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

Exploring the value of FAP-targeted PET/CT in differentiating breast cancer molecular subtypes: a preliminary study

PURPOSE

This prospective study aims to evaluate the value of [18F]AlF-NOTA-fibroblast activation protein inhibitor (FAPI)-04 positron emission tomography-computed tomography (PET/CT) in predicting molecular subtypes of breast cancer.

METHODS

The study consecutively recruited patients suspected of having breast cancer from a single center who were prospectively enrolled from July 2023 to May 2024 and underwent [18F]AlF-NOTA-FAPI-04 PET/CT. This study compared the differences in tracer uptake among breast cancers with different adverse prognostic factors and molecular subtypes. The classification performance for each molecular subtype of breast cancer was assessed using a receiver operating characteristic (ROC) curve.

RESULTS

Fifty-three participants (mean age, 51 ± 11 years; 52 females) were evaluated. Breast cancer lesions with adverse prognostic factors showed higher tracer uptake. The five different molecular subtypes exhibited varying levels of uptake. The luminal A and luminal B (HER2-negative) subtypes had relatively low uptake, while the luminal B (HER2-positive), HER2-positive, and triple-negative subtypes had relatively high uptake. ROC analysis identified the max standardized uptake value (SUVmax) as a significant classifier (AUC = 0.912, P = 0.0005) for the luminal A subtype, with 100% sensitivity and 83% specificity. For predicting the luminal B (HER2-negative) subtype, SUVmax had an AUC of 0.770 (P = 0.0015). SUVmax, with an AUC of 0.781 (P = 0.003), was used to identify the triple-negative subtype tumors, resulting in a sensitivity of 100% and specificity of 51%. Lastly, the ROC curve showed the cut-off 15.40 (AUC = 0.921, P < 0.0001) could classify luminal A & luminal B (HER2-negative), and luminal B (HER2-positive) & HER2-positive & triple-negative, yielding a sensitivity of 94% and specificity of 79%.

CONCLUSION

The uptake of [18F]AlF-NOTA-FAPI-04 is significantly correlated with the molecular subtypes of breast cancer, and [18F]AlF-NOTA-FAPI-04 PET/CT is a potential tool for noninvasive identification of luminal A subtypes and guidance of FAP-targeted therapies.

The Role of FAPI PET Imaging in Pancreatic Cancer: A Meta-analysis Compared with 18F-FDG PET

PURPOSE

Fibroblast activating protein is a promising target for tumor molecular imaging and therapy. Studies showed that fibroblast activating protein inhibitor (FAPI) radioactive tracers presented superiority over 18F-FDG PET/CT in the evaluation of various cancer types, including pancreatic cancer (PC). Therefore, we conducted this meta-analysis to evaluate and analyze the differences between 68Ga/18F-FAPI and 18F-FDG in PC, in order to provide evidence for the clinical application of FAPI PET imaging.

METHODS

In the current meta-analysis, original studies published as of January 1, 2024 were analyzed using radiolabeled FAPI as a diagnostic radioactive tracer and compared to 18F-FDG for PET in PC. Databases searched included pubmed and web of science, and subject headings searched included PC and FAPI. The quality of the enrolled studies was evaluated by Quality Assessment of Diagnostic Accuracy Studies 2, and the meta-analysis was conducted using R language.

RESULTS

A total of seven studies including 322 patients compared the diagnostic performance of FAPI PET imaging and 18F-FDG PET/CT in PC. Overall, FAPI PET imaging showed higher pooled sensitivity (0.99 [95% CI: 0.97-1.00] vs. 0.84 [95% CI: 0.70-0.92]) and area under the curve (0.99 [95% CI: 0.98-1.00] vs. 0.91 [95% CI: 0.88-0.93]) than 18F-FDG PET/CT. The evidence showed that FAPI PET imaging is superior to 18F-FDG in pooled sensitivity to primary tumor, lymph node metastasis, and distant metastasis. Moreover, FAPI PET imaging improved TNM staging in 25% of PC patients and changed clinical management in 11.7% of PC patients compared to 18F-FDG.

CONCLUSION

FAPI PET imaging is superior to that of 18F-FDG in the detection of primary PC, nodal and distant metastases, TNM staging and clinical management.

The Contribution of 68Ga-FAPI-04 PET/CT to Staging and Prognosis in Gastric Cancer

AIM

This study aimed to compare the diagnostic capabilities of 18F-FDG PET/CT and 68Ga-FAPI-04 PET/CT imaging in staging gastric carcinoma, exploring the impact of 68Ga-FAPI-04 PET/CT on treatment planning and its prognostic significance.

METHODS

The research included 31 patients undergoing staging for gastric cancer, who received both 18F-FDG PET/CT and 68Ga-FAPI-04 PET/CT scans. We compared the SUVmax and SUVmean of the primary tumor and lymph nodes, the count of organ metastases, tumor-to-background ratios, and overall staging accuracy. Additionally, the study evaluated radiological progression-free survival and overall survival rates.

RESULTS

The 68Ga-FAPI-04 PET/CT demonstrated superior efficacy in identifying the primary tumor compared with 18F-FDG PET/CT, particularly in cases of poorly cohesive, signet-ring cell, and mucinous subtypes, with detection rates of 96.7% versus 77.4% (P = 0.006 and P = 0.008, respectively). Analysis of lymph nodes showed a significantly higher detection of positive nodes with 68Ga-FAPI-04 (P = 0.026), although no significant differences were observed in SUVmax and tumor-to-background ratio on a patient basis (P > 0.05). SUVmax and tumor-to-background ratios for peritoneal involvement were notably higher with 68Ga-FAPI-04 PET/CT compared with 18F-FDG PET/CT (P = 0.04 for both). No significant differences were found in the detection of organ metastases and disease stage between the 2 imaging modalities (P > 0.05). Primary tumor uptake did not significantly impact radiological progression-free survival or overall survival in either modality.

CONCLUSION

68Ga-FAPI-04 PET/CT imaging surpasses 18F-FDG PET/CT in detecting the primary tumor, especially in poorly cohesive and signet-ring cell gastric cancer types, and offers improved accuracy in disease staging. This indicates its potential to enhance treatment management and prognostic assessment in gastric cancer patients.

The pons as an optimal background reference region for spinal 18F-FET PET/MRI evaluation

BACKGROUND

This study aims to evaluate the effect of various background reference regions on spinal 18F-FET PET imaging, with a focus on distinguishing between spinal tumors and myelitis. To enhance diagnostic accuracy, we investigated the pons and several other spinal cord area as potential references, given the challenges in interpreting spinal PET results.

RESULTS

A retrospective analysis was conducted on 30 patients, 15 with cervical myelitis and 15 with cervical tumors, who underwent O-(2-[18F]-fluoroethyl)-L-tyrosine (FET) PET/MR imaging. The stability of uptake across four regions, including the pons, C2, C2-C7, and T1-T3, was compared. The standardized uptake value ratio (SUVR) was then evaluated using various background regions, and their effectiveness in differentiating between spinal tumors and myelitis was compared. Additionally, we correlated the SUVR values derived from these regions with the Ki-67 proliferation index in tumor patients. The study found no significant difference in SUVmax (U = 110, p = 0.93) and SUVmean (U = 89, p = 0.35) values at lesion sites between myelitis and tumor patients. The pons had the highest average uptake (p < 0.001) compared to the other three regions. However, its coefficient of variation (CV) was significantly lower than that of the C2-C7 (p < 0.0001) and T1-T3 segments (p < 0.05). The SUVRmax values, calculated using the regions of pons, C2-C7 and T1-T3, were found to significantly differentiate between tumors and myelitis (p < 0.05). However, only the pons-based SUVRmean was able to significantly distinguish between the two groups (p < 0.05). Additionally, the pons-based SUVRmax (r = 0.63, p = 0.013) and SUVRmean (r = 0.67, p = 0.007) demonstrated a significant positive correlation with the Ki-67 index.

CONCLUSIONS

This study suggests that the pons may be considered a suitable reference region for spinal 18F-FET PET imaging, which can improve the differentiation between spinal tumors and myelitis. The significant correlation between pons-based SUVR values and the Ki-67 index further highlights the potential of this approach in assessing tumor cell proliferation.

Intense 18 F-FAPI Uptake in Small Recurrent Lesions of Combined Hepatocellular-Cholangiocarcinoma Negative on 18 F-FDG PET/CT

ABSTRACT

A 70-year-old man presented with combined hepatocellular-cholangiocarcinoma underwent partial hepatectomy and chemoradiotherapy approximately 3 months ago. Follow-up abdominal ultrasound detected a new small lesion with decreased echogenicity in the hepatic segment I, potentially indicating recurrence. The patient was enrolled in a clinical trial of comparison of 18 F-FDG and 18 F-FAPI PET/CT in hepatic lesions. Compared with non- 18 F-FDG avidity, 18 F-FAPI PET/CT showed intense tracer uptake of the hepatic lesion. Resection of the lesion was subsequently performed, and pathologic analysis confirmed the diagnosis of recurrent combined hepatocellular-cholangiocarcinoma.

The earliest optimal timing for total-body 68Ga-fibroblast activation protein inhibitor-04 PET scans: an evidence-based single-centre study

OBJECTIVES

To investigate the earliest optimal timing for positron emission tomography (PET) scans after 68Ga-fibroblast activation protein inhibitor-04 ([68Ga]Ga-FAPI-04) injection.

METHODS

This prospective study enrolled patients who underwent 60-min dynamic 68Ga-FAPI-04 total-body PET/CT scans; the images were reconstructed at 10-min intervals (G0-10, G10-20, G20-30, G30-40, G40-50, and G50-60), and the [68Ga]Ga-FAPI-04 uptake patterns were evaluated. The standardised uptake value (SUV), liver signal-to-noise ratio (SNR), and lesion-to-background ratios (LBRs) for different time windows were calculated to evaluate image quality and lesion detectability. The period from 30 to 40 min was then split into overlapping 5-min intervals starting 1 min apart for further evaluation. G50-60 was considered the reference.

RESULTS

A total of 30 patients with suspected malignant tumours were analysed. In the images reconstructed over 10-min intervals, longer acquisition times were associated with lower background uptake and better image quality. Some lesions could not be detected until G30-40. The lesion detection rate, uptake, and LBRs did not differ significantly among G30-40, G40-50, and G50-60 (all p > 0.05). The SUVmean and LBRs of primary tumours in the reconstructed images did not differ significantly among the 5-min intervals between 30 and 40 min; for metastatic and benign lesions, G34-39 and G35-40 showed significantly better SUVmean and LBR values than the other images. The G34-39 and G50-60 scans showed no significant differences in uptake, LBRs, or detection rates (all p > 0.05).

CONCLUSION

The earliest optimal time to start acquisition was 34 min after injection of half-dose [68Ga]Ga-FAPI-04.

CLINICAL RELEVANCE STATEMENT

This study evaluated 68Ga-fibroblast activation protein inhibitor-04 ([68Ga]Ga-FAPI-04) uptake patterns by comparing the image quality and lesion detection rate with 60-min dynamic [68Ga]Ga-FAPI-04 total-body PET/CT scans and identified the earliest optimal scan time after [68Ga]Ga-FAPI-04 injection.

KEY POINTS

• A prospective single-centre study showed that the earliest optimal time point to start acquisition was 34 min after injection of half-dose [68Ga-fibroblast activation protein inhibitor-04 (68Ga]Ga-FAPI-04). • There were statistically significant differences in standardised uptake value, lesion-to-background ratios, and lesion detectability between scans before and after 34 min from the injection of [68Ga]Ga-FAPI-04, but these values did not change further from 34 to 60 min after injection. • With a reasonable acquisition time, the image quality could still meet diagnostic requirements.

18 F-FAPI-04 PET/CT in a Case of Primary Gastric Plasmacytoma

ABSTRACT

Primary plasmacytoma of the stomach is very rare. We describe contrast-enhanced CT and 18 F-FAPI-04 PET/CT findings in a patient with primary gastric plasmacytoma and Helicobacter pylori infection. The gastric tumor appeared as a large hypervascular polypoid mass on contrast-enhanced CT and showed intense 18 F-FAPI-04 uptake with SUV max of 11.8 on 18 F-FAPI-04 PET/CT.

Development and first-in-human study of PSMA-targeted PET tracers with improved pharmacokinetic properties

PURPOSE

A series of new 68Ga-labeled tracers based on [68Ga]Ga-PSMA-617 were developed to augment the tumor-to-kidney ratio and reduce the activity accumulation in bladder, ultimately minimize radiation toxicity to the urinary system.

METHODS

We introduced quinoline group, phenylalanine and decanoic acid into different tracers to enhance their lipophilicity, strategically limiting their metabolic pathway through the urinary system. Their binding affinity onto LNCaP cells was determined through in vitro saturation assays and competition binding assays. In vivo metabolic study, PET imaging and biodistribution experiment were performed in LNCaP tumor-bearing B-NSG male mice. The most promising tracer was selected for first-in-human study.

RESULTS

Four radiotracers were synthesized with radiochemical purity (RCP) > 95% and molar activity in a range of 20.0-25.5 GBq/μmol. The binding affinities (Ki) of TWS01, TWS02 to PSMA were in the low nanomolar range (< 10 nM), while TWS03 and TWS04 exhibited binding affinities with Ki > 20 nM (59.42 nM for TWS03 and 37.14 nM for TWS04). All radiotracers exhibited high stability in vivo except [68Ga]Ga-TWS03. Micro PET/CT imaging and biodistribution analysis revealed that [68Ga]Ga-TWS02 enabled clear tumor visualization in PET images at 1.5 h post-injection, with higher tumor-to-kidney ratio (T/K, 0.93) and tumor-to-muscle ratio (T/M, 107.62) compared with [68Ga]Ga-PSMA-617 (T/K: 0.39, T/M: 15.01) and [68Ga]Ga-PSMA-11 (T/K: 0.15, T/M: 24.00). In first-in-human study, [68Ga]Ga-TWS02 effectively detected PCa-associated lesions including primary and metastatic lesions, with lower accumulation in urinary system, suggesting that [68Ga]Ga-TWS02 might be applied in the detection of bladder invasion, with minimized radiation toxicity to the urinary system.

CONCLUSION

Introduction of quinoline group, phenylalanine and decanoic acid into different tracers can modulate the binding affinity and pharmacokinetics of PSMA in vivo. [68Ga]Ga-TWS02 showed high binding affinity to PSMA, excellent pharmacokinetic properties and clear imaging of PCa-associated lesions, making it a promising radiotracer for the clinical diagnosis of PCa. Moreover, TWS02 with a chelator DOTA could also label 177Lu and 225Ac, which could be used for PCa treatment without significant side effects.

TRIAL REGISTRATION

The clinical evaluation of this study was registered On October 30, 2021 at https://www.chictr.org.cn/ (No: ChiCTR2100052545).

Diagnostic Performances of PET/CT Using Fibroblast Activation Protein Inhibitors in Patients with Primary and Metastatic Liver Tumors: A Comprehensive Literature Review

PET/CT using radiolabeled fibroblast activation protein inhibitors (FAPIs) is a promising diagnostic tool in oncology, especially when non-increased and/or physiologically high [18F]FDG uptake (as in liver parenchyma) is observed. We aimed to review the role of PET/CT using radiolabeled FAPIs in primary and/or metastatic liver lesions, and to compare their performances with more "conventional" radiopharmaceuticals. A search algorithm based on the terms "FAPI" AND ("hepatic" OR "liver") was applied, with the last update on 1st January 2024. Out of 177 articles retrieved, 76 studies reporting on the diagnostic application of radiolabeled FAPI PET/CT in at least one patient harboring primary or metastatic liver lesion(s) were fully analyzed. Although there was some heterogeneity in clinical conditions and/or study methodology, PET/CT with radiolabeled FAPIs showed an excellent performance in common primary liver malignancies (hepatocarcinoma, intrahepatic cholangiocarcinoma) and liver metastases (mostly from the gastrointestinal tract and lungs). A higher tumor-to-background ratio for FAPIs than for [18F]FDG was found in primary and metastatic liver lesions, due to lower background activity. Despite limited clinical evidence, radiolabeled FAPIs may be used to assess the suitability and effectiveness of FAPI-derived therapeutic agents such as [177Lu]Lu-FAPI. However, future prospective research on a wider population is needed to confirm the excellent performance.

Increased 68 Ga-FAPI Uptake in Capillary Hemangiomas in an Adult Patient

ABSTRACT

A 67-year-old woman was enrolled in our 68 Ga-FAPI PET/CT tumor clinical trial due to her lung adenocarcinoma. The PET/CT scan additionally revealed increased uptake of FAPI in the tongue. Combined with the patient's medical history and the contrast-enhanced CT of the maxillofacial region, it was suspected to be a hemangioma. Subsequently, the patient underwent surgery and was diagnosed with capillary hemangioma of the left side of her tongue.

Value of Semi-Quantitative Parameters of 68Ga-FAPI-04 PET/CT in Primary Malignant and Benign Diseases: A Comparison with 18F-FDG

Objectives: We aimed to compare the value of the semiquantitative parameters of 68Ga-labeled FAP inhibitor (68Ga-FAPI)-04 positron emission tomography/computed tomography (PET/CT) and 18F-fluorodeoxyglucose (18F-FDG) in diagnosing primary malignant and benign diseases. Materials and Methods: 18F-FDG and 68Ga-FAPI-04 PET/CT images of 80 patients were compared. Semiquantitative parameters, including maximum standardized uptake value (SUVmax), mean SUV (SUVmean), peak SUV (SUVpeak), peak SUV by lean body mass (SULpeak), metabolic tumor volume (or tumor volume of FAPI; FAPI-TV), and TLG (or total lesion activity of FAPI; FAPI-TLA), were automatically obtained using the IntelliSpace Portal image processing workstation with a threshold of 40% SUVmax. The liver blood pool was measured as the background, and the tumor-to-background ratio (TBRliver) was calculated. Results: In all malignant lesions, FAPI-TV and FAPI-TLA were higher in 68Ga-FAPI-04 PET/CT than in 18F-FDG. In the subgroup analysis, 68Ga-FAPI-04 had higher FAPI-TV and FAPI-TLA and lower SUVmax than 18F-FDG had in group A, including gynecological tumor, esophageal, and colorectal cancers. However, six semiquantitative parameters were higher in group B (the other malignant tumors). For the benign diseases, SUVmax, SUVmean, SUVpeak, and SULpeak were lower in 68Ga-FAPI-04 PET/CT than in 18F-FDG. 68Ga-FAPI-04 PET/CT showed a lower liver background and a higher TBRliver than 18F-FDG did. 68Ga-FAPI-04 PET/CT had higher accuracy, sensitivity, and specificity than 18F-FDG had. Conclusion: More accurate semiquantitative parameters and lower abdominal background in 68Ga-FAPI-04 PET/CT make it more competitive in the differential diagnosis of malignant and benign diseases than in 18F-FDG.

Non-specific uptake of 18F-FAPI-04 in the pancreas and its related factors: a post-hoc analysis of an ongoing prospective clinical trial

This study aimed to analyze the characteristics of the non-specific uptake (NSU) of 18F-labeled fibroblast activation protein inhibitor (18F-FAPI) of the pancreas and investigate the related factors. Totally, 78 patients who underwent both 18F-fluorodeoxyglucose (FDG) and 18F-FAPI PET/CT examinations were divided into normal (n = 53) and NSU (n = 25) groups. The differences in general information, medical history, laboratory indexes and uptake were compared. Receiver operating characteristic (ROC) curves were used to analyze the optimal cut-off values. The correlations between 18F-FAPI-SUVmax and blood cell analysis, liver function indexes, tumor markers, and inflammatory indices were analyzed. The logistic regression model was used to estimate the independent factors. Both 18F-FAPI (4.48 ± 0.98 vs. 2.01 ± 0.53, t = 11.718, P < 0.05) and 18F-FDG (2.23 ± 0.42 vs. 2.02 ± 0.44, t = 2.036, P = 0.045) showed significantly higher in NSU group. Patients in the NSU group tended to be complicated with a history of drinking (P = 0.034), chronic liver diseases (P = 0.006), and surgery of gastrectomy (P = 0.004). ROC analysis showed cutoff values of 3.25 and 2.05 for 18F-FAPI and 18F-FDG in identifying the NSU. Patients in the NSU group showed less platelet count, higher platelet volume, higher total bilirubin, direct or indirect bilirubin (P < 0.05). Platelet count, platelet crit, large platelet ratio, aspartate aminotransferase (AST), α-L-fucosidase, and total, direct or indirect bilirubin were correlated with 18F-FAPI-SUVmax (P < 0.05). AST [1.099 (1.014, 1.192), P = 0.021] and total bilirubin [1.137 (1.035, 1.249), P = 0.007] were two independent factors in the step forward logistic regression, and platelet/% [1.079 (1.004, 1.160), P = 0.039] and total bilirubin [1.459 (1.016, 2.095), P = 0.041] were two independent factors in the step backward logistic regression for the prediction of pancreatic uptake of 18F-FAPI. 18F-FAPI-PET/CT was better than 18F-FDG in predicting the pancreatic NSU, and NSU is related to a history of drinking, chronic liver diseases, gastrectomy, heteromorphic platelet, and impaired liver function.

Unusual Metastasis of Signet-Ring Cell Gastric Cancer That Could Not Be Detected With 18 F-FDG PET But With 68 Ga-FAPI PET/CT

ABSTRACT

A 70-year-old man who was scheduled for surgery because of the recurrence of gastric cancer was referred to our clinic preoperatively. The patient underwent a comprehensive evaluation through 18 F-FDG and 68 Ga-FAPI ( 68 Ga-labeled FAP inhibitors) PET/CT scans. The 68 Ga-FAPI PET/CT scan was particularly valuable in this case because of its ability to detect recurrent mass lesions and identify unusual metastatic sites compared with the 18 F-FDG PET/CT scan.

Head-to-head comparison of the diagnostic performance between 68Ga-FAPI-04 PET/CT and 18F-FDG PET/CT in colorectal cancer: a systematic review and meta-analysis

This study aimed to compare the detection rates of 68Ga-FAPI-04 PET/CT and 18F-FDG PET/CT in colorectal cancer. A systematic search of major medical databases was conducted to identify studies up to September 2023. The primary outcome assessed was the detection rate of 68Ga-FAPI-04 PET/CT and 18F-FDG PET/CT in the primary tumor. Pooled risk ratios with a 95% CI were calculated using random-effect models to adjust for heterogeneity. Eight studies were included in the meta-analysis. 68Ga-FAPI-04 PET/CT has higher uptakes in lymph nodes, bone, and peritoneal metastasis compared with 18F-FDG PET/CT. The detection rate of 68Ga-FAPI-04 PET/CT based on lesion was better for lymph node metastasis (RR = 0.63, 95% CI 0.47-0.84, P = 0.002) and peritoneal metastasis (RR = 0.52, 95% CI 0.32-0.85, P = 0.009), both imaging modalities had essentially the same diagnostic efficacy in primary tumor (RR = 0.99, 95% CI 0.96-1.02, P = 0.49). 68Ga-FAPI-04 as a highly promising PET/CT tracer was superior to 18F-FDG PET/CT in colorectal cancer, especially in detecting lymph node metastases and peritoneal metastases.

From basic research to clinical application: targeting fibroblast activation protein for cancer diagnosis and treatment

PURPOSE

This study aims to review the multifaceted roles of a membrane protein named Fibroblast Activation Protein (FAP) expressed in tumor tissue, including its molecular functionalities, regulatory mechanisms governing its expression, prognostic significance, and its crucial role in cancer diagnosis and treatment.

METHODS

Articles that have uncovered the regulatory role of FAP in tumor, as well as its potential utility within clinical realms, spanning diagnosis to therapeutic intervention has been screened for a comprehensive review.

RESULTS

Our review reveals that FAP plays a pivotal role in solid tumor progression by undertaking a multitude of enzymatic and nonenzymatic roles within the tumor stroma. The exclusive presence of FAP within tumor tissues highlights its potential as a diagnostic marker and therapeutic target. The review also emphasizes the prognostic significance of FAP in predicting tumor progression and patient outcomes. Furthermore, the emerging strategies involving FAPI inhibitor (FAPI) in cancer research and clinical trials for PET/CT diagnosis are discussed. And targeted therapy utilizing FAP including FAPI, chimeric antigen receptor (CAR) T cell therapy, tumor vaccine, antibody-drug conjugates, bispecific T-cell engagers, FAP cleavable prodrugs, and drug delivery system are also introduced.

CONCLUSION

FAP's intricate interactions with tumor cells and the tumor microenvironment make it a promising target for diagnosis and treatment. Promising strategies such as FAPI offer potential avenues for accurate tumor diagnosis, while multiple therapeutic strategies highlight the prospects of FAP targeting treatments which needs further clinical evaluation.

Contribution of 68 Ga-DOTA-FAPI-04 PET/CT to Prostate Cancer Imaging : Complementary Role in PSMA-Negative Cases

PURPOSE

Prostate-specific membrane antigen (PSMA)-targeted PET/CT is a well-established imaging method in prostate cancer (PC) for both staging and restaging, and also for theranostic applications. An alternative imaging method is crucial for 15% PSMA-negative cases. We aimed to investigate the contribution of 68 Ga-DOTA-FAPI-04 PET/CT to PC imaging.

PATIENTS AND METHODS

Thirty-six patients diagnosed with PC were included. Patients underwent both 68 Ga-PSMA PET/CT and 68 Ga-DOTA-FAPI-04 PET/CT imaging within 1 week. In staging group, primary tumor uptake values were compared, and also correlations were done with histopathological findings, MRI findings, and total PSA levels. In biochemical recurrence group, the uptake values in prostatic region and metastases were evaluated to define the local recurrence or metastatic disease.

RESULTS

In staging group, PSMA PET showed increased uptake in the primary lesion area in 14/27 (52%) patients, whereas 20/27 (74%) patients were positive in FAPI-04 PET. FAPI-04 positivity was found to be quite high, such as 54%, in PSMA-negative patients. A significant difference was observed between ISUP grade 1-3 patients and ISUP grade 4-5 patients in FAPI-04 PET ( P = 0.03). Local recurrence was detected in 3 patients, pelvic lymph node metastasis in 1 patient, and sacrum metastasis in 1 patient in biochemical recurrence group, and all of the lesions had more intense uptake in PSMA PET than FAPI-04 PET.

CONCLUSIONS

FAPI PET imaging seems to have a potential to contribute PSMA PET imaging with FAPI positivity in more than half of PSMA-negative cases. Also, FAPI-targeted radionuclide therapy may be a promising method in patients resistant to PSMA-targeted therapy.

The role of [68 Ga]Ga-FAPI-04 PET/CT in renal cell carcinoma: a preliminary study

PURPOSE

We aimed to investigate the role of [68 Ga]Ga-FAPI-04 PET/CT and uptake patterns of primary and metastatic lesions in patients with renal cell carcinoma (RCC).

METHODS

Twenty patients with a suspicious lesion considered primary renal malignancy or a history of RCC were included in our study. Two patients were excluded from further analyses due to other confirmed malignancies. Six patients were newly diagnosed, while the indication of 12 patients was restaging. All patients underwent [68 Ga]Ga-FAPI-04 and [18F]F-FDG PET/CT. SUVmax and tumor-to-background ratio (TBR) of primary (n = 7) and local recurrent lesions (n = 6) and lymph node (n = 26), lung (n = 32), bone (n = 5), and other metastases (n = 14) were compared between the two tracers.

RESULTS

We detected 90 lesions in 18 patients with varying FAPI and FDG uptake values on both PET/CT. The median TBR of FAPI-PET/CT of all lesions was higher than TBR of FDG-PET/CT with statistically significance (5.6 vs. 2.1, p < 0.001). In primary and recurrent lesions, the median SUVmax, TBR, and tumor volume on FAPI-PET/CT were higher than FDG-PET/CT. The median SUVmax of lung lesions on FAPI-PET/CT was statistical significantly higher than FDG-SUVmax (3.8 vs. 1.8, p = 0.02). The median of FAPI-SUVmax on primary lesions was lower in the early stage based on TNM compared to the advanced stage. FAPI-SUVmax in 49% of all lesions were SUVmax ≥ 6, and 13% were SUVmax ≥ 10. In patient-based analyses, seven patients (39%) had at least one lesion with FAPI-SUVmax ≥ 10; 12 patients (67%) had at least one lesion with FAPI-SUVmax ≥ 6.

CONCLUSION

This study showed the potential utility of [68 Ga]Ga-FAPI-04 PET/CT showing promising results in RCC. We have presumed that FAPI-PET/CT may be performed for complementary imaging modality providing prognosis and possibility of theranostic application in selected patients.

Feasibility of One-Day PET/CT Scanning Protocol with 68Ga-DOTA-FAPI-04 and 18F-FDG for the Detection of Ovarian Cancer Recurrence and Metastasis

Objective: The objective of this study was to investigate the feasibility of 1-d 68Ga-DOTA-FAPI-04 and 18F-FDG (2-deoxy-2[18F]fluoro-d-glucose) positron emission tomography/computed tomography (PET/CT) for detecting ovarian cancer recurrence and metastasis. Materials and Methods: Fifty-two patients who underwent 18F-FDG and 68Ga-DOTA-FAPI-04 PET/CT were divided into 1- and 2-d groups. Image acquisition, injection time, and total waiting time were compared. For the 68Ga-DOTA-FAPI-04 PET/CT scans, low-dose CT scans and low injection dosages were employed, and total radiation dose was assessed for both protocols. The comparative analysis included assessment of patient-based detection rates and lesion-based diagnostic efficacy. Results: The total waiting time was significantly shorter in the 1-d group than in the 2-d group (p = 0.000). The radiation doses stemming from internal radiation and external radiation between the groups showed no differences (p = 0.151 vs. 0.716). In the patient-based analysis, the detection rates for local recurrence, peritoneal, lymph node, and other metastases were not significantly different in both protocols (p ∈ [0.351, 1.000]). For the lesion-based analysis, no differences were noted in terms of sensitivity, specificity, positive predictive value, negative predictive value, and accuracy (p ∈ [0.371, 1.000]). Conclusions: The 1-d PET/CT protocol reduced waiting time and exhibited equivalent detectability compared with the 2-d protocol, suggesting its clinical value.

18F-FAPI PET/CT performs better in evaluating mediastinal and hilar lymph nodes in patients with lung cancer: comparison with 18F-FDG PET/CT

BACKGROUND

The aim of this study was to evaluate the efficacy of fluorine 18 (18F) labeled fibroblast activation protein inhibitor (FAPI) in identifying mediastinal and hilar lymph node metastases and to develop a model to quantitatively and repeatedly identify lymph node status.

METHODS

Twenty-seven patients with 137 lymph nodes were identified by two PET/CT images. The sensitivity, specificity, accuracy, positive predictive value (PPV), and negative predictive value (NPV) of lymph node status were analyzed, and the optimal cut-off value was identified by ROC analysis.

RESULTS

The SUVmax of metastatic lymph nodes on 18F-FAPI was higher than that on 18F-FDG PET/CT (10.87 ± 7.29 vs 6.08 ± 5.37, p < 0.001). 18F-FAPI presented much greater lymph node detection sensitivity, specificity, accuracy, PPV and NPV than 18F-FDG PET/CT (84% vs. 71%; 92% vs. 67%; 90% vs. 69%, 84% vs. 52%, and 92% vs. 83%, respectively). Additionally, the diagnostic effectiveness of 18F-FAPI in small lymph nodes was greater than that of 18F-FDG PET/CT (specificity: 96% vs. 72%; accuracy: 93% vs. 73%; PPV: 77% vs. 33%, respectively). Notably, the optimal cut-off value for specificity and PPV of 18F-FAPI SUVmax was 5.3; the optimal cut-off value for sensitivity and NPV was 2.5.

CONCLUSION

18F-FAPI showed promising diagnostic efficacy in metastatic mediastinal and hilar lymph nodes from lung cancer patients, with a higher SUVmax, especially in small metastatic nodes, compared with 18F-FDG. In addition, this exploratory work recommended optimal SUVmax cutoff values to distinguish between nonmetastatic and metastatic lymph nodes, thereby advancing the development of image-guided radiation. Trial registration ClinicalTrials.gov identifier: ChiCTR2000036091.

Elevated FAPI Activity in Ulcerative Fungal Esophagitis

ABSTRACT

We report a case of ulcerative fungal esophagitis with elevated activity of 18 F-FDG and 68 Ga-FAPI (fibroblast-activating protein inhibitor). Our findings suggest that ulcerative fungal esophagitis should be considered in the differential diagnosis of cancer-like esophageal mass with increased 68 Ga-FAPI uptake.

Development and Characterization of Novel FAP-Targeted Theranostic Pairs: A Bench-to-Bedside Study

Fibroblast activation protein (FAP) is among the most popular targets in nuclear medicine imaging and cancer theranostics. Several small-molecule moieties (FAPI-04, FAPI-46, etc.) are used for developing FAP-targeted theranostic agents. Nonetheless, the circulation time of FAP inhibitors is relatively short, resulting in rapid clearance via kidneys, low tumor uptake, and associated unsatisfactory treatment efficacy. To address the existing drawbacks, we engineered 3 peptides named FD1, FD2, and FD3 with different circulation times through solid-phase peptide synthesis. All the 3 reported peptides bind to human and murine FAP with single-digit nanomolar affinity measured by surface plasmon resonance. The diagnostic and therapeutic potential of the agents labeled with 68Ga and 177Lu was assessed in several tumor models exhibiting different levels of FAP expression. While radiolabeled FD1 was rapidly excreted from kidneys, radiolabeled FD2/FD3 have significantly prolonged circulation, increased tumor uptake, and decreased kidney accumulation. Our findings indicated that [68Ga]Ga-DOTA-FD1 positron emission tomography (PET) effectively detected FAP dynamics, whereas [177Lu]Lu-DOTA-FD2 and [177Lu]Lu-DOTA-FD3 exhibited remarkable therapeutic efficacy in FAP-overexpressing tumor models, including pancreatic cancer cell models characterized by abundant stroma. Moreover, a pilot translational investigation demonstrated that [68Ga]Ga-DOTA-FD1 had the capability to identify both primary and metastatic tumors with precision and distinction. In summary, we developed [68Ga]Ga-DOTA-FD1 for same-day PET imaging of FAP dynamics and [177Lu]Lu-DOTA-FD2 and [177Lu]Lu-DOTA-FD3 for effective radioligand therapy of FAP-overexpressing tumors.

[18F] AlF‑NOTA‑FAPI‑04 PET/CT as a promising tool for imaging fibroblast activation protein in gastrointestinal system cancers: a prospective investigation of comparative analysis with 18F-FDG

PURPOSE

The radiopharmaceutical [18F]AlF-NOTA-FAPI-04 presents a promising alternative to 68 Ga-FAPI owing to its relatively longer half-life. This study aimed to evaluate the clinical usefulness of [18F]AlF-NOTA-FAPI-04 PET/CT for the diagnosis of primary and metastatic lesions in various types of gastrointestinal system cancers, compared with 18F-FDG PET/CT.

METHODS

Patients diagnosed with gastrointestinal system malignancies were prospectively enrolled. All patients underwent both 18F-FDG and 18F-FAPI-04 PET/CT scans within one week, with 44 (73.3%) for cancer staging and 16 (26.7%) for tumor restaging. Diagnostic efficacy of the primary tumor, as well as the presence and number of lymph nodes and distant metastases, were assessed. Tumor uptake was quantified by the maximum standard uptake value (SUVmax).

RESULTS

For detection of primary tumor, the diagnostic sensitivity of 18F-FDG PET/CT was 72.7%, while it was 97.7% for 18F-FAPI-04 PET/CT. Based on per-lymph node analysis, the sensitivity, specificity, and accuracy of 18F-FAPI-04 PET/CT in diagnosing metastatic lymph nodes were 91.89%, 92.00%, and 91.96%, respectively. These values were notably higher than those 18F-FDG PET/CT (79.72%, 81.33% and 80.80%, respectively). The 18F-FAPI-04 PET/CT surpassed 18F-FDG PET/CT in detecting suspected metastases in the brain (7 vs. 3), liver (39 vs. 20), bone (79 vs. 51), lung (11 vs. 4), and peritoneal carcinoma (48 vs. 22). Based on per-patient analysis, differential diagnostic accuracies (18F-FAPI-04 vs. 18F-FDG PET/CT) were observed in all patients (91.7% vs. 76.7%), the initial staging group (90.9% vs. 79.5%), and the re-staging group (93.8% vs. 68.7%). Additionally, 18F-FAPI-04 PET/CT revised final diagnosis in 31.7% of patients, contrasting with 18F-FDG PET/CT, and prompted changes in clinical management for 21.7% of the patients.

CONCLUSION

18F-FAPI-04 PET/CT outperforms 18F-FDG PET/CT in delineating the primary gastrointestinal tumors and detecting suspected metastatic lesions due to a higher target-to-background ratio (TBR). Moreover, 18F-FAPI-04 PET/CT could provide valuable guidance for tumor staging, thereby having a potential impact on patient management.

Increased 18F-FAPI Uptake in Radiation-Induced Liver Injury

ABSTRACT

A 51-year-old woman with breast cancer underwent a complete surgical resection and chemoradiotherapy approximately 3 months ago. Follow-up abdominal ultrasound detected a new lesion with decreased echogenicity in the hepatic segment IV/VIII. 18F-FDG PET/CT showed the hepatic lesion without abnormal uptake. The patient was subsequently enrolled in a clinical trial of 18F-FAPI PET/CT to assess the hepatic lesion. An intense 18F-FAPI activity was identified in the hepatic lesion. Finally, pathological analysis combined with imaging follow-up confirmed the diagnosis of radiation-induced liver injury.

The potential role of 68Ga-FAPI-04 PET/CT for screening malignancy in suspected colonic lesions

AIM

Benign colonic lesions like tubular adenoma may show intense uptake on F-18-FDG PET/CT and can be mistaken for malignancy. In this study, we evaluated the role of 68Ga-FAPI-04 PET/CT for discriminating the benign and malignant colonic lesions.

METHODS

Forty patients with diagnosis of colorectal cancer who had undergone 18F-FDG-PET/CT and 68Ga-FAPI-04 PET/CT for initial staging were retrospectively analyzed. The unexpected foci of uptake in colon on 18F-FDG PET/CT were compared with 68Ga-FAPI-04 PET/CT with lesion and background SUVmax.

RESULTS

The primary colorectal lesion SUVmax on both PET/CTs was similar. A total of 9 incidental colon lesions in 7 patients were detected showing intense 18F-FDG uptake and no 68Ga-FAPI-04 uptake. All of the lesions were consistent with tubular adenoma histopathologically.

CONCLUSION

68Ga-FAPI PET/CT may have a crucial role for discrimination of benign and malignant colonic lesions and avoid the unnecessary interventions and extended surgeries in patients with colorectal cancer.

One-stop [18F]FDG and [68Ga]Ga-DOTA-FAPI-04 total-body PET/CT examination with dual-low activity: a feasibility study

PURPOSE

Positron emission tomography/computed tomography (PET/CT) based on fibroblast activation protein inhibitors (FAPI) has shown complementary values to 2-[18F]-fluoro-2-deoxy-D-glucose ([18F]FDG) in cancer imaging. This study aimed to investigate the feasibility of a one-stop FDG-FAPI dual-tracer imaging protocol with dual-low activity for oncological imaging.

METHODS

Nineteen patients with malignancies underwent one-stop [18F]FDG (0.37 MBq/kg) PET (PETFDG) and dual-tracer PET 30-40 and 50-60 min (hereafter, PETD30-40 and PETD50-60, respectively) after additional injection of [68Ga]Ga-DOTA-FAPI-04 (0.925 MBq/kg), with a single diagnostic CT to generate the PET/CT. The lesion detection rate and tumor-to-normal ratios (TNRs) of tracer uptake were compared between PETFDG/CT and PETD50-60/CT and between PETD50-60/CT and PETD30-40/CT. In addition, a visual scoring system was established to compare the lesion detectability.

RESULTS

The dual-tracer PETD50-60 and PETD30-40/CT showed similar performance in detecting primary tumors but presented significantly higher lesion TNRs than PETFDG. Significantly, more metastases with higher TNRs were identified on PETD50-60 than PETFDG (491 vs. 261, P < 0.001). The dual-tracer PETD50-60 received significantly higher visual scores than single PETFDG (111 vs. 10) in demonstrating both primary tumors (12 vs. 2) and metastases (99 vs. 8). However, these differences were not significant between PETD50-60 and PETD30-40. These resulted in tumor upstaging in 44.4% patients taking PET/CT for initial assessment, and more recurrences (68 vs. 7) were identified in patients taking PET/CT for restaging, both on PETD50-60 and PETD30-40, compared to PETFDG. The reduced effective dosimetry per patient (26.2 ± 2.57 mSv) was equal to that of a single standard whole-body PET/CT.

CONCLUSION

The one-stop dual-tracer dual-low-activity PET imaging protocol combines the strengths of [18F]FDG and [68Ga]Ga-DOTA-FAPI-04 with shorter duration and lesser radiation and is thus clinically applicable.

FAPI PET Positivity in Fibrolamellar Hepatocellular Carcinoma

ABSTRACT

Fibrolamellar hepatocellular carcinoma (HCC) is a variant of HCC. It is a malignant tumor, but its imaging features often overlap focal nodular hyperplasia, which is a benign entity. FDG PET/CT is also not much help in these cases because both lesions do not concentrate FDG. We present one such case of fibrolamellar HCC with FAPI PET/CT positivity.

Evaluation of the Diagnostic Accuracy of FAPI PET/CT in Oncologic Studies: Systematic Review and Metaanalysis

Fibroblast-activation protein is a promising target for oncologic molecular imaging. Studies show that fibroblast activation protein inhibitor (FAPI) radiotracers are accurate diagnostics with favorable tumor-to-background ratios across various cancers. Therefore, we performed a systematic review and metaanalysis to assess the diagnostic performance of FAPI PET/CT in comparison with [¹⁸F]FDG PET/CT, the most widely used radiotracer in oncology. Methods: We conducted a systematic search in MEDLINE, Embase, Scopus, PubMed, Cochrane Central Register of Controlled Trials, relevant trial registries, and bibliographies. The search consisted of combinations of terms for 3 topics: neoplasia, PET/CT, and FAPI. Two authors independently screened retrieved articles using predefined inclusion and exclusion criteria and extracted the data. Study quality was assessed using the criteria of QUADAS-2 (Quality Assessment of Diagnostic Accuracy Studies 2). For each study, the sensitivity, specificity, and 95% CIs were calculated to determine diagnostic accuracy for primary, nodal, and metastatic lesions. A random-effects metaanalysis was used for pooling the data, and heterogeneity was assessed (I² index). Results: Thirty-nine studies (1,259 patients) investigating the use of FAPI PET/CT were included. On a patient-based analysis, pooled sensitivity was 0.99 (95% CI, 0.97-1.0) for the detection of primary lesions. Pooled sensitivity for nodal and distant metastases was 0.91 (95% CI, 0.81-0.96) and 0.99 (95% CI, 0.96-1.0), respectively. On a paired analysis between FAPI and [¹⁸F]FDG PET/CT, FAPI had a higher sensitivity in the detection of primary, nodal, and metastatic lesions (all P < 0.001). The differences in sensitivities between FAPI and [¹⁸F]FDG were statistically significant. In terms of heterogeneity, analyses on primary lesions were moderately affected, distant metastatic lesions were highly affected, and the nodal metastatic analyses had negligible heterogeneity. Conclusion: The diagnostic performance of FAPI PET/CT is superior to that of [¹⁸F]FDG in the detection of primary, nodal, and distant metastases. However, further studies are needed to better evaluate its utility and indication in specific cancer types and clinical settings.

FAPI-Negative FDG-Avid Metastatic Relapse of Breast Cancer on PET/CT

ABSTRACT

A 69-year-old woman with breast cancer underwent 18F-FDG PET/CT because of the increased CA-15-3 level. 18F-FDG PET/CT showed multiple hypermetabolic lymph nodes (LNs) in the neck and mediastinum. The patient was also referred for 68Ga-fibroblast activation protein inhibitor (FAPI) 04 PET/CT for further evaluation. However, 18F-FDG-avid LNs were FAPI-negative on 68Ga-FAPI-04 PET/CT. Supraclavicular LN biopsy confirmed the metastasis of breast cancer. Recent reports have focused on the potential of FAPI PET imaging in breast cancer; however, this case highlights that false-negative 68Ga-FAPI-04-PET/CT findings should also be considered while evaluating metastatic spread.

Synthesis and Preclinical Evaluation of a Novel FAPI-04 Dimer for Cancer Theranostics

Overexpression of fibroblast activation protein (FAP) in cancer-associated fibroblasts in a wide variety of tumors enables a highly selective targeting strategy using FAP inhibitors (FAPIs). Quinoline-based FAPIs labeled with radionuclides have been widely developed for tumor-targeted nuclear medicine imaging. However, the short retention time of FAPIs at the tumor site limits their application in radionuclide therapy. In this study, a novel FAPI-04 dimer was synthesized and labeled with radionuclides to prolong the retention time in tumors for imaging and therapy. To prepare the FAPI-04 dimer complex, DOTA-Suc-Lys-(FAPI-04)₂, we used Fmoc-Lys(Boc)-OH as the linker to conjugate two FAPI-04 structures by an amide reaction. The resulting product was further modified by DOTA groups to allow for conjugation with radioactive metals. Both [⁶⁸Ga]Ga-(FAPI-04)₂ and [¹⁷⁷Lu]Lu-(FAPI-04)₂ showed a radiochemical purity of >99% and remained stable in vitro. In vivo, micro-PET images of SKOV3, A431, and H1299 xenografts revealed that the tumor uptake of [⁶⁸Ga]Ga-(FAPI-04)₂ was about twice that of [⁶⁸Ga]Ga-FAPI-04 and that the accumulation of [⁶⁸Ga]Ga-(FAPI-04)₂ at the tumor site did not significantly decrease even 3h after injection. The tumor-abdomen ratio of [⁶⁸Ga]Ga-(FAPI-04)₂ images was significantly higher than that of [¹⁸F]F-FDG images. For radionuclide therapy, [¹⁷⁷Lu]Lu-(FAPI-04)₂ effectively retarded tumor growth and displayed good tolerance. In conclusion, the DOTA-Suc-Lys-(FAPI-04)₂ design enhanced its uptake in FAP-expressing tumors, improved its retention time at the tumor site, and produced high-contrast imaging in xenografts after radionuclide labeling. Furthermore, it showed a noticeable antitumor effect. DOTA-Suc-Lys-(FAPI-04)₂ provides a new approach for applying FAPI derivatives in tumor theranostics.

Head-To-Head Comparison of 68Ga-FAPI PET/CT and FDG PET/CT for the Detection of Peritoneal Metastases: Systematic Review and Meta-Analysis

BACKGROUND. FDG PET/CT has limited diagnostic performance in the detection of peritoneal metastasis (PM). Gallium-68-labeled fibroblast activation protein inhibitor (FAPI) targets tumor stroma, leading to high accumulation across cancer types. OBJECTIVE. The purpose of this study was to conduct a meta-analysis to compare the diagnostic performances of ⁶⁸Ga-FAPI PET/CT and FDG PET/CT in detecting PM on the basis of studies providing head-to-head comparisons between the two tests. EVIDENCE ACQUISITION. PubMed, Embase, and Cochrane Library databases were searched through July 2022 to identify studies reporting head-to-head comparison of ⁶⁸Ga-FAPI PET/CT and FDG PET/CT for detection of PM. The reference standard was classified as histopathology for all patients or as a combination of histopathologic, clinical, imaging, laboratory, and follow-up information (multidisciplinary reference standard). A random-effects statistical model was applied to conduct a meta-analysis of the diagnostic performances of the tests in patient-based and lesion-based analyses. The QUADAS-2 and QUADAS Comparative tools were used to assess study quality. EVIDENCE SYNTHESIS. Eleven studies were included. Patient-based analysis was reported in nine studies including 340 patients, and lesion-based analysis was reported in four studies including 222 lesions. The pooled sensitivity of ⁶⁸Ga-FAPI PET/CT was significantly higher than that of FDG PET/CT in patient-based analysis (98.2% [95% CI, 96.1-100.0%] vs 55.9% [95% CI, 33.9-77.9%]) and lesion-based analysis (99.9% [95% CI, 99.5-100.0%] vs 27.3% [95% CI, 11.2-43.4%]). Eight studies were rated at high risk of bias in the reference standard domain because the multidisciplinary reference standard was not sufficiently explained and may have included one of the two index tests, which would have artificially increased sensitivity. In three studies specificity was reported as 100.0% for both tests; these studies were considered at uncertain risk of bias in the patient selection domain because patients with benign peritoneal conditions may have been excluded, resulting in underestimation of potential false-positive results. CONCLUSION. The current evidence suggests excellent sensitivity of ⁶⁸Ga-FAPI PET/CT for the detection of PM in comparison with poorer sensitivity of FDG PET/CT. However, most included studies had high risk of bias. Further studies are needed to more convincingly characterize true- and false-positive results. CLINICAL IMPACT. The sensitivity of ⁶⁸Ga-FAPI PET/CT may be substantially greater than that of FDG PET/CT for the evaluation of PM, facilitating surgical planning and candidate selection.

68 Ga-FAPI-04 PET/CT In Primary Signet Ring-Like Cell Carcinoma of Prostate With Bone Metastases

ABSTRACT

We presented a 69-year-old man with liver cirrhosis who underwent 68 Ga-fibroblast activation protein (FAPI)-04 PET/CT imaging for an ongoing study. In addition to the significant activity in liver cirrhosis on FAPI PET, a primary prostate tumor was incidentally detected with bone metastases. Further, FAPI-negative metastases were not observed on CT evaluation. In this context, we think that FAPI may be helpful with the potential theranostic aspect, especially in selected patients when current treatment options are not applicable or unresponsive. However, we should await the results of prospective studies investigating both prognostic and theranostic use of FAPI and demonstrating its effectiveness in cancer therapy.

Comparison of 18 F-FDG and 68 Ga-FAPI-04 Uptake in Postoperative Re-evaluation of Gastric, Duodenal, and Colorectal Cancers

PURPOSE

To compare the potential efficacy of 68 Ga-FAPI-04 PET/CT with that of 18 F-FDG PET/CT for detecting tumor recurrence and nodal and distant metastases in gastric, duodenal, and colorectal cancers.

METHODS

This single-center retrospective clinical study was performed at the Affiliated Hospital of Southwest Medical University between January 2020 and June 2022. Participants with gastric, duodenal, and colorectal cancers after curative resection underwent both 68 Ga-FAPI-04 and 18 F-FDG PET/CT. Histopathologic examination, morphologic imaging, and/or follow-up imaging served as the reference standards. The SUV max of the tumor recurrence and nodal and distant metastases between 18 F-FDG and 68 Ga-FAPI-04 PET/CT were compared using the paired-sample t test.

RESULTS

Forty-one participants with gastric, duodenal, and colorectal cancers were enrolled in the study (median age, 51 years; range, 19-75 years). The sensitivity of 68 Ga-FAPI-04 PET/CT was higher than that of 18 F-FDG PET/CT for detecting tumor recurrence (6 of 6 [100%] vs 4 of 6 [67%]), nodal metastases (92 of 92 [100%] vs 31 of 92 [34%]), and distant metastases (28 of 30 [93%] vs 20 of 30 [67%]).

CONCLUSION

68 Ga-FAPI-04 PET/CT for tumor re-evaluation showed potential for more accurate performance of gastric, duodenal, and colorectal cancers, thereby improving treatment decision-making.

68Ga-PSMA and 68Ga-FAPI-04 PET/CT Findings With 18F-FDG PET/CT in a Patient With Recurrent Prostate Cancer

ABSTRACT

A 79-year-old man with prostate cancer was evaluated with 68Ga-prostate-specific membrane antigen (PSMA), 68Ga-FAPI-04, and 18F-FDG PET/CT scans since a rise in prostate-specific antigen was seen at last control while receiving chemotherapy. Abnormal FDG uptakes were observed in the tumoral areas of the left half of the prostate and walls of the bladder, although PSMA and FAPI activity were absent or lower in the relevant tumoral areas. Restaging 68Ga-PSMA and 18F-FDG PET/CT scans were obtained on the patient whose progression continued after transurethral tumor resection. Herein, we present a case proving intraindividual tumor heterogeneity in prostate cancer underwent PET/CT imaging with 3 different radiopharmaceuticals.

Role of 68 Ga-FAPI PET/CT in Screening Malignancy of Familial Adenomatous Polyposis

ABSTRACT

A 57-year-old man with familial adenomatous polyposis (FAP) and newly diagnosed colonic adenocarcinoma was referred to 18 F-FDG PET/CT for staging and 68 Ga-FAPI-04 PET/CT for ongoing trial. 18 F-FDG PET/CT showed equal intense 18 F-FDG uptake in the tumor and multiple hypermetabolic polypoid lesions in the entire colorectum. 68 Ga-FAPI-04 PET/CT showed intense 68 Ga-FAPI-04 uptake only at the colonic tumor, without uptake at polypoid lesions.

Current research topics in FAPI theranostics: a bibliometric analysis

PURPOSE

The study aimed to provide a comprehensive bibliometric overview of the current scientific publications on fibroblast activation protein inhibitor (FAPI) positron emission tomography imaging and radionuclide therapy.

METHODS

A PubMed search was performed to identify all MEDLINE-indexed publications on FAPI imaging and radionuclide therapy. The last update was performed on 31 May 2022. An online database of this literature was created, and hierarchical topic-related tags were subsequently assigned to all relevant studies. Frequency analysis was used to evaluate the distribution of the following characteristics: first author's country of origin, journal of publication, study design, imaging techniques and radiopharmaceutical used, histopathological correlation, the type of cancer, and benign disease/uptake types evaluated.

RESULTS

A total of 294 relevant publications on original studies were identified, consisting of 209 (71%) case reports/series and 85 cohort studies (29%). The majority of studies focused on imaging topics, predominantly comparing uptake on FAPI-PET/CT with 2-[¹⁸F]FDG-PET/CT, anatomical imaging, and/or histopathology results. 68% of studies focused on malignancies, with gastro-intestinal cancer, hepato-pancreato-biliary cancer, mixed cancers/metastases, lung cancer, sarcoma, head and neck cancer, and breast cancer being the most frequently reported. 42% of studies focused on benign disease categories, with cardiovascular, musculoskeletal, HPB, head and neck, and IgG4-related disease as most common categories. 16/294 (5%) studies focused on radionuclide therapy, with preliminary reports of acceptable toxicity profiles, tumour activity retention, and suggestion of disease control.

CONCLUSION

FAPI research is rapidly expanding from diagnostic studies in malignancies and benign diseases to the first reports of salvage radionuclide therapy. The research activity needs to shift now from low-level-of-evidence case reports and series to prospectively designed studies in homogenous patient groups to provide evidence on how and in which clinical situations FAPI theranostics can be of added value to clinical care. We have provided an overview of current research topics to build upon.

Comparison of the Detection Performance Between FAP and FDG PET/CT in Various Cancers: A Systemic Review and Meta-analysis

PURPOSE

18F-FDG is the dominant radiotracer in oncology; however, it has limitations. Novel labeled fibroblast activation protein (FAP) radiotracers have been developed and published in several studies. Thus, this meta-analysis aimed to compare the detection rates (DRs) of FDG and FAP, based on previous studies from a systematic review.

METHODS

PubMed/MEDLINE and Cochrane library databases were used to perform a comprehensive and systematic search and are updated to April 30, 2022. The DR, relative risk, and the SUVmax were calculated between the FAP and FDG tracers. Finally, the sensitivity, specificity, diagnostic odds ratio, and summary receiver operating characteristic curve of FAP and FDG were analyzed using gold and reference standards.

RESULTS

Thirty studies (1170 patients) were included in the meta-analysis. The relative risks of FAP DR for the primary tumor, recurrent tumor, lymph node metastasis, and distant metastasis were FDG 1.06- to 3.00-fold per patient and per lesion. For the primary tumor, FAP uptake was most intense in pancreatic cancer, followed by head and neck, cervical, colorectal, lung, gastric, and hepatocellular carcinoma, and was higher than FDG except for urological system cancer. The sensitivity (0.84-0.98), diagnostic odds ratio (19.36-358.47), and summary receiver operating characteristic curve (0.94-0.99) of FAP based on patient and lesion were better for primary tumors, LN metastasis, and distant metastasis than FDG.

CONCLUSIONS

Fibroblast activation protein is an extremely potential radiotracer to replace most of the use of FDG in oncology. It is noteworthy that the FAP tracers for primary tumors had low specificity despite excellent sensitivity and had lower uptake than FDG in urological system cancer. In addition, the difference in detection between FAP and FDG for LN metastasis could not be certain in sarcoma.

PET/CT with Fibroblast Activation Protein Inhibitors in Breast Cancer: Diagnostic and Theranostic Application-A Literature Review

Growing studies have recently reported on the promising application of radiolabeled-fibroblast activation protein inhibitors (FAPIs) as diagnostic and therapeutic agents in various oncological populations. To exclusively evaluate the current evidence on the diagnostic and therapeutic role of FAPI radiotracers in patients with breast cancer (BC), a narrative review of the available literature was performed. A search algorithm from PubMed/MEDLINE, based on the combination of "PET" OR "positron emission tomography" and "FAPI" and "cancer", with a last update in February 2022, was applied. From 233 identified articles, 33 studies conducted in BC patients and with available data on PET imaging or radiolabeled-FAPI therapy were finally considered, for a total of 191 patients. Despite some clinical and methodological heterogeneity among the reviewed articles, ⁶⁸Ga-FAPI PET/CT emerges as a valuable diagnostic tool in BC patients both at staging and restaging, also demonstrating several technical advantages and an overall better performance than ¹⁸F-FDG, especially in histotypes with well-known low ¹⁸F-FDG avidity. Moreover, although with still limited clinical evidence in BC, radiolabeled FAPIs emerge as promising therapeutic agents in a theranostic perspective, increasing the possibility of more personalized treatments. From these results, future research directions on FAPI radiotracers application in BC patients are suggested.

Increased 18F-FAPI PET/CT Uptake in a Case of Brucellosis of Lumbar Vertebral Body

ABSTRACT

Vertebral brucellosis is a relatively rare disease that usually emerges in animal husbandry areas. We report a case that brucellosis of lumbar vertebral body showed an intense uptake of FAPI on 18F-FAPI PET/CT, which mimics to malignant lesions or vertebral tuberculosis. It is an interesting finding to realize that vertebral brucellosis is also one of the reasons for intense uptake of FAPI.

Incidental Detection of a Type B3 Thymoma on 68Ga-FAPI-04 PET/CT Imaging

ABSTRACT

18F-FDG PET/CT performed for staging of colon cancer in a 60-year-old woman revealed a thymic neoplasm with increased radiopharmaceutical uptake in the anterior mediastinum. 68Ga-FAPI PET/CT showed low FAPI uptake in the anterior mediastinal mass. The patient was diagnosed with type B3 thymoma by histopathologic evaluation. In this case, thymoma demonstrated lower uptake with FAPI than FDG. Larger studies are required for the differentiation of malignant and benign mediastinal masses with FAPI.

Comparison of 68Ga-FAPI and 18F-FDG PET/CT for the diagnosis of primary and metastatic lesions in abdominal and pelvic malignancies: A systematic review and meta-analysis

Purpose

The purpose of this study is to compare the application value of ⁶⁸Ga-FAPI and ¹⁸F-FDG PET/CT in primary and metastatic lesions of abdominal and pelvic malignancies (APMs).

Materials

The search, limited to the earliest available date of indexing through 31 July 2022, was performed on PubMed, Embase, and Cochrane Library databases using a data-specific Boolean logic search strategy. We calculated the detection rate (DR) of ⁶⁸Ga-FAPI and ¹⁸F-FDG PET/CT in the primary staging and recurrence of APMs, and pooled sensitivities/specificities based on lymph nodes or distant metastases.

Results

We analyzed 473 patients and 2775 lesions in the 13 studies. The DRs of ⁶⁸Ga-FAPI and ¹⁸F-FDG PET/CT in evaluating the primary staging and recurrence of APMs were 0.98 (95% CI: 0.95-1.00), 0.76 (95% CI: 0.63-0.87), and 0.91(95% CI: 0.61-1.00), 0.56 (95% CI: 0.44-0.68), respectively. The DRs of ⁶⁸Ga-FAPI and ¹⁸F-FDG PET/CT in primary gastric cancer and liver cancer were 0.99 (95% CI: 0.96-1.00), 0.97 (95% CI: 0.89-1.00) and 0.82 (95% CI: 0.59-0.97), 0.80 (95% CI: 0.52-0.98), respectively. The pooled sensitivities of ⁶⁸Ga-FAPI and ¹⁸F-FDG PET/CT in lymph nodes or distant metastases were 0.717(95% CI: 0.698-0.735) and 0.525(95% CI: 0.505-0.546), and the pooled specificities were 0.891 (95% CI: 0.858-0.918) and 0.821(95% CI: 0.786-0.853), respectively.

Conclusions

This meta-analysis concluded that ⁶⁸Ga-FAPI and ¹⁸F-FDG PET/CT had a high overall diagnostic performance in detecting the primary staging and lymph nodes or distant metastases of APMs, but the detection ability of ⁶⁸Ga-FAPI was significantly higher than that of ¹⁸F-FDG. However, the ability of ⁶⁸Ga-FAPI to diagnose lymph node metastasis is not very satisfactory, and is significantly lower than that of distant metastasis.

Systematic review registration

https://www.crd.york.ac.uk/prospero/, identifier CRD42022332700.

68Ga-FAPI and 18F-FDG PET/CT Images of a Patient With Rosai-Dorfman Disease With Liver Involvement

ABSTRACT

Rosai-Dorfman disease is a rare non-Langerhans cell histiocytosis that is histopathologically characterized by the accumulation of CD68-positive and S100-positive histiocytes. The pathological changes are mostly discovered in lymph nodes. We report a case of Rosai-Dorfman disease with liver and bone marrow involvement. In this case, 18F-FDG PET/CT revealed FDG avidity in multiple lymph nodes, liver, and bone marrow. 68Ga-FAPI PET/CT showed higher uptake of 68Ga-FAPI than that of 18F-FDG in the same lesions. The findings of 68Ga-FAPI PET/CT in this patient highlighted the potential value of 68Ga-FAPI for staging in Rosai-Dorfman disease.

Case Report: 68Ga-FAPI PET/CT, a more advantageous detection mean of gastric, peritoneal, and ovarian metastases from breast cancer

Breast cancer is the most common malignant tumor in adult women. Its common metastatic sites are lymph nodes, bones, lungs, the liver, and the brain. It is so rare for a patient with breast cancer to have metastases of the gastrointestinal tract, peritoneum, and ovary at the same time that the clinical reporting rate is low. We present a case of a 61-year-old woman who underwent right mastectomy and chemoradiotherapy 3 years ago because of mixed invasive ductal-lobular breast cancer. This time, she came to the hospital due to the symptom of stomach discomfort for 2 weeks. The gastroscopy biopsy result showed gastric metastasis from breast cancer. Then, ¹⁸F-FDG imaging and ⁶⁸Ga-FAPI PET/CT imaging were performed for further diagnosis; ⁶⁸Ga-FAPI PET/CT demonstrated a significantly elevated FAPI activity in the thickened gastric wall, peritoneum, and bilateral adnexal areas, which was superior to that of ¹⁸F-FDG. Finally, a biopsy of suspicious lesions was taken for pathological and histochemical examination, which confirmed that, in addition to the gastric metastasis, the peritoneum and bilateral ovaries were all consistent with metastatic breast cancer.

Comparison of 18 F-FDG PET/CT and 68 Ga-FAPI-04 PET/CT in patients with non-small cell lung cancer

AIM

In this study, we aimed to compare the diagnostic accuracy of 18 F-fluorodeoxyglucose ( 18 F-FDG) and Gallium-68 labeled fibroblast activator protein inhibitor ( 68 Ga-FAPI)-04 PET/CT in the tumor-node-metastasis (TNM) staging of patients with nonsmall cell lung cancer (NSCLC) and investigate whether adenocarcinoma (ADC) and squamous cell cancer (SCC) exhibit different uptake patterns on 68 Ga-FAPI-04 PET/CT.

MATERIALS AND METHOD

Twenty-nine patients with a histopathologically-confirmed diagnosis of NSCLC, who had no history of previous radiation therapy or chemotherapy and underwent 18 F-FDG PET/CT and 68 Ga-FAPI-04 PET/CT imaging between January 2021 and December 2021 were included in this retrospective study. Staging was performed using the 8th edition of the TNM staging system on both 18 F-FDG PET/CT and 68 Ga-FAPI-04 PET/CT images. Standardized uptake value (SUV) max and tumor-to-background ratios (TBR) were calculated on primary lesions and metastases.

RESULTS

There was no statistically significant difference in primary lesions in terms of SUV max and TBR values. However, 68 Ga-FAPI-04 PET/CT was significantly superior to 18 F-FDG PET/CT in terms of the number of lymph nodes and bone metastases revealed. The SUV max and TBR values of lymph nodes, hepatic lesions and bone lesions were significantly higher on 68 Ga-FAPI-04 PET/CT than on 18 F-FDG PET/CT. 68 Ga-FAPI-04 PET/CT changed the disease stage of three patients (10.9%). The diagnostic accuracy of 68 Ga-FAPI-04 PET/CT was 100%, whereas the diagnostic accuracy of 18 F-FDG PET/CT was 89.6% ( P  = 0.250).

CONCLUSION

Although 68 Ga-FAPI-04 PET/CT detected more lesions and higher diagnostic accuracy than 18 F-FDG PET/CT in NSCLC, neither method was statistically superior to each other in terms of diagnostic accuracy in TNM staging.