Prognostic value of fibroblast activation protein expressing tumor volume calculated from [68 Ga]Ga-FAPI PET/CT in patients with esophageal squamous cell carcinoma

FAPI radiopharmaceuticals in nuclear oncology and theranostics of solid tumours: are we nearer to surrounding the hallmarks of cancer?

[18F]FDG PET/CT is the most widely used PET radiopharmaceutical in oncology, but it is not exempt of diagnostic limitations. FAPI have emerged as a great tool in the management of several different solid tumours in which [18F]FDG is not able to provide enough information. The aim of this work was to evaluate the available evidence on diagnostic and therapeutic applications of PET/CT with FAPI radiopharmaceuticals. We underwent a non-systematic review focusing in the utility of FAPI radiopharmaceuticals in PET/CT diagnosis and in the treatment of several malignancies. FAPI radiopharmaceuticals present characteristics that can potentially overcome some known diagnostic limitations of [18F]FDG. FAPI radiopharmaceuticals present a high target-to-background ratio (TBR) in many solid tumours such as oesophageal cancer, gastric cancer, pancreatic cancer, hepatic cancer, colorectal cancer, breast cancer, ovarian, cervical cancer, and head and neck cancer. Available evidence suggests the high TBR improves sensitivity and specificity compared to [18F]FDG, especially for the detection of lymphadenopathies and peritoneal metastases, and may improve patient management and radiation treatment planning. Moreover, it is important to underline the potential theranostic application of FAPI radiopharmaceuticals.

Association between cancer-associated fibroblasts and prognosis of neoadjuvant chemoradiotherapy in esophageal squamous cell carcinoma: a bioinformatics analysis based on single-cell RNA sequencing

BACKGROUND

Esophageal squamous cell carcinoma (ESCC) is a prevalent and aggressive subtype of esophageal cancer, posing a significant mortality and economic burden, especially in East and Southeast Asia. Current therapeutic strategies have limitations in improving patient survival, particularly regarding disease progression and resistance. This study aimed to investigate the impact of neoadjuvant chemoradiotherapy (NCRT) on the ESCC microenvironment.

METHODS

We utilized single-cell RNA sequencing to systematically characterize the tumor and cancer-associated fibroblasts (CAFs) subtypes. Marker genes of myofibroblastic CAFs (myCAFs) were employed to establish a prognostic model and verify its application in other datasets. Other experiments were conducted on clinical samples to explore potential ESCC risk-related genes.

RESULTS

Our bioinformatics and statistical analyses revealed an increased proportion of fibroblasts and epithelial cells in NCRT and identified the Ep_c1 subtype associated with a better prognosis. Further results indicated a complex communication network between Ep_c1 and myCAFs. The top 30 marker genes of myCAFs were used to construct a prognostic signature with a significant response to immunotherapy. Finally, experiments identified Complement C1s subcomponent (C1S), Decorin (DCN), and Neuroblastoma suppression of tumorigenicity 1 (NBL1) as potential ESCC risk-related genes.

CONCLUSION

Our findings highlight the dynamic alterations in the post-NCRT ESCC microenvironment and provide a foundation for the development of personalized treatment and immunotherapeutic approaches. Future studies are warranted to further validate these findings and explore their clinical implications.

FAPI-PET/CT guided radiotherapy for patients with esophageal cancer

BACKGROUND

Cancer associated fibroblasts have become a target of interest in different malignancies for positron emission tomography (PET) imaging, using positron emitter labelled fibroblast activation protein inhibitors (FAPI). New data underline the advanced imaging properties of FAPI-PET/CT for the staging of esophageal cancer compared to standard imaging. Potential benefits of FAPI-PET/CT in radiation therapy planning are the subject of this investigation.

METHODS

Ten patients with newly diagnosed esophageal cancer treated with radiochemotherapy (RCT) were retrospectively analyzed. All patients underwent [68Ga]OncoFAP-PET/CT in treatment position to facilitate radiation treatment planning. Six patients received neoadjuvant RCT as part of a trimodal therapy and four patients underwent definitive RCT. In five cases, restaging after initial treatment was performed with FAPI-PET/CT.

RESULTS

[68Ga]OncoFAP-PET/CT based imaging showed a high correlation with the endoscopic staging for initial imaging. In three cases, new sites of disease were unmasked, not visible in CT- and endosonographic staging. [68Ga]OncoFAP-PET/CT based RT delineation offered good definition of clinical target volumes, especially in retro-/paracardial areas and the gastroesophageal junction.

CONCLUSION

[68Ga]OncoFAP-PET/CT may aid and improve radiation treatment planning for patients with esophageal cancer.

Prognostic value of [68Ga]Ga-FAPI-04 PET in patients with newly diagnosed gastric carcinoma

PURPOSE

Gallium-68-labeled fibroblast activation protein inhibitor ([68Ga]Ga-FAPI) positron emission tomography (PET) has demonstrated excellent diagnostic performance in various malignancies, including gastric carcinoma. However, its prognostic utility is unclear. This study evaluates the prognostic value of [68Ga]Ga-FAPI-04 PET/MRI(CT) in gastric carcinoma.

METHODS

We retrospectively analyzed patients with gastric cancer who underwent [68Ga]Ga-FAPI-04 PET/MRI(CT) between June 2020 and June 2023. Semi-quantitative parameters, including maximum and mean standard uptake value (SUVmax, SUVmean), FAPI-avid tumor volume (FTV), total lesion FAP expression (TLF), tumor to background ratio (TBR), heterogeneity factor (HF) and coefficient of variation (CV) of the primary tumor were measured or calculated. Overall survival (OS) and progression-free survival (PFS) were obtained through follow-up. The relationships between disease prognosis and potential predictors were analyzed， and predictive models were established.

RESULTS

Eighty-six patients (median age 59 years) were included. Thirty-five patients experienced disease progression, and 26 of them died. Univariable analysis revealed SUVmax, FTV, TLF, TBR, HF and CV were significant prognostic factors for both OS and PFS. In multivariate Cox regression analysis, a nomogram model for OS was established, incorporating body mass index (BMI) and CV as independent predictors. The time-dependent C-index of the nomogram model > 0.75 indicates good predictive performance. When predicting PFS, a stratified analysis was performed based on distant metastasis, FTV was an independent prognostic factor among patients without distant metastasis.

CONCLUSION

CV and FTV, derived from [68Ga]Ga-FAPI-04 PET imaging, could serve as independent prognostic factor for OS and PFS in patients with gastric cancer, respectively.

Role of molecular imaging in prognosis, diagnosis, and treatment of gastrointestinal cancers: An update on new therapeutic methods

One of the leading causes of cancer-related death is gastrointestinal cancer, which has a significant morbidity and mortality rate. Although preoperative risk assessment is essential for directing patient care, its biological behavior cannot be accurately predicted by conventional imaging investigations. Potential pathophysiological information in anatomical imaging that cannot be visually identified can now be converted into high-dimensional quantitative image features thanks to the developing discipline of molecular imaging. In order to enable molecular tissue profile in vivo, molecular imaging has most recently been utilized to phenotype the expression of single receptors and targets of biological therapy. It is expected that molecular imaging will become increasingly important in the near future, driven by the expanding range of biological therapies for cancer. With this live molecular fingerprinting, molecular imaging can be utilized to drive expression-tailored customized therapy. The technical aspects of molecular imaging are first briefly discussed in this review, followed by an examination of the most recent research on the diagnosis, prognosis, and potential future clinical methods of molecular imaging for GI tract malignancies.

Feasibility, Tolerability, and Preliminary Clinical Response of Fractionated Radiopharmaceutical Therapy with 213Bi-FAPI-46: Pilot Experience in Patients with End-Stage, Progressive Metastatic Tumors

Radiopharmaceutical therapies (RPTs) based on fibroblast activation protein (FAP) and FAP inhibitors (FAPIs) are a new option for progressive metastatic cancer in patients pretreated multiple times. To date, published in-human data refer to initial experiences with β-emitting 90Y- and 177Lu-based RPT. However, the short tumor retention time of FAPI ligands is considered a major limitation of FAPI RPT. Therefore, fractionated FAPI RPT with 213Bi, an α-emitter with a half-life of 46 min, appears to be a promising FAPI RPT regimen. Here, we report on our initial experiences with regard to the feasibility, tolerability, and response of fractionated 213Bi-FAPI-46 RPT. Methods: Six patients (4 women and 2 men) with progressive metastatic solid tumors (3 colon cancer, 1 anal cancer, 1 breast cancer, and 1 prostate cancer) aged 16-77 y were treated with a mean of 1,609 MBq of 213Bi-FAPI-46, fractionated into 53 single applications (range, 5-12 RPT applications per patient; mean, 8.8 applications) over a period of up to 107 h per patient. Of the 6 patients, 4 patients received adjuvant treatment with pembrolizumab. 18F-FDG (4 patients) and 68Ga-FAPI-46 (5 patients) PET/CT scans were performed before and after RPT. PET images were assessed visually and by calculating total lesion glycolysis and total lesion FAPI. Results: RPT with 213Bi-FAPI-46 was well tolerated without adverse side effects. In terms of visual response assessment, there was 1 partial response (16.7%), 1 patient with stable disease (16.7%), and 4 patients with progressive disease (66.7%). Concordantly, total lesion glycolysis and total lesion FAPI were decreased in the responding patient (not applicable and -24.3%, respectively), slightly decreased in the patient with stable disease (-10.6% and -5.9%, respectively), and increased in the 4 patients with progression (mean, +104.4% and +321.3%, respectively). Conclusion: Fractionated FAPI RPT with the short-half-life α-emitter 213Bi-FAPI-46 is a promising approach that matches the pharmacokinetics of FAPI-46 better than the 177Lu- or 90Y-labeled compounds. In this pilot project, fractionated RPT with 213Bi-FAPI-46 showed good clinical tolerability and even led to regressive or stable disease in the short term in 2 of 6 patients. Further studies with larger patient cohorts are required to evaluate the actual efficacy and long-term effects of this variant of FAPI RPT.

Comparison of differences in immune cells and immune microenvironment among different kinds of oncolytic virus treatments

Oncolytic viruses are either naturally occurring or genetically engineered viruses that can activate immune cells and selectively replicate in and destroy cancer cells without damaging healthy tissues. Oncolytic virus therapy (OVT) represents an emerging treatment approach for cancer. In this review, we outline the properties of oncolytic viruses and then offer an overview of the immune cells and tumor microenvironment (TME) across various OVTs. A thorough understanding of the immunological mechanisms involved in OVTs could lead to the identification of novel and more effective therapeutic targets for cancer treatment.

68 Ga-FAPI Response Evaluation Pitfall in a Patient With Esophageal Cancer After Neoadjuvant Therapy

ABSTRACT

We report the 68 Ga-FAPI PET/CT findings of inflammatory changes and fibrosis in a 55-year-old woman with a history of esophageal cancer after neoadjuvant therapy, which needs to be differentiated from other esophageal diseases during evaluation.

Integrated 68 Ga-FAPI-04 PET/MR in Pancreatic Cancer : Prediction of Tumor Response and Tumor Resectability After Neoadjuvant Therapy

PURPOSE

This study aimed to investigate the value of 68 Ga-fibroblast activation protein inhibitor (FAPI) PET/MR semiquantitative parameters in the prediction of tumor response and resectability after neoadjuvant therapy in patients with pancreatic cancer.

PATIENTS AND METHODS

This study was performed retrospectively in patients with borderline resectable or locally advanced pancreatic cancer who underwent 68 Ga-FAPI PET/MRI from June 2020 to June 2022. The SUV max , SUV mean , SUV peak , uptake tumor volume (UTV), and total lesion FAP expression (TLF) of the primary tumor were recorded. The target-to-background ratios (TBRs) of the primary tumor to normal tissue muscle (TBR muscle ) and blood (TBR blood ) were also calculated. In addition, the minimum apparent diffusion coefficient value of the tumor was measured. After 3-4 cycles of gemcitabine + nab-paclitaxel chemotherapy, patients were divided into responders and nonresponders groups according to RECIST criteria (v.1.1). They were also divided into resectable and unresectable groups according to the surgical outcome. The variables were compared separately between groups.

RESULTS

A total of 18 patients who met the criteria were included in this study. The UTV and TLF were significantly higher in nonresponders than in responders ( P < 0.05). The SUV max , SUV mean , and TBR muscle were significantly higher in unresectable patients than in resectable ones ( P < 0.05). Receiver operating characteristic curve analysis identified UTV (area under the curve [AUC] = 0.840, P = 0.015) and TLF (AUC = 0.877, P = 0.007) as significant predictors for the response to gemcitabine + nab-paclitaxel chemotherapy, with cutoff values of 25.05 and 167.38, respectively. In addition, SUV max (AUC = 0.838, P = 0.016), SUV mean (AUC = 0.812, P = 0.026), and TBR muscle (AUC = 0.787, P = 0.041) were significant predictors of the resectability post-NCT, with cutoff values of 14.0, 6.0, and 13.9, respectively. According to logistic regression analysis, TLF was found to be significantly associated with tumor response ( P = 0.032) and was an independent predictor of tumor response ( P = 0.032). In addition, apparent diffusion coefficient value was an independent predictor of tumor resectability ( P = 0.043).

CONCLUSIONS

This pilot study demonstrates the value of 68 Ga-FAPI PET/MR for the prediction of tumor response and resectability after neoadjuvant therapy. It may aid in individualized patient management by guiding the treatment regimens.

Fibroblast Activation Protein Inhibitor Tracers and Their Preclinical, Translational, and Clinical Status in China

Quinoline-based fibroblast activation protein (FAP) inhibitors (FAPIs) have recently emerged as a focal point in global nuclear medicine, underscored by their promising applications in cancer theranostics and the diagnosis of various nononcological conditions. This review offers an in-depth summary of the existing literature on the evolution and use of FAPI tracers in China, tracing their journey from preclinical to clinical research. Moreover, this review also assesses the diagnostic accuracy of FAPI PET for the most common cancers in China, analyzes its impact on oncologic management paradigms, and investigates the potential of FAP-targeted radionuclide therapy in patients with advanced or metastatic cancer. This review also summarizes studies using FAPI PET for nononcologic disorders in China. Thus, this qualitative overview presents a snapshot of China's engagement with FAPI tracers, aiming to guide future research endeavors.

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.

PET/CT FAPI: Procedure and evidence review in oncology

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

18F-FAPI-04 PET/CT parameters predict PD-L1 expression in esophageal squamous cell carcinoma

Purpose

This prospective study examined whether metabolism parameters obtained using the tracer 18F-AlFNOTA-fibroblast activation protein inhibitor (FAPI)-04 (denoted as 18F-FAPI-04) in positron emission tomography/computed tomography (PET/CT) can predict programmed death ligand-1 (PD-L1) expression in patients with locally advanced esophageal squamous cell carcinoma (LA-ESCC).

Patients and methods

The 24 enrolled LA-ESCC patients underwent an 18F-FAPI-04 PET/CT scan. The maximum, mean, peak and standard deviation standard uptake values (SUVmax, SUVmean, SUVpeak and SUVsd), metabolic tumor volume (MTV), and total lesion FAP (TLF) expression of the primary tumor were collected. Additionally, we evaluated PD-L1 expression on cancer cells by immunohistochemistry and immunofluorescence methods. Patients were divided into negative and positive expressions according to the expression of PD-L1 (CPS < 10 and CPS ≥ 10), and the variables were compared between the two groups.

Results

The SUVmax, SUVmean, SUVpeak and SUVsd were significantly higher in patients with positive expression than in negative expression (all p < 0.05). Receiver operating characteristic curve analysis identified SUVmean (area under the curve [AUC] = 0.882, p = 0.004), SUVsd (AUC = 0.874, p = 0.005), SUVpeak (AUC = 0.840, p = 0.010) and SUVmax (AUC = 0.765, p = 0.045) as significant predictors of the PD-L1 positive expression, with cutoff values of 9.67, 1.90, 9.67 and 13.71, respectively. On univariate logistic regression analysis, SUVmean (p = 0.045), SUVsd (p = 0.024), and SUVpeak (p = 0.031) were significantly correlated with the PD-L1 positive expression. On multivariable logistic regression analysis, SUVsd (p = 0.035) was an optimum predictor factor for PD-L1 positive expression.

Conclusion

18F-FAPI-04 PET/CT parameters, including SUVmean, SUVpeak, and SUVsd, correlated with PD-L1 expression in patients with LA-ESCC, and thus SUVsd was an optimum predictor for PD-L1 positive expression, which could help to explore the existence of immune checkpoints and select ESCC candidates for immunotherapy.

[18F] AlF-NOTA-FAPI-04 PET/CT can predict treatment response and survival in patients receiving chemotherapy for inoperable pancreatic ductal adenocarcinoma

PURPOSE

We investigated whether uptake of [18F] AlF-NOTA-FAPI-04 on positron emission tomography/computed tomography (PET/CT) could predict treatment response and survival in patients with pancreatic ductal adenocarcinoma (PDAC).

METHODS

We prospectively evaluated 47 patients with histopathologically confirmed primary PDAC who provided pretreatment [18F] AlF-NOTA-FAPI-04 scans to detect fibroblast activation protein (FAP) on the tumor surface by uptake of [18F] AlF-NOTA-FAPI-04. PDAC specimens were immunohistochemically stained with cancer-associated fibroblast (CAF) markers. We obtained a second PET scan after one cycle of chemotherapy to study changes in FAPI uptake variables from before to during treatment. Correlations between baseline PET variables and CAF-related immunohistochemical markers were assessed with Spearman's rank test. Cox regression and Kaplan-Meier methods were used to assess relationships between disease progression and potential predictors. Receiver operating characteristic (ROC) curve analysis was used to define the optimal cut-off points for distinguishing patients according to good response vs. poor response per RECIST v.1.1.

RESULTS

The FAPI PET variables maximum and mean standardized uptake values (SUVmax, SUVmean), metabolic tumor volume (MTV), and total lesion FAP expression (TLF) were positively correlated with CAF markers (FAP, α-smooth muscle actin, vimentin, S100A4, and platelet-derived growth factor receptor α/β, all P < 0.05). MTV was associated with survival in patients with inoperable PDAC (all P < 0.05). Cox multivariate regression showed that MTV was associated with overall survival (MTV hazard ratio [HR] = 1.016, P = 0.016). Greater changes from before to during chemotherapy in SUVmax, MTV, and TLF were associated with good treatment response (all P < 0.05). ΔMTV, ΔTLF, and ΔSUVmax had larger areas under the curve than ΔCA19-9 for predicting treatment response. Kaplan-Meier analysis showed that the extent of change in MTV and TLF from before to after treatment predicted progression-free survival, with cut-off values (based on medians) of - 4.95 for ΔMTV (HR = 8.09, P = 0.013) and - 77.83 for ΔTLF (HR = 4.62, P = 0.012).

CONCLUSIONS

A higher baseline MTV on [18F] AlF-NOTA-FAPI-04 scans was associated with poorer survival in patients with inoperable PDAC. ΔMTV was more sensitive for predicting response than ΔCA19-9. These results are clinically meaningful for identifying patients with PDAC who are at high risk of disease progression.

FAP-targeted PET imaging in gastrointestinal malignancies: a comprehensive review

F18-fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) plays a crucial role in tumour diagnosis, staging, and therapy response evaluation of various cancer types and has been a standard imaging modality used in clinical oncology practice for many years. However, it has certain limitations in evaluating some particular gastrointestinal cancer types due to low FDG-avidity or interphering physiological background activity. Fibroblast activation protein (FAP), a protein of the tumour microenvironment, is overexpressed in a wide range of cancers which makes it an attractive target for both tumour imaging and therapy. Recently, FAP-targeted radiopharmaceuticals are widely used in clinical research and achieved great results in tumour imaging. Considering the limitations of FDG PET/CT and the lack of physiological FAP-targeted tracer uptake in liver and intestinal loops, gastrointestinal cancers are among the most promising indications of FAP-targeted imaging. Herein, we present a comprehensive review of FAP-targeted imaging in gastrointestinal cancers in order to clarify the current and potential future role of this class of molecules in gastrointestinal oncology.