Table 2.

Principal characteristics of the discussed FAPi agents.

FAPi Agents	FAPi Tracer Advantages	Histotype	Type of Publication	Limitations
[68Ga]FAPi *	Higher detection sensitivity in the liver, bones, and abdominal lymph nodes [40]; capable of localizing an abnormal foci of the uptake at the laryngeal mass, pulmonary nodules, the small nodule adjacent to the pulmonary hilum, which were previously ignored even in a non-contrast CT scan and an iodine scan [42].	PTC	Interesting image	[68Ga]Ga-FAPi uptake in mDTC lesions is not clearly associated with Tg levels; false positive uptake of [68Ga]Ga-FAPi in myelofibrosis; reactive LNs; arthritis; subcutaneous fibroma [34,42]; thyroiditis [63]; pancreatitis; tuberculous lesions [53]; and low uptake in MTCs [17].
	Capable of detecting primary thyroid diffuse large B-cell lymphoma due to the high degree of fibrosis (patient with previous Hashimoto’s thyroiditis) [53].	Hashimoto’s thyroiditis and primary thyroid diffuse large B-cell lymphoma	Case report
	Lower background value in liver, heart, brain, and gastrointestinal tract compared to [18F]FDG [68].	PTC
[18F]FAPi-42	Comparable diagnostic value with [18F]FDG; and a higher uptake, mainly in patients with a BRAFV600E gene mutation (prediction of mutation status) [35].	Different histotypes	Comparison between [18F]FAPi-42 and [18F]FDG	N.A.
[68Ga]FAPi-04 (otherwise named [68Ga]Ga-DOTA-FAPi-04)	Revealed more metastatic foci than [18F]FDG PET/CT, even if the detection rate rose to 93.1% when performed together [36]; and a higher detection power especially for lung lesions vs. [18F]FDG [39].	PTC	Comparative study between [68Ga]FAPi-04 and [18F]FDG	Diffuse uptake in chronic thyroiditis and immune-related thyroiditis [64,66] (confirmed also for [68Ga]Ga-FAPi-46 [62]) and also in follicular thyroid adenoma associated with fibrosis and calcification [65]; physiological uptake in myelofibrosis; reactive LNs; arthritis; and subcutaneous fibroma [34]. No statistical significance between the SUVmax of metastatic lesions and Tg level [37]. Faint or absent uptake in lesions less than 1 cm in size or with low Tg levels [37].
	Detected hepatic metastases, while [18F]FDG was negative (useful for restaging) [43]; and effective in evaluation of pleural metastasis and, therefore, in restaging [45].	PTC	Interesting image
	Capable of evaluating immune-mediated disease with activated fibroblast such as Graves ophthalmopathy [67].	PTC	Case report
	More sensitive than [18F]FDG for neck and distant metastases; and [68Ga]FAPi SUVmax of metastasis is higher than that of [18F]FDG [34].	Different histotypes	Comparative study between FAPi tracer and [18F]FDG
	Detection rate of 87.5% in metastatic and RR lesions, mainly LNs and distant metastases such as lung, pleura, and bone [37].	Different histotypes of RR-DTC (22/24 PTC)	Study on detection power of [68Ga]Ga-DOTA-FAPi-04
	Able to detect bone metastases at an earlier time point compared to [18F]FDG [69].	Different histotypes	Comparative studies
	Robust detection accuracy in liver lesions; and higher tumor-to-background value compared to [68Ga]Ga-DOTA-TATE [51].	MTC	Interesting image
	Higher detection power than that of [68Ga]Ga-DOTA-TOC [50].	Metastatic MTC	Case report
[68Ga]Ga-DOTA.SA.FAPi	Higher detection power than [18F]FDG PET/CT for lymph nodes, liver, brain, bowel, and lung metastases [38,52].	RR FCTC	Comparative study between [68Ga]Ga-DOTA.SA.FAPi and [18F]FDG	N.A.
[177Lu]Lu-DOTAGA.(SA.FAPi)2	Overall response rate of 92%, no grade III/IV hematological, renal, and hepatic toxicity [55].	RR-DTC	Theranostic study	N.A.
	Partial response [58].	High-grade MTC	Case report
	Negligible radiotracer uptake in the liver and colon at post-treatment [177Lu]Lu-DOTAGA.Glu.(FAPi)2 scintigraphy [57].	MTC	Comparative study between [177Lu]Lu-DOTAGA.(SA.FAPi)2 and [177Lu]Lu-DOTAGA.Glu.(FAPi)2
[177Lu]Lu-FAPi-46	Stable disease [56].	RR-DTC	Interesting image	N.A.

N.A.: not applicable; and *: the complete name of the molecule was not specified.