.1007/s00259-023-06478-9
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DOI: https://doi.org/10.1007/s00259-023-06478-9