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

Dynamic PET/CT scan of 68Ga-FAPI-04 for the optimal acquisition time in suspected malignant hepatic cancer patients

PURPOSE

Dynamic PET/CT scan of ⁶⁸Ga-FAPI-04 in patients with suspected malignant hepatic lesions were retrospectively analyzed to find the optimal acquisition time with better lesion detection rate.

METHODS

Twenty-two patients with lesions confirmed by CT or MRI were performed with dynamic ⁶⁸Ga-FAPI-04 PET/CT scan. Tracer uptake of lesions and normal organs at different time points were analyzed. Standardized uptake value (SUV) and tumor-to-background (TBR) were calculated based on the quantification of images.

RESULTS

SUV of normal organs decreased rapidly from 10 to 30 min and decreased gradually from 30 to 60 min. Besides, the uterus showed a particularly high uptake in all patients (12.62 ± 4.58 at 10 min p.i., 12.04 ± 3.99 at 30 min p.i., 10.92 ± 2.38 at 60 min p.i.). SUV of lesions decreased gradually, while TBR increased from 10- to 60-min post-injection. Visual analysis verified a comparable lesion detectability of 30 min and 60 min with images of 10 min showing a decreased lesion detection number.

CONCLUSION

This study revealed that similar detection rates were achieved at both 30 and 60 min, suggesting a static scan at 30 min to be appropriate in the clinic. Besides, although with high lesion uptake, early ⁶⁸Ga-FAPI-04 PET imaging at 10 min after tracer injection could cause missed lesion detection.

Comparison of 68 Ga-FAPI and 18 F-FDG PET/CT in Finger Hidradenocarcinoma

ABSTRACT

We report a case of hidradenocarcinoma, which showed only slight 18 F-FDG uptake. However, the rare sweat gland tumor 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 hidradenocarcinoma.

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.

68Ga-FAPI Versus 18F-FDG PET/CT in Evaluating Newly Diagnosed Breast Cancer Patients: A Head-to-Head Comparative Study

PURPOSE

This study aimed to compare the performance of 68Ga-FAPI and 18F-FDG PET/CT in the evaluation of patients with newly diagnosed breast cancer.

METHODS

Thirty-four women with newly diagnosed breast cancer who underwent both 68Ga-FAPI and 18F-FDG PET/CT within 1 week were prospectively included in the study. The imaging characteristics of primary lesions, diagnostic efficiency of lymph node metastasis (LNM), and accuracy of N stage evaluation between 2 PET/CTs were compared.

RESULTS

68Ga-FAPI showed higher SUVmax (11.06 ± 5.48 vs 8.33 ± 6.07, P = 0.02) and tumor-to-background ratio (15.32 ± 10.33 vs 8.25 ± 5.51, P < 0.001) than 18F-FDG in primary tumors. 68Ga-FAPI SUVmax was positively correlated with the pathological grade of the primary lesions and the final stage of the patients (P < 0.001). The specificity and accuracy of 68Ga-FAPI was higher than that of 18F-FDG in the diagnosis of LNMs on patient-based and lesion-based analysis (P < 0.001). The accuracy for the evaluation of N stage and N0 axillar status was 91.2% (31/34) and 85.7% (12/14) for 68Ga-FAPI, and 73.5% (25/34) and 42.9% (6/14) for 18F-FDG, respectively.

CONCLUSIONS

The 68Ga-FAPI SUVmax was positively correlated with the pathological grade of the primary lesions and the final stage of the patients. 68Ga-FAPI PET/CT has higher accuracy than 18F-FDG in the evaluation of N stage, especially N0 axillar status, which is helpful to improve the treatment strategy for breast cancer patients.

PET tracers in glioblastoma: Toward neurotheranostics as an individualized medicine approach

Over the past decade, theragnostic radiopharmaceuticals have been used in nuclear medicine for both diagnosis and treatment of various tumors. In this review, we carried out a literature search to investigate and explain the role of radiotracers in the theragnostic approach to glioblastoma multiform (GBM). We primarily focused on basic and rather common positron emotion tomography (PET) radiotracers in these tumors. Subsequently, we introduced and evaluated the preclinical and clinical results of theranostic-based biomarkers including integrin receptor family, prostate-specific membrane antigen (PSMA), fibroblast activated protein (FAP), somatostatin receptors (SRS), and chemokine receptor-4 (CXCR4) for patients with GBM to confer the benefit of personalized therapy. Moreover, promising research opportunities that could have a profound impact on the treatment of GBM over the next decade are also highlighted. Preliminary results showed the potential feasibility of the theragnostic approach using theses biomarkers in GBM patients.

Fibroblast Activation Protein Inhibitor (FAPI)-Based Theranostics-Where We Are at and Where We Are Heading: A Systematic Review

Cancer is the leading cause of death around the globe, followed by heart disease and stroke, with the highest mortality to this day. We have reached great levels of understanding of how these various types of cancer operate at a cellular level and this has brought us to what we call "precision medicine" where every diagnostic examination and the therapeutic procedure is tailored to the patient. FAPI is among the new tracers that can be used to assess and treat many types of cancer. The aim of this review was to gather all the known literature on FAPI theranostics. A MEDLINE search was conducted on four web libraries, PUBMED, Cochrane, Scopus, and Web of Sciences. All of the available articles that included both diagnoses and therapy with FAPI tracers were collected and put through the CASP (Critical Appraisal Skills Programme) questionnaire for systematic reviewing. A total of 8 records were deemed suitable for CASP review, ranging from 2018 to November 2022. These studies were put through the CASP diagnostic checklist, in order to assess the goal of the study, diagnostic and reference tests, results, descriptions of the patient sample, and future applications. Sample sizes were heterogeneous, both for size as well as for tumor type. Only one author studied a single type of cancer with FAPI tracers. Progression of disease was the most common outcome, and no relevant collateral effects were noted. Although FAPI theranostics is still in its infancy and lacks solid grounds to be brought into clinical practice, it does not show any collateral effects that prohibit administration to patients, thus far, and has good tolerability profiles.

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.

Diagnosis of Seronegative Rheumatoid Arthritis by 68 Ga-FAPI PET/CT

Early diagnosis of rheumatoid arthritis with the initiation of disease-modifying antirheumatic drugs is important to prevent future disability. Seronegative rheumatoid arthritis lacks the classical immunological markers, thus imposing clinical diagnostic difficulty. In this case, we reported 68 Ga-FAPI PET/CT findings of seronegative rheumatoid arthritis in a 60-year-old lady. This case illustrates how 68 Ga-FAPI PET/CT aids in the diagnosis of seronegative rheumatoid arthritis.

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.

Role of 68Ga-FAPI-04 PET/CT in the Initial Staging of Esophageal Cancer

AIM

To investigate the clinical value of 68Ga-FAPI-04 PET/CT for initial staging of esophageal cancer.

METHODS

A total of 44 newly diagnosed patients with esophageal cancer were included in the analysis on the basis of postoperative pathology or clinical and radiologic follow-up.

RESULTS

All primary lesions showed increased 68Ga-FAPI-04 uptake, with an SUVmax of 14.92 ± 6.91. A total of 561 lymph nodes were verified by surgery (507) or clinical and radiologic follow-up (54), of which 92 lymph nodes were diagnosed as showing metastases. Seventy-five lymph nodes with metastases showed positive findings on 68Ga-FAPI-04, with a diameter of about 1.06 ± 0.53 cm and SUVmax of 8.10±4.71. The sensitivity, specificity, accuracy, positive predictive value, and negative predictive value for lymph node metastasis detection were 81.5%, 99.3%, 96.6%, 96.2%, and 96.5%, respectively.

CONCLUSION

68Ga-FAPI-04 PET/CT showed good diagnostic performance in detecting lymph node metastases of esophageal cancer.

Mesenteric Mesonephric Adenocarcinoma on 68 Ga-FAPI PET/CT

ABSTRACT

Mesenteric mesonephric adenocarcinoma is an uncommon mesenteric neoplasm, which was arising from the mesonephric remnant of the female reproductive tract. Herein, we report the 68 Ga-FAPI PET/CT findings in a 66-year-old woman with mesenteric mesonephric adenocarcinoma.

Comparison of [68Ga]Ga-FAPI and [18F]FDG uptake in patients with gastric signet-ring-cell carcinoma: a multicenter retrospective study

OBJECTIVE

In this study, we investigated the role of [⁶⁸Ga]Ga-FAPI PET imaging in the detection of primary and metastatic gastric signet-ring-cell carcinoma (GSRCC) and compared with [¹⁸F]FDG PET.

METHODS

This retrospective multicenter analysis included 34 patients with histologically confirmed GSRCCs from four medical centers. The maximum standard uptake value (SUV_max), tumor-to-background ratio (TBR), and diagnostic accuracy were compared between the two modalities. [¹⁸F]FDG and [⁶⁸Ga]Ga-FAPI uptakes were compared by using the Wilcoxon signed-rank test. McNemar's test was used to compare the diagnostic accuracy between the two techniques.

RESULTS

Data were analyzed from 27 paired PET/CT and 7 paired PET/MRI scans for 34 GSRCC patients (16 men and 18 women) who had a median age of 51 years (range: 25-85 years). [⁶⁸Ga]Ga-FAPI PET showed higher SUV_max and TBR values than did [¹⁸F]FDG PET in the primary tumors (SUV_max: 5.2 vs. 2.2, p = 0.001; TBR: 7.6 vs. 1.3, p < 0.001), involved lymph nodes (SUV_max: 6.8 vs. 2.5, p < 0.001; TBR: 5.8 vs. 1.3, p < 0.001), and bone and visceral metastases (SUV_max: 6.5 vs. 2.4, p < 0.001; TBR: 6.3 vs. 1.3, p < 0.001). In diagnostic performance, [⁶⁸Ga]Ga-FAPI PET exhibited higher sensitivity than [¹⁸F]FDG PET for detecting primary tumors (73% [16/22] vs. 18% [4/22], p < 0.001), local recurrences (100% [7/7] vs. 29% [2/7], p = 0.071), lymph node metastases (77% [59/77] vs. 23% [18/77], p < 0.001), and distant metastases (93% [207/222] vs. 39% [86/222], p < 0.001).

CONCLUSION

The results from this multicenter retrospective analysis justify the clinical use of [⁶⁸Ga]Ga-FAPI tracers for GSRCC diagnosis and staging.

KEY POINTS

• [⁶⁸Ga]Ga-FAPI PET/CT is a promising imaging modality for the detection of primary and metastatic disease and has implications for TNM staging in GSRCC. • In this multicenter study of 34 patients with GSRCC, [⁶⁸Ga]Ga-FAPI PET exhibited greater radiotracer uptake, tumor-to-background ratios, and diagnostic accuracy than [¹⁸F]FDG PET for detecting primary/recurrent tumors and metastatic lesions.

Clinical Pharmacology of Radiotheranostics in Oncology

The combined use of diagnostic and therapeutic radioligands with the same molecular target, also known as theranostics, enables accurate patient selection, targeted therapy, and prediction of treatment response. Radioiodine, bone-seeking radioligands and norepinephrine analogs have been used for many years for diagnostic imaging and radioligand therapy of thyroid carcinoma, bone metastases, pheochromocytoma, paraganglioma, and neuroblastoma, respectively. In recent years, radiolabeled somatostatin analogs and prostate-specific membrane antigen ligands have shown clinical efficacy in the treatment of neuroendocrine tumors and prostate cancer, respectively. Several candidate compounds are targeting novel theranostic targets such as fibroblast activation protein, C-X-C chemokine receptor 4, and gastrin-releasing peptide receptor. In addition, several strategies to improve efficacy of radioligand therapy are being evaluated, including dosimetry-based dose optimization, multireceptor targeting, upregulation of target receptors, radiosensitization, pharmacogenomics, and radiation genomics. Design and evaluation of novel radioligands and optimization of dose and dose schedules, within the complex context of individualized multimodal cancer treatment, requires a multidisciplinary approach that includes clinical pharmacology. Significant increases in the use of these radiopharmaceuticals in routine oncological practice can be expected, which will have major impact on patient care as well as (radio)pharmacy utilization.

FAPI PET: Fibroblast Activation Protein Inhibitor Use in Oncologic and Nononcologic Disease

Gallium 68 (68Ga)-labeled fibroblast activation protein (FAP) inhibitor (FAPI) PET is based on the molecular targeting of the FAP, which is known to be highly expressed in the major cell population in tumor stroma, termed cancer-associated fibroblasts. Among many FAP-targeted radiopharmaceuticals developed so far, 68Ga-FAPI exhibits rapid tracer accumulation in target lesions and low background signal, which results in excellent imaging features. FAPI PET can be integrated in the clinical workflow and enables the detection of small primary or metastatic lesions, especially in the brain, liver, pancreas, and gastrointestinal tract due to the low tracer accumulation in these organs. Moreover, the DOTA (1,4,7,10-tetraazacylclododecane-1,4,7,10-tetrayl tetraacetic acid) chelator in the molecular structure allows coupling of the FAPI molecules with therapeutic emitters such as yttrium 90 for theranostic applications. This review provides an overview of the state of the art in FAP imaging, summarizes the current knowledge of relevant cancer biology, and highlights the latest findings in the clinical use of 68Ga-FAPI PET and other current FAPI tracers. Published under a CC BY 4.0 license.

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

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

Advances in PET/CT Imaging for Breast Cancer Patients and Beyond

Breast cancer is the most common cancer in women around the world and the fifth leading cause of cancer-related death [...].

FAPI PET/CT in Diagnostic and Treatment Management of Colorectal Cancer: Review of Current Research Status

FAPI PET/CT is a novel imaging tool targeting fibroblast activation protein (FAP), with high tumor uptake rate and low background noise. Therefore, the appearance of FAPI PET/CT provides a good tumor-to-background ratio between tumor and non-tumor tissues, which is beneficial to staging, tumor description and detection. Colorectal cancer has the biological characteristics of high expression of FAP, which provides the foundation for targeted FAP imaging. FAPI PET/CT may have a potential role in changing the staging and re-staging of colorectal cancer, monitoring recurrence and treatment management, and improving the prognosis of patients. This review will summarize the application status of FAPI PET/CT in colorectal cancer and provide directions for further application research.

Diagnostic value of [68Ga]Ga-FAPI-04 in patients with colorectal cancer in comparison with [18F]F-FDG PET/CT

Purpose

This study aimed to compare the diagnostic performance of [68Ga]Ga-FAPI-04 PET/CT and [18F]F-FDG PET/CT in primary and metastatic colorectal cancer (CRC) lesions.

Methods

This single-center preliminary clinical study (NCT04750772) was conducted at the Peking University Cancer Hospital & Institute and included 61 participants with CRC who underwent sequential evaluation through PET/CT with [18F]F-FDG and [68Ga]Ga-FAPI-04. Their PET/CT images were analysed to quantify the uptake of the two tracers in the form of maximum standardised uptake (SUVmax) values and target-to-background ratio (TBR), which were then compared using Wilcoxon's signed-rank test. The final changes in the tumour-node-metastasis (TNM) stage of all participants were recorded.

Results

Of all the participants, 21 were treatment naïve and 40 had been previously treated. In primary CRC lesions, the average TBRs of [68Ga]Ga-FAPI-04 and [18F]F-FDG were 13.3 ± 8.9 and 8.2 ± 6.5, respectively. The SUVmax of [68Ga]Ga-FAPI-04 in signet-ring/mucinous carcinomas (11.4 ± 4.9) was higher than that of [18F]F-FDG (7.9 ± 3.6) (P = 0.03). Both median SUVmax in peritoneal metastases and TBR in liver metastases of [68Ga]Ga-FAPI-04 were higher than those of [18F]F-FDG (5.2 vs. 3.8, P < 0.001; 3.7 vs. 1.9, P < 0.001, respectively). Compared with [18F]F-FDG PET/CT, clinical TNM staging based on [68Ga]Ga-FAPI-04 PET/CT led to upstaging and downstaging in 10 (16.4%) and 5 participants (8.2%), respectively. Therefore, the treatment options were changed in 13 participants (21.3%), including 9 with additional chemo/radiotherapy and/or surgery and others with avoidance or narrowed scope of surgery.

Conclusion

[68Ga]Ga-FAPI-04 showed potential as a novel PET/CT tracer to detect lymph nodes and distant metastases, which improved CRC staging, thus prompting the optimisation or adjustment of treatment decisions.

68Ga-FAPI-04 PET/CT in the Detection of Non-FDG-Avid Solid Pseudopapillary Neoplasm of the Pancreas

ABSTRACT

Solid pseudopapillary neoplasm of the pancreas is a rare tumor. A 46-year-old woman presented with chest pain for 6 months. Chest CT revealed a large mass of the right mediastinum. Then, she underwent 18F-FDG and 68Ga-FAPI-04 PET/CT scans for staging. However, we accidentally found that a non-FDG focus nodule in the body of the pancreas with elevated FAPI activity. Finally, biopsy of the nodule in the body of the pancreas confirmed the diagnosis of solid pseudopapillary neoplasm.

Comparison of [68Ga]Ga-DOTA-FAPI-04 and [18F]FDG PET/MRI in the Preoperative Diagnosis of Gastric Cancer

Purpose

Our objective was to compare the value of positron emission tomography/magnetic resonance imaging (PET/MRI) with the new imaging agent [⁶⁸Ga]Ga-DOTA-FAPI-04 and the traditional imaging agent [¹⁸F]FDG for the preoperative diagnosis of gastric cancer.

Methods

Forty patients with gastric cancer diagnosed by gastroscopy in gastrointestinal surgery at our hospital from June 2020 to January 2021 were analyzed. All patients underwent simultaneous [⁶⁸Ga]Ga-DOTA-FAPI-04 and [¹⁸F]FDG PET/MRI. The standard uptake value (SUV), fat removal standard uptake value (SUL), and diagnostic sensitivity, specificity, and accuracy for primary and metastatic lesions were compared, and their diagnostic value for different lymph node dissection stages was analyzed.

Results

The median age of the patients in this cohort was 68 years. Twenty-nine patients underwent surgery, and 11 patients underwent gastroscopic biopsy. The SUV_max of primary lesions in the FDG group and the FAPI group was 5.74 ± 5.09 and 8.06 ± 4.88, respectively (P < 0.01); SUL_max values were 3.52 ± 2.80 and 5.64 ± 3.25, respectively (P < 0.01). The SUV_max of metastases in the two groups was 3.81 ± 3.08 and 5.17 ± 2.80, respectively (P < 0.05). The diagnostic sensitivities for primary lesions in the FDG group and the FAPI group were 0.72 and 0.94, respectively (P < 0.05). Combined with postoperative pathological staging, there was no difference in diagnostic sensitivity and specificity of lymph node staging between the FDG and FAPI groups (P > 0.05).

Conclusion

Compared with the traditional imaging agent, [⁶⁸Ga]Ga-DOTA-FAPI-04 has better diagnostic efficiency but no substantial advantage for preoperative lymph node staging.

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

Purpose

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

Materials

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

Results

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

Conclusions

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

Systematic review registration

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

Performance of 18 F-FAPI PET/CT in assessing glioblastoma before radiotherapy: a pilot study

BACKGROUND

We aimed to determine the performance of ¹⁸ F-FAPI PET/CT used for preprocedural assessment of glioblastoma before radiotherapy.

METHODS

Twelve glioblastoma patients having undergone incomplete surgical resection or biopsy were examined with ¹⁸ F-FAPI PET/CT and MRI scanning before radiotherapy. All patients had confirmed tumor residues according to findings of histopathological and/or long-term clinical and radiological follow-ups. Lesion characterization data, including SUV_max and tumor-to-background ratio (TBR) on PET/CT were attained. PET/CT and MRI findings were compared in terms of number of lesions. The correlation between immunohistochemistry, molecular expression, and PET/CT parameters was also evaluated.

RESULTS

¹⁸ F-FAPI PET/CT detected 16 FAPI-avid out of 23 lesions in 12 patients described on MRI. MRI was statistically different from ¹⁸ F-FAPI PET/CT for lesion detection according to the exact McNemar statistical test (P = 0.0156). The SUV_max and TBR of the glioblastomas was 7.08 ± 3.55 and 19.95 ± 13.22, respectively. The sensitivity and positive predictive value (PPV) of ¹⁸ F-FAPI PET were 69.6% and 100%, respectively. Neither the Ki-67 index nor the molecular expression was correlated with the FAPI-PET/CT parameters.

CONCLUSION

¹⁸ F-FAPI PET/CT detects glioblastomas at a lower rate than MRI. However, the 100% PPV of the examination may make it useful for differentiating controversial lesions detected on MRI. The ¹⁸ F-FAPI-avid lesions are displayed more clearly probably due to a higher TBR. ¹⁸ F-FAPI PET/CT imaging might find application in glioblastoma biopsy and radiotherapy planning.

Prospective comparison of 68Ga-FAPI-04 and 18F-FDG PET/CT for tumor staging in nasopharyngeal carcinoma

Purpose

To explore the difference in the effectiveness of gallium-68 fibroblast activation protein inhibitor (⁶⁸Ga-FAPI-04) PET/CT and fluorine-18 fluorodeoxyglucose (¹⁸F-FDG) PET/CT for the initial staging of patients with nasopharyngeal carcinoma (NPC).

Methods

The Affiliated Hospital of Southwest Medical University hosted this single-center prospective investigation (Clinical Trials registration No.ChiCTR2100044131) between March 2020 and September 2021. Within a week, all subjects underwent MR scans, ⁶⁸Ga-FAPI-04 PET/CT, and ¹⁸F-FDG PET/CT in order. The effectiveness of medical staging employing ⁶⁸Ga-FAPI-04 and ¹⁸F-FDG PET/CT was compared.

Results

Twenty-eight patients with primary NPC were evaluated (mean age53 ± 11 years). ⁶⁸Ga-FAPI-04 PET/CT indicated an elevated recognition rate for diagnosing primary tumors (28/28 [100%] vs. 27/28 [96%]) and lymph node metastases (263/285 [92%] vs. 228/285 [80%]), but a lower detection rate for distant metastases (5/7 [71%] vs. 7/7 [100%]) compared with ¹⁸F-FDG PET/CT. A significant association between the maximum standard uptake value (SUVmax) of ¹⁸F-FDG PET and ⁶⁸Ga-FAPI-04 PET was found in the primary cancers (r = 0.691, p < 0.001). In comparison to ¹⁸F-FDG PET/CT, ⁶⁸Ga-FAPI-04 PET/CT upstaged the T stage in five patients while downstaging the N stage in seven patients. ⁶⁸Ga-FAPI-04 PET/CT corrected the overall staging of five patients on¹⁸F-FDG PET/CT.

Conclusion

⁶⁸Ga-FAPI-04 PET/CT is preferable to ¹⁸F-FDG PET/CT for NPC staging in terms of the detection efficiency for primary tumors and lymph node metastasis. This is especially true when evaluating the primary cancer and any spread to contiguous tissues. It is possible to improve the staging assessment of NPC by using ⁶⁸Ga-FAPI-04 PET/CT in conjunction with ¹⁸F-FDG PET/CT.

Exploration of the threshold SUV for diagnosis of malignancy using 18F-FBPA PET/CT

Background

The goal of the study was to evaluate the diagnostic ability of 18F-FBPA PET/CT for malignant tumors. Findings from 18F-FBPA and 18F-FDG PET/CT were compared with pathological diagnoses in patients with malignant tumors or benign lesions.

Methods

A total of 82 patients (45 males, 37 females; median age, 63 years; age range, 20–89 years) with various types of malignant tumors or benign lesions, such as inflammation and granulomas, were examined by 18F-FDG and 18F-FBPA PET/CT. Tumor uptake of FDG or FBPA was quantified using the maximum standardized uptake value (SUVmax). The final diagnosis was confirmed by cytopathology or histopathological findings of the specimen after biopsy or surgery. A ROC curve was constructed from the SUVmax values of each PET image, and the area under the curve (AUC) and cutoff values were calculated.

Results

The SUVmax for 18F-FDG PET/CT did not differ significantly for malignant tumors and benign lesions (10.9 ± 6.3 vs. 9.1 ± 2.7 P = 0.62), whereas SUVmax for 18F-FBPA PET/CT was significantly higher for malignant tumors (5.1 ± 3.0 vs. 2.9 ± 0.6, P < 0.001). The best SUVmax cutoffs for distinguishing malignant tumors from benign lesions were 11.16 for 18F-FDG PET/CT (sensitivity 0.909, specificity 0.390) and 3.24 for 18F-FBPA PET/CT (sensitivity 0.818, specificity 0.753). ROC analysis showed significantly different AUC values for 18F-FDG and 18F-FBPA PET/CT (0.547 vs. 0.834, p < 0.001).

Conclusion

18F-FBPA PET/CT showed superior diagnostic ability over 18F-FDG PET/CT in differential diagnosis of malignant tumors and benign lesions. The results of this study suggest that 18F-FBPA PET/CT diagnosis may reduce false-positive 18F-FDG PET/CT diagnoses.

68Ga-DOTA-FAPI-04 PET/CT Imaging in a Case of Radioactive Iodine-Induced Chronic Parotitis

ABSTRACT

68Ga-DOTA-FAPI-04 is a promising PET agent for tumor imaging. However, inflammatory lesions can also show increased FAPI uptake. Herein, we reported a 52-year-old woman who underwent total thyroidectomy for thyroid papillary carcinoma 1 year ago and underwent adjuvant radioiodine therapy 1 month later. After 131I therapy, she began to develop pain and swelling in bilateral cheeks, which developed into oral dryness. The patient was diagnosed with radioactive iodine-induced parotitis. 68Ga-DOTA-FAPI-04 PET/CT showed the density of bilateral parotid glands increased, and the volume decreased with intense tracer uptake. 99mTcO4- salivary gland scintigraphy showed decreased tracer uptake in the bilateral parotid glands.

Repetitive Early 68Ga-FAPI PET Acquisition Comparing 68Ga-FAPI-02, 68Ga-FAPI-46, and 68Ga-FAPI-74: Methodologic and Diagnostic Implications for Malignant, Inflammatory/Reactive, and Degenerative Lesions

⁶⁸Ga-labeled fibroblast activation protein (FAP) inhibitor (⁶⁸Ga-FAPI) PET targets ⁶⁸Ga-FAPI-positive activated fibroblasts and is a promising imaging technique for various types of cancer and nonmalignant pathologies. However, discrimination between malignant and nonmalignant ⁶⁸Ga-FAPI-positive lesions based on static PET with a single acquisition time point can be challenging. Additionally, the optimal imaging time point for ⁶⁸Ga-FAPI PET has not been identified yet, and different ⁶⁸Ga-FAPI tracer variants are currently used. In this retrospective analysis, we evaluate the diagnostic value of repetitive early ⁶⁸Ga-FAPI PET with ⁶⁸Ga-FAPI-02, ⁶⁸Ga-FAPI-46, and ⁶⁸Ga-FAPI-74 for malignant, inflammatory/reactive, and degenerative lesions and describe the implications for future ⁶⁸Ga-FAPI imaging protocols. Methods: Whole-body PET scans of 24 cancer patients were acquired at 10, 22, 34, 46, and 58 min after the administration of 150-250 MBq of ⁶⁸Ga-FAPI tracer molecules (8 patients each for ⁶⁸Ga-FAPI-02, ⁶⁸Ga-FAPI-46, and ⁶⁸Ga-FAPI-74). Detection rates and SUVs (SUV_max and SUV_mean) for healthy tissues, cancer manifestations, and nonmalignant lesions were measured, and target-to-background ratios (TBR) versus blood and fat were calculated for all acquisition time points. Results: For most healthy tissues except fat and spinal canal, biodistribution analysis showed decreasing uptake over time. We analyzed 134 malignant, inflammatory/reactive, and degenerative lesions. Detection rates were minimally reduced for the first 2 acquisition time points and remained at a constant high level from 34 to 58 min after injection. The uptake of all 3 variants was higher in malignant and inflammatory/reactive lesions than in degenerative lesions. ⁶⁸Ga-FAPI-46 showed the highest uptake and TBRs in all pathologies. For all variants, TBRs versus blood constantly increased over time for all pathologies, and TBRs versus fat were constant or decreased slightly. Conclusion: ⁶⁸Ga-FAPI PET/CT is a promising imaging modality for malignancies and benign lesions. Repetitive early PET acquisition added diagnostic value for the discrimination of malignant from nonmalignant ⁶⁸Ga-FAPI-positive lesions. High detection rates and TBRs over time confirmed that PET acquisition earlier than 60 min after injection delivers high-contrast images. Additionally, considering clinical feasibility, acquisition at 30-40 min after injection might be a reasonable compromise. Different ⁶⁸Ga-FAPI variants show significant differences in time-dependent biodistributional behavior and should be selected carefully depending on the clinical setting.

68 Ga-FAPI PET/CT Detected Non-PSMA/FDG-Avid Primary Tumor in De Novo Metastatic Prostate Cancer

ABSTRACT

68 Ga-labeled PET tracer targeting PSMA is a promising diagnostic approach for staging and restating of prostate cancer (PCa), but cases with clinically relevant PCa and false-negative PSMA PET/CT have been reported. In this case, we reported 68 Ga-PSMA, 18 F-FDG, and 68 Ga-FAPI PET/CT findings in a 65-year-old man with de novo metastatic PCa. 68 Ga-FAPI PET/CT detected non-PSMA/FDG-avid primary PCa, consisting with multiparametric MRI findings. The subsequent histopathologic examination confirmed a Gleason 4 + 5 PCa. This case highlighted that 68 Ga-FAPI PET/CT may be a useful imaging modality for primary PCa detection and localization.

[18F]FAPI-42 PET/CT versus [18F]FDG PET/CT for imaging of recurrent or metastatic gastrointestinal stromal tumors

PURPOSE

PET has been important for monitoring recurrence and metastasis of Gastrointestinal Stromal Tumors (GISTs) and the selection of therapeutic strategies. A significant portion of GISTs lesions show negative FDG uptake and therefore calls for more tumor-specific imaging biomarkers. This study compared the imaging performance of [18F]FAPI-42 PET/CT and [18F]FDG PET/CT in recurrent or metastatic gastrointestinal stromal tumors (R/M GISTs).

METHODS

This study retrospectively included 35 patients with R/M GISTs who underwent both FAPI PET/CT and FDG PET/CT. The definite diagnosis was confirmed by pathology or follow-up drug treatment effects. The differences in detection rates and tumor-to-background SUVmax ratio (SUVTBR) of different locations between dual-tracer PET/CT were compared. Factors including tumor size, degree of enhancement, type of gene mutation, and targeted treatment potentially influencing the uptake of both tracers were assessed. The excised lesions (n = 3) underwent immunohistochemical staining to verify FAP expression in the tissue.

RESULTS

A total of 106 lesions in 35 patients were identified, out of which 38/106 (35.8%) lesions (FAPI + /FDG -) were additionally detected by FAPI PET/CT as compared to that by FDG, including 26 liver metastases, ten peritoneal metastases, one gastrointestinal recurrence, and one bone metastasis. The positive detection rate of FAPI PET/CT for recurrent or metastatic GISTs was higher than that of FDG (80.2% vs. 53.8%,  P< 0.001), especially in liver metastases (87.5% vs. 33.3%, P< 0.001). Moreover, the SUVTBR of liver metastases of GISTs in FAPI PET/CT was higher than that in FDG [2.4 (0.3 to 11.2) vs. 0.9 (0.3 to 6.5), P< 0.001]. The longest diameter of tumors in the FDG-positive group was higher than that of the FDG-negative group (P= 0.005); still, it did not differ between the FAPI-positive group and the FAPI-negative group. No difference in the degree of enhancement was observed between both tracers' positive and negative groups. Besides, the SUVTBR of FDG but not FAPI differed significantly among various gene mutations (P< 0.001) as well as the targeted therapy and no targeted therapy groups (P= 0.001). FAP was expressed in R/M GISTs, and the uptake of FAPI corresponded to the level of FAP expression.

CONCLUSION

In conclusion, FAPI for imaging of R/M GISTs could be superior to FDG, specifically for liver metastases. The uptake of FAPI could reflect the level of FAP expression, and it was independent of tumor size, degree of enhancement, type of gene mutation, and targeted therapy as compared to FDG.

[68Ga]Ga-FAPI PET/CT Improves the T Staging of Patients with Newly Diagnosed Nasopharyngeal Carcinoma: A Comparison with [18F]F-FDG

PURPOSE

This study aimed to explore the value of [⁶⁸Ga]Ga-labelled fibroblast activation protein inhibitor ([⁶⁸Ga]Ga-FAPI) positron emission tomography/computed tomography (PET/CT) in the initial staging of patients with newly diagnosed nasopharyngeal carcinoma (NPC), compared with 2-deoxy-2[¹⁸F]fluoro-D-glucose ([¹⁸F]F-FDG) PET/CT.

MATERIALS AND METHODS

Forty-seven treatment-naïve patients with newly diagnosed NPC underwent magnetic resonance imaging (MRI), [⁶⁸Ga]Ga-DOTA-FAPI-04 PET/CT and [¹⁸F]F-FDG PET/CT within 1 week. The diagnostic efficiency of all imaging modalities for evaluating primary tumour extension was compared from the two aspects of soft tissue and bony structure involvement. The accuracy of two PET/CT methods for diagnosing cervical lymph node (CLN) metastases was compared, and MRI served as the standard reference. T and N stages were assessed by MRI, [⁶⁸Ga]Ga-FAPI PET/CT and [¹⁸F]F-FDG PET/CT. Immunohistochemical (IHC) staining for FAP was conducted in 22 of the patients.

RESULTS

[⁶⁸Ga]Ga-FAPI PET/CT outperformed [¹⁸F]F-FDG PET/CT in the assessment of primary tumour invasion in the cavernous sinus (10 vs. 1, p < 0.001) and bony structures (207 vs. 177, p < 0.001). Compared with MRI, [⁶⁸Ga]Ga-FAPI PET/CT upgraded and underestimated T stage in 13 and 2 patients, while [¹⁸F]F-FDG PET/CT upgraded and underestimated T stage in 5 and 13 patients. However, [⁶⁸Ga]Ga-FAPI PET/CT was inferior to [¹⁸F]F-FDG PET/CT in diagnosing positive CLNs based on the analyses of patients, neck sides, neck levels and individual nodes. [⁶⁸Ga]Ga-FAPI PET/CT changed therapeutic schedules in 8 patients because of stage group changes. The presence of FAP with high quantity and intensity in cancer-associated fibroblasts (CAFs) was confirmed in all tumour specimens.

CONCLUSION

[⁶⁸Ga]Ga-FAPI PET/CT outperformed [¹⁸F]F-FDG PET/CT in detecting the cavernous sinus and bony structure involvement of primary NPC tumours, suggesting its value in improving T staging and therapeutic regimen selection. However, the performance of [⁶⁸Ga]Ga-FAPI PET/CT is less promising for N staging because it detected fewer positive CLNs than [¹⁸F]F-FDG PET/CT.

A systematic review of [68Ga]Ga-DOTA-FAPI-04 and [18F]FDG PET/CT in the diagnostic value of malignant tumor bone metastasis

OBJECTIVE

This study aims to perform a systemic analysis of [68Ga]Ga-DOTA-FAPI-04 positron emission tomography (PET)/computerized tomography (CT) and [18F]FDG PET/CT for the diagnosis of malignant tumor bone metastasis based on existing clinical evidence.

METHODS

This systematic review followed the guidelines of the Preferred Reporting Project (PRISMA) for systematic reviews and meta-analysis. This is a retrospective study of articles published in PubMed. Embase was searched online from the start of May 2022. The main endpoints were the maximum standardized uptake value and the tumor-to-background ratio to determine the examination performance of [68Ga]Ga-DOTA-FAPI-04 and [18F]FDG for bone transfer stoves. Based on the entry and discharge standards, two researchers extracted documents and data and then performed the quality evaluation.

RESULTS

A total of eight studies on the metastasis of malignant tumors on bone were included, which involved 358 patients in the final analysis.

CONCLUSION

[68Ga]Ga-DOTA-FAPI-04 showed better detection performance for bone metastasis. The sensitivity of [68Ga]Ga-DOTA-FAPI-04 for the diagnosis of the primary tumor was higher than that of [18F]FDG, whereas the specificity of [18F]FDG was higher than that of [68Ga]Ga-DOTA-FAPI-04. However, further randomized controlled trials and prospective clinical trials are warranted to compare the diagnostic performance of [68Ga]Ga-DOTA-FAPI-04 PET/CT and [18F]FDG PET/CT.

SYSTEMATIC REVIEW REGISTRATION

https://www.crd.york.ac.uk/PROSPERO/, identifier (CRD42022313019).

Fibroblast heterogeneity in solid tumors: From single cell analysis to whole-body imaging

Cancer-Associated Fibroblasts (CAFs) represent the most prominent component of the tumor microenvironment (TME). Recent studies demonstrated that CAF are heterogeneous and composed of different subpopulations exerting distinct functions in cancer. CAF populations differentially modulate various aspects of tumor growth, including cancer cell proliferation, extra-cellular matrix remodeling, metastatic dissemination, immunosuppression and resistance to treatment. Among other markers, the Fibroblast Activation Protein (FAP) led to the identification of a specific CAF subpopulation involved in metastatic spread and immunosuppression. Expression of FAP at the surface of CAF is detected in many different cancer types of poor prognosis. Thus, FAP recently appears as an appealing target for therapeutic and molecular imaging applications. In that context, ⁶⁸Ga-labeled radiopharmaceutical-FAP-inhibitors (FAPI) have been recently developed and validated for quantitatively mapping FAP expression over the whole-body using Positron Emission Tomography (PET/CT). In this review, we describe the main current knowledge on CAF subpopulations and their distinct functions in solid tumors, as well as the promising diagnostic and therapeutic implications of radionuclides targeting FAP.

The Superiority of 68 Ga-FAPI-04 over 18F-FDG in a Case of Gallbladder Cancer

A 56-year-old man presented with vague upper abdominal pain for more than 4 months. His abdominal ultrasound and MRI showed thickening of the neck and base of the gallbladder and nodule formation at the base of the gallbladder. 18F-FDG PET/CT revealed intense FDG uptake in the base of the gallbladder and multiple lymph nodes. 68 Ga-FAPI-04 PET/CT not only showed intense FAPI uptake in the above mentioned FDG-avid lesions but also showed intense FAPI uptake in the neck lesion of the gallbladder and some other additional lymph nodes. Finally, histopathological examination confirmed poorly differentiated tubular adenocarcinoma of the neck and base of the gallbladder. Our case illustrated that 68 Ga-FAPI-04 PET/CT may outperform 18F-FDG PET/CT in the detection of gallbladder cancer primary and metastatic lesions.

Comparisons of Quantitative Parameters of Ga-68-Labelled Fibroblast Activating Protein Inhibitor (FAPI) PET/CT and [18F]F-FDG PET/CT in Patients with Liver Malignancies

PURPOSE

To compare quantitative parameters and tumour detection rates of [68 Ga]Ga-FAPI PET/CT with those of dedicated liver PET/MRI and 18F-FDG PET in patients with liver malignancies.

PROCEDURES

Twenty-seven patients (29 imaging studies) with diagnosed or suspected liver malignancies who underwent [68 Ga]Ga-FAPI-46 PET/CT, liver PET/MRI, and [18F]FDG PET/CT between September 2020 and June 2021 were retrospectively analysed. MRI findings were used as the reference standard for diagnosis.

RESULTS

The 27 patients had a median age of 68 years (interquartile range: 60-74 years; 21 men). Primary intrahepatic tumours were reported in 13 patients (15 imaging studies) with cholangiocarcinoma (CCA) and in 14 patients with hepatocellular carcinoma (HCC). All intrahepatic lesions detectable on MRI were also detected on [68 Ga]Ga-FAPI-46 PET/CT giving a sensitivity of 100% (19/19), whereas the sensitivity of [18F]FDG PET/CT was 58% (11/19). All intrahepatic lesions were detected on [68 Ga]Ga-FAPI-46 PET/CT, on which they showed higher activity (median SUVmax: 15.61 vs. 5.17; P < .001) and higher target-to-background ratio (TBR; median, 15.90 vs. 1.69, P < .001) than on [18F]FDG, especially in patients with CCA (median TBR, 21.08 vs. 1.47, respectively; P < .001). The uptake positivity rate in regional node metastasis was 100% (12/12) on [68 Ga]Ga-FAPI-46 PET/CT compared with 58% (7/12) on [18F]FDG PET/CT. All patients with distant metastasis (100%, 14/14) were detected on both [18F]FDG and [68 Ga]Ga-FAPI-46 PET/CT imaging, although more distant metastatic lesions were detected on [68 Ga]Ga-FAPI-46 PET/CT than on [18F]FDG (96% (42/44) vs. 89% (39/44), respectively).

CONCLUSION

[68 Ga]Ga-FAPI PET/CT with dedicated liver PET/MRI shows potential for superior detection of hepatic malignancy compared with [18F]FDG PET/CT or MRI alone.

18 F-FDG and 68 Ga-FAPI-04 in the Evaluation of Aggressive Perivascular Epithelioid Cell Tumor

ABSTRACT

A 10-year-old girl with a right renal mass underwent 18 F-FDG PET/CT and 68 Ga-FAPI-04 PET/MRI for presurgical assessment of tumor invasion and malignant potential. The mass showed low 18 F-FDG uptake and intense 68 Ga-FAPI-04 uptake. Nephrectomy was performed, and the histopathologic diagnosis was aggressive PEComa (perivascular epithelioid cell tumor). This case showed that 68 Ga-FAPI-04 PET outperformed 18 F-FDG PET in detecting aggressive PEComa.

[Oncological theranostics in nuclear medicine]

The theranostic principle describes the diagnostic and therapeutic use of radioactive nuclides linked to biochemically active ligands. The oldest and most prominent field of application of theranostics in oncology is differentiated thyroid cancer treated by radioiodine therapy, which allows imaging of the iodine uptake and thus tumor manifestations by gamma (γ) radiation of radioiodine. Other areas of application include neuroendocrine tumors, castration-resistant prostate cancer and, in the context of individual therapeutic approaches, fibroblastic tumors. Imaging with beta-plus (β⁺) emitters is mainly performed using so-called hybrid imaging: positron emission tomography (PET) in combination with computed tomography or magnetic resonance imaging (PET/CT or PET/MRI). Beta-minus (β^-) emitters are predominantly used in therapy, but the use of alpha (α) emitters is also increasing, thus, enabling targeted cancer treatment with mostly low-grade side effects.

68 Ga-FAPI-46 and 18 F-FDG in Advanced Metastatic Pancreatic Cancer

ABSTRACT

Recently imaging with new PET radiotracers that act as fibroblast activation protein inhibitors (FAPIs) showed promising results in oncology and even nononcology imaging. Here we report a case of advanced pancreatic adenocarcinoma, imaged with both 18 F-FDG and 68 Ga-FAPI-46 PET/CT scans. The result indicated that imaging with 68 Ga-FAPI-46 showed significant improvement in detection of metastases as well as local malignancy recurrence. Moreover, the intensity and SUVs of the lesions were higher in 68 Ga-FAPI-46 scan compared with 18 F-FDG.

68Ga-FAPI-04 PET/CT in Solitary Choroid Plexus Metastasis From Renal Cell Carcinoma

ABSTRACT

Intraventricular metastasis from extracranial tumor is rare. We describe MRI and 68Ga-FAPI-04 PET/CT findings in a case of histologically proved solitary choroid plexus metastasis from clear cell renal cell carcinoma. The tumor showed remarkable enhancement on MRI and increased FAPI uptake with high tumor-to-background activity ratio on PET/CT. This case indicates FAPI PET may be useful for detection of intraventricular metastasis from renal cell carcinoma.

Comparison of physiological uptake of normal tissues in patients with cancer using 18F-FAPI-04 and 18F-FAPI-42 PET/CT

Purpose

To calculate the physiological uptake of various tissues in patients with cancer using 18F-AlF-NOTA-FAPI-04 (18F-FAPI-04) and 18F-AlF-NOTA-FAPI-42 (18F-FAPI-42) PET/CT and to compare the variation in standard uptake values between the two scans.

Materials and methods

This retrospective analysis included 40 patients with cancer who underwent 18F-FAPI; the first 20 patients received 18F-FAPI-04 PET/CT and the remaining 20 patients received 18F-FAPI-42 PET/CT. A total of 49 normal tissues, including the brain (cerebrum/cerebellum), parotid and submandibular glands, palatine tonsils, and thyroid, were identified on CT images. For these normal tissues, maximum standardized uptake value (SUVmax) and mean standardized uptake value (SUVmean) were calculated. We also compared the SUVmean of identical tissues to explore the difference in biodistribution between the two radiotracers.

Results

The accumulation of 18F-FAPI-04 and 18F-FAPI-42 showed an analogous pattern. High uptake of both radiotracers in the gallbladder, uterus, submandibular gland, and renal pelvis was demonstrated (range: SUVmax, 4.01-5.75; SUVmean, 2.92-4.22). Furthermore, the uptake of bony tissues was slightly higher in 18F-FAPI-42 than in 18F-FAPI-04 (range: SUVmean, 0.4 ± 0.22-0.9 ± 0.34 and 0.3 ± 0.24-0.7 ± 0.18, respectively, p < 0.05), while the uptake of some soft tissues was higher in 18F-FAPI-04 than in 18F-FAPI-42 (range: SUVmean, 0.9 ± 0.24-1.5 ± 0.35 and 0.9 ± 0.26-1.2 ± 0.37, respectively, p < 0.05).

Conclusions

Both radioligands exhibited similar physiological uptake of normal tissues in patients with cancers. In addition, 18F-FAPI-42 demonstrated higher uptake of bone tissues than 18F-FAPI-04 while showing lower uptake of soft tissues than 18F-FAPI-04.

Different Features of 18F-FAPI, 18F-FDG PET/CT and MRI in the Evaluation of Extrahepatic Metastases and Local Recurrent Hepatocellular Carcinoma (HCC): A Case Report and Review of the Literature

Background

Recurrence and metastasis are important causes of postoperative death in most HCC patients. Conventional imaging modalities such as ¹⁸F-FDG PET/CT and enhanced MRI are still unsatisfactory in evaluating these patients in the clinical setting. PET/CT imaging with a radiolabeled fibroblast activation protein inhibitor (FAPI) has emerged as a new imaging technique for the diagnosis and radiotherapy of malignant tumors. While many studies have focused on the diagnostic accuracy of intrahepatic primary HCC, the evaluation of recurrent and metastatic HCC remains only poorly investigated.

Case Presentation

A 71-year-old man with a five-year history of HCC after radical resection underwent ¹⁸F-FDG PET/CT due to further surgery for tumor recurrence, which revealed two iso-metabolic lesions in the right peritoneum and a hypo-metabolic lesion in the right liver. ¹⁸F-FAPI PET/CT was performed to further complement ¹⁸F-FDG PET/CT in the detection of these suspected metastatic lesions. Importantly, multiple diffuse intense radioactivity was shown in the hepatic capsule, suggesting metastatic lesions, but a wedge-shaped elevated ¹⁸F-FAPI uptake disorder around the FDG-unavid necrotic lesion after radiofrequency ablation (RFA) demonstrated benign stromal fibrosis.

Conclusion

This case suggested that ¹⁸F-FAPI may have an advantage over ¹⁸F-FDG in detecting peritoneal metastasis even in tiny or early hepatic capsules of HCC, but its false positives due to postoperative stromal fibrosis should be noted. Wedge- or strip-shaped FAPI-avid lesions with sharp edges may be post-treatment stromal fibrosis.

PET/CT for Predicting Occult Lymph Node Metastasis in Gastric Cancer

A portion of gastric cancer patients with negative lymph node metastasis at an early stage eventually die from tumor recurrence or advanced metastasis. Occult lymph node metastasis (OLNM] is a potential risk factor for the recurrence and metastasis in these patients, and it is highly important for clinical prognosis. Positron emission tomography (PET)/computed tomography (CT) is used to assess lymph node metastasis in gastric cancer due to its advantages in anatomical and functional imaging and non-invasive nature. Among the major metabolic parameters of PET, the maximum standardized uptake value (SUVmax) is commonly used for examining lymph node status. However, SUVmax is susceptible to interference by a variety of factors. In recent years, the exploration of new PET metabolic parameters, new PET imaging agents and radiomics, has become an active research topic. This paper aims to explore the feasibility and predict the effectiveness of using PET/CT to detect OLNM. The current landscape and future trends of primary metabolic parameters and new imaging agents of PET are reviewed. For gastric cancer patients, the possibility to detect OLNM non-invasively will help guide surgeons to choose the appropriate lymph node dissection area, thereby reducing unnecessary dissections and providing more reasonable, personalized and comprehensive treatments.

Advancement and Future Perspective of FAPI PET/CT In Gynecological Malignancies

Fibroblast activation protein (FAP) is ubiquitously present in healthy tissue, and additionally upregulated by cancer associated fibroblasts (CAFs) leading to high levels of FAP. Thus, neoplastic tissue, which is containing CAFs, characterized by a high presence of FAP. Moreover, in more than 90% of all epithelial tumors this phenomenon seems to occur, including many gynecological tumors, providing the foundation for a successful application of FAP-ligands. However, FAP upregulation, can also be initiated by benign conditions such as inflammation, hormonal-influence, and wound healing. Gynecological cancers seem to represent a field of interest for the utilization of FAPI-PET/CT to potentially improve staging, restaging and therapeutic management. First highly promising investigations demand further research in order to validate these preliminary findings.

68 Ga-DOTA-FAPI-04 PET/CT Imaging in a Case of Cardiac Angiosarcoma

ABSTRACT

A 30-year-old woman presented with sudden syncope. Further examination revealed a mass in the right atrium. 18 F-FDG showed increased tracer uptake in the mass. 68 Ga-DOTA-FAPI-04 showed increased tracer uptake of thickened pericardium around the mass, but no obviously increased tracer uptake in the mass. The mass that invaded the adjacent pericardium was found during the operation. Postoperative pathology confirmed the diagnosis of right atrium angiosarcoma. Our case demonstrated that 68 Ga-DOTA-FAPI-04 is not superior to 18 F-FDG in the imaging of cardiac angiosarcoma, but it is still possible to produce beneficial value in the evaluation of the involvement of the lesion.

Superiority of [68Ga]Ga-FAPI-04/[18F]FAPI-42 PET/CT to [18F]FDG PET/CT in delineating the primary tumor and peritoneal metastasis in initial gastric cancer

OBJECTIVE

This study aimed to compare [⁶⁸Ga]Ga-FAPI-04/[¹⁸F]FAPI-42 PET/CT with [¹⁸F]FDG PET/CT in the evaluation of initial gastric cancer.

METHODS

We retrospectively compared [⁶⁸Ga]Ga-FAPI-04/[¹⁸F]FAPI-42 PET/CT with [¹⁸F]FDG PET/CT in patients with initial gastric cancer from September 2020 to March 2021. Lesion detectability and the uptake of lesions quantified by the maximum standardized uptake value (SUVmax) and target-to-background ratio (TBR) were compared between the two modalities using the Wilcoxon signed-rank test, Mann-Whitney U test, and McNemar's chi-square test.

RESULTS

A total of 61 patients (37 males, aged 23-81 years) were included, of which 22 underwent radical gastrectomy. For primary lesions, higher uptake of [⁶⁸Ga]Ga-FAPI-04/[¹⁸F]FAPI-42 was observed compared to [¹⁸F]FDG (median SUVmax, 14.60 vs 4.35, p < 0.001), resulting in higher positive detection using [⁶⁸Ga]Ga-FAPI-04/[¹⁸F]FAPI-42 PET/CT than [¹⁸F]FDG PET/CT (95.1% vs 73.8%, p < 0.001), particularly for tumors with signet-ring cell carcinoma (SRCC) (96.4% vs 57.1%, p < 0.001). [⁶⁸Ga]Ga-FAPI-04/[¹⁸F]FAPI-42 PET/CT detected more positive lymph nodes than [¹⁸F]FDG PET/CT (637 vs 407). However, both modalities underestimated N staging compared to pathological N staging. [⁶⁸Ga]Ga-FAPI-04/[¹⁸F]FAPI-42 PET/CT showed a higher sensitivity (92.3% vs 53.8%, p = 0.002) and peritoneal cancer index score (18 vs 3, p < 0.001) in peritoneum metastasis and other suspect metastases compared to [¹⁸F]FDG PET/CT.

CONCLUSION

Our findings indicate that [⁶⁸Ga]Ga-FAPI-04/[¹⁸F]FAPI-42 PET/CT outperformed [¹⁸F]FDG PET/CT in the evaluation of primary tumors with SRCC and peritoneum metastasis in initial gastric cancer. However, no clinically useful improvement was seen in N staging.

KEY POINTS

• The uptake of [⁶⁸Ga]Ga-FAPI-04/[¹⁸F]FAPI-42 in primary tumor and metastasis was intensely higher than that of [¹⁸F]FDG (p < 0.001) in 61 patients with initial gastric cancer. • [⁶⁸Ga]Ga-FAPI-04/[¹⁸F]FAPI-42 PET/CT had a higher sensitivity detection in primary tumors (95.1% vs 73.8%, p < 0.001) and peritoneal metastases (92.3% vs 53.8%, p = 0.002) than [¹⁸F]FDG PET/CT. • [⁶⁸Ga]Ga-FAPI-04/[¹⁸F]FAPI-42 PET/CT depicted more positive lymph nodes than [¹⁸F]FDG PET/CT (637 vs 407); however, both underestimated N staging compared to pathological N staging.

FAP-Specific Signalling Is an Independent Diagnostic Approach in ACC and Not a Surrogate Marker of MRI Sequences

Background: Fibroblast Activation Protein (FAP) is a new target for positron emission tomography and computed tomography (PET/CT) imaging of epithelial tumours embedded in a fibrous stroma. Adenoid cystic carcinomas (ACCs) have shown elevated tracer uptake in 68Gallium (68Ga)-labelled FAPIs in previous studies. The current gold standard for ACC imaging is contrast-enhanced (ce) MRI, where intertumoural heterogeneity leads to variable appearance on T1-weighted (T1w) and T2-weighted (T2w) images. In this retrospective analysis, we correlated 68Ga-FAPI PET signalling at three time points with ceT1w and T2w MRI signals to further characterise the significance of 68Ga-FAPI uptake in ACCs. Methods: Clinical PET/CT scans of 12 ACC patients were performed at 10, 60 and 180 min post i.v. administration of 68Ga-labelled-FAPI tracer molecules. 68Ga-PET- and corresponding MRI-scans were co-registered, and 3D volumetric segmentations were performed on ceT1w and T2w lesions of co-registered MRI slides. Signal intensity values of 68Ga-FAPI PET signalling and ceT1w/T2w MRI scans were analysed for their pixelwise correlation in each patient. Pooled estimates of the correlation coefficients were calculated using the Fisher z-transformation. Results: 68Ga-FAPI PET signals showed a very weak positive correlation with ceT1w values (pooled correlation 0.114, 0.147 and 0.162 at 10, 60 and 180 min) and a weak negative correlation with T2w values (pooled correlation −0.148, −0.121 and −0.225 at 10, 60 and 180 min). Individual r-values at 60 min ranged from −0.130 to 0.434 in ceT1w and from −0.466 to 0.637 in T2w MRI scans. Conclusion: There are only slight correlations between the intensity of 68Ga-FAPI PET signals and tumour appearance in ceT1w or T2w MRI scans, which underlines that 68Ga-FAPI PET signalling is not a surrogate marker of MRI sequences but an independent signal.

Advances in nuclear medicine-based molecular imaging in head and neck squamous cell carcinoma

Head and neck squamous cell carcinomas (HNSCCs) are often aggressive, making advanced disease very difficult to treat using contemporary modalities, such as surgery, radiation therapy, and chemotherapy. However, targeted therapy, e.g., cetuximab, an epidermal growth factor receptor inhibitor, has demonstrated survival benefit in HNSCC patients with locoregional failure or distant metastasis. Molecular imaging aims at various biomarkers used in targeted therapy, and nuclear medicine-based molecular imaging is a real-time and non-invasive modality with the potential to identify tumor in an earlier and more treatable stage, before anatomic-based imaging reveals diseases. The objective of this comprehensive review is to summarize recent advances in nuclear medicine-based molecular imaging for HNSCC focusing on several commonly radiolabeled biomarkers. The preclinical and clinical applications of these candidate imaging strategies are divided into three categories: those targeting tumor cells, tumor microenvironment, and tumor angiogenesis. This review endeavors to expand the knowledge of molecular biology of HNSCC and help realizing diagnostic potential of molecular imaging in clinical nuclear medicine.

Radiosynthesis and First Preclinical Evaluation of the Novel 11C-Labeled FAP Inhibitor 11C-FAPI: A Comparative Study of 11C-FAPIs and (68Ga) Ga-DOTA-FAPI-04 in a High–FAP-Expression Mouse Model

Purpose: ⁶⁸Ga-labeled fibroblast activation protein inhibitors, such as [⁶⁸Ga]Ga-DOTA-FAPI-04 and [⁶⁸Ga]Ga-DOTA-FAPI-46, have been successfully applied in positron emission tomography imaging of various tumor types. To broaden the PET tracers of different positron nuclides for imaging studies of FAP-dependent diseases, we herein report the radiosynthesis and preclinical evaluation of two ¹¹C-labeled FAP inhibitors, ¹¹C-RJ1101 and ¹¹C-RJ1102. Methods: Two phenolic hydroxyl precursors based on a quinoline amide core coupled with a 2-cyanopyrrolidine moiety were coupled with [¹¹C]CH₃I to synthesize ¹¹C-RJ1101 and ¹¹C-RJ1102. In vivo small-animal PET and biological distribution studies of ¹¹C-RJ1101 and ¹¹C-RJ1102 compared to [⁶⁸Ga]Ga-DOTA-FAPI-04 were conducted in nude mice bearing U87MG tumor xenografts at 30, 60, and 90min, respectively. Results: ¹¹C-RJ1101 and ¹¹C-RJ1102 were synthesized in over 15% radiochemical yields, with specific activities of 67 GBq/μmol and 34 GBq/μmol, respectively, at the end of synthesis and radiochemical purities greater than 99%. In U87MG tumor xenograft PET studies, the three tracers experienced higher specific uptake at the tumor site. However, because of significant differences in metabolism and clearance, [⁶⁸Ga]Ga-DOTA-FAPI-04 experienced high uptake in the kidney, whereas ¹¹C-RJ1101 and ¹¹C-RJ1102 showed high uptake in the liver and intestine. Biodistribution studies revealed significant hepatobiliary excretion of ¹¹C-RJ1101 and ¹¹C-RJ1102. 11C-RJ1102 showed higher specific tumor uptake in U87MG xenografts (1.71 ± 0.08% injected dose per Gram of tissue [ID/g]) than ¹¹C-RJ1101 (1.34 ± 0.10%ID/g) and [⁶⁸Ga]Ga-DOTA-FAPI-04 (1.29 ± 0.04%ID/g) after 30 min p. i. In orthotopic glioma models, the uptake values were 0.07 ± 0.03% ([⁶⁸Ga]Ga-DOTA-FAPI-04) and 0.16 ± 0.03% (¹¹C-RJ1102), respectively. Conclusion: ¹¹C-RJ1101 and ¹¹C-RJ1102 are interesting candidates for translation to the clinic, taking advantage of the shorter half-life and physical imaging properties of C-11.

Development of Fibroblast Activation Protein Inhibitor-Based Dimeric Radiotracers with Improved Tumor Retention and Antitumor Efficacy

Fibroblast activation protein (FAP), a fundamental component of the tumor stroma, is overexpressed in cancer-associated fibroblasts (CAFs). As a promising theranostic probe, we evaluated whether the FAP inhibitor (FAPI) dimer (DOTA-2P[FAPI]₂) is more effective than its monomeric analogs for FAP-targeted radionuclide therapy. [⁶⁸Ga]Ga/[¹⁷⁷Lu]Lu-DOTA-2P(FAPI)₂ were assayed in a stability study, small-animal positron emission tomography (PET) and single-photon emission computed tomography (SPECT), biodistribution, and radionuclide therapy to comprehensively evaluate their preclinical pharmacokinetics. The pharmacokinetics of [⁶⁸Ga]Ga-DOTA-2P(FAPI)₂ and [¹⁷⁷Lu]Lu-DOTA-2P(FAPI)₂ were determined in FAP-positive hepatocellular carcinoma patient-derived xenografts (PDXs) and HT-1080-FAP cell-derived xenografts (CDXs). [⁶⁸Ga]Ga-DOTA-2P(FAPI)₂ and [¹⁷⁷Lu]Lu-DOTA-2P(FAPI)₂ were stable in phosphate-buffered saline for 4 h. The tumor retention of [⁶⁸Ga]Ga-DOTA-2P(FAPI)₂ was better than that of [⁶⁸Ga]Ga-FAPI-46 in HT-1080-FAP CDXs, while healthy organs showed low tracer uptake and fast body clearance. In single-photon emission computed tomography, [¹⁷⁷Lu]Lu-DOTA-2P(FAPI)₂ showed a higher uptake and longer retention for tumors in both PDXs and CDXs from 1-48 h. [¹⁷⁷Lu]Lu-DOTA-2P(FAPI)₂ showed the best inhibition of tumor growth in PDXs and CDXs. DOTA-2P(FAPI)₂ has increased tumor uptake and retention properties compared to FAPI-46, which significantly improves the use of FAPI-based vectors for PET imaging and radionuclide therapy. [¹⁷⁷Lu]Lu-DOTA-2P(FAPI)₂ may be safe and effective for the treatment of FAP-positive malignant tumors.