First Clinical Experience of 68Ga-FAPI PET/CT in Tertiary Cancer Center: Identifying Pearls and Pitfalls

Abstract

Background/Objectives: Over the past four years, ⁶⁸Ga-fibroblast activation protein inhibitor (FAPI) positron emission tomography/computed tomography (PET/CT) has been established at a tertiary cancer care facility in Jordan. This retrospective study aims to explore tracer uptake metrics across various epithelial neoplasms, identify diagnostic pitfalls associated with ⁶⁸Ga-FAPI PET/CT, and evaluate the influence of ⁶⁸Ga-FAPI PET/CT staging results on changes in therapeutic intent compared to gold standard molecular imaging modalities. Methods: A total of 48 patients with biopsy-confirmed solid tumors underwent 77 ⁶⁸Ga-FAPI PET/CT examinations for molecular imaging assessment, encompassing neoplasms originating from the gastrointestinal tract, head and neck, hepatobiliary system, pancreas, breast, and lung. Results: Notably, pancreaticobiliary tumors exhibited the highest tracer uptake, with mean maximum standardized uptake values (SUVmax) and tumor-to-background ratios (TBR) surpassing 10. A comparative sub-analysis of ⁶⁸Ga-FAPI PET metrics in 20 treatment-naïve patients revealed a significant correlation between ⁶⁸Ga-FAPI uptake metrics and tumor grade (Spearman's rho 0.83; p = 0.00001). Importantly, the results from ⁶⁸Ga-FAPI PET/CT influenced treatment decisions in 35.5% of the cases, primarily resulting in an escalation of management plans. A total of 220 diagnostic challenges were identified across 88.3% of the scans, predominantly within the musculoskeletal system, attributed to degenerative changes (99 observations). Conclusions: This comprehensive analysis highlights the potential significance of ⁶⁸Ga-FAPI PET/CT in oncological imaging and treatment strategy, while also emphasizing the necessity for meticulous interpretation to mitigate diagnostic challenges.

Keywords: FAPI; PET/CT; SUVmax; TBR; diagnostic pitfalls; fibroblast activation protein; hepatobiliary tumors; management; pancreatic adenocarcinoma; therapeutic management.

Figure 1

(A) Box plots demonstrating the distribution of average maximum standardized uptake values (SUVmax) for various cancer subtypes. (B) Box plots demonstrating the distribution of average tumor-to-background ratios (TBRs) for various cancer subtypes.

Figure 2

(A) Box plots demonstrating the distribution of average SUVmax for various cancer subtypes in therapy naïve patients. (B) Box plots demonstrating the distribution of average TBR for various cancer subtypes in therapy naïve patients.

Figure 3

A 74-year-old male patient with histopathology-proven gastric adenocarcinoma with signet ring following subtotal gastrectomy and abdominal lymphadenectomy and adjuvant chemotherapy. (A,B) At the end of chemotherapy, the maximum intensity projection (MIP) and sagittal views of ¹⁸F-FDG PET/CT were unremarkable for residual and/or recurrent disease. (C,D) On the contrary, ⁶⁸Ga-FAPI MIP and sagittal views of ⁶⁸Ga-FAPI PET/CT acquired 18 days later demonstrated interval development of intensely ⁶⁸Ga-FAPI-avid peritoneal deposition consistent with peritoneal carcinomatosis (arrows), prompting an upgrade in the patient’s treatment plan.

Figure 4

(A) A multitude of diagnostic pitfalls were encountered during the ⁶⁸Ga-FAPI PET/CT evaluation of a 61-year-old male patient with colonic mucinous following right hemicolectomy and adjuvant chemotherapy as evident in the MIP image (annotations). (B) An axial chest PET/CT image revealed a mildly ⁶⁸Ga-FAPI-avid focus involving the right axillary fold, likely of non-specific nature (dotted arrow). (C) An axial pelvic PET/CT image exposed diffuse ⁶⁸Ga-FAPI localization at the site of an enlarged prostate due to benign prostatic hyperplasia (curved arrow). (D) An axial pelvic PET/CT image identified sphincteric ⁶⁸Ga-FAPI localization at the anorectal junction (asterisk). (E) An axial lower extremity PET/CT image demonstrated ⁶⁸Ga-FAPI localization within both knee joints, which can be best ascribed to the degenerative process (arrows).