Comparison of [68Ga]Ga-DOTA-FAPI-04 and [18F] FDG PET/CT for the diagnosis of primary and metastatic lesions in patients with various types of cancer

Peritoneal Tuberculosis Mimicking Peritoneal Carcinomatosis on 68 Ga-FAPI-04 and 18 F-FDG PET/CT

ABSTRACT

We report a case of tuberculosis peritonitis in a 26-year-old woman who presented with abdominal pain, fatigue, and weight loss for the last 4 months. Abdominal US and CT demonstrated intra-abdominal massive ascites, misty mesentery, and diffuse peritoneal thickening. In addition, 3 nodular lesions were detected in the right lung. 18 F-FDG PET/CT showed hypermetabolism in lung nodules, mesenteric area, peritoneal thickening, and ascites. 68 Ga-FAPI-04 (fibroblast activation protein-specific inhibitor) PET/CT imaging was also performed; high uptakes were detected in the same regions of 18 F-FDG PET/CT. Tuberculosis diagnosis was made after histopathological examination of wedge resection of the right lung.

Recent topics of the clinical utility of PET/MRI in oncology and neuroscience

Since the inline positron emission tomography (PET)/magnetic resonance imaging (MRI) system appeared in clinical, more than a decade has passed. In this article, we have reviewed recently-published articles about PET/MRI. There have been articles about staging in rectal and breast cancers by PET/MRI using fluorodeoxyglucose (FDG) with higher diagnostic performance in oncology. Assessing possible metastatic bone lesions is considered a proper target by FDG PET/MRI. Other than FDG, PET/MRI with prostate specific membrane antigen (PSMA)-targeted tracers or fibroblast activation protein inhibitor have been reported. Especially, PSMA PET/MRI has been reported to be a promising tool for determining appropriate sites in biopsy. Independent of tracers, the clinical application of artificial intelligence (AI) for images obtained by PET/MRI is one of the current topics in this field, suggesting clinical usefulness for differentiating breast lesions or grading prostate cancer. In addition, AI has been reported to be helpful for noise reduction for reconstructing images, which would be promising for reducing radiation exposure. Furthermore, PET/MRI has a clinical role in neuroscience, including localization of the epileptogenic zone. PET/MRI with new PET tracers could be useful for differentiation among neurological disorders. Clinical applications of integrated PET/MRI in various fields are expected to be reported in the future.

Elevated 68Ga-FAPI Uptake by Primary Benign Intraosseous Meningioma

ABSTRACT

Intraosseous meningioma is an extremely rare benign tumor. We present the 68Ga-fibroblast activation protein inhibitor (FAPI) PET/CT findings of primary intraosseous meningioma in a 71-year-old woman. 68Ga-FAPI PET/CT revealed an intraosseous mass in the right parietal bone with increased FAPI activity. Primary skull malignancy was suspected. However, pathological examination after resection of the mass in the right parietal bone confirmed the diagnosis of benign meningioma (WHO I). A final diagnosis of benign intraosseous meningioma was made.

99m Tc bone scintigraphy does not affect preoperative workup for patients with potentially resectable esophageal squamous cell carcinoma

Background

^99mTc bone scintigraphy (BS) is the mainstay and most widely used technique in evaluation of bone metastasis (BM) in China. This study aimed to investigate the value of ^99mTc BS in preoperative workup for patients with potentially resectable (cT_1−4aN₀₋₃) esophageal squamous cell carcinoma (ESCC).

Methods

This prospective cross‐section clinical trial (ChiCTR1800020304) enrolled a total of 385 patients with ESCC diagnosed at thoracic surgery clinic from October 2018 to September 2020. All patients were diagnosed with stage cT_1−4aN₀₋₃ and were potential candidates for surgical resection. BS was performed preoperatively and the treatment strategy was changed after confirmation of BM. The primary endpoint was the rate of change of the treatment regimen because of BM, while the secondary endpoint was the rate of positive BS findings.

Results

Out of the 385 patients, only two (0.5%) changed their treatment regimen because of BM. The rate of positive BS findings was 1%, while two patients (0.5%) had false‐positive or false‐negative results. The BS diagnostic performance for BM was sensitivity 50%, specificity 99.5%, positive predictive value 50%, negative predictive value 99.5%, and accuracy 99.0%. There was no significant difference in BM in relation to age, sex, tumor location or clinical stage.

Conclusion

Our data demonstrated that ^99mTc bone scintigraphy does not significantly affect the preoperative workup in patients with potentially resectable ESCC, especially in early clinical stage patients.

Comparison of 68Ga-FAPI and 18F-FDG PET/CT in the Evaluation of Patients With Newly Diagnosed Non-Small Cell Lung Cancer

Purpose

Several studies have demonstrated that ⁶⁸Ga-FAPI PET/CT shows high intratumoral tracer uptake and low normal tissue uptake, allowing for excellent visualization of cancer. The purpose of this study was to compare the ability of ⁶⁸Ga-FAPI and ¹⁸F-FDG PET/CT for the evaluation of newly diagnosed NSCLC.

Materials and Methods

A prospective analysis of 28 individuals with histopathologically newly confirmed NSCLC that underwent ⁶⁸Ga-FAPI and ¹⁸F-FDG PET/CT was conducted. The performance of two imaging modalities was compared based upon visual assessment, rates of cancer detection, and semi-quantitative parameters (target-to-background ratio [TBR], maximum standard uptake value [SUVmax]) for both primary tumors and metastases.

Results

In total, this study enrolled 28 participants (13 male, 15 female; median age: 60.5 years, range: 34 – 78 years. <u>For primary tumors, ⁶⁸Ga-FAPI and ¹⁸F-FDG PET/CT have similar detection performance (28 vs. 27). However, ⁶⁸Ga-FAPI PET/CT was found to more effectively evaluate most metastases as compared to ¹⁸F-FDG PET/CT. ⁶⁸Ga-FAPI PET/CT detecting more metastases present within the lymph nodes (53 vs. 49), pleura (8 vs. 7), liver (4 vs. 1), and bone (41 vs. 35).</u> The SUVmax and TBR values for ⁶⁸Ga-FAPI were substantially superior to those for ¹⁸F-FDG in lymph node, pleural, and bone metastases. While the SUVmax for these two imaging approaches was comparable for hepatic metastases, ⁶⁸Ga-FAPI exhibited a significantly higher TBR in relation to that of ¹⁸F-FDG. In addition, ⁶⁸Ga-FAPI PET/CT demonstrates excellent N (80% [8/10]) and M (92.9% [26/28]) staging accuracy in NSCLC patients.

Conclusions

⁶⁸Ga-FAPI PET/CT as an examination modality is excellent for evaluation of newly diagnosed NSCLC. ⁶⁸Ga-FAPI PET/CT improves the detection rates of most metastases and facilitating the superior staging of patients with newly diagnosed NSCLC, relative to that achieved by ¹⁸F-FDG PET/CT.

Comparison of the diagnostic efficacy of 68 Ga-FAPI-04 PET/MR and 18F-FDG PET/CT in patients with pancreatic cancer

PURPOSE

We sought to assess the performance of 68 Ga-FAPI-04 PET/MR for the diagnosis of primary tumours as well as metastatic lesions in patients with pancreatic cancer and to compare the results with those of 18F-FDG PET/CT.

METHODS

Prospectively, we evaluated 33 patients suspected to have pancreatic adenocarcinoma, of whom thirty-two were confirmed by histopathology, and one had autoimmune pancreatitis confirmed by needle biopsy and glucocorticoid treatment. Within 1 week, each patient underwent both 68 Ga-FAPI-04 PET/MR and 18F-FDG PET/CT. Comparisons of the detection abilities for primary tumours, lymph nodes, and metastases were conducted for the two imaging approaches. The original maximum standard uptake values (SUVmax) and normalised SUVmax (SUVmax/SUVbkgd) of paired lesions on 68 Ga-FAPI-04 PET/MR and 18F-FDG PET/CT were measured and compared.

RESULTS

Thirty pancreatic cancer patients and three pancreatitis patients were enrolled. 68 Ga-FAPI-04 PET/MR and 18F-FDG PET/CT exhibited equivalent (100%) detection rates for primary tumours. The original/normalised SUVmax of primary tumours on 68 Ga-FAPI-04 PET was markedly higher than that on 18F-FDG (p < 0.05). Sixteen pancreatic cancer patients had pancreatic parenchymal uptake, whereas 18F-FDG PET images showed parenchymal uptake in only four patients (53.33% vs. 13.33%, p < 0.001). 68 Ga-FAPI-04 PET detected more positive lymph nodes than 18F-FDG PET (42 vs. 30, p < 0.001), while 18F-FDG PET was able to detect more liver metastases than 68 Ga-FAPI-04 (181 vs. 104, p < 0.001). In addition, multisequence MR imaging helped explain ten pancreatic cancers that could not be definitively revealed due to 68 Ga-FAPI-04 inflammatory uptake and identified more liver metastases than 18F-FDG (256 vs. 181, p < 0.001).

CONCLUSION

68 Ga-FAPI-04 PET might be better than 18F-FDG PET in the detection of suspicious lymph node metastases. MR multiple sequence imaging of 68 Ga-FAPI-04 PET/MR was helpful for explaining pancreatic lesions in patients with obstructive inflammation and detecting tiny liver metastases.

Fibroblast Activation Protein Inhibitor Theranostics

The evolution of the fibroblast activation protein inhibitor molecules over the past decade has brought into the forefront a novel theranostic agent that has the potential of matching the workhorse of PET/computed tomography, [fluorine-18] fluoro-2-deoxy-d-glucose (18F-FDG). It is hoped that in the next decade it can act as a complementary tracer to 18F-FDG, in providing phenotypic and biomarker information and also in directing fibroblast activation protein-targeted therapies.

Research progress on the role of fibroblast activation protein in diagnosis and treatment of cancer

Fibroblast activation protein (FAP) is a type II transmembrane protein, which is over-expressed in cancer-associated fibroblasts (CAFs). CAFs are tumor stromal cells that constitute a major component of cancer volume and are reportedly related to tumorigenesis, angiogenesis, metastasis, promotion of drug resistance and induction of tumor immunity. FAP is widely acknowledged as the signature protein of CAFs. At present, FAP inhibitors (FAPI) have achieved ideal results in tumor PET/computed tomography (CT) imaging. Theoretically, FAP-targeted drugs can inhibit tumor progression. Nonetheless, no satisfactory therapeutic effect has been observed so far, which has impeded their implementation in clinical practice. In this review, we describe the characteristics of FAP and its role in the occurrence and development of cancer. We also highlight the potential value of targeting FAP to improve current diagnostic and therapeutic approaches.

Comparison of Diagnostic Efficacy of [68Ga]Ga-FAPI-04 and [18F]FDG PET/CT for Staging and Restaging of Gastric Cancer

Purpose

This study aimed to compare the potential diagnostic efficacy of gallium68-fibroblast-activation protein inhibitor ([⁶⁸Ga]Ga-FAPI-04) and fluorine18-fluorodeoxyglucose ([¹⁸F]-FDG) positron emission tomography-computed tomography (PET/CT) for primary tumors, lymph nodes, and distant metastatic lesions of gastric cancer (GC), and to explore the effects of [⁶⁸Ga]Ga-FAPI-04 and [¹⁸F]-FDG on tumor staging and restaging in GC.

Methods

This single-center retrospective study (NCT2100044131) was conducted at the Affiliated Hospital of the Southwest Medical University between June 2020 and December 2021. Images of patients with GC who were pathologically confirmed and underwent contemporaneous [¹⁸F]-FDG and [⁶⁸Ga]Ga-FAPI-04 PET/CT within 1 week were analyzed. The diagnostic efficacy of [⁶⁸Ga]Ga-FAPI-04 PET/CT and [¹⁸F]-FDG PET/CT for TNM staging of GC was compared using McNemar test. The maximum standard uptake value (SUVmax) of each lesion in the two imaging types was compared using the Mann-Whitney U test.

Results

In total, 25 patients with GC (mean age, 56 ± 12 years) were evaluated. [⁶⁸Ga]Ga-FAPI-04 PET/CT exhibited higher sensitivity compared to [¹⁸F]-FDG PET/CT for detecting primary tumors (18/19 [94.74%] vs. 13/19 [68.42%], χ2 = 6.866, P < 0.01), lymph node metastasis (75/77 [97.40%] vs. 32/77 [41.56%], χ2 = 2.888, P =0.089), and distant metastases (275/283 [97.17%] vs. 122/283 [43.11%], χ2 = 11.858, P < 0.01). [⁶⁸Ga]Ga-FAPI-04 accumulation was significantly higher than that of [¹⁸F]FDG in tumors (median SUVmax, 10.28 vs 3.20; U=59.00, P < 0.01), lymph node metastasis metastases (median SUVmax, 9.20 vs 3.15; U=53.50, P < 0.01), and distant metastases (median SUVmax, 8.00 vs 4.20; U=200.00, P < 0.01). Compared to [¹⁸F]-FDG PET/CT, [⁶⁸Ga]Ga-FAPI-04 PET/CT resulted in new oncological findings in 14/25 patients and corrected tumor staging or restaging in 7/25 patients.

Conclusion

Our preliminary results regarding the impact of [⁶⁸Ga]Ga-FAPI-04 PET/CT on tumor staging highlight the potential of this approach for increasing the accuracy of GC diagnosis, which may facilitate treatment decision-making.

18F-FDG and 68 Ga-FAPI PET/CT for the evaluation of periprosthetic joint infection and aseptic loosening in rabbit models

Purpose

We built a joint replacement loosening model based on the original rabbit model of infection and evaluated the performance characteristics of ¹⁸F-FDG and ⁶⁸ Ga-FAPI in evaluating infection and loosening.

Methods

After surgery, the rabbits were divided into four groups, with six individuals in the control group and 10 each in the aseptic loosening, S. aureus and S. epidermidis groups. PET/CT and serological examination were performed three times at two-week intervals. After the rabbits were euthanized, micro-CT, tissue pathology, pullout tests and scanning electron microscopy (SEM) were performed.

Results

The pullout test and SEM showed the feasibility of the aseptic loosening model. ¹⁸F-FDG showed similar performance in the control and loosening groups. The SUVmax of the S. aureus group was consistently higher than that of the S. epidermidis group. As for ⁶⁸ Ga-FAPI, the SUVmax of the control group was lowest in the second week and gradually increased over subsequent weeks. The SUVmax of the loosening group began to exceed that of the control group after the second week. The SUVmax of the S. aureus group in the second week was the lowest among the four groups and increased as the number of weeks increased. The pathology results showed concordance with the performance of PET/CT. Linear regressions between SUVmax and serology showed that ¹⁸F-FDG was positively correlated with CRP and IL-6, while ⁶⁸ Ga-FAPI revealed negative correlations with CRP and IL-6 in the second week and positive correlations in the sixth week. In addition, the SUVmax and MT(target)V of both ¹⁸F-FDG and ⁶⁸ Ga-FAPI were negatively correlated with bone volume/trabecular volume (TV) and bone surface area/TV.

Conclusion

In this longitudinal observation, ⁶⁸ Ga-FAPI showed greater sensitivity than ¹⁸F-FDG in detecting diseases, and ⁶⁸ Ga-FAPI had no intestinal or muscular uptake. The MT(target)V of ⁶⁸ Ga-FAPI was larger than that of ¹⁸F-FDG, which meant that ⁶⁸ Ga-FAPI had the potential to define the scope of lesions more accurately. Finally, the SUVmax of ⁶⁸ Ga-FAPI could not differentiate between loosening and infection; further study of the diagnostic criteria is warranted.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-022-05537-w.

Comparison of [68Ga]Ga-DOTA-FAPI-04 and [18F]FDG Uptake in Esophageal Cancer

Purpose

Accurate clinical staging is crucial to managing esophageal cancer. [⁶⁸Ga]Ga-DOTA-FAPI-04 exhibits good diagnostic performance in various tumors, showing a promising alternative to [¹⁸F]FDG. Here, we investigated the diagnostic performance of [⁶⁸Ga]Ga-DOTA-FAPI-04 PET/CT and [¹⁸F]FDG PET/CT in the diagnosis of primary and metastatic lesions of esophageal cancer.

Methods

Patients with esophageal cancer who underwent concurrent [⁶⁸Ga]Ga-DOTA-FAPI-04 and [¹⁸F]FDG PET/CT between January 2020 and June 2021 were retrospectively analyzed. [⁶⁸Ga]Ga-DOTA-FAPI-04 and [¹⁸F]FDG PET/CT uptakes were compared by using the paired samples t test. The McNemar test was used to compare the diagnostic performance between the two techniques.

Results

Thirty-five patients (ranging from 44-83 years old with a median age of 63.5 years) were evaluated in our study. In treatment-naive patients (n=25), [⁶⁸Ga]Ga-DOTA-FAPI-04 PET could detect all esophageal cancers, whereas 1 patient with superficial esophageal cancer was negative in FDG but positive in [⁶⁸Ga]Ga-DOTA-FAPI-04 (T1). [⁶⁸Ga]Ga-DOTA-FAPI-04 uptake was higher than [¹⁸F]FDG in primary lesions (13.8 ± 6.9 vs 10.9 ± 6.8, respectively, P=0.004), involved lymph nodes (9.3 ± 5.2 vs 6.4 ± 5.9, respectively, P=0.002), and bone and visceral metastases (10.4 ± 6.0 vs 6.1 ± 7.5, respectively, P=0.001). In addition, [⁶⁸Ga]Ga-DOTA-FAPI-04 PET/CT has a higher detection sensitivity than [¹⁸F]FDG PET/CT for primary tumors [100% (25/25) vs. 96.0% (24/25), respectively], lymph nodes [95.0% (57/60) vs 75.0% (45/60), P<0.001], and bone and visceral metastases [100% (25/25) vs 72% (18/25), respectively; P= 0.008].

Conclusion

[⁶⁸Ga]Ga-DOTA-FAPI-04 PET/CT has higher tracer uptake value and is superior to [¹⁸F]FDG PET/CT in detecting primary and metastatic lesions in patients with esophageal cancer.

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

Fibroblast activation protein (FAP), a type II transmembrane serine protease, is highly expressed in more than 90% of epithelial tumors and is closely associated with various tumor invasion, metastasis, and prognosis. Using FAP as a target, various FAP inhibitors (FAPIs) have been developed, most of which have nanomolar levels of FAP affinity and high selectivity and are used for positron emission tomography (PET) imaging of different tumors. We have conducted a systematic review of the available data; summarized the biological principles of FAPIs for PET imaging, the synthesis model, and metabolic characteristics of the radiotracer; and compared the respective values of FAPIs and the current mainstream tracer ¹⁸F-Fludeoxyglucose (¹⁸F-FDG) in the clinical management of tumor and non-tumor lesions. Available research evidence indicates that FAPIs are a molecular imaging tool complementary to ¹⁸F-FDG and are expected to be the new molecule of the century with better imaging effects than ¹⁸F-FDG in a variety of cancers, including gastrointestinal tumors, liver tumors, breast tumors, and nasopharyngeal carcinoma.

Gallium-68-labeled fibroblast activation protein inhibitor PET in gastrointestinal cancer: insights into diagnosis and management

PURPOSE

Gallium-68-labeled fibroblast activation protein inhibitor (⁶⁸Ga-FAPI) is an emerging promising tumor tracer. This study aims to evaluate the diagnostic efficiency of ⁶⁸Ga-FAPI PET in gastrointestinal cancer, and to determine its potential impact on clinical management.

METHODS

Patients with malignancies were prospectively enrolled in a clinical trial to evaluate the diagnostic value of ⁶⁸Ga-FAPI PET. One hundred twenty patients with gastrointestinal malignancies (121 ⁶⁸Ga-FAPI PET scans) between June 2020 and May 2021 were retrospectively analyzed. Initial staging of untreated patients and restaging of treated patients were evaluated. The treatment scheme promoted by imaging was determined according to NCCN guidelines. Final diagnosis and treatment reference standards were determined by a dedicated multidisciplinary team. The diagnostic performance and treatment guidance of ⁶⁸Ga-FAPI PET were compared with those of conventional imaging (CI) and ¹⁸F-FDG PET.

RESULTS

The diagnostic accuracy of ⁶⁸Ga-FAPI PET was much higher than that of CI and ¹⁸F-FDG PET (95.0% vs. 65.1% and 69.0%, respectively, both p < 0.001). ⁶⁸Ga-FAPI PET revised diagnosis in 30.3% and 26.2% of patients compared with CI and ¹⁸F-FDG PET. The accordance rate of ⁶⁸Ga-FAPI PET-guided treatment in comparison with the reference standard was significantly higher than that of CI and ¹⁸F-FDG PET (96.7% vs. 75.2% and 76.2%, respectively, both p < 0.001). ⁶⁸Ga-FAPI PET changed treatment in 22.9% and 23.8% of patients compared with CI and ¹⁸F-FDG PET.

CONCLUSIONS

⁶⁸Ga-FAPI PET showed remarkable diagnostic performance in gastrointestinal cancer, resulting in more accurate staging and guidance for timely treatment revision, thereby having a critical impact on clinical management.

TRIAL REGISTRATION

NCT04554719. Registered September 8, 2020-retrospectively registered, http://clinicaltrails.gov/show/NCT04554719.

Schmorl Node Can Cause Increased 68Ga-FAPI Activity on PET/CT

ABSTRACT

68Ga-FAPI is a newly developed tumor imaging agent with promising clinical applications. However, benign lesions may also show increased FAPI activity. We accidentally discovered that Schmorl node expressed FAPI activity in a patient with sweat gland cancer. Thus, greater awareness is needed that Schmorl nodes are a potential reason for false-positive uptake on 68Ga-FAPI PET/CT.

First-in-Human Experience With 177Lu-DOTAGA.(SA.FAPi)2 Therapy in an Uncommon Case of Aggressive Medullary Thyroid Carcinoma Clinically Mimicking as Anaplastic Thyroid Cancer

ABSTRACT

A 56-year-old man was diagnosed with calcitonin negative, plasma chromogranin A-positive, immunohistochemistry-negative, high-grade MTC (medullary thyroid cancer) behaving clinically like anaplastic thyroid cancer and presented with progressive disease after conventional therapies. A theranostic approach of 68Ga-DOTA.SA.FAPi-guided 177Lu-DOTAGA.(SA.FAPi)2 radionuclide therapy was administered on compassionate grounds as per the Declaration of Helsinki because known standard lines of treatment were ineffective. Treatment with a single cycle of 1.65 GBq 177Lu-DOTAGA.(SA.FAPi)2 demonstrated a sustainable reduction in the neck mass with significant improvement in the quality of life of the patient. 177Lu-DOTAGA.(SA.FAPi)2 is a potential theranostic option for high-grade MTC refractory to standard therapeutic options.

Interobserver Agreement Rates on Fibroblast Activation Protein Inhibitor-Directed Molecular Imaging and Therapy

OBJECTIVES

Fibroblast activation protein (FAP) has emerged as a novel target for FAP inhibitor (FAPI)-directed molecular imaging and endoradiotherapy (ERT). We aimed to assess the interobserver agreement rates for interpretation of 68Ga-FAPI-4 PET/CT and decision for ERT.

PATIENTS AND METHODS

A random order of 68Ga-FAPI-4 PET/CTs from 49 oncology patients were independently interpreted by 4 blinded readers. Per scan, visual assessment was performed, including overall scan impression, number of organ/lymph node (LN) metastases, and number of affected organs/LN regions. Moreover, a maximum of 3 target lesions, defined as largest in size and/or most intense, per organ compartment were identified, which allowed for an additional quantitative interobserver assessment of LN and organ lesions. To investigate potential reference tissues, quantification also included unaffected liver parenchyma and blood pool. Readers also had to indicate whether FAPI-directed ERT should be considered (based on intensity of uptake and widespread disease). Interobserver agreement rates were evaluated using intraclass correlation coefficients (ICCs) and interpreted according to Cicchetti (with 0.4-0.59 indicating fair, and 0.6-0.74 good, agreement).

RESULTS

On a visual basis, the agreement rate for an overall scan impression was fair (ICC, 0.42; 95% confidence interval [CI], 0.27-0.57). The concordance rate for number of affected LN areas was also fair (ICC, 0.59; 95% CI, 0.45-0.72), whereas the number of LN metastases, number of affected organs, and number of organ metastases achieved good agreement rates (ICC, ≥0.63). In a quantitative analysis, concordance rates for LN were good (ICC, 0.70; 0.48-0.88), but only fair for organ lesions (ICC, 0.43; 0.26-0.60). In regards to background tissues, ICCs were good for unaffected liver parenchyma (0.68; 0.54-0.79) and fair for blood pool (0.43; 0.29-0.58). When readers should decide on ERT, concordance rates were also fair (ICC, 0.59; 95% CI, 0.46-0.73).

CONCLUSIONS

For FAPI-directed molecular imaging and therapy, a fair to good interobserver agreement rate was achieved, supporting the adoption of this radiotracer for clinical routine and multicenter trials.

68Ga-DOTA-FAPI-04 Uptake of Accessory Breast in a Patient With Breast Cancer

ABSTRACT

68Ga-DOTA-FAPI-04 is a promising PET agent for tumor imaging. However, some nonneoplastic lesions can also show increased FAPI uptake. Herein, we presented a case of a patient with left breast cancer who showed a right accessory breast with increased tracer uptake on 68Ga-DOTA-FAPI-04 PET/CT. Final histopathology confirmed there were no malignant components in the accessory breast.

Prospective Comparison of 68Ga-FAPI versus 18F-FDG PET/CT for Tumor Staging in Biliary Tract Cancers

Background Gallium 68-labeled fibroblast-activation protein inhibitor (⁶⁸Ga-FAPI), an imaging agent for detecting tumors, represents a promising alternative to fluorine 18 fluorodeoxyglucose (¹⁸F-FDG). Purpose To compare the potential efficacy of ⁶⁸Ga-FAPI PET/CT with that of ¹⁸F-FDG PET/CT for detecting primary tumor and nodal and distant metastases in biliary tract cancer (BTC) and to explore the impact (tumor staging) of ⁶⁸Ga-FAPI compared with ¹⁸F-FDG on clinical management of BTC. Materials and Methods This single-center prospective clinical study was performed at the Affiliated Hospital of Southwest Medical University between June 2020 and June 2021. Participants with BTC underwent both ⁶⁸Ga-FAPI and ¹⁸F-FDG PET/CT. Histopathologic examination, morphologic imaging, and/or follow-up imaging served as the reference standard. The maximum standardized uptake value (SUV_max) of the primary tumor and nodal and distant metastases between ¹⁸F-FDG and ⁶⁸Ga-FAPI PET/CT were compared using the paired-sample t test. Results Eighteen participants with primary or recurrent BTC were evaluated (mean age, 61 years ± 10 [SD]). The sensitivity of ⁶⁸Ga-FAPI PET/CT was higher than that of ¹⁸F-FDG PET/CT for detecting primary tumors (16 of 16 [100%] vs 13 of 16 [81%]), nodal metastases (41 of 42 [98%] vs 35 of 42 [83%]), and distant metastases (99 of 99 [100%] vs 78 of 99 [79%]). ⁶⁸Ga-FAPI PET/CT resulted in new oncologic findings in 10 of 18 participants and upgraded tumor staging or restaging in five of 18 participants compared with ¹⁸F-FDG PET/CT. ⁶⁸Ga-FAPI PET/CT demonstrated higher sensitivity than ¹⁸F-FDG PET/CT in inflammatory processes secondary to tumor-related obstruction (seven of eight [88%] vs one of eight [13%]). ⁶⁸Ga-FAPI showed lower average SUV_max in inflammatory processes than in oncologic lesions (4.9 ± 2.6 vs 10.0 ± 4.6, respectively; P = .003). Conclusion Gallium 68-labeled fibroblast-activation protein inhibitor PET/CT for tumor staging showed potential for more accurate staging of biliary tract cancer, thereby improving treatment decision making. Clinical trial registration no. ChiCTR2100044131 © RSNA, 2022 Online supplemental material is available for this article. See also the editorial by Choyke in this issue.

Comparison of [68 Ga]Ga-DOTA-FAPI-04 PET/CT and [18F]FDG PET/CT in colorectal cancer

AIM

In this study, we aimed to evaluate the diagnostic sensitivity of [⁶⁸ Ga]Ga-DOTA-FAPI-04 PET/CT in the evaluation of primary or recurrent tumor, and nodal, peritoneal, and distant organ metastases in patients with newly diagnosed or relapsed colorectal cancer (CRC) in comparison with [¹⁸F]FDG PET/CT.

MATERIALS AND METHOD

Thirty-nine patients with histopathologically confirmed primary or relapsed CRC were included in our study. All patients underwent both [¹⁸F]FDG and [⁶⁸ Ga]Ga-DOTA-FAPI-04 PET/CT imaging in the same week. Primary lesions, lymph nodes, and metastatic lesions were recorded on both scans. SUVmax and background values were measured from the primary and metastatic lesions; tumor-to-background ratio (TBR) was calculated and compared. The results of the operation were compared with PET findings in patients who underwent surgical treatment without neoadjuvant chemotherapy (NAC).

RESULTS

The sensitivity and specificity of [⁶⁸ Ga]Ga-DOTA-FAPI-04 PET/CT in the evaluation of primary tumors were 100%, while the sensitivity of [¹⁸F]FDG PET/CT was 100% and its specificity was 85.3%. When evaluated with surgical results in the detection of lymph nodes, [⁶⁸ Ga]Ga-DOTA-FAPI-04 PET/CT had a sensitivity of 90% and a specificity of 100%, whereas [¹⁸F]FDG PET/CT had a sensitivity of 80% and a specificity of 81.8%. The sensitivity and specificity of [⁶⁸ Ga]Ga-DOTA-FAPI PET/CT for peritoneal implants were 100%, and the sensitivity of [¹⁸F]FDG PET/CT was 55%. The SUVmax of primary lesions was higher with [¹⁸F]FDG (p < 0.001), while TBR was higher in [⁶⁸ Ga]Ga-DOTA-FAPI PET/CT than [¹⁸F]FDG PET/CT (p: 0.008). SUVmax and TBR of the lymph nodes were significantly higher in [⁶⁸ Ga]Ga-DOTA-FAPI PET/CT than [¹⁸F]FDG PET/CT (p < 0.001 for both).

CONCLUSION

[⁶⁸ Ga]Ga-DOTA-FAPI-04 PET/CT achieved much higher sensitivity and specificity in the detection of primary lesions, and especially the lymph nodes and peritoneal metastases, suggesting that it can be employed in the assessment of primary tumor and metastases in patients with CRC in routine clinical practice.

68Ga-DOTA-FAPI-04 PET/CT imaging in radioiodine-refractory differentiated thyroid cancer (RR-DTC) patients

OBJECTIVE

This study aimed to assess the potential of ⁶⁸Ga-DOTA-FAPI-04 PET/CT for the detection of the radioiodine-refractory differentiated thyroid cancer (RR-DTC) lesions.

METHODS

We analyzed the ⁶⁸Ga-DOTA-FAPI-04 PET/CT imaging data of 24 RR-DTC patients (7 men and 17 women; 49.6 ± 10.5 year). Clinical data were collected including history, last post-therapeutic radioiodine whole body scan, contemporary CT, thyroglobulin, and antithyroglobulin. Target lesions were selected and measured by the RECIST 1.1. The mean growth rates of the target lesions in the past 6 months were recorded. Tumor uptake of lesions were quantified by SUVmax and the tumor-to-background ratios. The correlation between SUVmax and target lesion growth rate and thyroglobulin was analyzed.

RESULTS

On patient-based analysis, positive metastases were detected in 87.5% (21/24) patients. Except for the lymph node (LN) metastasis of 3 patients (patient 6, 12 and 17#) and the lung metastasis of another 3 patients (patient 9, 13 and 21#), most of the lesions were positive on ⁶⁸Ga-DOTA-FAPI-04 PET/CT images, including LN metastasis and distant metastasis such as lung, bone and pleura. There were altogether 33 target lesions including 30 lung metastases and 3 LN metastases with the mean SUVmax and the growth rate were 4.25 and 6.51%, respectively. SUVmax was statistically associated with the growth rates of the target lesions (p = 0.047). No statistically significant correlation was found between the SUVmax and the serum thyroglobulin levels (p = 0.139).

CONCLUSIONS

⁶⁸Ga-DOTA-FAPI-04 PET/CT has a promising detection rate for RR-DTC metastasis. The FAPI uptake of the tumor may provide a potential therapeutic target for RR-DTC.

TRIAL REGISTRY

NIH Clinical Trials.gov (NCT04499365).

Higher accuracy of [68 Ga]Ga-DOTA-FAPI-04 PET/CT comparing with 2-[18F]FDG PET/CT in clinical staging of NSCLC

PURPOSE

This study aimed to explore the clinical staging performance of [⁶⁸ Ga]Ga-DOTA-FAPI-04 PET/CT compared with that of 2-[¹⁸F]FDG PET/CT in non-small cell lung cancer (NSCLC) patients lesion by lesion.

METHODS

A total of 134 diagnosed or suspected NSCLC patients were enrolled in the prospective study (ChiCTR2000038080); they received paired 2-[¹⁸F]FDG PET/CT and [⁶⁸ Ga]Ga-DOTA-FAPI-04 PET/CT. Of these patients, the retrospective analysis of 74 NSCLC patients with pathological results was conducted from primary tumor (T) diagnosis, lymph node (N), and metastatic lesion (M) staging. The imaging characteristics of the lung nodules and suspected metastases were obtained and analyzed, and the staging performance of 2-[¹⁸F]FDG PET/CT and [⁶⁸ Ga]Ga-DOTA-FAPI-04 PET/CT was compared.

RESULTS

For T diagnosis, [⁶⁸ Ga]Ga-DOTA-FAPI-04 showed better diagnostic performance than 2-[¹⁸F]FDG in 79 lung nodules of 72 patients, especially for nonsolid and small-dimension adenocarcinoma nodules. For N staging, 98 lymph nodes (LNs) with pathological results in 37 patients were analyzed. The SUV_max of [⁶⁸ Ga]Ga-DOTA-FAPI-04 in the nonmetastatic LNs was significantly lower than that in the metastatic LNs. Regarding metastatic LN identification, the calculated optimum cut-off value of [⁶⁸ Ga]Ga-DOTA-FAPI-04 SUV_max was 5.5, and the diagnostic accuracy using [⁶⁸ Ga]Ga-DOTA-FAPI-04 and 2-[¹⁸F]FDG criteria was 94% and 30%, respectively (P < 0.001). For M staging, [⁶⁸ Ga]Ga-DOTA-FAPI-04 identified more lesions than 2-[¹⁸F]FDG (257 vs. 139 lesions) in 14 patients with multiple metastases. Overall, the staging accuracy of [⁶⁸ Ga]Ga-DOTA-FAPI-04 was better than that of 2-[¹⁸F]FDG in 52 patients with different pathological stages [43/52 (82.7%) vs. 27/52 (51.9%), P = 0.001].

CONCLUSION

Compared with 2-[¹⁸F]FDG PET/CT, [⁶⁸ Ga]Ga-DOTA-FAPI-04 PET/CT demonstrated better staging performance in NSCLC patients with different pathological stages, especially those with localized disease.

[99mTc]Tc-iFAP Radioligand for SPECT/CT Imaging of the Tumor Microenvironment: Kinetics, Radiation Dosimetry, and Imaging in Patients

Tumor microenvironment fibroblasts overexpress the fibroblast activation protein (FAP). We recently reported the preclinical evaluation of [99mTc]Tc-iFAP as a new SPECT radioligand capable of detecting FAP. This research aimed to evaluate the kinetic and dosimetric profile of [99mTc]Tc-iFAP in healthy volunteers, and to assess the radioligand uptake by different solid tumors in three cancer patients. [99mTc]Tc-iFAP was obtained from lyophilized formulations prepared under GMP conditions with >98% radiochemical purity. Whole-body scans of six healthy subjects were obtained at 0.5, 2, 4, and 24 h after [99mTc]Tc-iFAP (740 MBq) administration. A 2D-planar/3D-SPECT hybrid activity quantitation method was used to fit the biokinetic models of the source organs (volume of interest: VOI) as exponential functions (A(t)VOI). The total nuclear transformations (N) that occurred in the source organs were calculated from the mathematical integration (0,∞) of A(t)VOI. The OLINDA code was used to estimate the radiation doses. Three treatment-naive patients (breast, lung, and cervical cancer) with a prior [18F]FDG PET/CT scan underwent whole-body, chest, and abdominal SPECT/CT scanning after [99mTc]Tc-iFAP (740 MBq) administration. Both imaging methods were compared visually and quantitatively. Oncological diagnoses were performed histopathologically. The results showed favorable [99mTc]Tc-iFAP biodistribution and kinetics due to rapid blood activity removal (t1/2α = 2.22 min and t1/2β = 90 min) and mainly renal clearance. The mean radiation equivalent doses were 5.2 ± 0.8 mSv for the kidney and 1.7 ± 0.3 mSv for the liver after administration of 740 MBq. The effective dose was 2.3 ± 0.4 mSv/740 MBq. [99mTc]Tc-iFAP demonstrated high and reliable uptake in the primary tumor lesions and lymph node metastases in patients with breast, cervical, and lung cancer, which correlated with that detected by [18F]FDG PET/CT. The tumor microenvironment molecular imaging from cancer patients obtained in this research validates the performance of additional clinical studies to determine the utility of [99mTc]Tc-iFAP in the diagnosis and prognosis of different types of solid tumors.

68Ga Fibroblast Activation Protein Inhibitor PET/CT in the Detection of Metastatic Thyroid Cancer: Comparison with 18F-FDG PET/CT

Background Gallium 68 (⁶⁸Ga)-labeled fibroblast activation protein inhibitor (FAPI) has been proposed as a potential radiotracer for visualizing cancerous lesions, but its utility for identifying metastatic differentiated thyroid cancer (DTC) is not well established in the literature. Purpose To evaluate the clinical utility of ⁶⁸Ga-FAPI PET/CT for detecting metastatic DTC and to compare the results with those of fluorine 18 (¹⁸F) fluorodeoxyglucose (FDG) PET/CT. Materials and Methods Participants with clinically suspected or confirmed metastatic DTC were prospectively enrolled and underwent paired ⁶⁸Ga-FAPI and ¹⁸F-FDG PET/CT from May to August 2020. Histopathologic results and clinical follow-up (mean, 12 months ± 0.7 [SD]; range, 11-13 months) were used as reference standards for the final diagnosis. ¹⁸F-FDG and ⁶⁸Ga-FAPI uptake was compared by using the Wilcoxon signed-rank test. The McNemar test was used to compare the diagnostic accuracy of the two techniques, and the influence of various clinicopathologic characteristics on ¹⁸F-FDG and ⁶⁸Ga-FAPI uptake was evaluated with Mann-Whitney and Kruskal-Wallis tests. Results In total, 35 participants (median age, 44 years; IQR, 28-58 years; 18 [51%] men) were evaluated. In all 35 participants, the ⁶⁸Ga-FAPI-derived maximum standardized uptake value (SUV_max) was higher than the ¹⁸F-FDG-derived SUV_max in the metastatic lateral compartment (6.0 vs 3.5; P = .001), axillary (8.5 vs 4.3; P = .01), mediastinal lymph nodes (9.1 vs 5.0; P = .001), and pulmonary metastases (1.7 vs 1.1; P = .004). ⁶⁸Ga-FAPI PET/CT had a higher sensitivity than ¹⁸F-FDG PET/CT for depicting neck lesions (83% [65 of 78; 95% CI: 73, 90] vs 65% [51 of 78; 95% CI: 54, 75], P = .01) and distant metastases (79% [87 of 110; 95% CI: 71, 86] vs 59% [65 of 110; 95% CI: 50, 68], P < .001). Conclusion Gallium 68-labeled fibroblast activation protein inhibitor PET/CT was superior to fluorine 18 fluorodeoxyglucose PET/CT for depicting metastatic differentiated thyroid cancer, especially in lymph nodes and pulmonary metastases. Published under a CC BY 4.0 license. Online supplemental material is available for this article.

New PET Radiotracers for the Imaging of Neuroendocrine Neoplasms

OPINION STATEMENT

Neuroendocrine neoplasms (NEN) are a heterogeneous group of tumours derived from cells of neuroendocrine origin and can potentially arise everywhere in the human body. The diagnostic assessment of NEN can be performed using a variety of PET radiopharmaceuticals. Well-differentiated NEN (NET) present a high expression of SSTR (somatostatin receptors) and can therefore be studied with 68Ga-DOTA-peptides ([68Ga]Ga-DOTANOC, [68Ga]Ga-DOTATOC, [68Ga]Ga-DOTATATE). Current guidelines recommend the use of SSTR imaging to assess disease extension at staging/restaging, follow-up, assessment of response to therapy and selection of patients who may benefit from radionuclide therapy (PRRT). [18F]F-FDG is used for the assessment of high-grade tumours (high-grade G2, G3 and NEC) and in every case, there is one or more mismatched lesions between diagnostic CT (positive) and SSTR-PET/CT (negative). [18F]F-DOPA is currently used for the assessment of medullary thyroid carcinoma, neuroblastoma, primary pheochromocytoma and abdominal paraganglioma. In recent years, however, several new tracers were designed exploiting the many potential targets of the neuroendocrine cell and were employed in clinical trials for both imaging and therapy. Currently, the real-life clinical impact of these tracers is still mostly not known; however, the favourable biodistribution (e.g. [68Ga]Ga-FAPI, SSTR antagonists) and the possibility to use new theranostic pairs may provide novel diagnostic as well as therapeutic options (e.g. [68Ga]Ga-PSMA, [64Cu]Cu-SARTATE, [68Ga]Ga-CXCR4) for NEN patients.

Pleural Metastasis of Papillary Thyroid Cancer Depicted by 68Ga-FAPI PET/CT

ABSTRACT

A 43-year-old woman with history of papillary thyroid cancer status post total thyroidectomy and neck dissection and multiple radioiodine therapy developed dyspnea and cough. CT scan of the chest showed left pleural thickening and pleural effusion. The pathology from pleural biopsy demonstrated the metastases from papillary thyroid cancer. 68Ga-fibroblast activation protein inhibitor PET/CT showed inhomogeneously increased uptake of fibroblast activation protein inhibitor in the thickened pleura.

Progressive Multifocal Leukoencephalopathy Mimicking Malignancy on 68Ga-FAPI PET/CT: Potential Advantages of FAPI

ABSTRACT

A 43-year-old man presented with weakness in his right upper limb for 2 months. Head MRI showed intracranial multiple abnormal signal foci. Malignancy was suspected. The patient was subsequently enrolled in the clinical trial of 68Ga-FAPI PET/CT. 68Ga-FAPI PET/CT showed intracranial multiple FAPI-avid foci. It was also highly suggestive of malignancy. However, the combination of clinical manifestations, imaging findings, cerebral spinal fluid examinations, and effective immunotherapy confirmed the diagnosis of progressive multifocal leukoencephalopathy. 68Ga-FAPI may have potential advantages in the diagnosis of progressive multifocal leukoencephalopathy.

Characteristics of tumour stroma in regional lymph node metastases in colorectal cancer patients: a theoretical framework for future diagnostic imaging with FAPI PET/CT

Purpose

The recently developed fibroblast activation protein inhibitor (FAPI) tracer for PET/CT, binding tumour-stromal cancer-associated fibroblasts, is a promising tool for detection of positive lymph nodes. This study provides an overview of features, including sizes and tumour-stromal content, of lymph nodes and their respective lymph node metastases (LNM) in colorectal cancer (CRC), since literature lacks on whether LNMs contain sufficient stroma to potentially allow FAPI-based tumour detection.

Methods

Haematoxylin and eosin-stained tissue slides from 73 stage III colon cancer patients were included. Diameters and areas of all lymph nodes and their LNMs were assessed, the amount of stroma by measuring the stromal compartment area, the conventional and total tumour-stroma ratios (TSR-c and TSR-t, respectively), as well as correlations between these parameters. Also, subgroup analysis using a minimal diameter cut off of 5.0 mm was performed.

Results

In total, 126 lymph nodes were analysed. Although positive correlations were observed between node and LNM for diameter and area (r = 0.852, p < 0.001 and r = 0.960, p < 0.001, respectively), and also between the LNM stromal compartment area and nodal diameter (r = 0.612, p < 0.001), nodal area (r = 0.747, p < 0.001) and LNM area (r = 0.746, p < 0.001), novel insight was that nearly all (98%) LNMs contained stroma, with median TSR-c scores of 35% (IQR 20–60%) and TSR-t of 20% (IQR 10–30%). Moreover, a total of 32 (25%) positive lymph nodes had a diameter of < 5.0 mm.

Conclusion

In LNMs, stroma is abundantly present, independent of size, suggesting a role for FAPI PET/CT in improved lymph node detection in CRC.

Clinical Evaluation of Nuclear Imaging Agents in Breast Cancer

Precision medicine is the customization of therapy for specific groups of patients using genetic or molecular profiling. Noninvasive imaging is one strategy for molecular profiling and is the focus of this review. The combination of imaging and therapy for precision medicine gave rise to the field of theranostics. In breast cancer, the detection and quantification of therapeutic targets can help assess their heterogeneity, especially in metastatic disease, and may help guide clinical decisions for targeted treatments. Positron emission tomography (PET) or single-photon emission tomography (SPECT) imaging has the potential to play an important role in the molecular profiling of therapeutic targets in vivo for the selection of patients who are likely to respond to corresponding targeted therapy. In this review, we discuss the state-of-the-art nuclear imaging agents in clinical research for breast cancer. We reviewed 17 clinical studies on PET or SPECT agents that target 10 different receptors in breast cancer. We also discuss the limitations of the study designs and of the imaging agents in these studies. Finally, we offer our perspective on which imaging agents have the highest potential to be used in clinical practice in the future.

Comparison of 68Ga-FAPI and 18F-FDG PET/CT in Dermatofibrosarcoma Protuberans

ABSTRACT

Dermatofibrosarcoma protuberans is a rare soft tissue sarcoma with a high recurrence rate. Herein, we present 68Ga-FAPI and 18F-FDG PET/CT findings of dermatofibrosarcoma protuberans in a 45-year-old man. Dermatofibrosarcoma protuberans only shows limited FDG uptakes on 18F-FDG PET/CT, but demonstrated intense tracer uptakes on 68Ga-FAPI PET/CT. In this case, 68Ga-FAPI was superior to 18F-FDG PET/CT in detecting dermatofibrosarcoma protuberans.

Overview of positron emission tomography in functional imaging of the lungs for diffuse lung diseases

Positron emission tomography (PET) is a quantitative molecular imaging modality increasingly used to study pulmonary disease processes and drug effects on those processes. The wide range of drugs and other entities that can be radiolabeled to study molecularly targeted processes is a major strength of PET, thus providing a noninvasive approach for obtaining molecular phenotyping information. The use of PET to monitor disease progression and treatment outcomes in DLD has been limited in clinical practice, with most of such applications occurring in the context of research investigations under clinical trials. Given the high costs and failure rates for lung drug development efforts, molecular imaging lung biomarkers are needed not only to aid these efforts but also to improve clinical characterization of these diseases beyond canonical anatomic classifications based on computed tomography. The purpose of this review article is to provide an overview of PET applications in characterizing lung disease, focusing on novel tracers that are in clinical development for DLD molecular phenotyping, and briefly address considerations for accurately quantifying lung PET signals.

Clinical Utility of F-18 Labeled Fibroblast Activation Protein Inhibitor (FAPI) for Primary Staging in Lung Adenocarcinoma: a Prospective Study

PURPOSE

The purpose of this study was to compare the primary staging of F-18 labeled fibroblast activation protein inhibitor ([18F]F-FAPI) with that of F-18 labeled fluordesoxyglucose positron emission tomography/computed tomography ([18F]F-FDG PET/CT) in patients with lung adenocarcinoma (LAD).

PROCEDURES

We prospectively analyzed the images of LAD patients who underwent [18F]F-FAPI and [18F]F-FDG PET/CT between May 2020 and August 2021. [18F]F-FAPI and [18F]F-FDG uptakes were compared using the paired samples t test, and lesion numbers were compared using the Wilcoxon signed-rank test.

RESULTS

Thirty-four LAD patients were evaluated. Patients showed high [18F]F-FAPI uptake in primary lesions (SUVmax 12.54 ± 3.77). Both [18F]F-FAPI and [18F]F-FDG had 100% detection rates for primary tumors. However, [18F]F-FAPI showed higher SUVmax than [18F]F-FDG in lesions of the lymph nodes, pleura, bones, and other tissues (all P ≤ 0.05). Although the absolute uptake values of [18F]F-FAPI in brain lesions were lower than those of [18F]F-FDG (1.56 ± 2.19 vs.7.34 ± 3.54, P < 0.0001), the tumor-to-background (T/B) ratios were significantly higher than those of [18F]F-FDG (9.53 ± 12.07 vs.1.01 ± 0.49, P < 0.0001). Generally, [18F]F-FAPI PET/CT could visualize more total lesions than [18F]F-FDG (554 vs.464, P = 0.003), especially in lymph nodes (258 vs.229, P = 0.039), the brain (34 vs.9, P = 0.002), and pleura (56 vs.30, P = 0.041). However, contrast-enhanced brain magnetic-resonance imaging (MRI) showed more brain lesions than [18F]F-FAPI PET/CT (56 vs.34, P = 0.002). Compared with the [18F]F-FDG-based TNM stage, the [18F]F-FAPI-based TNM stage was upgraded in six patients (17.6%).

CONCLUSIONS

[18F]F-FAPI PET/CT showed a very high detection rate for primary LAD. In addition, 18F-FAPI PET/CT demonstrated clearer tumor delineation and more lesions than [18F]F-FDG PET/CT, especially in lymph nodes, the brain, and pleura. Therefore, [18F]F-FAPI had an advantage over [18F]F-FDG for primary staging of LAD. However, brain MRI could identify more and smaller lesions than [18F]F-FAPI PET/CT.

Peritoneal malignancy: anatomy, pathophysiology and an update on modern day imaging

With increasing subspecialised experience in radical cytoreductive surgery and intra-abdominal chemotherapy for peritoneal malignancy, outcomes have improved significantly in selected patients. The surgery and the treatment regimens are radical and therefore correct patient selection is critical. The radiologist plays a central role in this process by estimating, as precisely as possible, the pre-treatment disease burden. Because of the nature of the disease process, accurate staging is not an easy task. Tumour deposits may be very small and in locations where they are very difficult to detect. It must be acknowledged that no form of modern day imaging has the capability of detecting the smallest peritoneal nodules, which may only be visible to direct inspection or histopathological evaluation. Nonetheless, it behoves the radiologist to be as exact and precise as possible in the reporting of this disease process. This is both to select patients who are likely to benefit from radical treatment, and just as importantly, to identify patients who are unlikely to achieve adequate cytoreductive outcomes. In this review, we outline the patterns of spread of disease and the anatomic basis for this, as well as the essential aspects of reporting abdominal studies in this patient group. We provide an evidence-based update on the relative strengths and limitations of our available multimodality imaging techniques namely CT, MRI and positron emission tomography/CT.

Tumor Imaging With 68Ga-DOTA-FAPI-04 PET/CT: Comparison With 18F-FDG PET/CT in 22 Different Cancer Types

INTRODUCTION AND AIM

Cancer-associated fibroblasts, which are densely found in tumor tissue, express high levels of fibroblast activation protein (FAP), and FAP inhibitors (FAPIs) labeled with radionuclides can be used in the diagnosis and treatment of cancer. In this study, the role of 68Ga-DOTA-FAPI-04 PET/CT in imaging of primary, metastatic, and recurrent cancers was investigated.

PATIENTS AND METHODS

A total of 42 patients (16 females, 26 males; mean age, 58.5 years; range, 31-84 years) with 22 different types of malignant diseases were included in the study. 68Ga-DOTA-FAPI-04 PET/CT imaging was performed 1 to 7 days after 18F-FDG PET/CT. Pathological uptake levels in primary tumoral lesions, lymph nodes, skeletal system, liver, peritoneal surfaces, and other body parts were compared between 2 PET/CTs. In addition, physiological uptake levels of 18F-FDG and 68Ga-FAPI were defined measuring the liver, thoracic aorta, gluteal muscle activities, and uterus activity in female patients.

RESULTS

Of the 42 patients in the study group, 33 patients were included for staging, 8 patients for restaging, and 1 patient for evaluation of treatment response. 68Ga-DOTA-FAPI-04 PET/CT showed intense uptake in 94.2% of primary tumoral lesions. In patients with multiple myeloma, 18F-FDG uptake in the bone marrow was significantly higher than 68Ga-FAPI uptake, whereas in gastric signet ring cell tumors, 68Ga-FAPI uptake was found to be significantly higher than 18F-FDG uptake. It was observed that 68Ga-DOTA-FAPI-04 PET/CT detected bone, liver, and peritoneum metastases with higher sensitivity and accuracy compared 18F-FDG PET/CT.

CONCLUSIONS

The preliminary findings of this study showed that 68Ga-DOTA-FAPI-04 PET/CT can contribute to the diagnostic process in solid tumors. Especially in malignancies with mild uptake on 18F-FDG PET/CT, it stands out in diagnosis, staging, and restaging. It is also predicted that FAPI molecules can be used for radionuclide therapy in patients with metastatic disease and unresponsive to other treatments showing intense uptake on 68Ga-DOTA-FAPI-04 PET/CT.

Bone Tuberculous Granulomatous Inflammation Mimicking Malignancy on 68Ga-FAPI PET/CT

ABSTRACT

A 50-year-old woman presented with back pain for 1 month. Chest CT showed osteolytic destruction of T6 vertebral body. A malignancy was suspected. The patient was subsequently enrolled in the clinical trial of 68Ga-FAPI PET/CT. 68Ga-FAPI PET/CT revealed multiple bone destruction with increased FAPI activity. It was also highly suggestive of malignancy or metastases. However, pathological examination after T6 vertebral surgery confirmed the diagnosis of tuberculous granulomatous inflammation.

Accurate preoperative staging with [68Ga]Ga-FAPI PET/CT for patients with oral squamous cell carcinoma: a comparison to 2-[18F]FDG PET/CT

OBJECTIVE

To evaluate the potential value of [⁶⁸Ga]Ga-labelled fibroblast activation protein inhibitor ([⁶⁸Ga]Ga-FAPI) positron emission tomography/computed tomography (PET/CT) in preoperative staging for patients with oral squamous cell carcinoma (OSCC) as compared to 2-[¹⁸F]fluoro-2-deoxy-D-glucose (2-[¹⁸F]FDG) PET/CT.

METHODS

Thirty-six treatment-naïve patients with OSCC who underwent 2-[¹⁸F]FDG and [⁶⁸Ga]Ga-FAPI PET/CT for preoperative staging were enrolled. The maximum standardised uptake value (SUV_max) of the primary tumour and suspected cervical metastatic lymph nodes, and the tumour-to-background ratio (TBR) of the primary tumour, were measured. The accuracy of two imaging modalities for preoperative diagnosis of metastatic lymph nodes was analysed. Histopathology served as the standard of reference.

RESULTS

Thirty-seven primary lesions of 36 patients were accurately detected by both [⁶⁸Ga]Ga-FAPI and 2-[¹⁸F]FDG PET/CT. Regarding primary tumours, the SUV_max and TBR of the two imaging modalities in stage T3-T4 were significantly higher than those of stage T1-T2 (all p < 0.05). On the patient analysis, the accuracy for the evaluation of N1-N3 neck status was 52.6% (10/19) for [⁶⁸Ga]Ga-FAPI PET/CT and 57.9% (11/19) for 2-[¹⁸F]FDG PET/CT. Notably, the accuracy for the evaluation of the N0 neck status between [⁶⁸Ga]Ga-FAPI and 2-[¹⁸F]FDG PET/CT was 100% (17/17) and 29% (5/17), respectively. Based on the patient, neck side and neck level, [⁶⁸Ga]Ga-FAPI PET/CT resulted in higher specificity and accuracy in diagnosing metastatic neck lymph nodes than 2-[¹⁸F]FDG PET/CT (all p < 0.05).

CONCLUSION

[⁶⁸Ga]Ga-FAPI PET/CT is a promising tool for preoperative staging of OSCC, and appears to reduce the false positivity seen with 2-[¹⁸F]FDG PET/CT for the detection of neck lymph node metastases.

KEY POINTS

• [⁶⁸Ga]Ga-FAPI PET/CT is a promising tool targeting cancer-associated fibroblasts with comparable diagnostic performance to 2-[¹⁸F]FDG PET/CT for identifying the primary lesions of OSCC. • [⁶⁸Ga]Ga-FAPI PET/CT showed higher specificity and accuracy for the evaluation of neck lymph node metastases of OSCC than 2-[¹⁸F]FDG PET/CT, especially for N0 neck status.

A 68Ga-FAPI-46 PET/CT Imaging Pitfall in Assessing Residual Gastric Cancer Early After Chemotherapy

ABSTRACT

After neoadjuvant chemotherapy, preoperative imaging with 68Ga-FAPI-46 PET/CT showed a similar level of tracer uptake at the location of the primary tumors in 2 patients with gastric cancer. Postoperative histopathology revealed residual malignant cells only in one of the patients, whereas the elevated FAPI uptake in the other patient correlated to an inflammatory reaction and fibrosis. With this case, we would like to highlight that an increased FAPI uptake in inflammatory and fibrotic tissue early after chemotherapy may represent a potential interpretation pitfall. Further studies evaluating the clinical application of FAPI-PET in assessing residual cancer tissue are warranted.

Head-to-head Intra-individual Comparison of [68Ga]-FAPI and [18F]-FDG PET/CT in Patients with Bladder Cancer

AIM/PURPOSE

Fibroblast activation protein-(FAP)-ligands, a novel class of tracers for PET/CT imaging, demonstrated promising results in previous studies in various malignancies compared to standard [¹⁸F]FDG PET/CT. ⁶⁸Ga-labeled fibroblast activation protein inhibitor-([⁶⁸Ga]Ga-DOTA-FAPI)-PET/CT impresses with sharp contrasts in terms of high tumor uptake and low background noise leading to clear delineation. [¹⁸F]FDG PET/CT has limited accuracy in bladder cancer due to high background signal. Therefore, we sought to evaluate the diagnostic potential of [⁶⁸Ga]FAPI in patients with bladder cancer.

MATERIAL AND METHODS

This retrospective analysis consisted of 8 patients (median age 66), 7 of whom underwent both [⁶⁸Ga]FAPI and [¹⁸F]FDG PET/CT scans with a median time interval of 5 days (range 1-20 days). Quantification of tracer uptake was determined with SUV_max and SUV_mean. Furthermore, the tumor-to-background ratio (TBR) was derived by dividing the SUV_max of tumor lesions by the SUV_max of adipose tissue, skeletal muscle, and blood pool.

RESULTS

Overall, 31 metastases were detected in five patients including lymph node metastases (n = 23), bone metastases (n = 4), lung metastases (n = 3), and a peritoneal metastasis (n = 1). In one patient, [⁶⁸Ga]FAPI demonstrated significant uptake in the primary tumor located in the bladder wall. [⁶⁸Ga]FAPI-PET/CT demonstrated significantly higher uptake compared to [¹⁸F]FDG PET/CT with higher mean SUV_max (8.2 vs. 4.6; p = 0.01). Furthermore, [⁶⁸Ga]FAPI detected additional 30% (n = 9) lesions, missed by [¹⁸F]FDG. TBR demonstrated favorable uptake for [⁶⁸Ga]FAPI in comparison to [¹⁸F]FDG. Significant differences were determined with regard to metastasis/blood pool ([⁶⁸Ga]FAPI 5.3 vs [¹⁸F]FDG 1.9; p = 0.001).

CONCLUSION

[⁶⁸Ga]FAPI-PET/CT is a promising diagnostic radioligand for patients with bladder cancer. This first described analysis of FAP-ligand in bladder cancer revealed superiority over [¹⁸F]FDG in a small patient cohort. Thus, this so far assumed potential has to be confirmed and extended by larger and prospective studies.

Ascites of Unexplained Origin: A Case Report

Ascites is defined as a massive collection of fluid in the peritoneal cavity, and it is most commonly caused by portal hypertension due to liver cirrhosis, acute liver failure, and heart failure. We report a case of ascites in a 39-year-old male who presented to the ED complaining of abdominal distention, sporadic pain on the epigastric area, unintentional weight loss over the past two months, night sweats, and blood-mixed stool. We conducted several imaging investigations and laboratory studies and none of them revealed any significant findings except for the abdominal CT with contrast, which showed large ascites along with submucosal fat deposition in the long segment of the transverse colon, suggestive of chronic inflammation [probably inflammatory bowel disease (IBD)], omental caking, and thickening. Peritoneal malignancy was highly suspected.

A diagnostic/therapeutic paracentesis was performed, through which 8 L of fluid was drained. Cytology was also performed and this showed mostly reactive mesothelial cells, negative acid-fast bacilli (AFB) culture, and negative polymerase chain reaction (PCR). We also discuss the other investigations performed, none of which helped in establishing a diagnosis.

18F- or 177Lu-labeled bivalent ligand of fibroblast activation protein with high tumor uptake and retention

PURPOSE

Fibroblast activation protein (FAP) has become a promising cancer-related target for diagnosis and therapy. The aim of this study was to develop a bivalent FAP ligand for both diagnostic PET imaging and endoradiotherapy.

METHODS

We synthesized a bivalent FAP ligand (ND-bisFAP) and labeled it with ¹⁸F or ¹⁷⁷Lu. FAP-positive A549-FAP cells were used to study competitive binding to FAP, cellular internalization, and efflux properties in vitro. Micro-PET imaging with [¹⁸F]AlF-ND-bisFAPI was conducted in mice bearing A549-FAP or U87MG tumors. Biodistribution and therapeutic efficacy of [¹⁷⁷Lu]Lu-ND-bisFAPI were conducted in mice bearing A549-FAP tumors.

RESULTS

The FAP binding affinity of ND-bisFAPI is 0.25 ± 0.05 nM, eightfold higher in potency than the monomeric DOTA-FAPI-04 (IC₅₀ = 2.0 ± 0.18 nM). In A549-FAP cells, ND-bisFAPI showed specific uptake, a high internalized fraction, and slow cellular efflux. Compared to the monomeric [¹⁸F]AlF-FAPI-42, micro-PET imaging with [¹⁸F]AlF-ND-bisFAPI showed higher specific tumor uptake and retention for at least 6 h. Biodistribution studies showed that [¹⁷⁷Lu]Lu-ND-bisFAPI had higher tumor uptake than [¹⁷⁷Lu]Lu-FAPI-04 at the 24, 72, 120, and 168 h time points (all P < 0.01). [¹⁷⁷Lu]Lu-ND-bisFAPI delivered fourfold higher radiation than [¹⁷⁷Lu]Lu-FAPI-04 to A549-FAP tumors. For the endoradiotherapy study, 37 MBq of [¹⁷⁷Lu]Lu-ND-bisFAPI significantly reduced tumor growth compared to the same dose of [¹⁷⁷Lu]Lu-FAPI-04. Half of the dose of [¹⁷⁷Lu]Lu-ND-bisFAPI (18.5 MBq) has comparable median survival as 37 MBq of [¹⁷⁷Lu]Lu-FAPI-04 (37 vs 36 days).

CONCLUSION

The novel bivalent FAP ligand was developed as a theranostic radiopharmaceutical and showed promising properties including higher tumor uptake and retention compared to the established radioligands [¹⁸F]AlF-FAPI-42 and [¹⁷⁷Lu]Lu-FAPI-04. Preliminary experiments with ¹⁸F- or ¹⁷⁷Lu-labeled ND-bisFAPI showed promising imaging properties and favorable anti-tumor responses.

[18F]AlF-NOTA-FAPI-04: FAP-targeting specificity, biodistribution, and PET/CT imaging of various cancers

PURPOSE

In this pilot study, we developed a new tracer, [¹⁸F]AlF-labeled FAPI-04 chelated with NOTA, denoted as [¹⁸F]AlF-NOTA-FAPI-04, and tested the specificity, biodistribution, and clinical application for PET/computed tomography (CT) imaging of various types of cancers in patients.

METHODS

In vitro binding specificity of FAPI-04 to FAP was verified in U87 cells confocal of a fluorescence-labeled variant. In vivo imaging, competition, and dynamic scanning analyses were conducted to evaluate [¹⁸F]AlF-NOTA-FAPI-04 imaging in xenograft mouse model using small-animal PET/CT. The application of [¹⁸F]AlF-NOTA-FAPI-04 was analyzed by imaging different types of cancers in patients.

RESULTS

Both in vitro and in vivo results showed high binding specificity of FAPI-04 to FAP. High intratumoral uptake and fast body clearance of the tracer were observed in the xenograft mouse model and cancer patients. High-contrast images and negligible radiation exposure to normal tissue were observed on [¹⁸F]AlF-NOTA-FAPI-04 PET/CT in 28 patients with 8 different types of cancers. Five of 28 patients underwent PET/CT scanning at 1 h, 2 h, and 4 h after intravenous injection of [¹⁸F]AlF-NOTA-FAPI-04. Seven patients with advanced lung cancer underwent dual-tracer imaging, and 44 and 37 metastatic lesions were detected by [¹⁸F]AlF-NOTA-FAPI-04 PET/CT and [¹⁸F]F-FDG PET/CT, respectively. Overall, 80.0% of metastatic lesions was identified by both [¹⁸F]AlF-NOTA-FAPI-04 and ¹⁸F-FDG, 17.8% by [¹⁸F]AlF-NOTA-FAPI-04 PET/CT only, and 2.2% by [¹⁸F]FDG PET/CT only.

CONCLUSION

[¹⁸F]AlF-NOTA-FAPI-04 offers high specificity as a tracer for FAP imaging and allows fast imaging with high contrast in tumors. [¹⁸F]AlF-NOTA-FAPI-04 is better at identifying metastatic lesions in patients with advanced lung cancer than [¹⁸F]FDG, and its use may facilitate tumor staging.

Presacral Benign Schwannoma Mimics Malignancy on 18F-FDG and 68Ga-FAPI PET/CT

ABSTRACT

We present findings of FDG PET/CT and FAPI PET/CT in a 55-year-old woman with a history of black stools and low-back pain. Pelvic CT detected a giant presacral mass that was suspected to be malignant. 18F-FDG and 68Ga-FAPI PET/CT showed that the mass had intense activity. Pathological examination confirmed the mass as a benign schwannoma.

68Ga-DOTA-FAPI-04 PET/CT Imaging in a Case of SAPHO Syndrome

ABSTRACT

A 66-year-old woman presented with anterior chest wall and knee joints pain and multiple skin lesions. 99mTc-MDP bone scintigraphy showed increased bone density in the sternal angle with abnormal bone metabolism. The patient was enrolled in a 68Ga-DOTA-FAPI-04 PET/CT tumor clinical trial, and it showed increased tracer uptake in the sternum and right knee joint. Subsequently, ultrasound of the right knee joint confirmed the existence of synovitis, and no malignant components were found in sternal biopsy. The patient's final diagnosis was synovitis, acne, pustulosis, hyperostosis, and osteitis (SAPHO) syndrome. The case confirmed that 68Ga-DOTA-FAPI-04 imaging is helpful for evaluating the involved sites of SAPHO syndrome.

68Ga-FAPI PET/CT Detected Non-FDG-Avid Gastric Stromal Tumor

ABSTRACT

We presented a case of 67-year-old man with epigastric discomfort and anorexia for more than 2 months. No abnormal 18F-FDG uptake was found throughout the gastrointestinal tract on 18F-FDG PET/CT. The patient was enrolled in the 68Ga-FAPI PET/CT clinical trial, and a 68Ga-FAPI PET/CT was performed to help detect primary lesion. This examination demonstrated a nodular thickening of the gastric wall with an increased 68Ga-FAPI uptake in the greater curvature of the stomach. Finally, the pathological result confirmed the diagnosis of gastric stromal tumor. This case highlights that 68Ga-FAPI PET/CT might outperform 18F-FDG PET/CT in helping identify gastrointestinal stromal tumors.

Intraoperative fluorescence molecular imaging accelerates the coming of precision surgery in China

Purpose

China has the largest cancer population globally. Surgery is the main choice for most solid cancer patients. Intraoperative fluorescence molecular imaging (FMI) has shown its great potential in assisting surgeons in achieving precise resection. We summarized the typical applications of intraoperative FMI and several new trends to promote the development of precision surgery.

Methods

The academic database and NIH clinical trial platform were systematically evaluated. We focused on the clinical application of intraoperative FMI in China. Special emphasis was placed on a series of typical studies with new technologies or high-level evidence. The emerging strategy of combining FMI with other modalities was also discussed.

Results

The clinical applications of clinically approved indocyanine green (ICG), methylene blue (MB), or fluorescein are on the rise in different surgical departments. Intraoperative FMI has achieved precise lesion detection, sentinel lymph node mapping, and lymphangiography for many cancers. Nerve imaging is also exploring to reduce iatrogenic injuries. Through different administration routes, these fluorescent imaging agents provided encouraging results in surgical navigation. Meanwhile, designing new cancer-specific fluorescent tracers is expected to be a promising trend to further improve the surgical outcome.

Conclusions

Intraoperative FMI is in a rapid development in China. In-depth understanding of cancer-related molecular mechanisms is necessary to achieve precision surgery. Molecular-targeted fluorescent agents and multi-modal imaging techniques might play crucial roles in the era of precision surgery.

Positron emission tomography and computed tomography with [68Ga]Ga-fibroblast activation protein inhibitors improves tumor detection and staging in patients with pancreatic cancer

PURPOSE

This study aimed to investigate the diagnostic performance of [68Ga]Ga-FAPI PET/CT for primary and metastatic pancreatic carcinoma lesions and compare the results with those of [18F]-fluorodeoxyglucose ([18F]FDG) PET/CT.

METHODS

Patients with suspected or diagnosed pancreatic malignancy, who underwent contemporaneous [18F]FDG and [68Ga]Ga-FAPI PET/CT between June 2020 and January 2021, were retrospectively analyzed. Routine contrast-enhanced CT (CE-CT) is performed in all patients as standardized care. Findings were confirmed by histopathology or radiographic follow-up. We compared radiotracer uptake, diagnostic performance, and TNM (tumor-node-metastasis) classifications.

RESULTS

We evaluated 36 participants (25/36 men; median age, 60 years), including 26 patients with pancreatic malignancies and ten patients with pancreatic benign lesions. [68Ga]Ga-FAPI PET/CT showed higher radiotracer uptake and higher sensitivity than [18F]FDG PET/CT in evaluating primary tumors (SUVmax, 21.4 vs. 4.8; sensitivity, 100% vs. 73.1%), involved lymph nodes (SUVmax, 8.6 vs. 2.7; sensitivity, 81.8% vs. 59.1%), and metastases (SUVmax, 7.9 vs. 3.5; sensitivity, 91.5% vs. 44.0%); Compared with [18F]FDG, [68Ga]Ga-FAPI PET/CT upstaged six patients' TNM staging (6/23, 26.1%) and changed two patients' clinical management (2/23, 8.7%). Compared with CE-CT, [68Ga]Ga-FAPI PET/CT upgraded TNM staging in five patients (5/23, 21.7%) and changed the therapeutic regimen in only one patient (1/23, 4.3%). Intense [68Ga]Ga-FAPI uptake was observed throughout the pancreas in 12/26 pancreatic malignancies; dual-time point [68Ga]Ga-FAPI PET/CT may differentiate pancreatitis from malignancy.

CONCLUSIONS

Compared with [18F]FDG PET/CT, [68Ga]Ga-FAPI PET/CT shows higher sensitivity in detecting primary pancreatic tumors, involved lymph nodes, and metastases and is superior in terms of TNM staging. Prospective trials with larger patient population are needed to evaluate whether [68Ga]Ga-FAPI PET/CT could elicit treatment modification in pancreatic cancer when compared with standard of care imaging.