Non-oncologic incidental uptake on FAPI PET/CT imaging

Diagnostic accuracy and clinical value of [68Ga]Ga-FAPI-46 PET/CT for staging patients with ovarian cancer: study protocol for a prospective clinical trial

BACKGROUND

[18F]Fluorodeoxyglucose ([18F]FDG) positron emission tomography (PET) is recommended during diagnostic work-up for ovarian cancer; however, [18F]FDG PET has several inherent limitations. The novel oncologic PET-tracer fibroblast activation protein inhibitor (FAPI) has demonstrated promising results in multiple cancer types, including ovarian cancer, and could overcome the limitations of [18F]FDG PET; however, high-quality clinical studies are lacking. The primary objective of the present study is to compare the diagnostic accuracy of [68Ga]Ga-FAPI-46 PET/CT and [18F]FDG PET/CT in ovarian cancer patients and to investigate how this potential difference impacts staging and patient management.

METHODS AND DESIGN

Fifty consecutive ovarian cancer patients will be recruited from Aalborg University Hospital, Denmark. This study will be a single-center, prospective, exploratory clinical trial that adheres to the standards for reporting diagnostic accuracy studies (STARD). This study will be conducted under continuous Good Clinical Practice monitoring. The eligibility criteria for patients are as follows: (1) biopsy verified newly diagnosed ovarian cancer or a high risk of ovarian cancer and referred for primary staging with [18F]FDG PET/CT; and (2) resectable disease, i.e., candidate for primary debulking surgery or neoadjuvant chemotherapy followed by interval debulking surgery. All recruited study subjects will undergo [68Ga]Ga-FAPI-46 PET/CT at primary staging, before primary debulking surgery or neoadjuvant chemotherapy (Group A + B), in addition to conventional imaging (including [18F]FDG PET/CT). Study subjects in Group B will undergo an additional [68Ga]Ga-FAPI-46 PET/CT following neoadjuvant chemotherapy prior to interval debulking surgery. The results of the study-related [68Ga]Ga-FAPI-46 PET/CTs will be blinded, and treatment allocation will be based on common clinical practice in accordance with current guidelines. The histopathology of surgical specimens will serve as a reference standard. A recruitment period of 2 years is estimated; the trial is currently recruiting.

DISCUSSION

To our knowledge, this trial represents the largest, most extensive, and most meticulous prospective FAPI PET study conducted in patients with ovarian cancer thus far. This study aims to obtain a reliable estimation of the diagnostic accuracy of [68Ga]Ga-FAPI-46 PET/CT, shed light on the clinical importance of [68Ga]Ga-FAPI-46 PET/CT, and examine the potential applicability of [68Ga]Ga-FAPI-46 PET/CT for evaluating chemotherapy response.

TRIAL REGISTRATION

clinicaltrials.gov: NCT05903807, 2nd June 2023; and euclinicaltrials.eu EU CT Number: 2023-505938-98-00, authorized 11th September 2023.

Rational Design and Pharmacomodulation of 18F-Labeled Biotin/FAPI-Conjugated Heterodimers

Due to the complex heterogeneity in different cancer types, the heterodimeric strategy has been intensively practiced to improve the effectiveness of tumor diagnostics. In this study, we developed a series of novel 18F-labeled biotin/FAPI-conjugated heterobivalent radioligands ([18F]AlF-NSFB, [18F]AlF-NSFBP2, and [18F]AlF-NSFBP4), synergistically targeting both fibroblast activation protein (FAP) and biotin receptor (BR), to enhance specific tumor uptake and retention. The in vitro and in vivo biological properties of these dual-targeting tracers were evaluated, with a particular focus on positron emission tomography imaging in A549 and HT1080-FAP tumor-bearing mice. Notably, in comparison to the corresponding FAP-targeted monomer [18F]AlF-NSF, biotin/FAPI-conjugated heterodimers exhibited a high uptake in tumor and prolong retention. In conclusion, as a proof-of-concept study, the findings validated the superiority of biotin/FAPI-conjugated heterodimers and the positive influence of biotin and linker on pharmacokinetics of radioligands. Within them, the bispecific [18F]AlF-NSFBP4 holds significant promise as a candidate for further clinical translational studies.

A retrospective study of 68Ga-FAPI PET/CT in differentiating the nature of pulmonary lesions

Purpose

This study aimed to investigate the characteristics of various pulmonary lesions as revealed by 68Ga-FAPI PET/CT and to determine the utility of 68Ga-FAPI PET/CT in distinguishing the nature of these pulmonary lesions.

Methods

A retrospective analysis was conducted on 99 patients with pulmonary lesions, who were categorized into three distinct groups: primary lung tumors (G1), metastatic lung tumors (G2), and benign lesions (G3). Each participant underwent a 68Ga-FAPI PET/CT scan. Among these groups, variables such as the Tumor/Background Ratio (TBR), Maximum Standardized Uptake Value (SUVmax), and the true positive rate of the lesions were compared. Furthermore, the FAPI uptake in nodular-like pulmonary lesions (d<3cm) and those with irregular borders was evaluated across the groups. A correlation analysis sought to understand the relationship between FAPI uptake in primary and pulmonary metastatic lesions.

Results

The study's participants were composed of 52 males and 47 females, with an average age of 56.8 ± 13.2 years. A higher uptake and detection rate for pulmonary lesions were exhibited by Group G1 compared to the other groups (SUVmax [G1 vs. G2 vs. G3: 9.1 ± 4.1 vs. 6.1 ± 4.1 vs. 5.3 ± 5.8], P<0.05; TBR [G1 vs. G2 vs. G3: 6.2 ± 2.4 vs. 4.1 ± 2.2 vs. 3.2 ± 2.7], P<0.01; true positive rate 95.1% vs. 88% vs. 75.6%]. In nodular-like lung lesions smaller than 3 cm, G1 showed a significantly higher FAPI uptake compared to G2 and G3 (SUVmax [G1 vs. G2 vs. G3: 8.8 ± 4.3 vs. 5.2 ± 3.2 vs. 4.9 ± 6.1], P<0.01; TBR [G1 vs. G2 vs. G3: 5.7 ± 2.7 vs. 3.7 ± 2.1 vs. 3.3 ± 4.4], P<0.05). Both G1 and G2 demonstrated significantly elevated FAPI agent activity in irregular-bordered pulmonary lesions when compared to G3 (SUVmax [G1 vs. G2 vs. G3: 10.9 ± 3.3 vs. 8.5 ± 2.7 vs. 4.6 ± 2.7], P<0.01; TBR [G1 vs. G2 vs. G3: 7.2 ± 2.1 vs. 6.4 ± 1.3 vs. 3.2 ± 2.4], P<0.01). A positive correlation was identified between the level of 68Ga-FAPI uptake in primary lesions and the uptake in pulmonary metastatic lesions within G2 (r=0.856, P<0.05).

Conclusion

68Ga-FAPI PET/CT imaging proves to be of significant value in the evaluation of pulmonary lesions, offering distinctive insights into their nature.

Diagnostic and Therapeutic Application of Fibroblast Activation Protein Inhibitors in Oncologic and Nononcologic Diseases

ABSTRACT

Fibroblast activation protein inhibitor positron emission tomography (PET) has gained interest for its ability to demonstrate uptake in a diverse range of tumors. Its molecular target, fibroblast activation protein, is expressed in cancer-associated fibroblasts, a major cell type in tumor microenvironment that surrounds various types of cancers. Although existing literature on FAPI PET is largely from single-center studies and case reports, initial findings show promise for some cancer types demonstrating improved imaging when compared with the widely used 18F-fludeoxyglucose PET for oncologic imaging. As we expand our knowledge of the utility of FAPI PET, accurate understanding of noncancerous uptake seen on FAPI PET is crucial for accurate evaluation. In this review, we summarize potential diagnostic and therapeutic applications of radiolabeled FAP inhibitors in oncological and nononcological disease processes.

Incidental Intense Fibroblast Activation Protein Inhibitor (FAPI) Uptake in Bilateral Gluteal Myositis Ossificans: A Case Report

Positron emission tomography/computed tomography (PET/CT) using 18F-fluorodeoxyglucose ([18F]-FDG) is a widely adopted imaging modality for detecting hypermetabolic lesions. However, emerging positron-emitting tracers, such as radiopharmaceuticals featuring fibroblast activation protein (FAP) inhibitors (FAPI) labeled with [18F] or [68Ga], have opened new avenues in nuclear medicine. This case report focuses on the unique behavior of [68Ga]-FAPI in bilateral gluteal myositis ossificans, an infrequent condition characterized by soft tissue ossification. A 45-year-old woman with gastric adenocarcinoma underwent subtotal gastrectomy and received neoadjuvant and adjuvant chemotherapy; [68Ga]-FAPI PET revealed metastatic processes and unexpected [68Ga]-FAPI avid intramuscular ossifications in the pelvic and bilateral thigh muscles. Even though there was no history of trauma, the patient was diagnosed with myositis ossificans, a condition marked by non-cancerous ectopic ossifications. Diagnosis relies on history, radiology, and/or histology. FAPI imaging, increasingly used for inflammatory and infectious diseases, can exhibit uptake in benign conditions, including those involving bones and joints. This case report is the first to document incidental bilateral [68Ga]-FAPI uptake in bilateral gluteal myositis ossificans. The robust [68Ga]-FAPI activity in myositis ossificans highlights the importance of considering myositis ossificans in the context of soft tissue calcifications with intense [68Ga]-FAPI uptake.

Impact of FAPI-46/dual-tracer PET/CT imaging on radiotherapeutic management in esophageal cancer

BACKGROUND

Fibroblast activation protein (FAP) is expressed in the tumor microenvironment (TME) of various cancers. In our analysis, we describe the impact of dual-tracer imaging with Gallium-68-radiolabeled inhibitors of FAP (FAPI-46-PET/CT) and fluorodeoxy-D-glucose (FDG-PET/CT) on the radiotherapeutic management of primary esophageal cancer (EC).

METHODS

32 patients with EC, who are scheduled for chemoradiation, received FDG and FAPI-46 PET/CT on the same day (dual-tracer protocol, 71%) or on two separate days (29%) We compared functional tumor volumes (FTVs), gross tumor volumes (GTVs) and tumor stages before and after PET-imaging. Changes in treatment were categorized as "minor" (adaption of radiation field) or "major" (change of treatment regimen). Immunohistochemistry (IHC) staining for FAP was performed in all patients with available tissue.

RESULTS

Primary tumor was detected in all FAPI-46/dual-tracer scans and in 30/32 (93%) of FDG scans. Compared to the initial staging CT scan, 12/32 patients (38%) were upstaged in nodal status after the combination of FDG and FAPI-46 PET scans. Two lymph node metastases were only visible in FAPI-46/dual-tracer. New distant metastasis was observed in 2/32 (6%) patients following FAPI-4 -PET/CT. Our findings led to larger RT fields ("minor change") in 5/32 patients (16%) and changed treatment regimen ("major change") in 3/32 patients after FAPI-46/dual-tracer PET/CT. GTVs were larger in FAPI-46/dual-tracer scans compared to FDG-PET/CT (mean 99.0 vs. 80.3 ml, respectively (p < 0.001)) with similar results for nuclear medical FTVs. IHC revealed heterogenous FAP-expression in all specimens (mean H-score: 36.3 (SD 24.6)) without correlation between FAP expression in IHC and FAPI tracer uptake in PET/CT.

CONCLUSION

We report first data on the use of PET with FAPI-46 for patients with EC, who are scheduled to receive RT. Tumor uptake was high and not depending on FAP expression in TME. Further, FAPI-46/dual-tracer PET had relevant impact on management in this setting. Our data calls for prospective evaluation of FAPI-46/dual-tracer PET to improve clinical outcomes of EC.

PET/CT FAPI: Procedure and evidence review in oncology

Neoplasms are composed of malignant tumor cells, which are surrounded by other non-tumor cellular elements, in what has been defined as the microenvironment or tumor stroma. Evidence on the importance of the tumor microenvironment has not stopped growing in recent years. It plays a central role in cell proliferation, tissue invasion, angiogenesis and cell migration. The paradigm is the family of new FAPI radiopharmaceuticals that show the density of the fibroblast activation protein (FAP) which is overexpressed in the cell membrane of activated cancer-associated fibroblasts (CAF), and its presence is related to poor prognosis. This educational document includes the procedure for performing PET/CT FAPI, biodistribution and the main potentially clinical applications in oncology to date.

Characterizing Normal Variant [68Ga]Ga-FAPI-46 Uptake in the Epididymis

The biodistribution of fibroblast activation protein inhibitor (FAPI) PET tracers includes the kidneys, bladder, uterus, breast, muscles, and bone marrow. We describe its occasional uptake patterns in the epididymis. Methods: Epididymal [68Ga]Ga-FAPI-46 uptake was retrospectively analyzed in 55 PET/CT studies of 55 men. Uptake intensity (SUV), pattern (diffuse, focal, or multifocal), laterality, and location (epididymal head with or without body/tail) were analyzed. Electronic medical records were reviewed to determine the presence of epididymis-related disease. Results: Epididymal [68Ga]Ga-FAPI-46 uptake was observed in 8 of 55 (15%) subjects, with bilateral epididymal head uptake in all cases and epididymal body/tail uptake in 6 of 8 (75%) cases, 5 of 6 (83%) bilaterally and 1 of 6 (17%) unilaterally. The average SUVmax was greater in the epididymal heads than in the epididymal bodies/tails, with an SUVmax of 4.1 versus 3.0 (P < 0.001). No subject had epididymal disease related to the uptake. Conclusion: [68Ga]Ga-FAPI-46 uptake in the epididymis occurs occasionally and does not appear related to epididymal disease.

Recent topics in fibroblast activation protein inhibitor-PET/CT: clinical and pharmacological aspects

Recently, positron emission tomography (PET) with fibroblast activation protein inhibitor (FAPI) has gained significant attention as an advanced tumor diagnostic imaging tool. FAPI PET has a promising potential owing to its ability to accurately depict most malignant tumors. It has an accuracy that is comparable to or surpassing the diagnostic accuracy of PET using 18F-fluorodeoxyglucose (FDG). Moreover, FAPI PET can identify malignant lesions that may be inconclusive on FDG PET. Beyond its application in neoplastic disorders, there have been encouraging reports suggesting the utility of FAPI PET in non-neoplastic conditions such as respiratory or cardiac diseases. This article aimed to provide a comprehensive overview of the recently published articles investigating FAPI and discuss its clinical utility with an emphasis on its application in tumor diagnostics. Numerous radiopharmaceutical FAPIs, including 18F- and 68Ga-labeled compounds, have been developed, and they offer various advantages and applications. With the progress in the FAPI PET synthesis to enhance accumulation and retention in pathological lesions, future studies are expected to provide valuable data on its therapeutic efficacy.

Increased 18 F-FAPI-04 Uptake in Vertebral Hemangioma

ABSTRACT

A 54-year-old man with a history of colectomy for colorectal cancer and subsequent liver metastasectomy underwent 18 F-FDG PET/CT and 18 F-FAPI-04 PET/CT scans to evaluate possible hepatic metastasis revealed by contrast-enhanced MRI. Both studies showed similarly increased uptake in liver metastases, and 18 F-FDG detected a metastatic lung nodule. Furthermore, the images showed an incidental finding of increased uptake of 18 F-FAPI-04 in the L3 vertebral, which was not 18 F-FDG-avid. A review of the patient's previous CT and MRI scans suggests vertebral hemangioma.

Design, Synthesis, and Evaluation of 18F-Labeled Tracers Targeting Fibroblast Activation Protein for Brain Imaging

Fibroblast activation protein (FAP) is closely related to central nervous system diseases such as stroke and brain tumors, but PET tracers that can be used for brain imaging have not been reported. Here, we designed, synthesized, and evaluated 18F-labeled UAMC1110 derivatives suitable for brain imaging targeting FAP. By substituting the F atom for the H atom on the aromatic ring of compound UAMC1110, 1a-c were designed and prepared. 1a-c were confirmed to have a high affinity for FAP through molecular docking and enzyme assay. [18F]1a-c were successfully prepared and confirmed to have high affinity. The stability in vivo indicates that no obvious metabolites of [18F]1a,b were found in the plasma 1 h after injection, which is beneficial for brain imaging. In vitro cell uptake experiments showed that [18F]1a,b and [68Ga]FAPI04 exhibited similar uptake and internalization rates. PET imaging of U87MG subcutaneous tumor showed that [18F]1a,b could penetrate the blood-brain barrier with higher uptake and longer retention time than [68Ga]FAPI04 (uptake at 62.5 min, 1.06 ± 0.23, 1.09 ± 0.25% ID/g vs 0.21 ± 0.10% ID/g, respectively). The brain-to-blood ratios of [18F]1a,b were better than [68Ga]FAPI04. Biodistribution and PET imaging showed that [18F]1a had better uptake on tumors and a higher tumor-to-muscle ratio than [18F]1b and [68Ga]FAPI04. Further imaging of U87MG intracranial glioma showed that [18F]1a outlined high-contrast gliomas in a short period of time compared to [18F]1b. Therefore, [18F]1a is expected to be useful in the diagnosis of FAP-related brain diseases.

From FDG and beyond: the evolving potential of nuclear medicine

The radiopharmaceutical 2-[fluorine-18]fluoro-2-deoxy-D-glucose (FDG) has been dominantly used in positron emission tomography (PET) scans for over 20 years, and due to its vast utility its applications have expanded and are continuing to expand into oncology, neurology, cardiology, and infectious/inflammatory diseases. More recently, the addition of artificial intelligence (AI) has enhanced nuclear medicine diagnosis and imaging with FDG-PET, and new radiopharmaceuticals such as prostate-specific membrane antigen (PSMA) and fibroblast activation protein inhibitor (FAPI) have emerged. Nuclear medicine therapy using agents such as [177Lu]-dotatate surpasses conventional treatments in terms of efficacy and side effects. This article reviews recently established evidence of FDG and non-FDG drugs and anticipates the future trajectory of nuclear medicine.

Clinical application of Al18F-NOTA-FAPI PET/CT in diagnosis and TNM staging of pancreatic adenocarcinoma, compared to 18F-FDG

PURPOSE

This study aimed to investigate the ability of Al18F-NOTA-FAPI PET/CT to diagnose pancreatic carcinoma and tumor-associated inflammation with the comparison of 18F-FDG PET/CT.

METHODS

Prospective analysis of Al18F-NOTA-FAPI PET/CT and 18F-FDG PET/CT scans of 31 patients from 05/2021 to 05/2022 were analyzed. Al18F-NOTA-FAPI imaging was performed in patients who had Ce-CT and FDG PET/CT and the diagnosis was still unclear. Follow-up histopathology or radiographic examination confirmed the findings. Radiotracer uptake, diagnostic performance, and TNM (tumor-node-metastasis) classifications were compared.

RESULTS

A total of 31 patients with pancreatic carcinoma (all were adenocarcinoma) underwent Al18F-NOTA-FAPI-04 PET/CT, including 20 male and 11 female patients, with a mean age of 58.2 ± 8.5 years. FAPI-04 PET/CT imaging showed a higher value of SUVmax-15min/30min/60min, SUVmean-15min/30min/60min, TBR1, and TBR2 in pancreatic carcinoma than FDG (all P < 0.01). The mean level of Al18F-NOTA FAPI-04 uptake values of the pancreatic ductal adenocarcinoma was higher than that of pancreatitis in both SUVmax-30min (P < 0.01), SUVmean-30min (P < 0.05), SUVmax-60min (P < 0.01), and SUVmean-60min (P < 0.01). The FAPI △SUVmax-1, △SUVmax-2, and △SUVmean-2 uptake values of pancreatic carcinoma were higher than tumor-associated inflammation (all P < 0.01). TNM staging of 16/31 patients changed after Al18F-NOTA FAPI-04 PET/CT examination with all upstaging changes.

CONCLUSION

Al18F-NOTA-FAPI-04 PET/CT at 15 and 30 min also demonstrated an equivalent detection ability of pancreatic lesion to 18F-FDG PET/CT. Delayed-phase Al18F-NOTA-FAPI-04 PET/CT can help differentiate pancreatic carcinoma and tumor-associated inflammation. Al18F-NOTA FAPI-04 PET/CT also performed better than FDG PET/CT in TNM staging.

TRIAL REGISTRATION

Chinese Clinical Trial Registry, ChiCTR2100051406. Registered 23 September 2021, https://www.chictr.org.cn/showproj.html?proj=133033.

FAPI-avid nonmalignant PET/CT findings: An expedited systematic review

Fibroblast activation protein inhibitor (FAPI) is a promising tracer in oncologic positron emission tomography/computed tomography (PET/CT). Numerous studies have demonstrated the superior sensitivity of FAPI PET/CT over fluorodeoxyglucose (FDG) PET/CT in several types of cancer. However, the cancer specificity of FAPI uptake remains understudied, and several cases of false-positive FAPI PET/CT findings have been reported. A systematic search of PubMed, Embase, and Web of Science was conducted for studies published prior to April 2022 reporting nonmalignant FAPI PET/CT findings. We included original peer-reviewed articles of studies in humans using FAPI tracers radiolabeled with 68Ga or 18F that were published in English. Papers without original data and studies with insufficient information were excluded. Nonmalignant findings were presented on a per-lesion basis and grouped according to the type of organ or tissue involved. The search identified a total of 1.178 papers, of which 108 studies were eligible. Eighty studies were case reports (74%), and the remaining 28 were cohort studies (26%). A total of 2.372 FAPI-avid nonmalignant findings were reported, with the most frequent being uptake in the arteries, e.g., related to plaques (n = 1178, 49%). FAPI uptake was also frequently related to degenerative and traumatic bone and joint lesions (n = 147, 6%) or arthritis (n = 92, 4%). For organs, diffuse or focal uptake was often seen in cases of inflammation, infection, fibrosis, and IgG4-related disease (n = 157, 7%). FAPI-avid inflammatory/reactive lymph nodes (n = 121, 5%) and tuberculosis lesions (n = 51, 2%) have been reported and could prove to be potential pitfalls in cancer staging. Periodontitis (n = 76, 3%), hemorrhoids (n = 47, 2%), and scarring/wound healing (n = 35, 2%) also presented as focal uptake on FAPI PET/CT. The present review provides an overview of the reported FAPI-avid nonmalignant PET/CT findings to date. A large number of benign clinical entities may show FAPI uptake and should be kept in mind when interpreting FAPI PET/CT findings in patients with cancer.

Incidental Finding of Intervertebral Disc Herniation With Increased 18F-FAPI-04 Uptake in a Healthy Volunteer

ABSTRACT

A 44-year-old healthy volunteer received an 18F-FAPI-04 scan for a normal biodistribution and dosimetry study. An incidental finding of an increased uptake of the radiotracer at the L4/5 subarticular disc herniation was noted, and a subsequent MRI scan confirmed the degenerative nature of the lesion.

Initial Evaluation of [18F]FAPI-74 PET for Various Histopathologically Confirmed Cancers and Benign Lesions

The ¹⁸F-labeled fibroblast activation protein inhibitor (FAPI) [¹⁸F]FAPI-74 has the benefit of a higher synthetic yield and better image resolution than ⁶⁸Ga-labeled FAPI. We preliminarily evaluated the diagnostic performance of [¹⁸F]FAPI-74 PET in patients with various histopathologically confirmed cancers or suspected malignancies. Methods: We enrolled 31 patients (17 men and 14 women) with lung cancer (n = 7), breast cancer (n = 5), gastric cancer (n = 5), pancreatic cancer (n = 3), other cancers (n = 5), and benign tumors (n = 6). Twenty-seven of the 31 patients were treatment-naïve or preoperative, whereas recurrence was suspected in the remaining 4 patients. Histopathologic confirmation was obtained for the primary lesions of 29 of the 31 patients. In the remaining 2 patients, the final diagnosis was based on the clinical course. [¹⁸F]FAPI-74 PET scanning was performed 60 min after the intravenous injection of [¹⁸F]FAPI-74 (240 ± 31 MBq). The [¹⁸F]FAPI-74 PET images were compared between the primary or local recurrent lesions of malignant tumors (n = 21) and nonmalignant lesions (n = 8: type-B1 thymomas, granuloma, solitary fibrous tumor, and postoperative or posttherapeutic changes). The uptake and number of detected lesions on [¹⁸F]FAPI-74 PET were also compared with those on [¹⁸F]FDG PET for available patients (n = 19). Results: [¹⁸F]FAPI-74 PET showed higher uptake in primary lesions of various cancers than in nonmalignant lesions (median SUV_max, 9.39 [range, 1.83-25.28] vs. 3.49 [range, 2.21-15.58]; P = 0.053), but some of the nonmalignant lesions showed high uptake. [¹⁸F]FAPI-74 PET also showed significantly higher uptake than [¹⁸F]FDG PET (median SUV_max, 9.44 [range, 2.50-25.28] vs. 5.45 [range, 1.22-15.06] in primary lesions [P = 0.010], 8.86 [range, 3.51-23.33] vs. 3.84 [range, 1.01-9.75] in lymph node metastases [P = 0.002], and 6.39 [range, 0.55-12.78] vs. 1.88 [range, 0.73-8.35] in other metastases [P = 0.046], respectively). In 6 patients, [¹⁸F]FAPI-74 PET detected more metastatic lesions than [¹⁸F]FDG PET. Conclusion: [¹⁸F]FAPI-74 PET showed higher uptake and detection rates in primary and metastatic lesions than did [¹⁸F]FDG PET. [¹⁸F]FAPI-74 PET is a promising novel diagnostic modality for various tumors, especially for precise staging before treatment, including characterization of tumor lesions before surgery. Moreover, ¹⁸F-labeled FAPI ligand might serve a higher demand in clinical care in the future.

Benign lesions with 68Ga-FAPI uptake: a retrospective study

OBJECTIVES

Although FAPI, as a pan-tumor tracer, shows high expression in the malignancy imaging, FAPI uptake is also seen in some benign lesions. The purpose of this study was to retrospectively analyze the characteristics of benign lesions with FAPI uptake on 68Ga-FAPI PET/CT imaging.

METHODS

The electronic medical and imaging records of patients undergoing 68Ga-FAPI PET/CT imaging in the Department of Nuclear Medicine of our hospital from March 2020 to March 2022 were retrospectively analyzed. Patients with benign lesions confirmed by histopathological analysis or long-term follow-up of FAPI-positive lesions were included in the study.

RESULTS

A total of 44 patients (i.e., 44 benign lesions) were included in this study, including 14 women and 30 men, ranging in age from 19 to 74 years. Benign lesions involved eight systems, including liver (n = 3), tail of pancreas (n = 3), stomach (n = 3), esophagus (n = 1), lung (n = 14), and mediastinum (n = 2), sinuses (n = 1), brain (n = 2), lymph nodes (n = 5), kidneys (n = 4), bones (n = 2), muscles (n = 1), thyroid (n = 1), parathyroid gland (n = 1), and breast (n = 1). The mean SUVmax (p = 0.471) and mean TBR (p = 0.830) of benign lesions in the eight systems were not significantly different.

CONCLUSION

Our studies have shown that in addition to malignant tumors, certain benign lesions also show uptake of FAPI, and it is necessary for doctors to distinguish these benign lesions from true malignant tumors.

ADVANCES IN KNOWLEDGE

Benign lesions may also show FAPI expression, which may make the differential diagnosis of benign and malignant lesions difficult and should be alerted by physicians.

Gallium-68 Labelled Radiopharmaceuticals for Imaging Inflammatory Disorders

Inflammation is an important component of several chronic and debilitating diseases that result in significant morbidity and mortality. This is best evidenced within the cardiovascular system where it may manifest as atherosclerosis or myocarditis, and at the extreme end of the spectrum as myocardial infarction, ventricular remodeling, or cardiac failure. Early non-invasive detection and monitoring of inflammation in these and other settings may better guide patient management with resultant improved outcomes. Key role players in inflammation pathophysiology include chemokines, macrophages, neutrophils, fibroblasts, integrins, and reactive oxygen species, amongst others. Examples of receptor expression and over-expression include somatostatin receptors, CXCR4-, folate-, mannose-, TSPO- receptors and secretion of various vascular adhesion molecules (such as VCAM and ICAM). Gallium-68-based PET offers imaging possibilities for nearly all the major pathophysiological role players in inflammation, with mounting recent interest in macrophage differentiation, various forms of receptor expression and secretion of chemokines and vascular adhesion molecules. The advantages in terms of logistics and costs of having generator-produced PET probes available is well known, and a ⁶⁸Ga-based tracer provides easily translatable theranostic possibilities to especially Lu-177. Some of the more versatile and better validated Ga-68-based inflammation probes include ⁶⁸Ga-DOTA-TATE/NOC/TOC, ⁶⁸Ga-NOTA-RGD, ⁶⁸Ga-CXCR4, ⁶⁸Ga-citrate and ⁶⁸Ga-FAPI.

Subclass Analysis of Malignant, Inflammatory and Degenerative Pathologies Based on Multiple Timepoint FAPI-PET Acquisitions Using FAPI-02, FAPI-46 and FAPI-74

Simple Summary

In a recent retrospective analysis, we evaluated the diagnostic value of repetitive early FAPI-PET-imaging with FAPI-02, FAPI-46 and FAPI-74 for malignant, inflammatory/reactive and degenerative pathologies in 24 cancer patients. Here, we apply a subgroup analysis to that dataset. Differential uptake behavior over time was observed in several subclasses of malignant lesions, inflammatory/reactive lesions and degenerative lesions. These differences over time were particularly manifested in the direct comparison between the uptakes associated with pancreatic carcinoma (stable or increasing over time) and inflammatory lesions of the pancreas (markedly decreasing over time). We conclude that multiple timepoint FAPI-PET/CT is a promising innovative imaging technique that provides additional imaging information compared to single timepoint imaging.

Abstract

Purpose: FAPI-PET is a promising imaging technique for various malignant as well as non-malignant pathologies. In a recent retrospective analysis, we evaluated the diagnostic value of repetitive early FAPI-PET-imaging with FAPI-02, FAPI-46 and FAPI-74 for malignant, inflammatory/reactive and degenerative pathologies. Here, we apply a subgroup analysis to that dataset and describe the tracer-wise uptake kinetic behavior of multiple types of FAPI-positive lesions, which are encountered frequently during clinical routine. Methods: A total of 24 cancer patients underwent whole-body FAPI-PET scans, and images were acquired at 10, 22, 34, 46 and 58 min after the administration of 150–250 MBq of ⁶⁸Ga-FAPI tracer molecules (eight patients each regarding FAPI-02, FAPI-46 and FAPI-74). Standardized uptake values (SUVmax and SUVmean) of healthy tissues, cancer manifestations and non-malignant lesions were measured and target-to-background ratios (TBR) versus blood and fat were calculated for all acquisition timepoints. Results: Differential uptake behavior over time was observed in several subclasses of malignant lesions, inflammatory/reactive lesions and degenerative lesions. These differences over time were particularly manifested in the direct comparison between the uptakes associated with pancreatic carcinoma (stable or increasing over time) and inflammatory lesions of the pancreas (markedly decreasing over time). Furthermore, marked differences were found between the three tracer variants regarding their time-dependent uptake and TBRs within different subclasses of malignant, inflammatory/reactive and degenerative pathologies. Conclusion: Multiple timepoint FAPI-PET/CT is a promising innovative imaging technique that provides additional imaging information compared to single timepoint imaging. Differences in the kinetic behavior of malignant and benign pathologies can facilitate the interpretation of FAPI-positive lesions.