FAP imaging in rare cancer entities—first clinical experience in a broad spectrum of malignancies

Abstract

Purpose 68 Ga-FAPI (fibroblast activation protein inhibitor) is a rapidly evolving and highly promising radiotracer for PET/CT imaging, presenting excellent results in a variety of tumor entities, particularly in epithelial carcinomas. This retrospective analysis sought to evaluate the potential and impact of FAPI-PET/CT in rare cancer diseases with respect to improvement in staging and therapy, based on tracer uptake in normal organs and tumors. Material and methods Fifty-five patients with rare tumor entities, defined by a prevalence of 1 person out of 2000 or less, received a 68 Ga-FAPI-PET/CT scan. Fourteen women and 41 men (median age 60) were included within the following subgroups: cancer of unknown primary (n = 10), head and neck cancer (n = 13), gastrointestinal and biliary-pancreatic cancer (n = 17), urinary tract cancer (n = 4), neuroendocrine cancer (n = 4), and others (n = 7). Tracer uptake was quantified by standardized uptake values SUVmax and SUVmean and the tumor-to-background ratio (TBR) was determined (SUVmax tumor/SUVmean organ). Results In 20 out of 55 patients, the primary tumor was identified and 31 patients presented metastases (n = 88), characterized by a high mean SUVmax in primary (10.1) and metastatic lesions (7.6). The highest uptake was observed in liver metastases (n = 6) with a mean SUVmax of 9.8 and a high TBR of 8.7, closely followed by peritoneal carcinomatosis (n = 16) presenting a mean SUVmax of 9.8 and an excellent TBR of 29.6. In terms of the included subgroups, the highest uptake regarding mean SUVmax was determined in gastrointestinal and biliary-pancreatic cancer with 9.8 followed closely by urinary tract cancer with 9.5 and head and neck cancer (9.1). Conclusion Due to excellent tumor visualization and, thereby, sharp contrasts in terms of high TBRs in primary and metastatic lesions in different rare malignancies, 68 Ga-FAPI-PET/CT crystallizes as a powerful and valuable imaging tool, particularly with respect to epithelial carcinomas, and therefore an enhancement to standard diagnostics imaging methodologies. The realization of further and prospective studies is of large importance to confirm the potential of FAP imaging in oncology.

FAP and FAPI-PET/CT in Malignant and Non-Malignant Diseases: A Perfect Symbiosis?

“…The overexpression of FAP in many malignancies is now well-known. Therefore, FAPI-PET/CT is a highly promising imaging method in a variety of malignancies [78][79][80] (Figure 4). The exact role of FAP in a tumorigenesis is unknown; however, its expression is related to the tumor proliferation, migration and invasion [46].…”

FAPI-PET/CT in Cancer Imaging: A Potential Novel Molecule of the Century

“…In a case report of liver metastasis from malignant melanoma, the lesion showed moderate 68 Ga-FAPI-04 uptake (SUVmax of 6.5) but was not compared with the current PET standard tracer 18 F-FDG ( 58 ). In another retrospective analysis of FAPI PET/CT imaging of rare malignancies, patients with melanoma (one case) also showed more favorable imaging results ( 59 ).…”

FAPI PET/CT in the Diagnosis of Abdominal and Pelvic Tumors

“…Kratochwil et al used 68 Ga-FAPI PET/CT to evaluate 80 patients with 28 different tumor entities, and found one of the highest SUV values in cholangiocarcinoma (mean SUV max > 12), which showed significantly-high uptake rates and image contrast on FAPI PET/ CT (19). Cholangiocarcinoma is a tumor with hyperplastic connective tissue and rich stroma, and the number of CAFs is usually several times that of actual cholangiocarcinoma cells, and thus 68 Ga-FAPI-04 has high sensitivity for the detection of cholangiocarcinoma (80,81). Similarly, 68 Ga-FAPI PET/CT has also been successfully applied to benign lesions of the biliary system.…”