68Ga-FAPI-PET/CT in patients with various gynecological malignancies

Development of an FAP-Targeted PET Probe Based on a Novel Quinolinium Molecular Scaffold

Fibroblast activation protein (FAP) has recently gained significant attention as a promising tumor biomarker for both diagnosis and therapeutic applications. A series of radiopharmaceuticals based on fibroblast activation protein inhibitors (FAPIs) have been developed and translated into the clinic. Though some of them such as radiolabeled FAPI-04 probes have achieved favorable in vivo imaging performance, further improvement is still highly desired for obtaining radiopharmaceuticals with a high theranostics potential. In this study, we innovatively designed an FAPI ligand SMIC-3002 by changing the core quinoline motif of FAPI-04 to the quinolinium scaffold. The engineered molecule was further radiolabeled with 68Ga to generate a positron emission tomography (PET) probe, [68Ga]Ga-SMIC-3002, which was then evaluated in vitro and in vivo. [68Ga]Ga-SMIC-3002 demonstrated high in vitro stability, nanomolar affinity for FAP (8 nM for protein, 23 nM for U87MG cells), and specific uptake in FAP-expressing tumors, with a tumor/muscle ratio of 19.1 and a tumor uptake of 1.48 ± 0.03 ID/g% at 0.5 h in U87MG tumor-bearing mice. In summary, the quinolinium scaffold can be successfully used for the development of the FAP-targeted tracer. [68Ga]Ga-SMIC-3002 not only shows high potential for clinical translation but also offers insights into designing a new generation of FAPI tracers.

Positron emission tomography in the evaluation of endometriosis: A systematic review

Despite the profound impact of endometriosis worldwide, delays in diagnosis and suboptimal surveillance techniques are well-recognised issues. Case studies have reported incidental uptake of 18F-FDG PET tracer in endometriotic lesions. However, the utility of PET imaging as a non-invasive diagnostic tool for endometriosis is currently unclear. The purpose of this systematic review was to summarise the existing evidence and determine the value of available PET scanning techniques in the detection and monitoring of endometriosis. MEDLINE, EMBASE, CENTRAL, SCOPUS and Web of Science were searched from conception to 05/03/23. Eligible studies included participants with a history of known or suspected endometriosis who underwent a PET scan for any indication. All PET tracers and protocols were eligible. Outcomes included correlation of PET tracer uptake with the presence of endometriosis seen at laparoscopy or confirmed on histology, sensitivity of tracer uptake, specificity of tracer uptake, site of lesions with tracer uptake, stage of lesions with tracer uptake, SUVmax of endometriosis lesions and adverse reactions to PET imaging. The protocol for this review was registered with PROSPERO (ID: CRD42023405260). Eight studies describing 110 participants were eligible for inclusion. Six studies assessed 18F-FDG with combined PET-CT, one study assessed 18F-FDG PET alone, and the remaining study assessed PET-CT with an alternative tracer, 68Ga-DOTATATE. For 18F-FDG imaging, the correlation of PET avidity with lesions or sites of endometriosis ranged from 0-55 %. Pre-operative 68Ga-DOTATATE PET-CT detected endometriosis in 33 % of cases. All included studies were cohort studies, six were assessed to have low risk of bias, one with moderate risk and one with high risk of bias. Overall, 18F-FDG PET scanning does not appear to consistently identify endometriotic lesions, and therefore its reliability and usefulness in endometriosis diagnosis is limited. The utility of 68Ga-DOTATATE PET-CT remains uncertain. Findings are constrained by limited available evidence reporting outcomes of PET imaging for endometriosis. Other existing PET tracers with biological plausibility in the detection or monitoring of endometriosis warrant further investigation.

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

BACKGROUND

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

METHODS AND DESIGN

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

DISCUSSION

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

TRIAL REGISTRATION

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

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.

[68Ga]Ga-FAPI-04 PET/MR imaging strategy in management of Krukenberg tumors (KTs) from gastric signet-ring-cell carcinoma: to overcome limitation of [68Ga]Ga-FAPI-04 PET imaging in KTs

PURPOSE

To compare performance of whole-body [68Ga]Ga-FAPI-04 and [18F]FDG PET imaging in the detection of Krukenberg tumors (KTs), primary site and extra-ovarian metastases of gastric signet-ring-cell carcinoma (GSRCC), and evaluate the value of [68Ga]Ga-FAPI-04 PET/MR imaging strategy and its potential impact on the management of KTs from GSRCC.

METHODS

Twelve patients with twenty-three KTs from GSRCC, who underwent both [68Ga]Ga-FAPI-04 pelvic PET/MR and whole-body [68Ga]Ga-FAPI-04 and [18F]FDG PET imaging were retrospectively analyzed. [68Ga]Ga-FAPI-04 and [18F]FDG uptakes were compared by using Wilcoxon signed-rank test or paired t test. McNemar's test was used to compare lesion detectability between two modalities. Two-tailed P<0.05 was considered statistically significant. Immunohistochemistry staining was utilized to analyze the fibroblast activation protein (FAP) expression in KTs.

RESULTS

A total of 12 patients with 23 KTs from GSRCC (8 synchronous and 4 metachronous) were evaluated. [68Ga]Ga-FAPI-04 was superior to [18F]FDG PET in detecting primary sites of GSRCC (100% [11/11] vs. 18.2% [2/11], p = 0.002), involved lymph nodes (90.9% [10/11] vs. 54.5% [6/11], p = 0.046) and peritoneal metastases (100% [12/12] vs. 41.7% [5/12], p = 0.008), with higher SUVmax and TBR (all p < 0.005). Both tracers had limited value in identifying KTs, with 100% false negative rate on [68Ga]Ga-FAPI-04 PET and a low detection rate of 8.7% on [18F]FDG PET. Fap immunohistochemistry showed negative or slight FAP expression in neoplastic signet ring cells and ovarian stroma. [68Ga]Ga-FAPI-04 PET/MR imaging strategy greatly improved the detection rate of Krukenberg tumors (87%, 20/23). After adding diffusion-weighted imaging (DWI), the detection rate was further improved (87.5% vs. 100%, p = 0.083). [68Ga]Ga-FAPI-04 PET/MR imaging strategy either upgraded TNM staging or changed treatment management in twelve patients.

CONCLUSIONS

[68Ga]Ga-FAPI-04 PET outperformed [18F]FDG PET in detecting primary site and most extra-ovarian metastases of GSRCC, but both tracers had limited value in identifying Krukenberg tumors. Pelvis MRI should be applied to compensate the limitation of [68Ga]Ga-FAPI-04 PET imaging to identify Krukenberg tumours. The [68Ga]Ga-FAPI-04 PET/MR imaging strategy has the potential to impact treatment decisions for GSRCC patients with KTs.

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.

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

ABSTRACT

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

A rationally designed nuclei-targeting FAPI 04-based molecular probe with enhanced tumor uptake for PET/CT and fluorescence imaging

PURPOSE

Fibroblast activation protein inhibitor (FAPI) -based probes have been widely studied in the diagnosis of various malignant tumors with positron emission tomography/computed tomography (PET/CT). However, current imaging studies of FAPI-based probes face challenges in rapid clearance rate and potential false-negative results. Furthermore, FAPI has been rarely explored in optical imaging. Considering this, further modifications are imperative to improve the properties of FAPI-based probes to address existing limitations and broaden their application scenarios. In this study, we rationally introduced methylene blue (MB) to FAPIs, thereby imparting nuclei-targeting and fluorescence imaging capabilities to the probes. Furthermore, we evaluated the added value of FAPI-based fluorescence imaging to traditional PET/CT, exploring the potential application of FAPI-based probes in intraoperative fluorescence imaging.

METHODS

A new FAPI-based probe, namely NOTA-FAPI-MB, was designed for both PET/CT and fluorescence imaging by conjugation of MB. The targeting efficacy of the probe was evaluated on fibroblast activation protein (FAP)-transfected cell line and human primary cancer-associated fibroblasts (CAFs). Subsequently, PET/CT and fluorescence imaging were conducted on tumor-bearing mice. The tumor detection and boundary delineation were assessed by fluorescence imaging of tissues from hepatocellular carcinoma (HCC) patients.

RESULTS

NOTA-FAPI-MB demonstrated exceptional targeting ability towards FAP-transfected cells and CAFs in comparison to NOTA-FAPI. This benefit arises from the cationic methylene blue (MB) affinity for anionic nucleic acids. PET/CT imaging of tumor-bearing mice revealed significantly higher tumor uptake of [18F]F-NOTA-FAPI-MB (standard uptake value of 2.20 ± 0.31) compared to [18F]F-FDG (standard uptake value of 1.66 ± 0.14). In vivo fluorescence imaging indicated prolonged retention at the tumor site, with retention lasting up to 24 h. In addition, the fluorescent probes enabled more precise lesion detection and tumor margin delineation than clinically used indocyanine green (ICG), achieving a 100.0% (6/6) tumor-positive rate for NOTA-FAPI-MB while 33.3% (2/6) for ICG. These findings highlighted the potential of NOTA-FAPI-MB in guiding intraoperative surgical procedures.

CONCLUSIONS

The NOTA-FAPI-MB was successfully synthesized, in which FAPI and MB simultaneously contributed to the targeting effect. Notably, the nuclear delivery mechanism of the probes improved intracellular retention time and targeting efficacy, broadening the imaging time window for fluorescence imaging. In vivo PET/CT demonstrated favorable performance of NOTA-FAPI-MB compared to [18F]F-FDG. This study highlights the significance of fluorescence imaging as an adjunct technique to PET/CT. Furthermore, the encouraging results obtained from the imaging of human HCC tissues hold promise for the potential application of NOTA-FAPI-MB in intraoperative fluorescent surgery guidance within clinical settings.

Surgical evidence-based comparison of [68Ga]Ga-FAPI-04 PET and MRI-DWI for assisting debulking surgery in ovarian cancer patients

PURPOSE

Imaging assessment of abdominopelvic tumor burden is crucial for debulking surgery decision in ovarian cancer patients. This study aims to compare the efficiency of [68Ga]Ga-FAPI-04 FAPI PET and MRI-DWI in the preoperative evaluation and its potential impact to debulking surgery decision.

METHODS

Thirty-six patients with suspected/confirmed ovarian cancer were enrolled and underwent integrated [68Ga]Ga-FAPI-04 PET/MRI. Nineteen patients (15 stage III-IV and 4 I-II stage) who underwent debulking surgery were involved in the diagnostic efficiency analysis. The images of [68Ga]Ga-FAPI-04 PET and MRI-DWI were visually analyzed respectively. Immunohistochemistry on FAP was performed in metastatic lesions to investigate the radiological missing of [68Ga]Ga-FAPI-04 PET as well as its different performance in primary debulking surgery (PDS) and interval debulking surgery (IDS) patients. Potential imaging impact on management was also studied in 35 confirmed ovarian cancer patients.

RESULTS

[68Ga]Ga-FAPI-04 PET displayed higher sensitivity (76.8% vs.59.9%), higher accuracy (84.9% vs. 80.7%), and lower missing rate (23.2% vs. 40.1%) than MRI-DWI in detecting abdominopelvic metastasis. The diagnostic superiority of [68Ga]Ga-FAPI-04 PET is more obvious in PDS patients but diminished in IDS patients. [68Ga]Ga-FAPI-04 PET outperformed MRI-DWI in 70.8% abdominopelvic regions (17/24), which contained seven key regions that impact the resectability and surgical complexity. MRI-DWI hold advantage in the peritoneal surface of the bladder and the central tendon of the diaphragm. Of the contradictory judgments between the two modalities (14.9%), [68Ga]Ga-FAPI-04 PET correctly identified more lesions, particularly in PDS patients (73.8%). In addition, FAP expression was independent of lesion size and decreased in IDS patients. [68Ga]Ga-FAPI-04 PET changed 42% of surgical planning that was previously based on MRI-DWI.

CONCLUSION

[68Ga]Ga-FAPI-04 PET is more efficient in assisting debulking surgery in ovarian cancer patients than MRI-DWI. Integrated [68Ga]Ga-FAPI-04 PET/MR imaging is a potential method for planning debulking surgery in ovarian cancer patients.

Radiolabelled FGF-2 for Imaging Activated Fibroblasts in the Tumor Micro-Environment

Tumor associated fibroblasts (TAFs) play a key role in tumor growth and metastatization. TAFs overexpress different biomarkers that are usually expressed at low levels in physiological conditions. Among them are the fibroblast growth factor receptors (FGFRs) that bind the fibroblast growth factors (FGFs). In particular, the overexpression of FGFR-2c in tumors has been associated with advanced clinical stages and increased metastatization. Here, we developed a non-invasive tool to evaluate, in vivo, the expression of FGFR-2c in metastatic cancer. This is based on 99mTc-labelled FGF-2.

METHODS

99mTc-FGF-2 was tested in vitro and in vivo in mice bearing allografts of sarcoma cells. Images of 99mTc-FGF-2 were acquired using a new portable high-resolution ultra-sensitive gamma camera for small animal imaging.

RESULTS

FGF-2 was labeled with high specific activity but low labelling efficiency, thus requiring post-labeling purification by gel-filtration chromatography. In vitro binding to 2C human keratinocytes showed a Kd of 3.36 × 10-9 M. In mice bearing J774A.1 cell allografts, we observed high and rapid tumor uptake of 99mTc-FGF-2 with a high Tumor/Blood ratio at 24 h post-injection (26.1 %ID/g and 12.9 %ID) with low kidney activity and moderate liver activity.

CONCLUSIONS

we labeled FGF-2 with 99mTc and showed nanomolar Kd in vitro with human keratinocytes expressing FGF-2 receptors. In mice, 99mTc-FGF-2 rapidly and efficiently accumulated in tumors expressing FGF-2 receptors. This new radiopharmaceutical could be used in humans to image TAFs.

PET/Computed Tomography Transformation of Oncology: Ovarian Cancers

Over the last quarter of a century, fluorine-18-fluorodeoxyglucose (FDG) PET/computed tomography (CT) has revolutionized the diagnostic algorithm of ovarian cancer, impacting on the initial disease evaluation including staging and surgical planning, treatment response assessment and prognostication, to the most important role in detection of recurrent disease. The role of FDG PET/CT is expanding with the adoption of new therapeutic agents. Other non-FDG tracers have been explored with fibroblast activation protein inhibitor being promising. Novel tracers may provide the basis for future theragnostic work. This article will review the evolution and impact of PET/CT in ovarian cancer management.

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.

Applications of FAPI PET/CT in the diagnosis and treatment of breast and the most common gynecologic malignancies: a literature review

The fibroblast activating protein (FAP) is expressed by some fibroblasts found in healthy tissues. However, FAP is overexpressed in more than 90% of epithelial tumors, including breast and gynecological tumors. As a result, the FAP ligand could be used as a target for diagnosis and treatment purposes. Positron emission tomography/computed tomography (PET/CT) is a hybrid imaging technique commonly used to locate and assess the tumor's molecular and metabolic functions. PET imaging involves the injection of a radiotracer that tends to accumulate more in metabolically active lesions such as cancer. Several radiotracers have been developed to target FAP in PET/CT imaging, such as the fibroblast-activation protein inhibitor (FAPI). These tracers bind to FAP with high specificity and affinity, allowing for the non-invasive detection and quantification of FAP expression in tumors. In this review, we discussed the applications of FAPI PET/CT in the diagnosis and treatment of breast and the most common gynecologic malignancies. Radiolabeled FAPI can improve the detection, staging, and assessment of treatment response in breast and the most common gynecologic malignancies, but the problem with normal hormone-responsive organs remains insurmountable. Compared to the diagnostic applications of FAPI, further research is needed for future therapeutic applications.

Nuclear Medicine and Molecular Imaging Applications in Gynecologic Malignancies: A Comprehensive Review

Gynecologic malignancies, consisting of endometrial, cervical, ovarian, vulvar, and vaginal cancers, pose significant diagnostic and management challenges due to their complex anatomic location and potential for rapid progression. These tumors cause substantial morbidity and mortality, often because of their delayed diagnosis and treatment. An estimated 19% of newly diagnosed cancers among women are gynecologic in origin. In recent years, there has been growing evidence supporting the integration of nuclear medicine imaging modalities in the diagnostic work-up and management of gynecologic cancers. The sensitivity of fluorine-18 fluorodeoxyglucose positron emission tomography (18F-FDG PET) combined with the anatomical specificity of computed tomography (CT) and magnetic resonance imaging (MRI) allows for the hybrid evaluation of metabolic activity and structural abnormalities that has become an indispensable tool in oncologic imaging. Lymphoscintigraphy, using technetium 99m (99mTc) based radiotracers along with single photon emission computed tomography/ computed tomography (SPECT/CT), holds a vital role in the identification of sentinel lymph nodes to minimize the surgical morbidity from extensive lymph node dissections. While not yet standard for gynecologic malignancies, promising therapeutic nuclear medicine agents serve as specialized treatment options for patients with advanced or recurrent disease. This article aims to provide a comprehensive review on the nuclear medicine applications in gynecologic malignancies through the following objectives: 1) To describe the role of nuclear medicine in the initial staging, lymph node mapping, response assessment, and recurrence/surveillance imaging of common gynecologic cancers, 2) To review the limitations of 18F-FDG PET/CT and promising applications of 18F-FDG PET/MRI in gynecologic malignancy, 3) To underscore the promising theragnostic applications of nuclear medicine, 4) To highlight the current role of nuclear medicine imaging in gynecologic cancers as per the National Comprehensive Cancer Network (NCCN), European Society of Surgical Oncology (ESGO), and European Society of Medical Oncology (ESMO) guidelines.

The Future Direction of Women in Nuclear Medicine and Nuclear Medicine in Women's Health

This work discusses the role of Nuclear Medicine for women's health, the role of women in the development of this emerging field and the various issues which arise from both. It emphasizes the importance of young women and their competing needs due to factors like pregnancy and work-related challenges. The objectives of this overview include improving imaging techniques, preserving fertility during cancer treatment, diagnosing pelvic and uterine conditions, developing radiopharmaceuticals for women's health, protecting female employees in Nuclear Medicine, and considering the role of artificial intelligence.

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.

Initial Experience with the Radiotracer 18F-Fluciclovine PET/CT in Ovarian Cancer

OBJECTIVE

Early and accurate staging of ovarian cancer is paramount to disease survival. Conventional imaging including FDG PET/CT are limited in the evaluation of small metastatic lesions. 18F-Fluciclovine has minimal urine and bowel excretion allowing optimal visualization of the abdomen and pelvis. This study examines 18F-fluciclovine uptake in known primary and recurrent ovarian cancer.

METHODS

Seven patients with a confirmed diagnosis of epithelial ovarian cancer underwent 18F-fluciclovine PET/CT imaging. Forty-one (41) lesions were identified with 18F-fluciclovine and confirmed to be true positive (n = 41). We aim to explore if 18F-fluciclovine uptake in ovarian lesions were greater than background uptake of bone marrow, blood pool, and bladder. Quantification analysis was performed to determine max and mean standard uptake values (SUVmax and SUVmean) of known and suspected lesions compared to SUVmean uptake of background structures.

RESULTS

18F-Fluciclovine demonstrated 100% sensitivity (41/41) for uptake in known ovarian lesions. The average SUVmax (±SD) uptake of known ovarian lesions was 5.9 (±2.6) and 5.1 (±2.0) on early and delayed images, respectively. The average tumor SUVmax to SUVmean of background (±SD) (T:B) ratios on early and delay were 1.9 (±0.8), 2.1 (±0.9) for marrow; 3.8 (±1.8), 3.4 (±1.5) for aorta; and 8.4 (±4.3), 1.5 (±1.7) for bladder, respectively.

CONCLUSION

18F-Fluciclovine uptake in malignant ovarian lesions was above background levels suggesting its feasibility in the imaging of ovarian cancer. Due to increasing tracer washout via the urinary bladder over time, early imaging at 4 min post injection is favorable.

Molecular image-guided surgery in gynaecological cancer: where do we stand?

PURPOSE

The aim of this review is to give an overview of the current status of molecular image-guided surgery in gynaecological malignancies, from both clinical and technological points of view.

METHODS

A narrative approach was taken to describe the relevant literature, focusing on clinical applications of molecular image-guided surgery in gynaecology, preoperative imaging as surgical roadmap, and intraoperative devices.

RESULTS

The most common clinical application in gynaecology is sentinel node biopsy (SNB). Other promising approaches are receptor-target modalities and occult lesion localisation. Preoperative SPECT/CT and PET/CT permit a roadmap for adequate surgical planning. Intraoperative detection modalities span from 1D probes to 2D portable cameras and 3D freehand imaging.

CONCLUSION

After successful application of radio-guided SNB and SPECT, innovation is leaning towards hybrid modalities, such as hybrid tracer and fusion of imaging approaches including SPECT/CT and PET/CT. Robotic surgery, as well as augmented reality and virtual reality techniques, is leading to application of these innovative technologies to the clinical setting, guiding surgeons towards a precise, personalised, and minimally invasive approach.

Menstruation Confounding the Correct Interpretation of 99m Tc-RBC Bleeding Scan

ABSTRACT

99m Tc-RBC bleeding scan in a 17-year-old adolescent girl showed an increased focal activity in the pelvis. However, SPECT/CT showed that this activity was located in the uterus, which was considered a normal variant considering that the patient was in her fourth day of the menstrual period. Subsequent 99m TcO 4- Meckel scan showed the typical characteristic of ectopic gastric mucosa in the small bowel. Postsurgical pathology confirmed the diagnosis of ectopic gastric mucosa. This case suggested the menstrual period uterus should be included as differential diagnosis of 99m Tc-RBC scan.

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

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

Tata Memorial Centre Evidence Based Use of Nuclear medicine diagnostic and treatment modalities in cancer

ABSTRACT

PET/CT and radioisotope therapy are diagnostic and therapeutic arms of Nuclear Medicine, respectively. With the emergence of better technology, PET/CT has become an accessible modality. Diagnostic tracers exploring disease-specific targets has led the clinicians to look beyond FDG PET. Moreover, with the emergence of theranostic pairs of radiopharmaceuticals, radioisotope therapy is gradually making it's way into treatment algorithm of common cancers in India. We therefore would like to discuss in detail the updates in PET/CT imaging and radionuclide therapy and generate a consensus-driven evidence based document which would guide the practitioners of Oncology.

68Ga-Labeled Fibroblast Activation Protein Inhibitor (68Ga-FAPI) PET for Pancreatic Adenocarcinoma: Data from the 68Ga-FAPI PET Observational Trial

The fibroblast activation protein (FAP) is highly expressed on carcinoma-associated fibroblasts in the stroma of pancreatic cancer and thus is a promising target for imaging and therapy. Preliminary data on PET imaging with radiolabeled FAP inhibitors (FAPIs) demonstrate superior tumor detection. Here we assess the accuracy of FAP-directed PET in patients with pancreatic cancer. Methods: Of 64 patients with suspected or proven pancreatic cancer, 62 (97%) were included in the data analysis of the 68Ga-FAPI PET observational trial (NCT04571086). All of these patients underwent contrast-enhanced CT, and 38 patients additionally underwent 18F-FDG PET. The primary study endpoint was the association of 68Ga-FAPI PET uptake intensity and histopathologic FAP expression. Secondary endpoints were detection rate, diagnostic performance, interreader reproducibility, and change in management. Datasets were interpreted by 2 masked readers. Results: The primary endpoint was met: The association between 68Ga-FAPI SUVmax and histopathologic FAP expression was significant (Spearman r, 0.48; P = 0.04). For histopathology-validated lesions, 68Ga-FAPI PET showed high sensitivity and positive predictive values (PPVs) on per-patient (sensitivity, 100%; PPV, 96.3%) and per-region (sensitivity, 100%; PPV, 97.0%) bases. In a head-to-head comparison versus 18F-FDG or contrast-enhanced CT, 68Ga-FAPI detected more tumor on a per-lesion (84.7% vs. 46.5% vs. 52.9%), per-patient (97.4% vs. 73.7% vs. 92.1%), or per-region (32.6% vs. 18.8% vs. 23.7%) basis, respectively. 68Ga-FAPI PET readers showed substantial overall agreement on the basis of the Fleiss κ: primary κ, 0.77 (range, 0.66-0.88). Minor and major changes in clinical management occurred in 5 patients (8.4%) after 68Ga-FAPI PET. Conclusion: We confirmed an association of 68Ga-FAPI PET SUVmax and histopathologic FAP expression in pancreatic cancer patients. Additionally, we found high detection rate and diagnostic accuracy, superior to those of 18F-FDG PET/CT. 68Ga-FAPI might become a powerful diagnostic tool for pancreatic cancer work-up.

Physiological Uptake Characteristics of Breast on 68Ga-FAPI-04 PET/CT

PURPOSE

Gallium 68 (68Ga)-labeled fibroblast activation protein inhibitor (FAPI) PET/CT is sensitive on breast cancer staging, but its clinical utility may be limited by the high physiological 68Ga-FAPI-04 uptake in normal breast tissue that can obscure primary tumors. The aim of this study was to elucidate the characteristics of physiological 68Ga-FAPI-04 uptake in normal breast.

PROCEDURES

A total of 143 consecutive women with 68Ga-FAPI-04 PET/CT data were reviewed retrospectively. SUVmax, density and thickness of breast, as well as SUVmax of nipple, were measured. Univariate and multivariate regression analyses were used to identify factors related to the breast and nipple SUVs.

RESULTS

Twenty-eight premenopausal, 62 menopausal and 10 post-operative (after bilateral adnexectomy) women with 103 examinations were included. All had a diffuse, symmetrical uptake in breast. There was no difference in 68Ga-FAPI-04 uptake between bilateral breasts (right: median, 1.14[IQR, 0.85-1.54] vs. left: median, 1.09[IQR, 0.86-1.54]; P = 0.253). Patients in menstrual status with expected high estrogen level (late follicular, ovulatory and mid luteal phases) had higher breast SUVs (median SUV, 3.91 [IQR, 2.85-4.35]) than those with expected moderate (early follicular, early luteal and late luteal phases; median SUV, 1.57 [IQR, 1.39-2.08]; P < 0.001) or low level (menopause and post-operation; median SUV, 0.98 [IQR, 0.83-1.21]; P < 0.001). Menstrual status was an independent predictors of breast SUV (r2 = 0.689, P < 0.001). All the patients had a focal, symmetrical uptake in nipples. Nipple SUV did not correlate with menstrual status (P = 0.913).

Staging of Cervical Cancer: A Practical Approach Using MRI and FDG PET

This review provides a practical approach to the imaging evaluation of patients with cervical cancer (CC), from initial diagnosis to restaging of recurrence, focusing on MRI and FDG PET. The primary updates to the International Federation of Gynecology and Obstetrics (FIGO) CC staging system, as well as these updates' relevance to clinical management, are discussed. The recent literature investigating the role of MRI and FDG PET in CC staging and image-guided brachytherapy is summarized. The utility of MRI and FDG PET in response assessment and posttreatment surveillance is described. Important findings on MRI and FDG PET that interpreting radiologists should recognize and report are illustrated. The essential elements of structured reports during various phases of CC management are outlined. Special considerations, including the role of imaging in patients desiring fertility-sparing management, differentiation of CC and endometrial cancer, and unusual CC histologies, are also described. Finally, future research directions including PET/MRI, novel PET tracers, and artificial intelligence applications are highlighted.

[68Ga]Ga-FAPI-04 PET/CT in the evaluation of epithelial ovarian cancer: comparison with [18F]F-FDG PET/CT

PURPOSE

To compare the efficacy of [68Ga]Ga-FAPI-04 PET/CT in primary or recurrent tumors and metastatic lesions of epithelial ovarian cancer (EOC) with that of fluorine-18 fluorodeoxyglucose ([18F]F-FDG) PET/CT.

METHODS

Forty-nine patients (median age, 57 years; IQR, 51-66 years) with histologically proven primary or relapsed EOC were enrolled. Participants underwent [18F]F-FDG and [68Ga]Ga-FAPI-04 PET/CT. The detection rate, diagnostic accuracy, semiquantitative parameters, tumor staging, and clinical management of the tracers were compared. The diagnostic performance of [18F]F-FDG and [68Ga]Ga-FAPI-04 PET/CT was evaluated and compared using surgical pathology. Differences between methods regarding the peritoneal cancer index (PCI) using preoperative imaging, surgical PCI, and tumor markers (CA125, HE4) were also assessed regarding peritoneal metastases.

RESULTS

Among the 49 patients, 28 had primary EOC; 21 had relapsed EOC. [68Ga]Ga-FAPI-04 PET/CT outperformed [18F]F-FDG PET/CT in detecting peritoneal metastases (96.8% vs. 83.0%; p < 0.001), retroperitoneal (99.5% vs. 91.4%; p < 0.001), and supradiaphragmatic lymph node metastases (100% vs. 80.4%; p < 0.001). Compared with [18F]F-FDG, [68Ga]Ga-FAPI-04 showed higher SUVmax for peritoneal metastases (17.31 vs. 13.68; p = 0.026) and retroperitoneal (8.72 vs. 6.56; p < 0.001) and supradiaphragmatic lymph node metastases (6.39 vs. 4.20; p < 0.001). Moreover, [68Ga]Ga-FAPI-04 PET/CT showed higher sensitivity compared with [18F]F-FDG PET/CT for detecting metastatic lymph nodes (80.6% vs. 61.3%; p = 0.031) and peritoneal metastases (97.5% vs. 75.9%; p < 0.001), using surgical pathology as the gold standard. Compared with [18F]F-FDG PET/CT, [68Ga]Ga-FAPI-04 PET/CT led to an upgrade in 14.3% and 33.3% of treatment-naive and relapse participants, resulting in management changes in 10.7% and 19.0% of the patients, respectively. The median PCIFAPI scores were significantly higher than PCIFDG (15 vs. 11; p < 0.001) and positively correlated with CA125 and HE4 levels and surgical PCI.

CONCLUSION

[68Ga]Ga-FAPI-04 PET/CT achieved higher sensitivity than [18F]F-FDG PET/CT in the detection and diagnosis of lymph node and peritoneal metastases, suggesting advantages regarding the preoperative staging of patients with EOC and, thereby, improving treatment decision-making.

TRIAL REGISTRATION

NCT05034146. Registered February 23, 2021.

Impact of 68Ga-FAPI PET/CT on Staging and Oncologic Management in a Cohort of 226 Patients with Various Cancers

Since the development of fibroblast activation protein-targeted radiopharmaceuticals, 68Ga-fibroblast activation protein inhibitor (FAPI) PET/CT has been found to be suitable for detecting primary and metastatic lesions in many types of tumors. However, there is currently a lack of reliable data regarding the clinical impact of this family of probes. To address this gap, the present study aimed to analyze the clinical impact of 68Ga-FAPI PET/CT by examining a large cohort of patients with various tumors. Methods: In total, 226 patients (137 male and 89 female) were included in this retrospective analysis. Pancreatic cancer and head and neck cancers were the most common tumor types in this cohort. TNM stage and oncologic management were initially determined with gold standard imaging, and these results were compared with 68Ga-FAPI PET/CT. Changes were classified as major and minor. Results: For 42% of all patients, TNM stage was changed by 68Ga-FAPI PET/CT results. Most of these changes resulted in upstaging. A change in clinical management occurred in 117 of 226 patients. Although a major change in management occurred in only 12% of patients, there was a significant improvement in the ability to accurately plan radiation therapy. In general, the highest clinical impact of 68Ga-FAPI PET/CT imaging was found in patients with lung cancer, pancreatic cancer, and head and neck tumors. Conclusion: 68Ga-FAPI PET/CT is a promising imaging probe that has a significant impact on TNM stage and clinical management. 68Ga-FAPI PET/CT promises to be a crucial new technology that will improve on conventional radiologic imaging methods such as contrast-enhanced CT and contrast-enhanced MRI typically acquired for cancer staging.

Define cancer-associated fibroblasts (CAFs) in the tumor microenvironment: new opportunities in cancer immunotherapy and advances in clinical trials

Despite centuries since the discovery and study of cancer, cancer is still a lethal and intractable health issue worldwide. Cancer-associated fibroblasts (CAFs) have gained much attention as a pivotal component of the tumor microenvironment. The versatility and sophisticated mechanisms of CAFs in facilitating cancer progression have been elucidated extensively, including promoting cancer angiogenesis and metastasis, inducing drug resistance, reshaping the extracellular matrix, and developing an immunosuppressive microenvironment. Owing to their robust tumor-promoting function, CAFs are considered a promising target for oncotherapy. However, CAFs are a highly heterogeneous group of cells. Some subpopulations exert an inhibitory role in tumor growth, which implies that CAF-targeting approaches must be more precise and individualized. This review comprehensively summarize the origin, phenotypical, and functional heterogeneity of CAFs. More importantly, we underscore advances in strategies and clinical trials to target CAF in various cancers, and we also summarize progressions of CAF in cancer immunotherapy.

Endoplasmic reticulum-mitochondrial calcium transport contributes to soft extracellular matrix-triggered mitochondrial dynamics and mitophagy in breast carcinoma cells

Although mitochondrial morphology and function are considered to be closely related to matrix stiffness-driven tumor progression, it remains poorly understood how extracellular matrix (ECM) stiffness affects mitochondrial dynamics and mitophagy. Here, we found that soft substrate triggered calcium transport by increasing endoplasmic reticulum (ER) calcium release and mitochondrial (MITO) calcium uptake. ER-MITO calcium transport promoted the recruitment of dynamin-related protein 1 (Drp1) to mitochondria and phosphorylation at the serine 616 site, which induced mitochondrial fragmentation and Parkin/PINK1-mediated mitophagy. Furthermore, in vivo experiments demonstrated that soft ECM enhanced calcium levels in tumor tissue, Drp1 activity was required for soft ECM-induced mitochondrial dynamics impairment, and inhibition of Drp1 activity enhanced soft ECM-induced tumor necrosis. In conclusion, we revealed a new mechanism whereby ER-MITO calcium transport regulated mitochondrial dynamics and mitophagy through Drp1 translocation in response to soft substrates. These findings provide valuable insights into ECM stiffness as a potential target for antitumor therapy. STATEMENT OF SIGNIFICANCE: Here, we examined the relationship between substrate stiffness and mitochondrial dynamics by using polyacrylamide (PAA) substrates to simulate the stages of breast cancer or BAPN to reduce tumor tissue stiffness. The results elucidated that soft substrate triggered the recruitment of DRP1 and subsequent mitochondrial fission and mitophagy by ER-MITO calcium transport. Furthermore, mitophagy partly attenuated soft ECM-mediated tumor tissue necrosis and contributed to tumor survival in vivo. Our discoveries revealed the molecular mechanisms by which mechanical stimulation regulates mitochondrial dynamics, providing valuable insights into ECM stiffness as a target for anti-tumor approaches, which could be beneficial for both biomechanics research and clinical applications.

Other Novel PET Radiotracers for Breast Cancer

Many novel PET radiotracers have demonstrated potential use in breast cancer. Although not currently approved for clinical use in the breast cancer population, these innovative imaging agents may one day play a role in the diagnosis, staging, management, and even treatment of breast cancer.

Theranostics in targeting fibroblast activation protein bearing cells: Progress and challenges

Cancer cells are surrounded by a complex and highly dynamic tumor microenvironment (TME). Cancer-associated fibroblasts (CAFs), a critical component of TME, contribute to cancer cell proliferation as well as metastatic spread. CAFs express a variety of biomarkers, which can be targeted for detection and therapy. Most importantly, CAFs express high levels of fibroblast activation protein (FAP) which contributes to progression of cancer, invasion, metastasis, migration, immunosuppression, and drug resistance. As a consequence, FAP is an attractive theranostic target. In this review, we discuss the latest advancement in targeting FAP in oncology using theranostic biomarkers and imaging modalities such as single-photon emission computed tomography (SPECT), positron emission tomography (PET), computed tomography (CT), fluorescence imaging, and magnetic resonance imaging (MRI).

Feasibility of a deep learning algorithm to achieve the low-dose 68Ga-FAPI/the fast-scan PET images: a multicenter study

OBJECTIVES

Our work aims to study the feasibility of a deep learning algorithm to reduce the 68Ga-FAPI radiotracer injected activity and/or shorten the scanning time and to investigate its effects on image quality and lesion detection ability.

METHODS

The data of 130 patients who underwent 68Ga-FAPI positron emission tomography (PET)/CT in two centers were studied. Predicted full-dose images (DL-22%, DL-28% and DL-33%) were obtained from three groups of low-dose images using a deep learning method and compared with the standard-dose images (raw data). Injection activity for full-dose images was 2.16 ± 0.61 MBq/kg. The quality of the predicted full-dose PET images was subjectively evaluated by two nuclear physicians using a 5-point Likert scale, and objectively evaluated by the peak signal-to-noise ratio, structural similarity index and root mean square error. The maximum standardized uptake value and the mean standardized uptake value (SUVmean) were used to quantitatively analyze the four volumes of interest (the brain, liver, left lung and right lung) and all lesions, and the lesion detection rate was calculated.

RESULTS

Data showed that the DL-33% images of the two test data sets met the clinical diagnosis requirements, and the overall lesion detection rate of the two centers reached 95.9%.

CONCLUSION

Through deep learning, we demonstrated that reducing the 68Ga-FAPI injected activity and/or shortening the scanning time in PET/CT imaging was feasible. In addition, 68Ga-FAPI dose as low as 33% of the standard dose maintained acceptable image quality.

ADVANCES IN KNOWLEDGE

This is the first study of low-dose 68Ga-FAPI PET images from two centers using a deep learning algorithm.

Correlation between [68Ga]Ga-FAPI-46 PET Imaging and HIF-1α Immunohistochemical Analysis in Cervical Cancer: Proof-of-Concept

Hypoxia leads to changes in tumor microenvironment (upregulated CAFs) with resultant aggressiveness. A key factor in the physiological response to hypoxia is hypoxia-inducible factor-1alpha (HIF-1α). [68Ga]Ga-FAPI PET imaging has been demonstrated in various cancer types. We hypothesized that [68Ga]Ga-FAPI PET may be used as an indirect tracer for mapping hypoxia by correlating the image findings to pathological analysis of HIF-1α expression. The [68Ga]Ga-FAPI PET/CT scans of women with cancer of the cervix were reviewed and the maximum and mean standardized uptake value (SUVmax and SUVmean) and FAPI tumor volume (FAPI-TV) were documented. Correlation analysis was performed between PET-derived parameters and immunohistochemical staining as well as between PET-derived parameters and the presence of metastasis. Ten women were included. All patients demonstrated tracer uptake in the primary site or region of the primary. All patients had lymph node metastases while only six patients had distant visceral or skeletal metastases. The mean SUVmax, SUVmean, and FAPI-TV was 18.89, 6.88, and 195.66 cm3, respectively. The average FAPI-TV for patients with additional sites of metastases was higher than those without. Immunohistochemistry revealed varying intensities of HIF-1α expression in all tested samples. There was a positive correlation between the presence of skeletal metastases and staining for HIF-1α (r=0.80;p=0.017). The presence of skeletal metastasis was correlated to the HIF-1⍺ staining (percentage distribution). Furthermore, the FAPI-TV was a better predictor of metastatic disease than the SUVmax.

The Role of 68Ga FAPI-04 and 18F-FDG PET/CT in Detecting Liver Metastases in Different Types of Cancer

OBJECTIVE

We compared the diagnostic accuracies of 68Ga FAPI-04 PET/CT and 18F-FDG PET/CT for detecting liver metastases (LMs) in patients with different cancer types.

MATERIALS AND METHODS

This retrospective study included 63 patients with liver lesions who underwent 18F-FDG PET/CT and 68Ga-FAPI-04 PET/CT between May 2020 and May 2022. Patients with histopathologically confirmed primary diagnoses, data that could be accessed retrospectively, liver lesions confirmed by biopsy over at least 3-6 months of follow-up (via ultrasonography, CT, magnetic resonance imaging, PET/CT, or laboratory tests) were included. Patients with secondary malignancies or primary liver malignancies, and/or who could not be followed-up, were excluded.

RESULTS

Of the 63 total patients, 34 (54%) were female, and the mean age was 61 (30-92) years. There were 582 LMs in 51 patients and 35 benign liver lesions in 20 (12 patients had only benign and 8 both benign and malignant lesions). Of the 582 LMs, 472 (81.1%) evidenced 18F-FDG uptake and 572 (98.2%) 68Ga-FAPI uptake. The diagnostic accuracies of 68Ga-FAPI PET/CT and 18F-FDG PET/CT were 98% and 82%, respectively (p < 0.001; McNemar test). When the LMs were compared, the maximum standardized uptake (SUVmax) value was significantly higher on 18F-FDG PET/CT than 68Ga-FAPI PET/CT (median: 6.0 vs. 5.4; p = 0.016). However, the LM-to-background ratio (TBR) was significantly higher on 68Ga-FAPI PET/CT than 18F-FDG PET/CT (median: 4.1 vs. 2.1; p < 0.001).

CONCLUSION

68Ga-FAPI PET/CT detected more LMs than did 18F-FDG PET/CT, and TBR was significantly higher on 68Ga-FAPI PET/CT than 18F-FDG PET/CT.

What radiolabeled FAPI pet can add in breast cancer? A systematic review from literature

To provide an overview of the current available data about FAPI PET in breast cancer patients, with a perspective point of view. A literature search for studies about FAPI PET in the last 5 years (from 2017 to January 2023) was carried out on MEDLINE databases, such as PubMed, EMBASE, Web of Science and Google Scholar using the following keywords: "PET" AND "FAPI" AND "Breast Cancer" AND "Fibroblast imaging". The Critical Appraisal Skills Program (CASP) checklist for diagnostic test studies was used for testing the quality of selected papers. 13 articles were selected, including 172 patients affected by breast cancer who underwent FAPI-based PET images. CASP checklist was used in 5/13 papers, demonstrating a general low quality. Different types of FAPI-based tracers were used. No difference in terms of FAPI uptake was reported based on the histopathological characteristics, such as immunohistochemistry and grading of breast cancer. FAPI demonstrated more lesions and yielded much higher tumor-to-background ratios than 2-[18F]FDG. Preliminary experiences with FAPI PET in breast cancer showed some advantages than the current available 2-[18F]FDG, although prospective trials are needed to further evaluate its diagnostic utility in clinical practice.

Current Status of Fibroblast Activation Protein Imaging in Gynecologic Malignancy and Breast Cancer

68Ga-FAPI-PET/computed tomography (CT) is a novel PET/CT radiotracer particularly developed for oncologic imaging. Gynecologic malignancies comprise a broad spectrum of entities and, along with breast cancer, constitute cancers occurring exclusively or primarily, respectively, in women. Thus, a tracer designed not only for one but multiple malignancies has theoretic attractions. Even in comparison with 18F-FDG, the current standard oncologic tracer of nuclear medicine, 68Ga-FAPI, has demonstrated advantages in several tumors. As breast cancer, ovarian cancer, and cervical cancer are among the most common tumor types in women and are often accompanied by high morbidity as well as mortality rates, a reliable staging tool is paramount for optimal therapeutic management.

FAPI PET/CT Imaging-An Updated Review

Despite revolutionizing the field of oncological imaging, Positron Emission Tomography (PET) with [¹⁸F]Fluorodeoxyglucose (FDG) as its workhorse is limited by a lack of specificity and low sensitivity in certain tumor subtypes. Fibroblast activation protein (FAP), a type II transmembrane glycoprotein, is expressed by cancer-associated fibroblasts (CAFs) that form a major component of the tumor stroma. FAP holds the promise to be a pan-cancer target, owing to its selective over-expression in a vast majority of neoplasms, particularly epithelial cancers. Several radiolabeled FAP inhibitors (FAPI) have been developed for molecular imaging and potential theranostic applications. Preliminary data on FAPI PET/CT remains encouraging, with extensive multi-disciplinary clinical research currently underway. This review summarizes the existing literature on FAPI PET/CT imaging with an emphasis on diagnostic applications, comparison with FDG, pitfalls, and future directions.

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

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

Increased 68 Ga-FAPI Activity in Hepatic Inflammatory Myofibroblastoma

ABSTRACT

Hepatic inflammatory myofibroblastoma is an uncommon borderline tumor. We present 68 Ga-FAPI PET/CT findings of hepatic inflammatory myofibroblastoma in a 58-year-old man. The rare hepatic inflammatory myofibroblastoma demonstrated intense tracer uptake on 68 Ga-FAPI PET/CT. This case demonstrates the potential value of 68 Ga-FAPI PET/CT for the evaluation of hepatic inflammatory myofibroblastoma.

68Ga-FAPI-04 PET/MR Versus 18F-FDG PET/CT in the Detection of Ovarian Cancer

ABSTRACT

A 75-year-old woman presented with right lower abdominal pain. Pelvic ultrasound showed a cystic solid mass in the right adnexa. Painless enlarged lymph nodes on the left supraclavicular side with biopsy were suggestive of metastatic cancer. 18F-FDG PET/CT performed to evaluate the primary tumor showed intense uptake in both regions of the right adnexa and the gastric sinus, but 68Ga-FAPI PET/MRI showed uptake only in the right adnexal region. A subsequent gastroscopic biopsy confirmed atrophic inflammation. Finally, surgery histopathology revealed ovarian cancer. This case demonstrated that 68Ga-FAPI PET/MRI may help exclude suspected primary gastric carcinoma with false-positive 18F-FDG uptake.

Next generation radiotheranostics promoting precision medicine

Radiotheranostics is a field of rapid growth with some approved treatments including 131I for thyroid cancer, 223Ra for osseous metastases, 177Lu-DOTATATE for neuroendocrine tumors, and 177Lu-PSMA (prostate-specific membrane antigen) for prostate cancer, and several more under investigation. In this review, we will cover the fundamentals of radiotheranostics, the key clinical studies that have led to current success, future developments with new targets, radionuclides and platforms, challenges with logistics and reimbursement and, lastly, forthcoming considerations regarding dosimetry, identifying the right line of therapy, artificial intelligence and more.

68Ga-FAPI PET/CT Interobserver Agreement on Tumor Assessment: An International Multicenter Prospective Study

⁶⁸Ga-fibroblast activation protein inhibitors (FAPIs) are promising radiotracers for cancer imaging, with emerging data in the recent years. Nonetheless, the interobserver agreement on ⁶⁸Ga-FAPI PET/CT study interpretations in cancer patients remains poorly understood. Methods: ⁶⁸Ga-FAPI PET/CT was performed on 50 patients with various tumor entities (sarcoma [n = 10], colorectal cancer [n = 10], pancreatic adenocarcinoma [n = 10], genitourinary cancer [n = 10], and other types of cancer [n = 10]). Fifteen masked observers reviewed and interpreted the images using a standardized approach for local, local nodal, and metastatic involvement. Observers were grouped by experience as having a low (<30 prior ⁶⁸Ga-FAPI PET/CT studies; n = 5), intermediate (30-300 studies; n = 5), or high level of experience (>300 studies; n = 5). Two independent readers with a high level of experience and unmasked to clinical information, histopathology, tumor markers, and follow-up imaging (CT/MRI or PET/CT) served as the standard of reference (SOR). Observer groups were compared by overall agreement (percentage of patients matching SOR) and Fleiss κ with mean and corresponding 95% CI. We defined acceptable agreement as a κ value of at least 0.6 (substantial or higher) and acceptable accuracy as at least 80%. Results: Highly experienced observers agreed substantially on all categories (primary tumor: κ = 0.71; 95% CI, 0.71-0.71; local nodal involvement: κ = 0.62; 95% CI, 0.61-0.62; distant metastasis: κ = 0.75; 95% CI, 0.75-0.75), whereas observers with intermediate experience showed substantial agreement on primary tumor (κ = 0.73; 95% CI, 0.73-0.73) and distant metastasis (κ = 0.65; 95% CI, 0.65-0.65) but moderate agreement on local nodal stages (κ = 0.55; 95% CI, 0.55-0.55). Observers with low experience had moderate agreement on all categories (primary tumor: κ = 0.57; 95% CI, 0.57-0.58; local nodal involvement: κ = 0.51; 95% CI, 0.51-0.52; distant metastasis: κ = 0.54; 95% CI, 0.53-0.54). Compared with SOR, the accuracy for readers with high, intermediate, and low experience was 85%, 83%, and 78%, respectively. In summary, only highly experienced readers showed substantial agreement and a diagnostic accuracy of at least 80% in all categories. Conclusion: The interpretation of ⁶⁸Ga-FAPI PET/CT for cancer imaging had substantial reproducibility and accuracy among highly experienced observers only, especially for local nodal and metastatic assessments. Therefore, for accurate interpretation of different tumor entities and pitfalls, we recommend training or experience with at least 300 representative scans for future clinical readers.

Distinguishing Benign and Malignant Findings on [68 Ga]-FAPI PET/CT Based on Quantitative SUV Measurements

AIM/PURPOSE

Fibroblast activation protein (FAP) is overexpressed by cancer-associated fibroblasts. However, activated fibroblasts have been shown to play a significant role also in certain benign conditions such as wound healing or chronic inflammation. Therefore, the current study aimed to identify whether FAPI uptake might differ between malignant lesions and benign conditions.

MATERIAL AND METHODS

We retrospectively analyzed 155 patients with various cancer types who received [⁶⁸ Ga]-FAPI-04/02-PET/CT between July 2017 and March 2020. SUV_max, SUV_mean, and lesion-to-background ratios (LBR) of FAPI uptake were measured in benign processes compared to malignant lesions (primary and/or 2 exemplary metastases). In addition, receiver operating characteristic (ROC) curve analysis was conducted to compare the predictive capabilities of semiquantitative PET/CT parameters. Furthermore, the sensitivity, specificity, optimal cutoff value, and 95% confidence interval (CI) were determined for each parameter.

RESULTS

Benign lesions exhibited significantly lower FAPI uptake compared to malignant lesions (mean SUV_max benign vs. malignant: 4.2 vs. 10.6; p < 0.001). In ROC analysis, cutoff values of these lesions (benign vs. malignant) were established based on SUV_max, SUV_mean, and LBR. The SUV_max cutoff value for all lesions was 5.5 and the corresponding sensitivity, specificity, accuracy, and AUC were 78.8%, 85.1%, 82.0%, and 0.89%, respectively.

CONCLUSION

Our aim was to systematically analyze the pattern of FAPI uptake in benign and malignant processes. This investigation demonstrates that FAPI uptake might be useful to differentiate malignant and benign findings due to different patho-physiological origins.

The Role of 68 Ga-FAPI PET/CT in Detection of Metastatic Lobular Breast Cancer

PURPOSE

Invasive lobular breast cancer (ILC) may be hard to detect using conventional imaging modalities and usually shows less avidity to 18 F-FDG PET/CT. 68 Ga-fibroblast activation protein inhibitor (FAPI) PET/CT has shown promising results in detecting non- 18 F-FDG-avid cancers. We aimed to assess the feasibility of detecting metastatic disease in patients with non- 18 F-FDG-avid ILC.

METHODS

This prospective study included patients with metastatic ILC, infiltrative to soft tissues, which was not 18 F-FDG avid. The patients underwent 68 Ga-FAPI PET/CT for evaluation, which was correlated with the fully diagnostic CT performed at the same time.

RESULTS

Seven women (aged 57 ± 10 years) were included. Among the 30 organs and structures found to be involved by tumor, the number of findings observed by FAPI PET/CT was significantly higher than that observed by CT alone ( P = 0.022), especially in infiltrative soft tissue and serosal locations.

CONCLUSIONS

This small pilot trial suggests a role for 68 Ga-FAPI PET/CT in ILC, which needs to be confirmed by subsequent trials.

Comparison of 68 Ga-FAPI-04 and fluorine-18-fluorodeoxyglucose PET/computed tomography in the detection of ovarian malignancies

BACKGROUND

Currently, fluorine-18-fluorodeoxyglucose ( 18 F-FDG) is the most frequently used diagnostical radiotracer for PET/computed tomography (PET/CT) in ovarian malignancies. However, 18 F-FDG has some limitations. The fibroblast activation protein inhibitor (FAPI) previously demonstrated highly promising results in studies on various tumor entities and 68 Ga-labeled FAPI presents a promising alternative to 18 F-FDG. This study aimed to compare the performance of 68 Ga-FAPI and 18 F-FDG PET/CT for imaging of ovarian malignancies.

METHODS

A total of 27 patients were included in this retrospective study conducted at the Affiliated Hospital of Southwest Medical University between June 2020 and February 2022. The 18 F-FDG and 68 Ga-FAPI uptakes of tumors, lymph nodes, and distant metastases were quantified using the maximum standardized uptake values, and the tumor-to-background ratios were also evaluated and calculated by using the Wilcoxon signed-rank test.

RESULTS

Twenty-one patients with suspected ( n  = 11) and previously treated ovarian malignancies ( n  = 10) were in statistical analysis finally. For detecting tumors, 68 Ga-FAPI PET/CT was more sensitive than 18 F-FDG PET/CT [14 of 14 (100%) vs. 11 of 14 (78%)], lymph node metastases [75 of 75 (100%) vs. 60 of 75 (80%)] and superior to 18 F-FDG PET/CT in terms of the peritoneal and pleural metastases [9 of 9 (100%) vs. 5 of 9 (56%)]. For four of the newly diagnosed patients ( n  = 11), 68 Ga-FAPI PET/CT upstaged the clinical stage compared to 18 F-FDG PET/CT.

CONCLUSION

68 Ga-FAPI PET/CT has superior potential in the detection of ovarian cancers, especially in peritoneal carcinomatosis. 68 Ga-FAPI PET/CT may be a promising supplement for staging and follow-up of ovarian malignancies.

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.

The Superiority of Fibroblast Activation Protein Inhibitor (FAPI) PET/CT Versus FDG PET/CT in the Diagnosis of Various Malignancies

Cancer represents a major cause of death worldwide and is characterized by the uncontrolled proliferation of abnormal cells that escape immune regulation. It is now understood that cancer-associated fibroblasts (CAFs), which express specific fibroblast activation protein (FAP), are critical participants in tumor development and metastasis. Researchers have developed various FAP-targeted probes for imaging of different tumors from antibodies to boronic acid-based inhibitor molecules and determined that quinoline-based FAP inhibitors (FAPIs) are the most appropriate candidate as the radiopharmaceutical for FAPI PET/CT imaging. When applied clinically, FAPI PET/CT yielded satisfactory results. Over the past few years, the utility and effectiveness of tumor detection and staging of FAPI PET/CT have been compared with FDG PET/CT in various aspects, including standardized uptake values (SUVs), rate of absorbance and clearance. This review summarizes the development and clinical application of FAPI PET/CT, emphasizing the diagnosis and management of various tumor types and the future prospects of FAPI imaging.

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.

18F-FDG and 68Ga-FAPI-04 PET/CT in Evaluating Clear-Cell Endometrial Cancer

ABSTRACT

A 60-year-old woman diagnosed with clear cell endometrial carcinoma received neoadjuvant chemotherapy. However, the patient was inoperable and referred to our clinic to evaluate the extent of the disease. The patient underwent 18FDG PET/CT and 68Ga-FAPI (fibroblast activated protein inhibitor)-04 PET/CT scans. 68Ga-FAPI-04 PET/CT outperformed 18FDG PET/CT demonstrating higher uptake in the metastatic lesions.

Non-oncologic incidental uptake on FAPI PET/CT imaging

Fibroblast-activation protein (FAP) is a serine protease classified in the dipeptidyl peptidase 4 (DPP4) family. FAP is predominantly expressed in activated fibroblasts such as the cancer-associated fibroblasts (CAFs). FAP expression in CAFs is associated with tumor progression and poor prognosis in solid cancers. Recently, radiolabeled FAP inhibitors (FAPI) has been developed, which enables positron emission tomography (PET) imaging of FAP. FAPI PET/CT can provide a higher tumor-to-background ratio (TBR) than 18F-fludeoxyglucose PET/CT in various cancers, and thus has attracted substantial attention. As studies on FAPI PET grow in number and size, incidental findings related to non-oncologic conditions have been increasingly reported. FAPI PET uptake has been reported in various conditions such as benign tumors, fibrotic, granulomatosis, scarring/wound, degenerative diseases, and inflammatory diseases.The knowledge of physiological and non-oncologic causes of FAPI uptake is indispensable for accurate FAPI PET/CT interpretation and can help appropriate management of incidental findings on FAPI PET/CT in patients referred for cancer staging indications. In this review article, we describe for each organ system (Brain, Oral mucosa, Salivary Glands, Thyroid, Lung, Myocardium, Breast, Esophagus, Stomach, Intestine, Liver, Gallbladder, Pancreas, Spleen, Kidney, , Uterus, Bone marrow, Joints, Muscle, Vessels, Lymph nodes), the patterns of physiological FAPI uptake and the main causes of non-oncological uptake reported from the literature with FAPI-02, FAPI-04 and FAPI-46. We also illustrate some examples from our institutional database at UCLA.