Radiolabeled fibroblast activation protein inhibitor (FAPI) PET in oncology: has the time come for 18 F-fluorodeoxygluco
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Radiolabeled fibroblast activation protein inhibitor (FAPI) PET in oncology: has the time come for 18F‑fluorodeoxyglucose to think to a well‑deserved retirement? Priscilla Guglielmo1 · Luca Guerra1,2 Received: 10 September 2020 / Accepted: 11 November 2020 © Italian Association of Nuclear Medicine and Molecular Imaging 2020
Keywords FAPI · FDG · Cancer · Positron emission tomography · Fibroblast activation protein Since the first application in human studies in 1976,18F-fluorodeoxyglucose (FDG) has gained importance over the decades in Nuclear Medicine departments, becoming at present the most used radiotracer not only in oncological studies but also in the management of several neurological entities, as well as in the assessment of myocardial viability. Despite the well-recognized role and the wide application of FDG in cancer imaging, many limitations have continuously emerged in these years, accounting for low sensitivity in well-differentiated cancers or in some histological types of tumors, as well as for poor detection rate in districts with high physiological uptake. These unmet needs have led in recent years to the development of a new class of radiopharmaceuticals, targeting the fibroblast activation protein (FAP), a type II membrane bound glycoprotein belonging to the dipeptidyl peptidase 4 family, which is able to activate cell signaling and contributes to tumor cell migration, invasion and tumor angiogenesis. This protein is highly expressed in cancer-associated fibroblasts of many epithelial carcinomas, especially in those characterized by a strong desmoplastic reaction, as they can comprise up to 90% of the tumor mass. Among these neoplasms, the most relevant are colorectal, breast, ovarian, pancreatic, and hepatocellular carcinomas [1, 2]. The new radiotracers are based on the FAP-specific inhibitor (FAPI) protein and several quinoline-based FAPIs labeled with positron emitters. Most recently, FAPI-04 and * Priscilla Guglielmo [email protected] 1
University of Milan Bicocca, Piazza dell’Ateneo Nuovo 1, Milan, Italy
School of Medicine and Surgery, University of Milan Bicocca, via Cadore 48, Monza, Italy
2
FAPI-02 labeled with 68Ga showed a rapid renal clearance and provided PET images with high tumor-to-background ratios in patients across a wide array of cancers, suggesting high potential for FAPI-targeted diagnostics [3]. Another tracer of this class, 68Ga-FAPI-46, emerged as the most promising tracer for therapeutic clinical application due to its high tumor uptake and retention, and lower uptake in normal organs compared with FAPI-04 [4]. Furthermore, because the 68Ga-FAPI tracers contain the universal DOTA-chelator, a theragnostic approach seems also an achievable goal [5]. In 2018, in fact, a first therapeutic application of 90Y-FAPI-04 had been published in a patient with advanced breast cancer [6]. A significant improvement in symptoms was achieved with a single administration and no toxicities were observed. However, due to a relatively fast clearance of
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