68Ga-FAPI-04 PET/CT in Non-Small Cell Lung Cancer: Accurate Evaluation of Lymph Node Metastasis and Correlation with Fibroblast Activation Protein Expression

Fibroblast activation protein (FAP) is a promising diagnostic and therapeutic target in various solid tumors. This study aimed to assess the diagnostic efficiency of 68Ga-labeled FAP inhibitor (FAPI)-04 PET/CT for detecting lymph node metastasis in non-small cell lung cancer (NSCLC) and to investigate the correlation between tumor 68Ga-FAPI-04 uptake and FAP expression. Methods: We retrospectively enrolled 136 participants with suspected or biopsy-confirmed NSCLC who underwent 68Ga-FAPI-04 PET/CT for initial staging. The diagnostic performance of 68Ga-FAPI-04 for the detection of NSCLC was evaluated. The final histopathology or typical imaging features were used as the reference standard. The SUVmax and SUVmean, 68Ga-FAPI-avid tumor volume (FTV), and total lesion FAP expression (TLF) were measured and calculated. FAP immunostaining of tissue specimens was performed. The correlation between 68Ga-FAPI-04 uptake and FAP expression was assessed using the Spearman correlation coefficient. Results: Ninety-one participants (median age, 65 y [interquartile range, 58-70 y]; 69 men) with NSCLC were finally analyzed. In lesion-based analysis, the diagnostic sensitivity and positive predictive value of 68Ga-FAPI-04 PET/CT for detection of the primary tumor were 96.70% (88/91) and 100% (88/88), respectively. In station-based analysis, the diagnostic sensitivity, specificity, and accuracy for the detection of lymph node metastasis were 72.00% (18/25), 93.10% (108/116), and 89.36% (126/141), respectively. Tumor 68Ga-FAPI-04 uptake (SUVmax, SUVmean, FTV, and TLF) correlated positively with FAP expression (r = 0.470, 0.477, 0.582, and 0.608, respectively; all P ≤ 0.001). The volume parameters FTV and TLF correlated strongly with FAP expression in 31 surgical specimens (r = 0.700 and 0.770, respectively; both P < 0.001). Conclusion: 68Ga-FAPI-04 PET/CT had excellent diagnostic efficiency for detecting lymph node metastasis, and 68Ga-FAPI-04 uptake showed a close association with FAP expression in participants with NSCLC.

Head to head comparison of 68Ga-DOTA-FAPI-04 vs 18F-FDG PET/CT in the evaluation of primary extrapulmonary tumors in the chest

OBJECTIVE

We conducted a prospective study using 18F-flurodeoxyglucose (18F-FDG) and 68Ga-DOTA-FAPI-04 (fibroblast-activation protein inhibitor, 68Ga-FAPI) PET/CT to diagnose, differentiate, and stage primary extrapulmonary tumors of the thorax.

METHODS

Fifty-four participants were undergoing 18F-FDG and 68Ga-FAPI PET/CT and divided into the benign, intermediate, and malignant based on pathology. The maximum standardized uptake value (SUVmax), the tumor-to-blood pool ratio, and tumor-to-liver ratio were compared for primary tumors, lymph nodes, and metastases between the two modalities by two independent samples t tests. One-way ANOVA was used to compare the uptake of 18F-FDG or 68Ga-FAPI among the three groups.

RESULTS

Fifty-four participants were confirmed to have 71 primary lesions, 56 metastatic lymph nodes, and 43 metastatic lesions. 18F-FDG PET/CT could both effectively distinguish malignant lesions from non-malignant lesions, accuracies of 87.32% (p < 0.001). 68Ga-FAPI PET/CT effectively differentiated benign lesions from the non-benign, accuracy being 91.55% (p < 0.001). The accuracies of 18F-FDG and 68Ga-FAPI for detecting lymph node metastasis were 77.22% (61/79) and 87.34% (69/79) (p = 0.096). The uptake of 68Ga-FAPI in metastatic lymph nodes was significantly higher than that of the nonmetastatic (p < 0.001). The detection rate of 68Ga-FAPI PET/CT for metastatic lesions was significantly higher than that of 18F-FDG, 100% (43/43) vs. 53.49% (23/43) (p < 0.001). Compared with 18F-FDG PET/CT, 68Ga-FAPI PET/CT changed the treatment strategy of 7.4% (4/54) participants.

CONCLUSION

68Ga-FAPI PET/CT is valuable in the diagnosis and differentiation of primary extrapulmonary tumors and superior to 18F-FDG PET/CT for evaluating lymph node and distant metastasis.

CLINICAL RELEVANCE STATEMENT

The application of 68Ga-FAPI PET/CT in primary extrapulmonary chest tumors is valuable, which is reflected in diagnosis, differentiation and exploration of lymph node metastasis and distant metastasis.

KEY POINTS

• 68Ga-FAPI PET/CT is valuable in the diagnosis, differentiation, and staging of primary extrapulmonary tumors. • 68Ga-FAPI PET/CT is superior to 18 F-FDG PET/CT for evaluating lymph node and distant metastasis.

Case report: diagnosis and treatment of advanced high-grade serous ovarian carcinoma aided by 68Ga-FAPI PET/MR scan

High-grade serous ovarian cancer (HGSOC) is the most common type of epithelial ovarian cancer with insidious onset, rapid growth, and invasive spread. Here, we reported the diagnosis and treatment of a 53-year-old patient with a history of hysterectomy aided by the 68Ga-FAPI PET/MR scan. The patient was first presented to the local hospital with a lump on the left side of the neck with a biopsy suggesting metastatic cancer. Pelvic ultrasonography revealed two irregular masses. After admission, tumor markers, pathology consultation of the biopsy, and the 68Ga-FAPI PET/MR scan were administered. The biopsy of the lump suggested poorly differentiated adenocarcinoma and CA125 was elevated at 530.6 U/ml. The 68Ga-FAPI PET/MR scan showed several abnormal lymph nodes and two soft tissue masses with borders of dispersed restriction displaying internally uneven signals depicted by slightly elongated T1 and T2 signals within the pelvic cavity suggesting that pelvic mass could be the primary lesion. The patient received cytoreductive surgery including bilateral adnexectomy, omentectomy, and appendectomy. Post-surgical pathology suggested left and right HGSOC with left fallopian tube invasion. The patient completed six courses of first-line chemotherapy and remained progression-free for 14 months up to date. To conclude, 68Ga-FAPI PET/MR aids in primary tumor determination and tumor burden assessment and provides a guide for the management of late-stage HGSOC patients.

Iliopsoas fibrosis after revision of total hip arthroplasty revealed by 68Ga-FAPI PET/CT: a case report

Background

Total hip arthroplasty (THA) is a well-established surgical procedure that has been extensively validated to alleviate pain, enhance joint function, improve the ability to perform daily activities, and enhance overall quality of life. However, this procedure is associated with certain complications, among which skeletal muscle fibrosis is a frequently overlooked but significant complication that can lead to persistent pain. Currently, there is no effective method for diagnosing skeletal muscle fibrosis following total hip arthroplasty.

Case report

We report a 75-year-old male patient who complained of left groin pain after revision total hip arthroplasty. Serological examinations, X-rays, and bone scan results were all normal. However, during the 68Ga-FAPI PET/CT examination, we observed significant radiotracer uptake along the iliopsoas muscle. This abnormal uptake pattern suggested potential biological activity in this specific area. Combined with physical examination, the patient was diagnosed with iliopsoas fibrosis.

Conclusions

The presented images indicated that the uptake pattern was an important indicator for diagnosis, and the prospect of fibroblast activation protein in the diagnosis of skeletal muscle fibrosis has shown certain application value.

Hepatic perivascular epithelioid cell tumor resembling hepatic adenoma and hepatocellular carcinoma on preoperative imaging: a case report

Perivascular epithelioid cell tumor (PEComa), an uncommon mesenchymal neoplasm, arises from specialized perivascular epithelioid cells exhibiting distinct features of smooth muscle and melanocytic differentiation with unpredictable behavior. PEComa tends to occur more commonly in the uterus and kidneys; its occurrence in the liver is exceedingly rare. We presented a case of a 29-year-old woman with hepatic PEComa and evaluated the tumor with MRI, integrated 18F-fluorodeoxyglucose (FDG), and 68Ga-fibroblast activation protein inhibitor (FAPI) PET/CT scans at presentation. The patient had a history of intermittent utilization of oral contraceptive drugs for several years. An abdominal ultrasound in a physical examination from an outside institution revealed a mass in the liver. A contrast-enhanced abdominal MRI revealed restricted diffusion on diffusion-weighted imaging (DWI) and rapid contrast enhancement and washout patterns in the hepatic lesion, suggesting hepatic adenoma (HA) or hepatocellular carcinoma (HCC). Further assessment was carried out using 18F-FDG and 68Ga-FAPI PET/CT scans. The hepatic lesion was non-FDG avid, whereas increased tracer uptake was observed on the 68Ga-FAPI PET/CT. Subsequently, laparoscopic partial resection of liver segment V was performed. Immunohistochemical analyses demonstrated positive staining for HMB45, Melan-A, and SMA while showing negative results for AFP, glypican-3, hepatocyte, and arginase-1. The results were indicative of a hepatic PEComa diagnosis based on these findings. We also review the current literature on the clinical characteristics, pathological features, and challenges in the diagnosis of hepatic PEComa.

Case Report: A case report of myocardial fibrosis activation assessment after unstable angina using 68Ga-FAPI-04 PET/CT

Myocardial ischemia may induce myocardial fibrosis, a condition that progressively leads to ventricular remodeling, heightening the risk of heart failure. The timely detection of myocardial fibrosis is crucial for intervention and improved outcomes. 68Ga-FAPI-04 PET/CT shows promise in assessing fibroblast activation in patients with early myocardial infarction characterized by prolonged myocardial ischemia. However, there is a notable absence of data regarding patients with short-term myocardial ischemia, such as those experiencing unstable angina (UA). In this report, we evaluated a 49-year-old male with UA and severe stenosis in multiple coronary arteries using 68Ga-FAPI-04 PET/CT. The results demonstrated tracer-specific uptake (SUVmax = 4.6) in the left anterior descending artery (LAD) territory, consistent with myocardial anterior wall ischemia indicated by the electrocardiogram. Following vascular recanalization therapy and regular medication treatment, the patient remained free of angina recurrence. A subsequent review at 2 months revealed a significant reduction in myocardial tracer uptake (SUVmax = 1.8). This case illustrates the validity of 68Ga-FAPI-04 PET/CT in assessing the extent of early myocardial fibroblast activation in patients with UA. This approach offers valuable insights for early detection and visual evidence, providing information on disease progression and treatment response.

68Ga-Labeled Fibroblast Activation Protein Inhibitor PET/CT for the Early and Late Prediction of Pathologic Response to Neoadjuvant Chemotherapy in Breast Cancer Patients: A Prospective Study

68Ga-labeled fibroblast activation protein inhibitor (68Ga-FAPI) PET/CT has demonstrated promising clinical results, with a higher SUVmax and tumor-to-background ratio (TBR) in breast cancer (BC) patients than 18F-FDG PET/CT. Here, we aimed to evaluate the suitability of 68Ga-FAPI PET/CT for the early and late prediction of the pathologic response to neoadjuvant chemotherapy (NAC) in BC. Methods: Twenty-two consecutive patients with newly diagnosed BC and an indication for NAC were prospectively included. All patients underwent standard chemotherapy and 68Ga-FAPI PET/CT at baseline, after 2 cycles of NAC (PET2), and 1 wk before surgery (PET3). SUVmax was measured in the primary tumor region and positive regional lymph nodes. The expression of fibroblast activation protein in the primary lesion was analyzed by immunohistochemistry. Results: Seven patients (31.8%) achieved a pathologic complete response (pCR), and 15 (68.2%) had residual tumors. Thirteen patients (59.1%) showed concentric withdrawal of the primary tumor, and 9 (40.9%) showed diffuse withdrawal. Between PET2 and PET3, the ΔSUVmax of the primary tumor (R 2 = 0.822; P = 0.001) and metastatic lymph nodes (R 2 = 0.645; P = 0.002) were significantly correlated. The absolute values of SUVmax and TBR at PET2 and PET3 were lower in patients with pCR than in those without pCR (P < 0.05). Moreover, a larger ΔSUVmax at any time point was strongly associated with pCR (P < 0.05). Similar downward trends in SUVmax, TBR, and ΔSUVmax were observed in the pattern of primary tumor reduction. For predicting pCR, the optimal cutoff values for ΔSUVmax after 2 chemotherapy cycles, ΔSUVmax before surgery, TBR after 2 chemotherapy cycles, and TBR before surgery of the primary tumor were 3.4 (area under the curve [AUC], 0.890), 1.1 (AUC, 0.978), -63.8% (AUC, 0.879), -90.8% (AUC, 0.978), 7.6 (AUC, 0.848), and 1.4 (AUC, 0.971), respectively. Immunohistochemistry showed that the SUVmax and TBR of 68Ga-FAPI PET/CT were positively correlated with fibroblast activation protein expression (P < 0.001 for both). Conclusion: Assessment of early changes in 68Ga-FAPI uptake during NAC by 68Ga-FAPI PET/CT can predict pCR and primary tumor concentric withdrawal in BC patients. 68Ga-FAPI PET/CT has great potential for the early and late prediction of the pathologic response to NAC in BC.

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.

Pneumonia with Intense 68Ga-FAPI Uptake Mimicking Metastasis on 68Ga-FAPI PET/CT in a Patient with Rectal Cancer

A 70-year-old man with newly diagnosed rectum adenocarcinoma was referred to 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) for staging, and 68Ga-fibroblast activation protein inhibitor (FAPI)-04 PET/CT for ongoing trial. Both 18F-FDG PET/CT and 68Ga-FAPI-04 PET/CT showed intense uptake in the primary rectal tumor, and also in nodular areas in the right lung. Due to intense 68Ga-FAPI-04 and 18F-FDG uptake, the lung lesions were considered as metastases. However the lesions were reduced in size on CT after 20 days antibiotherapy and diagnosed as pneumonia.

Comparison of Baseline 68Ga-FAPI and 18F-FDG PET/CT for Prediction of Response and Clinical Outcome in Patients with Unresectable Hepatocellular Carcinoma Treated with PD-1 Inhibitor and Lenvatinib

Fibroblast activation protein contributes to immunosuppression and resistance to immunotherapies. This study aimed to compare baseline 68Ga-labeled fibroblast activation protein inhibitor (68Ga-FAPI) PET/CT and 18F-FDG PET/CT in response and survival prediction in unresectable hepatocellular carcinoma (uHCC) patients treated with the combination of programmed cell death 1 (PD-1) inhibitor and lenvatinib. Methods: In this prospective cohort study, 22 patients with uHCC who underwent baseline 18F-FDG and 68Ga-FAPI PET/CT and soon began taking a combination of PD-1 inhibitor and lenvatinib were recruited. Semiquantitative indices of baseline PET/CT were measured as 18F-FDG SUVmax, metabolic tumor volume, total lesion glycolysis, 68Ga-FAPI SUVmax, 68Ga-FAPI-avid tumor volume (FTV), and total lesion fibroblast activation protein expression (TLF). The primary endpoint was durable or nondurable clinical benefit after treatment, and the secondary endpoints were progression-free survival (PFS) and overall survival (OS). Results: The overall response rate of the combination therapy was 41% (9/22). Fifty percent of patients had durable clinical benefit. Median PFS and OS were 4.8 and 14.4 mo, respectively. Patients with nondurable clinical benefit showed a significantly higher FTV and TLF than those with durable clinical benefit, whereas 18F-FDG parameters overlapped. A higher 68Ga-FAPI-avid tumor burden (FTV > 230.46 cm3 or TLF > 961.74 SUVbody weight⋅cm3) predicted both shorter PFS (4.0 vs. 13.5 mo, P = 0.016) and shorter OS (7.8 mo vs. not reached, P = 0.030). Patients with a higher metabolic tumor burden (metabolic tumor volume > 206.80 cm3 or total lesion glycolysis > 693.53 SUVbody weight⋅cm3) showed a shorter OS although the difference did not reach statistical significance (P = 0.085). In multivariate analysis, a higher 68Ga-FAPI-avid tumor burden (hazard ratio [HR], 3.88 [95% CI, 1.26-12.01]; P = 0.020) and macrovascular invasion (HR, 4.00 [95% CI, 1.06-15.14]; P = 0.039) independently predicted a shorter PFS, whereas a higher 68Ga-FAPI-avid tumor burden (HR, 5.92 [95% CI, 1.19-29.42]; P = 0.035) and bone metastases (HR, 5.88 [95% CI, 1.33-25.93]; P = 0.022) independently predicted a shorter OS. Conclusion: Volumetric indices on baseline 68Ga-FAPI PET/CT were potentially independent prognostic factors to predict durable clinical benefit, PFS, and OS in uHCC patients treated with a combination of PD-1 and lenvatinib. Baseline 68Ga-FAPI PET/CT may facilitate uHCC patient selection before combination therapy.

68Ga-FAPI-04 PET for Surveillance of Anastomotic Recurrence in Postoperative Patients with Gastrointestinal Cancer: a Comparative Study with 18F-FDG PET

PURPOSE

This study aims to compare the diagnostic efficacy of 68Ga-FAPI-04 PET and 18F-FDG PET for detecting anastomotic recurrence in postoperative patients with gastrointestinal cancer, and to characterize the signal pattern over time at surgical wounds on both PET imaging.

METHODS

Gastrointestinal cancer patients who planned to 68Ga-FAPI-04 and 18F-FDG PET/CT imaging for postoperative surveillance were involved. The SUVmax at surgical wounds were assessed. Endoscopic pathology confirmed anastomotic recurrence or it was ruled out by imaging and clinical follow-up. The sensitivity, specificity, positive and negative predictive values (PPV and NPV), and accuracy of the two PET imaging in detecting anastomotic recurrence were compared. Relationships between tracer uptake at surgical wounds and postoperative time were also analyzed.

RESULTS

Compared with non-recurrent patients, the recurrent patients exhibited a significantly higher anastomotic SUVmax on 68Ga-FAPI-04 PET (SUVmax: 9.92 ± 4.36 vs. 2.81 ± 1.86, P = 0.002). Sensitivity, specificity, PPV, NPV, and accuracy of detecting anastomotic recurrence were 100.0%, 87.3%, 41.7%, 100.0%, and 88.3% for 68Ga-FAPI-04 PET, and 60.0%, 81.8%, 23.1%, 95.7%, and 80.0% for 18F-FDG PET, respectively. Although 68Ga-FAPI-04 PET signal at surgical wounds showed a slight trend to decrease with time, no statistical difference was observed over months post-surgery (P > 0.05).

CONCLUSIONS

Both tracers displayed high NPVs in identifying anastomotic recurrence with a higher sensitivity to 68Ga-FAPI-04. Tracer uptake at anastomotic sites does not decrease significantly over time, which results in low PPVs for both PET. Therefore, it is difficult to differentiate anastomotic recurrence from inflammation on either PET imaging.

Comparison of 18F-FDG PET/CT and 68Ga-FAPI in Spindle Cell Rhabdomyosarcoma

We report a rare case of spindle cell rhabdomyosarcoma. Sarcomas generally exhibit an abnormal increased FDG uptake on 18F-FDG PET/CT imaging, while spindle cell rhabdosarcomas exhibits a significantly increased lesion uptake on 68Ga FAPI PET/CT imaging compared to 18F-FDG. This case suggests that 68Ga-FAPI PET/CT has potential value in evaluating spindle cell rhabdomyosarcoma.

Performance of 68Ga-Labeled Fibroblast Activation Protein Inhibitor PET/CT in Evaluation of Erdheim-Chester Disease: A Comparison with 18F-FDG PET/CT

Erdheim-Chester disease (ECD) involves multiple organs and tissues and has diverse manifestations, which makes it difficult to distinguish lesions caused by ECD from those caused by other diseases. Variable degrees of fibrosis are present in ECD. Therefore, we conducted a prospective cohort study to explore the ability of 68Ga fibroblast activation protein inhibitor (68Ga-FAPI) PET/CT to detect lesions in ECD patients. Methods: Fourteen patients diagnosed with ECD, as confirmed by histology, were included in this study. For every patient, 68Ga-FAPI PET/CT and 18F-FDG PET/CT were conducted within 1 wk. The positive rate and SUVmax of the lesions in the involved organs were compared between the examinations. Results: The most commonly involved organs were bone (100%), heart (57.1%), lung (57.1%), kidney (42.9%), and peritoneum or omentum (35.7%); other common manifestations were intracranial infiltration (50%) and cutaneous infiltration (35.7%). 68Ga-FAPI PET/CT detected 64 of 67 lesions in 14 patients, whereas 18F-FDG PET/CT detected 51 of 67 lesions (P = 0.004). The SUVmax for 68Ga-FAPI PET/CT was significantly higher than the SUVmax for 18F-FDG PET/CT of the heart (4.9 ± 2.4 vs. 2.8 ± 1.2, respectively; P = 0.050), lung or pleura (6.8 ± 4.9 vs. 3.1 ± 1.3, respectively; P = 0.025), peritoneum or omentum (5.7 ± 3.6 vs. 2.8 ± 1.7, respectively; P = 0.032), and kidney or perinephric infiltration (4.9 ± 1.2 vs. 2.9 ± 1.1, respectively; P = 0.009). Conclusion: The detectivity of 68Ga-FAPI PET/CT is superior to that of 18F-FDG PET/CT. Moreover, 68Ga-FAPI PET/CT has a better image contrast and higher SUVmax for lesions in multiple organs including the heart, lungs, peritoneum, and kidneys. 68Ga-FAPI PET/CT is a promising tool to assess pathologic features and disease extent in ECD patients.

Evaluation of FAPI PET imaging in gastric cancer: a systematic review and meta-analysis

Purpose: Recent studies suggest that 68Ga-FAPI PET/CT demonstrated superiority over 18F-FDG PET/CT in the evaluation of various cancer types, especially in gastric cancer (GC). By comprehensively reviewing and analysing the differences between 68Ga-FAPI and 18F-FDG in GC, some evidence is provided to foster the broader clinical application of FAPI PET imaging. Methods: In this review, studies published up to July 3, 2023, that employed radionuclide labelled FAPI as a diagnostic radiotracer for PET in GC were analysed. These studies were sourced from both the PubMed and Web of Science databases. Our statistical analysis involved a bivariate meta-analysis of the diagnostic data and a meta-analysis of the quantitative metrics. These were performed using R language. Results: The meta-analysis included 14 studies, with 527 patients, of which 358 were diagnosed with GC. Overall, 68Ga-FAPI showed higher pooled sensitivity (0.84 [95% CI 0.67-0.94] vs. 0.46 [95% CI 0.32-0.60]), specificity (0.91 [95% CI 0.76-0.98] vs. 0.88 [95% CI 0.74-0.96]) and area under the curve (AUC) (0.92 [95% CI 0.77-0.98] vs. 0.52 [95% CI 0.38-0.86]) than 18F-FDG. The evidence showed superior pooled sensitivities of 68Ga-FAPI PET over 18F-FDG for primary tumours, local recurrence, lymph node metastases, distant metastases, and peritoneal metastases. Furthermore, 68Ga-FAPI PET provided higher maximum standardized uptake value (SUVmax) and tumour-to-background ratios (TBR). For bone metastases, while 68Ga-FAPI PET demonstrated slightly lower patient-based pooled sensitivity (0.93 vs. 1.00), it significantly outperformed 18F-FDG in the lesion-based analysis (0.95 vs. 0.65). However, SUVmax (mean difference [MD] 1.79 [95% CI -3.87-7.45]) and TBR (MD 5.01 [95% CI -0.78-10.80]) of bone metastases showed no significant difference between 68Ga-FAPI PET/CT and 18F-FDG PET/CT. Conclusion: Compared with 18F-FDG, 68Ga-FAPI PET imaging showed improved diagnostic accuracy in the evaluation of GC. It can be effectively applied to the early diagnosis, initial staging, and detection of recurrence/metastases of GC. 68Ga-FAPI may have the potential of replacing 18F-FDG in GC in future applications.

68Ga-FAPI PET/CT for molecular assessment of fibroblast activation in right heart in pulmonary arterial hypertension: a single-center, pilot study

BACKGROUND

Positron emission tomography (PET) imaging with radiolabeled fibroblasts activation protein inhibitor (FAPI) provides the opportunity to directly visualize fibrosis. This study aimed to investigate the feasibility of 68Ga-FAPI PET imaging in assessing right ventricular (RV) fibrotic remodeling and the relationship between FAPI uptake with parameters of pulmonary hemodynamics and cardiac function in pulmonary arterial hypertension (PAH) patients.

METHODS

In this pilot study, sixteen PAH patients were enrolled to participate in cardiac 68Ga-FAPI PET/CT imaging. All patients underwent right heart catheterization and echocardiography for assessment of pulmonary hemodynamics and cardiac function within seven days. Cardiac FAPI uptake was visually assessed and quantified as maximum standardized uptake value (SUVmax).

RESULTS

Twelve PAH patients exhibited FAPI uptake in RV free wall and insertion point. The overall activity of FAPI accumulated in the RV free wall (SUVmax: 2.5 ± 1.8, P < 0.001) and insertion point (SUVmax:2.5 ± 1.7, P < 0.001) was significantly upregulated compared to left ventricle (SUVmax:1.5 ± 0.5). Patients with tricuspid annular plane systolic excursion (TAPSE) < 17 mm presented significantly higher uptake than those with TAPSE ≥ 17 mm in both RV free wall (SUVmax: 3.4 ± 1.9 vs 1.7 ± 1.1, P = 0.010) and insertion point (SUVmax: 3.4 ± 1.9 vs 1.6 ± 0.7, P = 0.028), indicating RV uptake of FAPI was associated with RV dysfunction. There was significant positive correlation between cardiac FAPI uptake and total pulmonary resistance and the level of N-terminal pro b-type natriuretic peptide.

CONCLUSIONS

68Ga-FAPI PET/CT imaging is feasible to directly visualize fibrotic remodeling of RV in patients with PAH.

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.

68Ga-FAPI PET visualize heart failure: from mechanism to clinic

PURPOSE

Heart failure (HF) is a chronic progressive clinical syndrome associated with structural and/or functional heart abnormalities. Active fibroblasts and ventricular remodelling play an essential role in HF progression. 68Ga-labelled fibroblast activation protein (FAP) inhibitor (68Ga-FAPI) binds to FAP. This study aimed to examine the feasibility of using 68Ga-FAPI positron emission tomography (PET)/computed tomography (CT) to visualize changes in cardiac fibrosis and function over time in the HF setting.

METHODS

After establishing an isoproterenol (ISO)-induced HF rat model (14 consecutive days of intraperitoneal ISO injections), echocardiography and 68Ga-FAPI PET/CT were performed weekly in experimental and control groups. Rat hearts were examined weekly for biodistribution analysis; autoradiography; and haematoxylin and eosin, FAP immunofluorescence and Masson's trichrome staining analysis. Rat blood was sampled weekly for enzyme-linked immunosorbent assay analysis of various plasma indicators. A preliminary clinical study was also performed in seven HF patients who underwent both 13N-amino (NH3) perfusion and 68Ga-FAPI cardiac PET imaging.

RESULTS

In the animal experiments, myocardial 68Ga-FAPI uptake, expression of FAP and myocardial contractility peaked on day 7 after the initial ISO injection. Only slight fibrotic changes were observed on histopathological examination. 68Ga-FAPI uptake and ventricular wall motion decreased over time as cardiac fibrosis and degree of myocardial injury gradually increased. In the human HF patient study, 68Ga-FAPI PET imaging identified varying degrees of 68Ga-FAPI uptake in the myocardium that did not precisely match with 13N-NH3 myocardial perfusion.

CONCLUSION

As HF progresses, 68Ga-FAPI uptake is high in the early stages and then gradually decreases. Although preliminary, our findings suggest that 68Ga-FAPI PET can be used to demonstrate active myocardial fibrosis. Active myocardial FAP expression is followed by myocardial remodelling and fibrosis. Detection of early active FAP expression may assist treatment decision making in HF patients.

CLINICAL TRIAL REGISTRATION

NCT04982458.

Localization of Pyelonephritis by 68Ga-FAPI PET CT

Fibroblast activation protein inhibitor (FAPI) is a quinoline-based membrane-bound glycoprotein enzyme that is not usually expressed in normal adult tissues, except for the myometrium and sometimes the pancreas. Its expression increases in inflammation and cancer-associated fibroblasts (CAF). As FAPI is a new molecule with a promising future, presented here is a case report of uncontrolled diabetes with abdominal pain that showed features of inflammation in the kidneys. The patient had been previously diagnosed with maxillary sinusitis with Aspergillus niger and was receiving antibiotic treatment. The urine culture performed later was negative, and the patient was referred for ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) PET Computed Tomography (CT) to look for the focus of infection. However, as blood sugar was 500 mg/dL, ¹⁸F-FDG PET CT could not be performed. Therefore, ⁶⁸Ga-FAPI PET CT was run instead after taking the patient's written informed consent. The ^99mTc-dimercaptosuccinic acid scan performed on another day confirmed the presence of pyelonephritis bilaterally. In situations where FDG cannot be used because of hyperglycemia, ⁶⁸Ga-FAPI PET CT scan may be considered an alternative in the detection of occult infection or inflammation, as demonstrated in this case report.

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.

Different uptake patterns of 68Ga-FAPI in aseptic loosening and periprosthetic joint infection of hip arthroplasty: A case series and literature review

Background

The diagnosis of a periprosthetic joint infection (PJI) is always a difficult point in research on the surgery of joints. The current diagnostic criteria include a comprehensive analysis of multiple tests; however, there are no effective visual examinations yet that can differentiate between aseptic loosening and the PJI.

Case presentation

This case report describes four patients with symptomatic total hip arthroplasty (THA), two cases of loosening and two cases of infection. Although the four cases were correctly diagnosed by the tissue culture, preoperative tests and pathological examination could not effectively distinguish an infection from a non-infection. Based on a preclinical study and theoretical feasibility, gallium-68 (⁶⁸Ga)-labeled fibroblast activation protein inhibitor positron emission tomography/computed tomography (⁶⁸Ga-FAPI PET/CT) was performed. Through ⁶⁸Ga-FAPI PET/CT scanning, not only were the causes diagnosed correctly but the lesions were also located.

Conclusion

When the lesion is located between the bone and the prosthesis, ⁶⁸Ga-FAPI PET/CT could differentiate aseptic loosening from periprosthetic joint infection (PJI). ⁶⁸Ga-FAPI PET/CT has clear advantages over routine examinations and has a prospective application in detecting PJI.

Clinical Significance of Diffusely Increased Uptake of 68Ga-FAPI in Thyroid Gland

Purpose: To determine the clinical significance of diffuse uptake of ⁶⁸Ga-FAPI in the thyroid.

Methods: From January 2020 to September 2021, all subjects with diffuse thyroid uptake in ⁶⁸Ga-FAPI PET/CT were investigated in our hospital, and compared with the age and sex matched control group. The ⁶⁸Ga-FAPI uptake in the thyroid gland was analyzed semi-quantitatively using the maximum standardized uptake value (SUVmax), and regression analysis was used to analyze the correlation between available serum thyroid stimulating hormone (TSH) and thyroid peroxidase antibody (TPOAb).

Results: Among 815 subjects, 39 subjects were found diffuse FAPI uptake in thyroid gland; 11 subjects refused further examination; a total of 28 subjects were included in the analysis, and 27 subjects were diagnosed with chronic thyroiditis (including 20 subjects with Hashimoto's thyroiditis), 3 subjects with Grave's disease, 3 subjects with only serum TSH elevated, and 1 subject with malignant of thyroid and thyroiditis. The SUVmax of 27 subjects with thyroiditis was 5.75 ± 5.45. No significant correlation was found between the SUVmax and the level of serum TSH (P = 0.389) or TPOAb (P = 0.426).

Conclusion: The incidentally discovered diffusely increased ⁶⁸Ga-FAPI uptake in the thyroid gland is mostly related to chronic lymphocytic (Hashimoto's) thyroiditis. ⁶⁸Ga-FAPI uptake level correlated neither with the degree of hypothyroidism nor with the titer of TPOAb. In addition, immune-related thyroiditis with immune checkpoint inhibitors may be accidentally found on ⁶⁸Ga-FAPI, which may be helpful in facilitate timely intervention.

A Case with 68Ga-FAPI Positive and 18F-FDG Negative Breast Cancer

A female patient diagnosed of infiltrative breast carcinoma using tru-cut biopsy underwent ¹⁸flourine-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT) for staging. The tumor was located in the superior external quadrant of the right breast, and did not exhibit pathological uptake in ¹⁸F-FDG PET/CT. Later, gallium-⁶⁸ (⁶⁸Ga) fibroblast activation protein-specific inhibitor (FAPI)-04 PET/CT imaging was performed and the primary tumor showed intense radiotracer accumulation. This presumes that ⁶⁸Ga-FAPI PET/CT imaging is superior to ¹⁸F-FDG imaging in detecting the primary tumor in breast cancer, thereby suggesting the replacement of FAPI by ¹⁸F-FDG in breast-cancer staging in the future.

Superiority of 68Ga-FAPI PET/CT scan in detecting additional lesions compared to 18FDG PET/CT scan in breast cancer

PURPOSE

We compared the ability of ⁶⁸Ga-FAPI PET//CT with ¹⁸FDG PET/CT imaging techniques to detect additional lesions in breast cancer patients that may affect further chemotherapy options.

METHODS

A total of 48 patients with breast cancer underwent concurrent ⁶⁸Ga-FAPI-04 and ¹⁸FDG PET/CT regardless of whether they had received chemotherapy or not in the last month before imaging. Both modalities were compared according to various parameters: clinical/pathological features, number of lesions detected, activity uptake (SUV_max), and the effect on the evaluation of response to treatment in the post-chemotherapy group.

RESULTS

This retrospective study included 48 patients with breast cancer (mean age 53.3 ± 11.7 years; IDC 89.6%; ILC 10.4%). In the comparison of both modalities, no statistical significance was obtained in terms of the pathological characteristics of the patients. More lesions were demonstrated in all categorized regions in ⁶⁸Ga-FAPI PET/CT imaging with higher uptake values compared to ¹⁸FDG PET/CT in this study. In the treatment response evaluation of the post-chemotherapy group, 12 cases (12/24) who were evaluated as PMR, CMR, or SD according to ¹⁸FDG PET/CT results were later accepted as PD due to newly detected lesions in complementary ⁶⁸Ga-FAPI PET/CT imaging and treatment of patients was managed accordingly by clinicians.

CONCLUSION

It was determined that ⁶⁸Ga-FAPI PET/CT was superior to ¹⁸FDG PET/CT in terms of accuracy and it was thought that ⁶⁸Ga-FAPI PET/CT could be utilized as an additional complementary imaging to ¹⁸FDG PET/CT. Moreover, ⁶⁸Ga-FAPI PET/CT, with its significant theranostic potential, could become a key element in predicting the pathological response of breast cancer patients in further researches.

68Ga-FAPI-04 PET/MR is helpful in differential diagnosis of pancreatitis from pancreatic malignancy compared to 18F-FDG PET/CT: a case report

Introduction

⁶⁸Ga-fibroblast activation protein-specific enzyme inhibitor 04 (FAPI-04) is a radiolabelled molecular agent targeting the inhibitor of fibroblast activation protein (FAP), which is often present in tumor stroma and inflammatory tissue with prominent fibroblast proliferation. FAPI-04 is a promising PET tracer for tumor imaging as well as IgG4-related disease (IgG4-RD).

Case description

We herein present a case where ⁶⁸Ga-FAPI PET/MR helped to diagnose IgG4-RD that involved pancreas and bile duct. A 62-year-old patient suffered from diffusive discomfort at middle upper abdomen and presented brown urine. Blood test revealed abnormal liver function and elevated IgG4 (4.830g/L↑). ¹⁸F-FDG PET showed enlarged uncinate process and dilated bile duct tree. Mild increase of FDG uptake in uncinate process and head of pancreas indicated possible pancreatic malignancy, but the clinical evidence was not sufficient and histology examination was negative. ⁶⁸Ga-FAPI PET revealed prominent increased radioactivity distribution in the entire pancreas and bile duct, suggesting IgG4-RD.

Conclusion

FAPI-04 is not only a good PET imaging tracer for tumors, but also for prominent fibroblast-mediated inflammation. FAPI imaging should be considered when the diagnosis using ¹⁸F-FDG imaging is ambiguous. The presented case illustrates that ⁶⁸Ga-FAPI-04 PET is helpful in improving the differential diagnosis of pancreatitis and pancreatic cancer.

68Ga-DOTA-FAPI-04 PET/MR in the Evaluation of Gastric Carcinomas: Comparison with 18F-FDG PET/CT

We sought to evaluate the performance of ⁶⁸Ga-DOTA-FAPI-04 ( ⁶⁸ Ga-FAPI) PET/MR for the diagnosis of primary tumor and metastatic lesions in patients with gastric carcinomas and to compare the results with those of ¹⁸F-FDG PET/CT. Methods: Twenty patients with histologically proven gastric carcinomas were recruited, and each patient underwent both ¹⁸F-FDG PET/CT and ⁶⁸ Ga-FAPI PET/MR. A visual scoring system was established to compare the detectability of primary tumors and metastases in different organs or regions (the peritoneum, abdominal lymph nodes, supradiaphragmatic lymph nodes, liver, ovary, bone, and other tissues). The original SUV_max and normalized SUV_max (calculated by dividing a lesion's original SUV_max with the SUV_mean of the descending aorta) of selected lesions on both ¹⁸F-FDG PET/CT and ⁶⁸Ga-FAPI PET/MR were measured. Original/normalized SUV_max-FAPI and SUV_max-FDG were compared for patient-based (including a single lesion with the highest activity uptake in each organ/region) and lesion-based (including all lesions [≤5] or the 5 lesions with highest activity [>5]) analyses, respectively. Results: The 20 recruited patients (median age: 56.0 y; range: 29-70 y) included 9 men and 11 women, 14 patients for initial staging and 6 for recurrence detection. ⁶⁸Ga-FAPI PET was superior to ¹⁸F-FDG PET for primary tumor detection (100.00% [14/14] vs. 71.43% [10/14]; P = 0.034), and the former had higher tracer uptake levels (P < 0.05). ⁶⁸Ga-FAPI PET was superior to ¹⁸F-FDG PET in both patient-based and lesion-based evaluation except for the metastatic lesions in supradiaphragmatic lymph nodes and ovaries. Additionally, multiple sequences of MR images were beneficial for the interpretation of hepatic metastases in 3 patients, uterine and rectal metastases in 1 patient, ovarian lesions in 7 patients, and osseous metastases in 2 patients. Conclusion: ⁶⁸Ga-FAPI PET/MR outperformed ¹⁸F-FDG PET/CT in visualizing the primary and most metastatic lesions of gastric cancer and might be a promising method, with the potential of replacing ¹⁸F-FDG PET/CT.

Fibroblast Activation Protein-Targeted PET/CT with 68Ga-FAPI for Imaging IgG4-Related Disease: Comparison to 18F-FDG PET/CT

IgG4-related disease (RD) is characterized by lymphoplasmacytic infiltration enriched in IgG4-positive plasma cells and variable degrees of fibrosis with a characteristic storiform pattern. Since fibrosis is an important feature of IgG4-RD, we performed a prospective cohort study to evaluate the performance of ⁶⁸Ga-fibroblast activation protein inhibitor (FAPI), a recently introduced PET agent targeting fibroblast activation protein, in IgG4-RD. Methods: Twenty-six patients with IgG4-RD were recruited. All patients underwent both ⁶⁸Ga-FAPI and ¹⁸F-FDG PET/CT. The positive rates of the PET/CT scans in the involved organs and the uptake values were compared. Results: In a total of 136 involved organs in the 26 patients, ⁶⁸Ga-FAPI PET/CT additionally detected 18 (13.2%) involved organs in 13 (50.0%) patients, compared with ¹⁸F-FDG PET/CT. ⁶⁸Ga-FAPI PET/CT had a higher positive rate than ¹⁸F-FDG PET/CT in detecting involvement in the pancreas, bile duct/liver, and lacrimal gland. ⁶⁸Ga-FAPI also demonstrated significantly higher uptake than ¹⁸F-FDG in the matched disease in the pancreas, bile duct/liver, and salivary gland (P < 0.01). However, lymph node involvement with flip-flop uptake of ¹⁸F-FDG did not accumulate ⁶⁸Ga-FAPI. Conclusion: ⁶⁸Ga-FAPI might be a promising imaging agent for the assessment of IgG4-RD.