Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5946_Библиотеки_им_академика_М_И_Перельмана

An attractive alternative for diagnostic pur­poses is represented by 18F-labeled FAPI­radiotracers, such as 18F-FAPI-74: aluminum uoride-NOTA complexes and 6- ouronicotineamides are involved in the syn­thesis and the uorination of this radiopharma­ceutical [3].

SUVmax of FAPi was low in brain and lung parenchyma, myocardial wall, parotid glands, normal liver, gastrointestinal tract, spleen, and bone marrow. Breast and pancreas healthy tissues showed low to mild FAPi uptake, with breast accumulation depending on the hormonal status. Conversely, thyroid, oral mucosa, esophagus, muscles, and blood pool exhibit only mild physi­ological uptake. Healthy kidney cortex shows mild to moderate uptake, submandibular salivary glands moderate to high physiologic accumula­tion of FAPi tracers. Intense activity is described in the urinary tract, due to kidneys as the main excretory organs, and some uptake in the gall­bladder and common bile duct, implying elimi­nation via hepatobiliary system as well [16]. Therefore, tumor-to-background ratios in most normal organs were equal to that of F18­FDG.However, high uptake of FAPi was reported in the uterus, higher in pre-menopausal than in post-menopausal status (average SUVmax: 11.7 (n=12) vs 3.0 (n =68)) [17]. Finally, reactive lymph nodes may show FAPi uptake, with SUV overlapping metastatic nodes SUV values [18]. However, as previously reported, FAP is also seen in benign tumors, brotic, granulomatosis, scarring/wound, degenerative and inammatory disease that can make interpreting FAPI-PET ndings tricky [18, 19] unless comorbidities and pitfalls are well-known.

Therefore, FAPIs demonstrated highly prom­ising results in previously conducted studies regarding various tumor entities [17] and in sev­eral clinical and research settings [22].

A recent interesting study quantied and com­pared the tumor uptake on Ga-FAPI PET/CT of 28 different primary and metastatic tumors, to identify the most promising indications for future application [11]. According to the authors, SUV varied across and within all tumor entities with a low background uptake in muscle and blood pool and reported the following:

– The intermediate average SUV was in hepato-

cellular, colorectal, head–neck, ovarian, pan-

In oral squamous cell carcinoma (OSCC), both FAPI and FDG imaging had comparable sensitivity and specicity for detecting primary tumors and cervical lymph node metastases [25,

The FAPI-PET imaging has been tested in dif­ferentiated thyroid cancer with thyroglobulin elevation and negative iodine scintigraphy, dem­onstrating its usefulness for localizing recurrent or metastatic lesions [

34], especially in lymph

FAPI-PET imaging demonstrated improved sensitivity in liver, gastric, and pancreatic cancers when compared with FDG, while the sensitivities of both tracers were comparable in colorectal and esophageal cancers [25].

In esophageal cancer, the FAPI-PET/CT methodology showed favorable tumor-to-back­ground contrast in esophageal cancer and might provide additional information for target volume delineation (and help avoid tumor geographic misses) [

For liver cancer, including hepatocellular car­cinoma and intrahepatic cholangiocarcinoma, FAPI-PET has been demonstrated to have a higher sensitivity than FDG in detecting primary liver tumors (partly attributed to higher tumor uptake and lower hepatic background uptake as compared with F-FDG) as well as extrahepatic metastases [25]. In addition, FAPI uptake is cor­related mainly with tumor size in the hepatocel­lular carcinoma [50]. FAPI-PET correctly identies primary liver tumors and metastasis equivalent to the CE-CT and liver MRI, but better than FDG PET. Therefore, FAPI-PET imaging may improve tumor staging, recurrence detec­tion, and implementation of necessary treatment modications [51]. Moreover, it was concluded that FAPI imaging was superior to FDG imaging in detection of liver metastases of gastrointestinal system cancer, especially in cases of negative FDG-PET imaging [52].

contrasts in primary and metastatic lesions and higher TBR than F-FDG-PET/CT, 68Ga-FAPI PET/CT presents a promising imaging method for staging and follow-up of gynecological tumors. The presence or absence of the menstrual cycle seems to correlate with FAPI accumulation in the normal endometrium and breast [

As regards lung cancer, both FAPI and FDG had comparable detection rates for primary tumors in a cohort of 34 patients [25]. Moreover, FAPI-42 showed higher SUVmax compared to FDG in the lymph nodes, pleura, bones, and other tissue lesions [58, 59]. Interestingly, several case reports and papers agree on the improved detec­tion rate of FAPI imaging, with respect to FDG, in brain lesions from lung cancers [60, 61], prob­ably due to the higher TBR compared to FDG, supporting the potential advantages over FDG for the primary staging of lung. However, these reports regard small samples and the results are heterogeneous, in some cases without signicant differences over the FDG imaging [62].

Notably, FAPI-PET imaging revealed differ­ences in FAP expression in metastases of lung cancer, with the highest expression specically in bone metastases, and thus, may be valuable for distinguishing different pathological types of lung cancer [63].

– In a case report of abdominal leiomyosarcoma

nary artery [67].

– In a case report of gastric Kaposi sarcoma [68]

in which, beyond the promising role in the detection of gastric inltration, the FDG seems more useful in the staging.

– In a case of recurrent undifferentiated pleo-

morphic sarcoma of colon mesentery [69].

[70].

– In a case of cardiac angiosarcoma [71] in

which FAPI was not superior to FDG.

– In a case of chondrosarcoma of nasal cavity

[72].

– A case report in bilateral primary angiosar-

coma of the breast [73].

Head-to-head comparison studies of hema­tological neoplasms are relatively rare com­pared to studies evaluating solid tumors [25]. Moreover, the results are not heterogeneous. Detecting FAP expression in lymphoma lesions may be an alternate method for characterizing lymphoma proles according to previous work on 73 patients with Hodgkin and non-Hodgkin lymphomas [74]. However, a direct compari­son with FDG imaging demonstrated FAPI’s inferior sensitivity and accuracy in a subgroup of eight patients with hematological neo­plasms, including multiple myeloma and lym­phoma [75].

76], hepatic

lesion of mucosa-associated lymphoid tissue lymphoma [77], and primary hepatic extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue [78].

As regards neuroendocrine tumors (NET), currently, the real-life clinical impact of these tracers is still mostly not known; however, the favorable biodistribution and the possibility to use new theragnostic pairs may provide novel diagnostic as well as therapeutic options [79].

The biodistribution of FAPI tracers has been described also in pheochromocytoma [11], in renal cell carcinoma [11] and prostate cancer [11] without performing a comparative study with fur­ther modalities.

As studies on FAPI-PET grow in number and size, incidental ndings related to non-oncologic conditions have been increasingly reported. FAPI-PET uptake has been reported in various conditions such as benign tumors, brotic, granu­lomatosis, scarring/wound, degenerative dis­eases, and inammatory diseases. The knowledge of physiological and non-oncologic causes of FAPI uptake is indispensable for accurate FAPI-

– Liver brosis and cirrhosis [82]. – Crohn’s disease where FAP is signicantly

[83]. – Arthritis [82]. – IgG4-related disease [82]. – Cardiovascular disease [82].

See Figs.15.1, 15.2, 15.3 and 15.4.