Static and Dynamic 68Ga-FAPI PET/CT for the Detection of Malignant Transformation of Intraductal Papillary Mucinous Neoplasia of the Pancreas

Prospective Comparison of [18F]FDG and [18F]AIF-FAPI-74 PET/CT in the Evaluation of Potentially Resectable Pancreatic Ductal Adenocarcinoma

PURPOSE

Accurate clinical staging of potentially resectable pancreatic ductal adenocarcinoma (PDAC) is critical for establishing optimal treatment strategies. While the efficacy of fluorine-18-fluorodeoxyglucose ([18F]FDG) positron emission tomography/computed tomography (PET/CT) in clinical staging is unclear, PET/CT detecting fibroblast-activation protein (FAP) expression has recently received considerable attention for detecting various tumors, including PDAC, with high sensitivity. We explored the efficacy of [18F]FDG and [18F]AIF-FAPI-74 PET/CT in the initial evaluation of potentially resectable PDAC.

PROCEDURES

Between 2021 and 2022, twenty participants with newly diagnosed potentially resectable PDAC were enrolled. After the initial evaluation with pancreatic CT, [18F]FDG PET/CT, and [18F]AIF-FAPI-74 PET/CT, treatment strategies were determined considering the participant's general status, clinical staging, and resectability. Pathological information from the surgical specimens was only available in 17 participants who underwent curative-intent surgery. Head-to-head comparisons of quantitative radiotracer uptake and diagnostic performance were performed among imaging modalities.

RESULTS

[18F]AIF-FAPI-74 PET/CT showed a significantly higher maximum standardized uptake value than [18F]FDG PET/CT did in evaluating primary pancreatic lesions (median [interquartile range]; 12.6 [10.7-13.7] vs. 6.3 [4.8-9.2]; P < 0.001). In contrast, [18F]AIF-FAPI-74 PET/CT showed a significantly lower mean standardized uptake value than [18F]FDG PET/CT did in evaluating background organ (median [interquartile range]) 0.8 [0.7-0.9] vs. 2.6 [2.3-2.7]; P < 0.001). In addition, the sensitivity of [18F]AIF-FAPI-74 PET/CT in detecting metastatic lymph nodes was higher than that of [18F]FDG PET/CT (50.0% vs. 0.0%; P = 0.026).

CONCLUSION

This study demonstrated that [18F]AIF-FAPI-74 PET/CT could improve the clinical staging of potentially resectable PDAC.

Pancreatic Cancer: A Review of Risk Factors

Pancreatic adenocarcinoma is one of the most lethal types of gastrointestinal cancer despite the latest medical advances. Its incidence has continuously increased in recent years in developed countries. The location of the pancreas can result in the initial symptoms of neoplasia being overlooked, which can lead to a delayed diagnosis and a subsequent reduction in the spectrum of available therapeutic options. The role of modifiable risk factors in pancreatic cancer has been extensively studied in recent years, with smoking and alcohol consumption identified as key contributors. However, the few screening programs that have been developed focus exclusively on genetic factors, without considering the potential impact of modifiable factors on disease occurrence. Thus, fully understanding and detecting the risk factors for pancreatic cancer represents an important step in the prevention and early diagnosis of this type of neoplasia. This review reports the available evidence on different risk factors and identifies the areas that could benefit the most from additional studies.

Diagnostic Potential of Supplemental Static and Dynamic 68Ga-FAPI-46 PET for Primary 18F-FDG-Negative Pulmonary Lesions

PET using 68Ga-labeled fibroblast activation protein (FAP) inhibitors (FAPIs) holds high potential for diagnostic imaging of various malignancies, including lung cancer (LC). However, 18F-FDG PET is still the clinical gold standard for LC imaging. Several subtypes of LC, especially lepidic LC, are frequently 18F-FDG PET-negative, which markedly hampers the assessment of single pulmonary lesions suggestive of LC. Here, we evaluated the diagnostic potential of static and dynamic 68Ga-FAPI-46 PET in the 18F-FDG-negative pulmonary lesions of 19 patients who underwent surgery or biopsy for histologic diagnosis after PET imaging. For target validation, FAP expression in lepidic LC was confirmed by FAP immunohistochemistry. Methods: Hematoxylin and eosin staining and FAP immunohistochemistry of 24 tissue sections of lepidic LC from the local tissue bank were performed and analyzed visually. Clinically, 19 patients underwent static and dynamic 68Ga-FAPI-46 PET in addition to 18F-FDG PET based on individual clinical indications. Static PET data of both examinations were analyzed by determining SUVmax, SUVmean, and tumor-to-background ratio (TBR) against the blood pool, as well as relative parameters (68Ga-FAPI-46 in relation to18F-FDG), of histologically confirmed LC and benign lesions. Time-activity curves and dynamic parameters (time to peak, slope, k 1, k 2, k 3, and k 4) were extracted from dynamic 68Ga-FAPI-46 PET data. The sensitivity and specificity of all parameters were analyzed by calculating receiver-operating-characteristic curves. Results: FAP immunohistochemistry confirmed the presence of strongly FAP-positive cancer-associated fibroblasts in lepidic LC. LC showed markedly elevated 68Ga-FAPI-46 uptake, higher TBRs, and higher 68Ga-FAPI-46-to-18F-FDG ratios for all parameters than did benign pulmonary lesions. Dynamic imaging analysis revealed differential time-activity curves for LC and benign pulmonary lesions: initially increasing time-activity curves with a decent slope were typical of LC, and steadily decreasing time-activity curve indicated benign pulmonary lesions, as was reflected by a significantly increased time to peak and significantly smaller absolute values of the slope for LC. Relative 68Ga-FAPI-46-to-18F-FDG ratios regarding SUVmax and TBR showed the highest sensitivity and specificity for the discrimination of LC from benign pulmonary lesions. Conclusion: 68Ga-FAPI-46 PET is a powerful new tool for the assessment of single 18F-FDG-negative pulmonary lesions and may optimize patient stratification in this clinical setting.

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.

Current considerations on intraductal papillary neoplasms of the bile duct and pancreatic duct

Pancreatobiliary intraductal papillary neoplasms (IPNs) represent precursors of pancreatic cancer or bile duct cholangiocarcinoma that can be detected and treated. Despite advances in diagnostic methods, identifying these premalignant lesions is still challenging for treatment providers. Modern imaging, biomarkers and molecular tests for genomic alterations can be used for diagnosis and follow-up. Surgical intervention in combination with new chemotherapeutic agents is considered the optimal treatment for malignant cases. The balance between the risk of malignancy and any risk of resection guides management policy; therefore, treatment should be individualized based on a meticulous preoperative assessment of high-risk stigmata. IPN of the bile duct is more aggressive; thus, early diagnosis and surgery are crucial. The conservative management of low-risk pancreatic branch-duct lesions is safe and effective.

[Hereditary and familial forms of pancreatic adenocarcinoma: Genetic determinism, patients eligible for systematic screening, screening methods and results]

Systematic screening for pancreatic cancer in high risk individuals is justified by the poor prognosis of the majority of cases diagnosed at a symptomatic stage that are mostly advanced and unresectable Individual risk assessment is based on both genetic data and family history. The screening of a panel of susceptibiility genes should be offered to any affected individual when a genetic predisposition is suspected. An international consortium has proposed a definition of the at risk population, candidate for screening, and there is a consensus on the target lesions of this screening: early adenocarcinoma and benign lesions with a high potential for malignant transformation: Intraductal Papillary Mucinous Neopasm (IPMN) and Pancreatic Intraepithelial Neoplasia (PanIN) with high-grade dysplasia. Its modalities currently consist of an annual pancreatic MRI and/or endoscopic ultrasound (EUS), associated with screening for diabetes mellitus. The main limitation of screening, the effectiveness of which has not yet been demonstrated, is its lack of sensitivity, which results in a non-negligible rate of interval cancers and sometimes advanced diagnoses. Insufficient specificity is also imperfect, in particular with regard to benign lesions with a low potential for degeneration, and can lead to the proposal of unjustified surgeries. This situation makes the future integration of new imaging techniques and promising new biological approaches that are being explored highly desirable.

Immunohistochemical FAP Expression Reflects 68Ga-FAPI PET Imaging Properties of Low- and High-Grade Intraductal Papillary Mucinous Neoplasms and Pancreatic Ductal Adenocarcinoma

Pancreatic intraductal papillary mucinous neoplasms (IPMNs) are grossly visible (typically > 5 mm) intraductal epithelial neoplasms of mucin-producing cells, arising in the main pancreatic duct or its branches. According to the current 2-tiered grading scheme, these lesions are categorized as having either low-grade (LG) dysplasia, which has a benign prognosis, or high-grade (HG) dysplasia, which formally represents a carcinoma in situ and thus can transform to pancreatic ductal adenocarcinoma (PDAC). Because both entities require different treatments according to their risk of becoming malignant, a precise pretherapeutic diagnostic differentiation is inevitable for adequate patient management. Recently, our group has demonstrated that 68Ga-fibroblast activation protein (FAP) inhibitor (FAPI) PET/CT shows great potential for the differentiation of LG IPMNs, HG IPMNs, and PDAC according to marked differences in signal intensity and tracer dynamics. The purpose of this study was to biologically validate FAP as a target for PET imaging by analyzing immunohistochemical FAP expression in LG IPMNs, HG IPMNs, and PDAC and comparing with SUV and time to peak (TTP) measured in our prior study. Methods: To evaluate the correlation of the expression level of FAP and α-smooth muscle actin (αSMA) in neoplasm-associated stroma depending on the degree of dysplasia in IPMNs, 98 patients with a diagnosis of LG IPMN, HG IPMN, PDAC with associated HG IPMN, or PDAC who underwent pancreatic surgery at the University Hospital Heidelberg between 2017 and 2023 were identified using the database of the Institute of Pathology, University Hospital Heidelberg. In a reevaluation of hematoxylin- and eosin-stained tissue sections of formalin-fixed and paraffin-embedded resection material from the archive, which was originally generated for histopathologic routine diagnostics, a regrading of IPMNs was performed by a pathologist according to the current 2-tiered grading scheme, consequently eliminating the former diagnosis of "IPMN with intermediate-grade dysplasia." For each case, semithin tissue sections of 3 paraffin blocks containing neoplasm were immunohistologically stained with antibodies directed against FAP and αSMA. In a masked approach, a semiquantitative analysis of the immunohistochemically stained slides was finally performed by a pathologist by adapting the immunoreactive score (IRS) and human epidermal growth factor receptor 2 (Her2)/neu score to determine the intensity and percentage of FAP- and αSMA-positive cells. Afterward, the IRS of 14 patients who underwent 68Ga-FAPI-74 PET/CT in our previous study was compared with their SUVmax, SUVmean, and TTP for result validation. Results: From 98 patients, 294 specimens (3 replicates per patient) were immunohistochemically stained for FAP and αSMA. Twenty-three patients had LG IPMNs, 11 had HG IPMNs, 10 had HG IPMNs plus PDAC, and 54 had PDAC. The tumor stroma was in all cases variably positive for FAP. The staining intensity, percentage of FAP-positive stroma, IRS, and Her2/neu score increased with higher malignancy. αSMA expression could be shown in normal pancreatic stroma as well as within peri- and intraneoplastic desmoplastic reaction. No homogeneous increase in intensity, percentage, IRS, and Her2/neu score with higher malignancy was observed for αSMA. The comparison of the mean IRS of FAP with the mean SUVmax, SUVmean, and TTP of 68Ga-GAPI-74 PET/CT showed a matching value increasing with higher malignancy in 68Ga-FAPI-74 PET imaging and immunohistochemical FAP expression. Conclusion: The immunohistochemical staining of IPMNs and PDAC validates FAP as a biology-based stromal target for in vivo imaging. Increasing expression of FAP in lesions with a higher degree of malignancy matches the expectation of a stronger FAP expression in PDAC and HG IPMNs than in LG IPMNs and corroborates our previous findings of higher SUVs and a longer TTP in PDAC and HG IPMNs than in LG IPMNs.

From FDG and beyond: the evolving potential of nuclear medicine

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

Comparison of early and late 68Ga-FAPI-46-PET in 33 patients with possible recurrence of pancreatic ductal adenocarcinomas

Positron emission tomography with 68Gallium (68Ga) labeled inhibitors of fibroblast activation protein (68Ga-FAPI-PET) is a promising imaging technique for patients with recurrent pancreatic ductal adenocarcinomas (PDAC). To date, it is not clear if different acquisition timepoints for 68Ga-FAPI-PET may result in comparable imaging information and if repetitive 68Ga-FAPI-PET imaging may add diagnostic value to single timepoint acquisition for recurrent PDAC. Here we analyzed retrospectively early (20 min p.i.) and late (60 min p.i.) 68Ga-FAPI-PET imaging using FAPI-46 of 33 patients with possible recurrence of PDAC concerning detection rates and uptake over time of local recurrences, metastases, inflammatory lesions of the pancreas, cholestatic lesions of the liver and reactive tissue. 33 patients with histologically confirmed PDAC after complete or partial resection of the pancreas and possible recurrence were examined by 68Ga-FAPI-46-PET acquired 20- and 60-min post injection (p.i.) of the radiotracer. FAPI-positive lesions were classified as local recurrences, metastases, inflammatory lesions of the pancreas (ILP), cholestatic lesions of the liver and reactive tissue based on histology, PET- and CT-morphology and clinical information. Lesions were contoured, and standardized uptake values (SUVmax and SUVmean) and target-to-background ratios (TBR) were analyzed for both acquisition timepoints. In total, 152 FAPI-positive lesions (22 local relapses, 47 metastases, 26 inflammatory lesions of the pancreas, 28 reactive tissues, and 29 cholestatic lesions) were detected. Detection rates for the early and late acquisition of 68Ga-FAPI-46-PET were almost identical except cholestatic lesions, which showed a higher detection rate at early imaging. SUV parameters and TBRs of ILP significantly decreased over time. Cholestatic lesions showed a tendency towards decreasing uptake. All other types of lesions showed relatively stable uptake over time. Early and late acquisition of 68Ga-FAPI-PET results in comparable imaging information in patients with possible recurrence of PDAC. Two timepoint imaging offers additional diagnostic potential concerning differential diagnoses.

Radiolabeled FAPI in pancreatic cancer: can it be an additional value in the management of patients?

INTRODUCTION

To discuss the current evidence about radiolabeled-FAPI in patients affected by pancreatic cancer by underlying the advantages, disadvantages, and the future perspectives also in the theragnostic field.

AREAS COVERED

A literature search up until February 2023 was performed in PubMed, EBSCO, and EMBASE databases. Clinical reports, conference abstracts, editorials, and letters-to-the-editor were excluded. The results were presented according to the PRISMA guidelines. The quality of studies was evaluated by using the Critical Appraisal Skill Program checklist.

EXPERT OPINION

From the initial 139 studies, 21 papers were selected for the final analysis. Ten papers were related to FAPI-uptake in health/benign/malignant pancreas, eight studies were focalized on the utility of radiolabeled-FAPI for the identification of premalignant and malignant pancreatic lesions and only three papers were related to the the theragnostic approach. Only two papers enrolled exclusively patients with pancreatic cancer undergoing FAPI-PET. In total, 55 patients underwent FAPI-PET for the identification of the suspicious mass/primary tumor (n = 43) and recurrent disease (n = 12). In both the studies, FAPI-PET detected more lesions than 2-[18F]FDG. Preliminary data about the FAPI-based theragnostic approach in patients with pancreatic cancer (n = 9 patients, totally) are now available. Radiolabeled-FAPI is a promising agent for the identification of pancreatic malignant lesions, but further prospective studies are still necessary.

Tumor Characterization by [68Ga]FAPI-46 PET/CT Can Improve Treatment Selection for Pancreatic Cancer Patients: An Interim Analysis of a Prospective Clinical Trial

Correct and timely diagnosis of pancreatic cancer (PC) is essential for treatment selection but is still clinically challenging. Standard-of-care imaging methods can sometimes not differentiate malignancies from inflammatory lesions or detect malignant transformation in premalignant lesions. This interim analysis of a prospective clinical trial aimed to evaluate the diagnostic accuracy of [⁶⁸Ga]fibroblast activation protein inhibitor (FAPI)-46 PET/CT for PC and determine the sample size needed to demonstrate whether this imaging technique improves the characterization of equivocal lesions detected by standard-of-care imaging methods. Methods: [⁶⁸Ga]FAPI-46 PET/CT imaging was performed on 30 patients scheduled for surgical resection of suspected PC. Target lesions were delineated, SUV_max and SUV_mean were determined, and the results were compared with those of standard-of-care imaging. Receiver operating characteristics were calculated for the whole cohort and a subcohort of 11 patients with an equivocal clinical imaging work-up preoperatively. Postoperative histopathologic findings served as a reference standard, and the statistical power was determined. Results: Histopathologic examination revealed malignancy in 20 patients and benign lesions in 10 patients. Significantly elevated [⁶⁸Ga]FAPI-46 uptake was observed in malignant tumors compared with benign lesions (P < 0.001). Receiver-operating-characteristic analyses established optimal cutoffs for both SUVs for differentiation of malignant from nonmalignant pancreatic tumors. The optimal SUV_max cutoff was 10.2 and showed 95% sensitivity and 80% specificity for the whole cohort, as well as 100% diagnostic accuracy when considering the subcohort with equivocal imaging work-up only. For sufficient statistical power, 38 equivocal observations are needed. Conclusion: We conclude that [⁶⁸Ga]FAPI-46 PET/CT can accurately differentiate malignant from benign pancreatic lesions deemed equivocal by standard-of-care imaging. This trial will therefore continue to recruit a total of 120 patients to reach those 38 equivocal observations needed for sufficient statistical power. On the basis of our findings, we propose that [⁶⁸Ga]FAPI-46 PET/CT not only can be clinically applied as a complement but also could become a necessary tool when standard-of-care imaging is inconclusive.

Head-to-Head Intra-Individual Comparison of Biodistribution and Tumor Uptake of [18F]FAPI-74 with [18F]FDG in Patients with PDAC: A Prospective Exploratory Study

BACKGROUND

Radiolabeled fibroblast activation protein (FAP) ligands, a novel class of tracers for PET/CT imaging, have demonstrated very promising results in various oncological, as well as in some benign, diseases with long-term potential to supplant the current pan-cancer agent [¹⁸F]FDG in some cancer types. Pancreatic ductal carcinoma (PDAC) belongs to the group of epithelial malignancies with a strong so-called "desmoplastic reaction", leading to a prominent tumor stroma with cancer-associated fibroblasts that exhibit a marked overexpression of fibroblast activation protein (FAP). The first clinical experiences in PDAC with ⁶⁸Ga-labeled FAP ligands suggested superior sensitivity to [¹⁸F]FDG. However, there is limited data with ¹⁸F-labeled FAP derivatives, i.e. [¹⁸F]FAPI-74, yet prospective single- and multicenter trials are already ongoing. In this proof-of-concept study, we sought to evaluate the biodistribution, tumor uptake, and lesion detectability in patients with PDAC using [¹⁸F]FAPI-74 PET/CT as compared to [¹⁸F]FDG PET/CT scans for staging.

METHODS

This study includes 7 patients (median age 69) who underwent both [¹⁸F]FDG PET/CT with contrast-enhancement and [¹⁸F]FAPI-74 PET with low-dose CT for primary staging (n = 3) and therapy response control after neoadjuvant (n = 1) or re-staging after palliative therapy (n = 3). The mean interval between PET scans was 11 ± 4 days (range 1-15 days). The [¹⁸F]FDG and [¹⁸F]FAPI-74 PET/CT scans were acquired at 64 ± 4.1 min (range 61-91 min) and 66.4 ± 6.3 min (range 60-76 min), respectively, after administration of 200 ± 94 MBq (range 79-318 MBq) and 235 ± 88 MBq (range 90-321 MBq), respectively. 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, 32 lesions were detected in 7 patients including primary (n = 7), lung (n = 7), bone (n = 3), lymph node (n = 13), and peritoneal metastases (n = 2). [¹⁸F]FAPI-74 detected 22% more lesions compared with [¹⁸F]FDG with a better TBR and visual lesion delineation. In one patient the primary lesion could be detected unequivocally with [¹⁸F]FAPI-74 but was missed by [¹⁸F]FDG imaging. Altogether, most of the lesions demonstrated markedly elevated uptake of [¹⁸F]FAPI-74 with a simultaneous lower uptake in the background, providing a very high visual contrast.

CONCLUSION

To the best of our knowledge, this is the first, prospective, intra-individual investigation comparing [¹⁸F]FAPI-74 with [¹⁸F]FDG imaging in PDAC with encouraging results. These pivotalresults supporta larger, multicentric, prospective study to determine the value of [¹⁸F]FAPI-74 in detecting and staging PDAC in comparison with current standard of care imaging.

Fibroblast Activation Protein Inhibitor PET in Pancreatic Cancer

Radiolabeled fibroblast activation protein inhibitor (FAPI) has been introduced as a promising PET tracer for imaging of pancreatic cancer. To date, FAPI PET/computed tomography (CT) has generally but not universally yielded higher radiotracer uptake and tumor-to-background contrast than ¹⁸F-fluorodeoxyglucose PET/CT in primary tumors, involved lymph nodes, and visceral metastases. It may also be useful for the evaluation of the tumor response to chemotherapy. However, increased FAPI uptake may be observed in benign conditions, including pancreatitis, pancreatic tuberculosis, IgG4-related disease, and serous cystadenoma, and therefore, clinical, radiological, and pathological correlations are required.

Tumor-to-blood ratio for assessment of fibroblast activation protein receptor density in pancreatic cancer using [68Ga]Ga-FAPI-04

PURPOSE

[⁶⁸Ga]Ga-FAPI PET/CT has been widely used in clinical diagnosis and radiopharmaceutical therapy. In this study, tumor-to-blood ratio (TBR) was evaluated as a powerful tool for semiquantitative assessment of [⁶⁸Ga]Ga-FAPI-04 tumor uptake and as an effective index for tumors with high FAP expression in theranostics.

METHODS

Nine patients with pancreatic cancer underwent a 60-min dynamic PET/CT scan by total-body PET/CT (with a long AFOV of 194 cm) after injection of [⁶⁸Ga]Ga-FAPI-04. After dynamic PET/CT scan, three patients received chemotherapy and underwent the second dynamic scan to evaluate treatment response. Time-activity curves (TACs) were obtained by drawing regions of interest for primary pancreatic lesions and metastatic lesions. The lesion TACs were fitted using four compartment models by the software PMOD PKIN kinetic modeling. The preferred pharmacokinetic model for [⁶⁸Ga]Ga-FAPI-04 was evaluated based on the Akaike information criterion. The correlations between simplified methods for quantification of [⁶⁸Ga]Ga-FAPI-04 (SUVs; tumor-to-blood ratios [TBRs]) and the total distribution volume (V_t) estimates obtained from pharmacokinetic analysis were calculated.

RESULTS

In total, 9 primary lesions and 25 metastatic lesions were evaluated. The reversible two-tissue compartment model (2TCM) was the most appropriate model among the four compartment models. The total distribution volume V_t values derived from 2TCM varied significantly in pathological lesions and background regions. A strong positive correlation was observed between TBR_mean and V_t from the 2TCM model in pathological lesions (R²=0.92, P<0.001). The relative difference range for TBR_mean was 2.1% compared to the reduction rate of V_t in the patients who were treated with chemotherapy.

CONCLUSIONS

A strong positive correlation was observed between TBR_mean and V_t for [⁶⁸Ga]Ga-FAPI-04. TBR_mean reflects FAP receptor density better than SUV_mean and SUV_max, and would be the preferred measurement tool for semiquantitative assessment of [⁶⁸Ga]Ga-FAPI-04 tumor uptake and as a means for evaluating treatment response.

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

Simple Summary

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

Abstract

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

Modern aspects of the management of pancreatic intraductal papillary mucinous neoplasms: a narrative review

Intraductal papillary mucinous neoplasms (IPMNs) account for approximately 35% of all cystic tumors in the pancreas and represent the largest subgroup. They are characterized by mucin production and intraductal papillary epithelium growth. IPMNs range from benign to malignant lesions. Biomarkers combined with 18F-Fluorodeoxyglucose-positron emission tomography (18FDG-PET) is the best diagnostic tool. The risk of malignant transformation for main-duct IPMNs is between 34-68% and for low-risk branch-duct (BD)-IPMNs it is 1.1%. Monitoring is crucial for determining the optimal time of surgical excision. Novel artificial intelligence combining clinical, tumor biomarkers, imaging and molecular genomics plays a determinant role in the evaluation of such lesions. The first diagnostic tool is multidetector helical computed tomography (MDHCT) or up-to-date magnetic resonance imaging (MRI). MRI detects malignancy by enhancing mural nodules ≥3 mm. Novel endosonographic interventional techniques have been added to the diagnostic armamentarium. Pancreatoscopy is feasible and effective but challenging for evaluating the diagnosis, invasiveness, and extent of IPMNs. Its findings may change the surgical approach. Pancreatic juice and duodenal fluid have been used recently for molecular biological analysis. The genes most frequently altered include Kirsten rat sarcoma viral proto-oncogene (KRAS), tumor protein p53 (TP53), cyclin-dependent kinase inhibitor 2A (CDKN2A), SMAD family member 4 (SMAD4), and guanine nucleotide-binding protein, alpha stimulating (GNAS). Despite the advances in diagnostic modalities, assessment of this premalignant lesion of pancreatic cancer, with its poor prognosis, is a challenging task. Pancreatectomy is the indicated approach for malignant or high-risk IPMNs with potent malignancy. Conservative management or enucleation for preserving the pancreas of low-risk BD-IPMNs is recommended, but long-term follow-up for recurrence is necessary. The management of IPMNs must be individualized based on preoperative high-risk stigmata and worrisome features.