[18F]AlF-NOTA-FAPI-04 PET/CT uptake in metastatic lesions on PET/CT imaging might distinguish different pathological types of lung cancer

Insights into lung cancer diagnosis and clinical management using [18F]F-fibroblast activation protein inhibitor (FAPI)-42 positron emission tomography/computed tomography (PET/CT)

PURPOSE

Accurate diagnosis and staging of lung cancer are critical for optimal clinical management. Fibroblast activation protein inhibitor (FAPI) imaging has emerged as a promising modality with superior detection capabilities for lung cancer. We hypothesized that [1⁸F]FAPI-42 PET/CT would enhance diagnosis, TNM staging, and influence oncologic management in patients with suspected or confirmed lung cancer.

METHODS

In this retrospective study, 155 patients with clinically suspected or confirmed lung cancer underwent both conventional imaging and [1⁸F]FAPI-42 PET/CT scans within a one-week interval, without any intervening treatment. Lesions were visually assessed and categorized to evaluate the diagnostic capability of [18F]FAPI-42 PET/CT. Tracer activity was quantified using maximum standardized uptake values (SUVmax) and tumor-to-background ratios. TNM staging was independently determined by a board-certified radiologist or nuclear medicine physician using both imaging modalities, and discrepancies were assessed. Changes in TNM staging were documented and evaluated for their impact on clinical management.

RESULTS

Of the 155 patients, 99 were evaluated for primary lesion diagnosis and staging. Pathological examination confirmed malignant tumors in 87 patients and benign tumors in 12. The diagnostic sensitivity and positive predictive value of [18F]FAPI-42 PET/CT for detecting primary lung tumors were 96.77% and 92.78%, respectively. Malignant lesions exhibited significantly higher SUVmax compared to benign lesions (5.2 vs. 1.5, P = 0.0002), with an area under the ROC curve of 0.87. In total, 1,556 malignant lesions were identified among patients with lung cancer, and [18F]FAPI-42 PET/CT demonstrated a diagnostic accuracy of 95.50%. However, its sensitivity for detecting adrenal metastases was lower at 33.33%, with a specificity of 100% and an accuracy of 53.85%. The use of [18F]FAPI-42 PET/CT resulted in changes in TNM staging for 46% of patients, leading to upstaging in 58 patients and downstaging in 5. These staging adjustments directly impacted clinical management in 34 patients, prompting modifications in treatment plans.

CONCLUSION

[18F]FAPI-42 PET/CT is a promising modality for lung cancer diagnosis and staging, demonstrating high sensitivity and specificity. Its use significantly altered TNM staging in nearly half of the patients, directly impacting oncologic management and treatment planning. However, its limited sensitivity for detecting adrenal metastases underscores the need for additional imaging techniques.

Imaging pancreatic cancer with [18F]F-AlF-NOTA-FAPI-04 positron emission tomography/computed tomography (PET/CT): distribution patterns and therapeutic implications

AIM

This study aimed to evaluate the diagnostic performance of [18F]F-AlF-NOTA-FAPI-04 positron emission tomography/computed tomography (PET/CT) in pancreatic cancer by comparing its uptake patterns with other tumour types and analysing intrapancreatic heterogeneity. The study also explored possible causes of physiological pancreatic uptake to aid in distinguishing non-malignant uptake from true pathological lesions and improve diagnostic accuracy.

MATERIALS AND METHODS

In this prospective study, 103 treatment-naïve cancer patients (36 pancreatic, 67 nonpancreatic) underwent [18F] AlF-NOTA-FAPI-04 PET/CT. Metabolic tumour volume (MTV), standardised uptake values (SUV), and total lesion Fibroblast Activation Protein (FAP) expression (TLF) were analysed. Hierarchical regression and independent t-tests were applied to assess correlations between imaging features and clinicopathological characteristics.

RESULTS

Pancreatic cancer exhibited significantly higher SUVmax (16.3 ± 4.4 vs 5.0 ± 4.3, P<0.001), SUVmean (6.3 ± 2.3 vs 1.7 ± 1.2, P<0.001), and TLF (321.5 ± 251.3 vs 89.4 ± 62.1, P<0.001) compared to non-pancreatic tumors. Tumours in the pancreatic head/neck region demonstrated greater [68 G]G-FAPI-04 uptake than body/tail lesions (SUVmean: 7.7 ± 3.1 vs 6.3 ± 2.9, P=0.016). TLF correlated positively with tumour size and stage (F = 2.576, P=0.027). Mild to moderate pancreatic uptake was also observed in a subset of patients with hepatocellular carcinoma, partially correlating with elevated alkaline phosphatase (ALP) levels.

CONCLUSION

[18F]F-AlF-NOTA-FAPI-04 PET/CT shows high specificity for pancreatic ductal adenocarcinoma, particularly in head/neck tumours. Physiological or nonspecific pancreatic uptake in nonpancreatic malignancies warrants careful interpretation to avoid misdiagnosis.

Detecting radiation esophagitis using 18F-FAPI-04 PET/CT in patients with LA-ESCC treated with concurrent chemoradiotherapy

PURPOSE

This prospective study examined whether 18F-AlF-NOTA-fibroblast activation protein inhibitor (FAPI)-04 (denoted as 18F-FAPI-04) positron emission tomography/computed tomography (PET/CT) can detect the development and severity of radiation esophagitis (RE) in patients with locally advanced esophageal squamous cell carcinoma (LA-ESCC) treated with concurrent chemoradiotherapy.

MATERIALS AND METHODS

From June 2021 to March 2022, images were collected from LA-ESCC patients who underwent 18F-FAPI-04 PET/CT examinations before and during radiotherapy. The development of RE was evaluated weekly according to Radiation Therapy Oncology Group criterion. The target-to-background ratio in blood (TBRblood) was analyzed at each time point and correlated with the onset and severity of RE. Factors that predicted RE were identified by multivariate logistic analyses.

RESULTS

Thirty patients were evaluated. Significantly higher TBRblood (during radiotherapy, P = 0.003) and change in TBRblood compared with pre-RT (ΔTBRblood, P = 0.002) were observed in patients with RE than patients without RE. Those with grade 3 RE had a significantly higher TBRblood (during radiotherapy, P = 0.003) and ΔTBRblood (P = 0.003) compared with those with RE < grade 3. On multivariate analysis, ΔTBRblood was identified as a significant detection of any grade RE (P = 0.021) and grade 3 RE (P = 0.038).

CONCLUSION

The ΔTBRblood on 18F-FAPI-04 PET/CT may be effective at identifying patients with RE, especially grade 3 RE.

Noninvasive diagnosis and classification of kidney transplantation rejection by 18F-FAPI-04 PET/CT

PURPOSE

Rejection, especially chronic rejection is a key factor influencing the prognosis of kidney transplantation patients. While 18F-fibroblast activation protein inhibitor (FAPI)-04 PET/CT has been widely utilized for diagnosing various diseases, its diagnostic efficacy in kidney transplant rejection remains unexplored.

METHODS

In this study, 24 kidney transplant recipients were prospectively enrolled and divided into a control cohort and a rejection cohort (KTR), which were further classified into acute rejection (AR), mixed rejection (MR), and chronic rejection (CR) subgroups. All patients underwent 18F-FAPI-04 PET/CT and 18F-FDG PET/CT scans, along with immunohistochemical FAP staining and Banff pathological scoring. The maximum and average standardized uptake values (SUVs) of the two imaging methods were calculated.

RESULTS

Compared with the control cohort, the KTR cohort showed significantly higher serum creatinine levels, lower estimated glomerular filtration rates, and lower hemoglobin levels. The SUVmax of 18F-FAPI-04 PET/CT in the allograft kidney cortex (AKC) and allograft kidney biopsy site (AKB) in the KTR cohort was significantly greater than that in the control cohort. The SUVmax of 18F-FDG PET/CT between the two cohorts was significantly different only in the AKC. For the KTR cohort, the SUVmax of 18F-FAPI-04 PET/CT in AKC and AKB was considerably greater than that of 18F-FDG PET/CT (5.5 vs. 2.8 and 3.6 vs. 2.5, respectively; both p < 0.01). In the CR cohort, the SUVmax of 18F-FAPI-04 PET/CT in the AKC, AKB, and allograft kidney medulla (AKM) was significantly greater (7.1, 5.3, and 3.2) than that of 18F-FDG PET/CT (2.5, 2.1 and 1.8) (p = 0.009, 0.009 and 0.016, respectively). The SUVmax of 18F-FAPI-04 PET/CT in AKB increased gradually in the AR, MR, and CR cohorts (2.8 vs. 3.6 vs. 5.3, p = 0.02). The above results were consistent with the SUVavg statistics. The number of FAP-positive stromal cells was different between the control and KTR groups and among the AR, MR, and CR subgroups.

CONCLUSION

18F-FAPI-04 PET/CT outperforms 18F-FDG PET/CT in distinguishing kidney transplant rejection, especially chronic rejection.

Value of [18F]AlF-NOTA-FAPI-04 PET/CT for predicting pathological response and survival in patients with locally advanced pancreatic ductal adenocarcinoma receiving neoadjuvant chemotherapy

OBJECTIVES

This study aimed to evaluate the predictive value of [18F]AlF-NOTA-FAPI-04 PET/CT for pathological response to neoadjuvant chemotherapy (NCT) and prognosis in patients with locally advanced pancreatic ductal adenocarcinoma (LAPDAC).

METHODS

This study included 34 patients with histopathologically and radiologically confirmed LAPDAC who received [18F]AlF-NOTA-FAPI-04 PET/CT scans before NCT. After 4-6 cycles of NCT, these patients underwent radical resection. Pathological response to NCT was assessed by pathological tumor regression grades (TRG) based on the Evans system. PET/CT parameters were evaluated for their association with TRG, recurrence-free survival (RFS) and overall survival (OS) after NCT, including the maximum standardized uptake value (SUVmax), FAPI-avid tumor volume (FTV), total lesion FAP expression (TLF) of primary tumor, total FAPI-avid pancreatic volume (FPV) and total pancreatic FAP expression (TPF) of total pancreas.

RESULTS

Of 34 patients with LAPDAC, 14 patients had a pathologic good response (PGR, Evans III-IV), and 20 patients had a pathologic poor response (PPR, Evans I-II). Both the primary tumor SUVmax, FTV and TLF, and total pancreas FPV and TPF in the PGR groups were significantly lower than those in the PPR groups. Furthermore, SUVmax and TLF were higher in poorly differentiated LAPDAC than in well-moderately differentiated neoplasms. The FTV, TLF, FPV and TPF were closely associated with RFS and OS. On multivariate analysis, patients with FTV > 54.21 and TLF > 290.21 had a worse RFS and OS, respectively (HR = 3.24, P = 0.014 and HR = 3.35, P = 0.019) and OS (HR = 7.35, P = 0.002 and HR = 7.09, P = 0.004) in LAPDAC after NCT.

CONCLUSIONS

The parameters of [18F]AlF-NOTA-FAPI-04 PET/CT had the excellent performance for predicting pathologic TRG after NCT in LAPDAC. FTV and TLF were independent postoperative prognostic factors for RFS and OS for LAPDAC.

Evaluating the diagnostic value of 18F-FAPI-04 PET/CT in various malignant tumors: a head-to-head comparison with 18F-FDG PET/CT

PURPOSE

This study aims to evaluate the diagnostic efficacy of 18F-fibroblast activation protein inhibitor-04 (18F-FAPI-04) PET/CT for various malignant tumors and compare it head-to-head with 18F-FDG PET/CT.

MATERIALS AND METHODS

This single-center, prospective study continuously recruited patients with suspected or confirmed malignant tumors for concurrent 18F-FDG and 18F-FAPI-04 PET/CT scans from April 2022 to October 2023. The pathological diagnosis or clinical follow-up served as the reference standard. The Z-test for two proportions was used to compare the sensitivity, specificity, and accuracy of tumor diagnosis between the two imaging agents. Wilcoxon signed-rank tests were employed to compare the uptake of the two radiotracers and the tumor-to-background ratio (TBR) differences in tumors.

RESULTS

The study involved 15 types of tumors and included 88 patients, comprising 53 males and 39 females, with an average age of 57.7 ± 10.8 years. In patient-based analysis, 18F-FAPI-04 PET/CT demonstrated higher diagnostic accuracy than 18F-FDG PET/CT for both initial staging and restaging patients (77.4% vs 56.6%, p = 0.0389; 94.3% vs 54.3%, p < 0.001), prompting treatment plan adjustments in 17% of restaged patients. The lesion-based analysis revealed comparable diagnostic accuracy of 18F-FAPI-04 PET/CT and 18F-FDG PET/CT for primary tumors (78.9% vs 75.4%, p = 0.8234), while showing superior accuracy for residual/recurrent tumors, lymph node metastases, and distant metastases compared to 18F-FDG PET/CT (100.0% vs 50.0%, p = 0.002; 98.8% vs 86.0%, p < 0.001; 98.3% vs 79.3%, p < 0.001).

CONCLUSION

18F-FAPI-04 PET/CT exhibits higher uptake and TBR in most tumors demonstrating superior diagnostic efficacy for primary lesions, residual/recurrent disease, and metastases compared to 18F-FDG PET/CT, particularly beneficial for restaging post-treatment patients.

[18F]FAPI- 04 PET/CT for pathologic response assessment in pancreatic cancer patients with systemic treatment

PURPOSE

To study the association between [18F]FAPI- 04 uptake on positron emission tomography/computed tomography (PET/CT) and pathologic treatment response (PTR) in patients with pancreatic cancer (PC).

METHODS

We enrolled 59 patients from August 2021, of whom 28 underwent surgical treatment after systemic therapy. The patients were investigated for a correlation between baseline fibroblast activation protein inhibitor (FAPI) uptake and PTR using College of American Pathologists (CAP) scores. The FAPI PET variables include standardised uptake value (SUV)max, SUVmean, metabolic tumour volume (MTV), and total lesion FAP expression (TLF). A PET/CT scan obtained before surgery in 14 patients facilitated assessing changes in FAPI uptake through treatment, and their association with PTR. Multiplex immunohistochemistry (mIHC) analysis identified the FAPI biodistribution in the PC tumours.

RESULTS

The SUVmax correlated positively with FAP expression in PC tissues. However, there was no correlation between baseline variables and the CAP scores. Treatment resulted in remarkably reduced MTV and TLF in all patients. The baseline SUVmax and SUVmean of patients with a good PTR (CAP score ≤ 2) differed from those after treatment (p = 0.001). An FITC-FAPI probe intuitively showed that cancer-associated fibroblasts (CAFs) and tumour cells had a similar FITC-FAPI fluorescence intensity, indicating a negative association between tumour regression and [18F]FAPI- 04 uptake.

CONCLUSION

Greater changes in FAPI uptake through treatment were associated with a better PTR in patients with PC and might be valuable in predicting prolonged survival. These results are clinically meaningful when selecting candidates for conversion surgery during systemic treatment.

[18F]F-FAPI-42 PET dynamic imaging characteristics and multiparametric quantification of lung cancer: an exploratory study using uEXPLORER PET/CT

PURPOSE

To explore the dynamic and parametric characteristics of [18F]F-FAPI-42 PET/CT in lung cancers.

METHODS

Nineteen participants with newly diagnosed lung cancer underwent 60-min dynamic [18F]F-FAPI-42 PET/CT. Time-activity curves (TAC) were generated for tumors and normal organs, with kinetic parameters (K1, K2, K3, K4, Ki) calculated. A new parameter, the K ratio (K1 + K3)/(K2 + K4), was introduced to measure net uptake efficiency.

RESULTS

In primary tumor (PT), [18F]F-FAPI-42 uptake showed a gradual increase followed by a plateau, contrasting with organs like the thyroid and pancreas, which showed rapid uptake and continuous washout. Compared to non-small cell lung cancer (NSCLC), small cell lung cancer (SCLC) lesions reached the plateau earlier (11 min vs. 14 min) but had a lower uptake. During the plateau phase, [18F]F-FAPI-42 demonstrated slight washout in SCLC, whereas its uptake increased slightly in NSCLC. Lymph node and distant metastases exhibited similar TAC profiles to primary tumors. Kinetic modeling revealed that an irreversible two-compartment model (irre-2TCM) best represented the pharmacokinetics of [18F]F-FAPI-42 in lung cancer, whereas re-2TCM was better suited for the pancreas and thyroid. Lower K1, K2, K3 and K4 were observed in PT compared to those in the pancreas and thyroid (P < 0.05), however, the K ratio in PT was found to be 2-3 times higher. SCLC had lower Ki and SUVmean than NSCLC (P < 0.05). Kinetic parameter differences were also observed between PT and metastatic lesions. Larger metastatic lymph nodes exhibited higher K1, Ki, and K ratio than smaller ones.

CONCLUSION

Lung cancers exhibit distinct [18F]F-FAPI-42 dynamic and kinetic characteristics compared to the thyroid gland and pancreas. Differences were also observed between SCLC and NSCLC, primary and metastatic lesions, as well as larger versus smaller lesions. These findings provide valuable insights into the in vivo pharmacokinetics of [18F]F-FAPI-42, potentially improving the diagnosis of lung cancer.

TRIAL REGISTRATION

ChiCTR2100045757. Registered April 24, 2021 retrospectively registered, http//www.chictr.org.cn.

Relationship between PD-L1 expression and [18F]FAPI versus [18F]FDG uptake on PET/CT in lung cancer

PURPOSE

To investigate the correlation between [18F] labeled fibroblast activation protein inhibitor (FAPI) positron emission tomography (PET)/computed tomography (CT) uptake and programmed death ligand 1 (PD-L1) expression in lung cancer and evaluate the predictive value of [18F]FAPI PET/CT for PD-L1 expression compared with [18F]fluorodeoxyglucose ([18F]FDG) PET/CT.

METHODS

This single-center retrospective study consecutively enrolled patients with pathologically confirmed lung cancer who underwent [18F]FAPI and [18F]FDG PET/CT scans within 2 weeks, with a minimum interval of 20 h. PD-L1 expression was assessed using immunohistochemistry and stratified into three groups. PET/CT uptake parameters included the maximum standard uptake value (SUVmax) in the biopsy tumor or mediastinal metastasis lymph nodes area and the mean SUVs (SUVmean) of normal tissue (lung and blood). The ratios of SUVmax to the SUVmean for each normal tissue were denoted as the tumor-to-background ratios (TBRlung and TBRblood). All statistical analyses were conducted using IBM SPSS Statistics. Normality was assessed, and for non-normally distributed data, the Kruskal-Wallis and Mann-Whitney U tests were applied. Associations between variables were evaluated using Spearman's rank correlation. All tests were two-sided, with a P-value < 0.05 considered statistically significant.

RESULTS

Among the 75 cases included on the final analysis, the TBRblood and TBRlung derived from [18F]FAPI PET/CT were significantly positively correlated with PD-L1 expression (r = 0.32, P < 0.01; r = 0.26, P < 0.05). Additionally, cases with high PD-L1 expression showed significantly higher [18F]FAPI uptake values (mean TBRlung=36.16; mean TBRblood=10.75) compared with those with low PD-L1 expression (mean TBRlung=25.10; mean TBRblood=8.04). No statistically significant correlation was observed between [18F]FDG uptake values and PD-L1 expression level. Receiver operating characteristic analysis identified TBRblood on [18F]FAPI PET/CT with a cutoff value of 7.76 (area under the curve = 0.68, P < 0.01, sensitivity = 75%, and specificity = 53.49%) as a significant predictor of the level of PD-L1 expression.

CONCLUSION

[18F]FAPI uptake was positively correlated with PD-L1 expression in lung cancer. The combination of [18F]FAPI PET/CT and PD-L1 expression may offer a more comprehensive approach to assessing the response of lung cancer to immunotherapy.

TRIAL REGISTRATION

This study was approved by the Clinical Research Ethics Committee of our institution (institutional review board approval no. SDZLEC2021-112-02).

FAPI PET in the Management of Lung Tumors

Fibroblast activation protein (FAP), selectively expressed on activated fibroblasts in proliferating tissues, is emerging as a promising target in oncology. In lung cancer, the leading cause of cancer-related deaths worldwide, [18F]FDG PET/CT has set the bar high and earned widespread recognition in clinical guidelines for its essential role in staging and follow-up. Yet, FAP-targeted imaging agents like FAPI PET/CT have demonstrated significant potential due to their high tumor specificity, rapid tracer uptake, and low background activity. This review focuses on the role of FAPI PET/CT in lung cancer, highlighting its applications in staging, biomarker evaluation, and clinical management. FAP expression correlates with cancer associated fibroblast-driven tumorigenesis in lung cancer, showing higher expression in nonsmall cell lung cancer (NSCLC) than in small cell lung cancer (SCLC) subtypes. Studies reveal that FAPI PET/CT provides comparable or superior detection rates for primary tumors and metastases compared to [18F]FDG PET/CT, particularly in brain, pleural, and bone lesions. It also enhances accuracy in lymph node staging, influencing disease management by enabling surgical resection in cases misclassified by [18F]FDG PET/CT. Despite these advantages, several challenges remain, such as differentiating benign from malignant lesions, assessing FAPI's prognostic implications or its role in treatment response monitoring. Future directions include exploring FAPI-based theranostics, standardizing radiopharmaceuticals, and conducting well-designed, adequately powered prospective trials. FAPI PET/CT represents a transformative diagnostic tool, complementing or potentially surpassing [18F]FDG PET/CT in precision lung cancer care.

Comparison of the diagnostic accuracy between 18F-FAPI-04 PET/CT and 18F-FDG PET/CT in the clinical stage IA of lung adenocarcinoma

Background

Fluorine 18-labeled fibroblast activation protein inhibitor (18F-FAPI-04) positron emission tomography/computed tomography (PET/CT) has shown promise for the visualization of advanced stage lung cancer. The accuracy of 18F-FAPI-04 compared with that of fluorine-18 labeled-fluorodeoxyglucose (18F-FDG) in detecting early lung adenocarcinoma (LUAD) remains unknown. Taking the surgical pathology of pulmonary nodule as the gold standard, the diagnostic performance of stage IA LUAD were compared between 18F-FAPI-04 PET/CT and 18F-FDG PET/CT, and the correlation between 18F-FAPI-04 uptake and pathological characteristics of stage IA LUAD.

Methods

This prospective study from February 2023 to October 2023 analyzed patients with stage IA LUAD who underwent simultaneous examinations with 18F-FAPI-04 and 18F-FDG PET/CT. Semi-quantitative parameters such as maximum standardized uptake value (SUVmax), tumor-to-background ratio (TBR), metabolic tumor volume (MTV), total lesion glycolysis (TLG), FAPI avid tumor volume (FTV), and total lesion FAP expression (TLF) were calculated. The two patterns were compared using either a paired Student's t-test or a Wilcoxon signed-rank test. Immunohistochemical (IHC) staining for detecting fibroblast activating protein (FAP) expression was performed in all resected tumor specimens. Correlation analysis was performed between 18F-FAPI-04 uptake and pathological features of stage IA LUAD.

Results

A total of 20 patients diagnosed with stage IA LUAD were included in this study. A total of 24 pulmonary nodules were identified in these 20 patients, all of whom were confirmed to have stage IA LUAD through operation and pathology. Of them, 17 nodules were stained by FAP immunohistochemistry. Compared with 18F-FDG, 18F-FAPI-04 PET/CT showed a statistically significant increase in SUVmax and TBR for stage IA LUAD, both in the overall and stratified analyses (adenocarcinoma in situ + minimally invasive adenocarcinoma groups vs. invasive adenocarcinoma groups; moderately vs. well-differentiated lesions; stage IA1 vs. IA2+3; P<0.05). The SUVmax of the intense FAP expression group was significantly higher than that of the mild FAP expression group, demonstrating a statistically significant difference (P=0.005). The FAP-IHC score was positively correlated with the SUVmax of 18F-FAPI-04 (r=0.64, P=0.005).

Conclusions

18F-FAPI-04 PET/CT demonstrates higher SUVmax and TBR than 18F-FDG PET/CT in the detection of stage IA LUAD. It was re-assured that the 18F-FAPI-04 uptake of stage IA LUAD was positively correlated with the expression of FAP in vitro.

68Ga-DOTA-FAPI-04 and 18F-FDG PET/CT: a head-to-head comparison for peritoneal carcinomatosis diagnostic accuracy

PURPOSE

The study aimed to compare the diagnostic accuracy of 68Ga-DOTA-FAPI-04 (68Ga-FAPI) and 18F-FDG PET/CT for peritoneal carcinomatosis (PC) in patients with various types of cancer.

METHODS

The study enrolled 113 patients with suspected peritoneal malignancy, each of whom underwent 68Ga-FAPI and 18F-FDG PET/CT scans. Lesions in all patients were confirmed through pathology or radiological follow-up. The evaluation and comparison of diagnostic performance, visual scores, maximum standardized uptake value (SUVmax), mean tumor-to-background ratio (TBR), and the peritoneal cancer index (PCI) score were conducted.

RESULTS

Compared to 18F-FDG, 68Ga-FAPI PET/CT presented higher sensitivity, negative predictive value, and accuracy for detecting PC on a patient-level (100% vs. 93.2%, 100% vs. 22.22% and 93.81% vs. 86.73%, respectively). Semi-quantitative evaluation revealed that 68Ga-FAPI PET/CT had significantly higher SUVmax and TBR for PC [(6.06 ± 3.04 vs. 4.82 ± 2.75, P = 0.001) and (8.50 ± 5.01 vs. 2.92 ± 1.67, P < 0.001)]. The PCI-FAPI score for PC was higher than the PCI-FDG score (11.28 ± 7.10 vs. 5.69 ± 5.15, P < 0.001).

CONCLUSIONS

68Ga-FAPI has demonstrated superior diagnostic accuracy compared to 18F-FDG PET/CT in detecting PC with various types of cancer, particularly gastric cancer. Additionally, 68Ga-FAPI has shown significantly higher uptake and PCI score in PC compared to 18F-FDG, indicating its potential importance in clinical.

Exploring the value of FAP-targeted PET/CT in differentiating breast cancer molecular subtypes: a preliminary study

PURPOSE

This prospective study aims to evaluate the value of [18F]AlF-NOTA-fibroblast activation protein inhibitor (FAPI)-04 positron emission tomography-computed tomography (PET/CT) in predicting molecular subtypes of breast cancer.

METHODS

The study consecutively recruited patients suspected of having breast cancer from a single center who were prospectively enrolled from July 2023 to May 2024 and underwent [18F]AlF-NOTA-FAPI-04 PET/CT. This study compared the differences in tracer uptake among breast cancers with different adverse prognostic factors and molecular subtypes. The classification performance for each molecular subtype of breast cancer was assessed using a receiver operating characteristic (ROC) curve.

RESULTS

Fifty-three participants (mean age, 51 ± 11 years; 52 females) were evaluated. Breast cancer lesions with adverse prognostic factors showed higher tracer uptake. The five different molecular subtypes exhibited varying levels of uptake. The luminal A and luminal B (HER2-negative) subtypes had relatively low uptake, while the luminal B (HER2-positive), HER2-positive, and triple-negative subtypes had relatively high uptake. ROC analysis identified the max standardized uptake value (SUVmax) as a significant classifier (AUC = 0.912, P = 0.0005) for the luminal A subtype, with 100% sensitivity and 83% specificity. For predicting the luminal B (HER2-negative) subtype, SUVmax had an AUC of 0.770 (P = 0.0015). SUVmax, with an AUC of 0.781 (P = 0.003), was used to identify the triple-negative subtype tumors, resulting in a sensitivity of 100% and specificity of 51%. Lastly, the ROC curve showed the cut-off 15.40 (AUC = 0.921, P < 0.0001) could classify luminal A & luminal B (HER2-negative), and luminal B (HER2-positive) & HER2-positive & triple-negative, yielding a sensitivity of 94% and specificity of 79%.

CONCLUSION

The uptake of [18F]AlF-NOTA-FAPI-04 is significantly correlated with the molecular subtypes of breast cancer, and [18F]AlF-NOTA-FAPI-04 PET/CT is a potential tool for noninvasive identification of luminal A subtypes and guidance of FAP-targeted therapies.

[18F]AlF-NOTA-FAPI-04 PET/CT for Predicting Pathologic Response of Resectable Esophageal Squamous Cell Carcinoma to Neoadjuvant Camrelizumab and Chemotherapy: A Phase II Clinical Trial

This single-center, single-arm, phase II trial (ChiCTR2100050057) investigated the ability of 18F-labeled fibroblast activation protein inhibitor ([18F]AlF-NOTA-FAPI-04, denoted as 18F-FAPI) PET/CT to predict the response to neoadjuvant camrelizumab plus chemotherapy (nCC) in locally advanced esophageal squamous cell carcinoma (LA-ESCC). Methods: This study included 32 newly diagnosed LA-ESCC participants who underwent 18F-FAPI PET/CT at baseline, of whom 23 also underwent scanning after 2 cycles of nCC. The participants underwent surgery after 2 cycles of nCC. Recorded PET parameters included maximum, peak, and mean SUVs and tumor-to-background ratios (TBRs), metabolic tumor volume, and total lesion FAP expression. PET parameters were compared between patient groups with good and poor pathologic responses, and the predictive performance for treatment response was analyzed. Results: The good and poor response groups each included 16 participants (16/32, 50.0%). On 18F-FAPI PET/CT, the posttreatment SUVs were significantly lower in good responders than in poor responders, whereas the changes in SUVs with treatment were significantly higher (all P < 0.05). SUVmax (area under the curve [AUC], 0.87; P = 0.0026), SUVpeak (AUC, 0.89; P = 0.0017), SUVmean (AUC, 0.88; P = 0.0021), TBRmax (AUC, 0.86; P = 0.0031), and TBRmean (AUC, 0.88; P = 0.0021) after nCC were significant predictors of pathologic response to nCC, with sensitivities of 63.64%-81.82% and specificities of 83.33%-100%. Changes in SUVmax (AUC, 0.81; P = 0.0116), SUVpeak (AUC, 0.82; P = 0.0097), SUVmean (AUC, 0.81; P = 0.0116), and TBRmean (AUC, 0.74; P = 0.0489) also were significant predictors of the pathologic response to nCC, with sensitivities and specificities in similar ranges. Conclusion: 18F-FAPI PET/CT parameters after treatment and their changes from baseline can predict the pathologic response to nCC in LA-ESCC participants.

[68Ga]Ga-FAPI-46 PET/CT for Staging Suspected/Confirmed Lung Cancer: Results on the Surgical Cohort Within a Monocentric Prospective Trial

BACKGROUND/OBJECTIVES

To evaluate T&N-staging diagnostic performance of [68Ga]Ga-FAPI-46 PET/CT (FAPI) in a suspected/confirmed lung cancer surgical cohort.

METHODS

Patients were enrolled in a prospective monocentric trial (EudraCT: 2021-006570-23) to perform FAPI, in addition to conventional-staging-flow-chart (including [18F]F-FDG PET/CT-FDG). For the current purpose, only surgical patients were included. PET-semiquantitative parameters were measured for T&N: SUVmax, target-to-background-ratios (using mediastinal blood pool-MBP, liver-L and pulmonary-parenchyma-P). Visual and semiquantitative T&N PET/CT performances were analysed per patient and per region for both tracers, with surgical histopathology as standard-of-truth.

RESULTS

63 FAPI scans were performed in 64 patients enrolled (26 May 2022-30 November 2023). A total of 50/63 patients underwent surgery and were included. Agreement (%) with histopathological-T&N-StagingAJCC8thEdition was slightly in favour of FAPI (T-66% vs. 58%, N-78% vs. 70%), increasing when T&N dichotomised (T-92% vs. 80%, N-78% vs. 72%). The performance of Visual-Criteria for T-per patient (n = 50) resulted higher FAPI than FDG. For N-per patient (n = 46), sensitivity and NPV were slightly lower with FAPI. Among 59 T-regions surgically examined, malignancy was excluded in 6/59 (10%). FAPI showed (vs. FDG): sensitivity 85% (vs. 72%), specificity 67% (vs. 50%), PPV 96% (vs. 93%), NPV 33% (vs. 17%), accuracy 83% (vs. 69%). Among 217 N-stations surgically assessed (overall 746 ln removed), only 15/217 (7%) resulted malignant; FAPI showed (vs. FDG): sensitivity 53% (vs. 60%), PPV 53% (vs. 26%), NPV 97% (vs. 97%), and significantly higher specificity (97% vs. 88%, p = 0.001) and accuracy (94% vs. 86%, p = 0.018). Semiquantitative-PET parameters performed similarly, better for N (p < 0.001) than for T, slightly in favour (although not significantly) of FAPI over FDG.

CONCLUSIONS

In a suspected/confirmed lung cancer surgical cohort, PET/CT performances for preoperative T&Nstaging were slightly in favour of FAPI than FDG (except for suboptimal N-sensitivity), significantly better only for N (region-based) specificity and accuracy using visual assessment. The trial's conventional follow-up is still ongoing; future analyses are pending, including non-surgical findings and theoretical impact on patient management.

Comparative assessment of the diagnostic efficacy of [18F]AlF-NOTA-FAPI-04 and [18F]FDG PET/CT imaging for detecting postoperative recurrence in gastric cancer patients: a pilot study

Purpose

This study aimed to compare the efficacy of [18F]AlF-NOTA-FAPI-04 PET/CT with that of [18F]FDG PET/CT for detecting postoperative recurrence in patients with gastric cancer.

Methods

This single-center retrospective clinical study was performed at Hunan Cancer Hospital between December 2020 and June 2022. The participants underwent both [18F]AlF-NOTA-FAPI-04 and [18F]FDG within 14 days. Histopathologic examination, morphological imaging, and/or follow-up imaging were used as a reference for the final diagnosis. We recorded the sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and accuracy of [18F]AlF-NOTA-FAPI-04 and [18F]FDG PET/CT for detecting local recurrence, lymph node metastasis and distant metastasis. The SUVmax and background ratio (TBR) of local recurrence and metastases between [18F]FDG and [18F]AlF-NOTA-FAPI-04 PET/CT were compared using paired-sample t tests.

Results

Forty-seven patients (27 males, aged 25-68 years) with gastric cancer after curative resection (27 with adenocarcinoma, 17 with signet ring cell carcinoma and 4 with mucinous adenocarcinoma) were included in the study. [18F]AlF-NOTA-FAPI-04 accumulation was significantly greater than that of [18F]FDG in terms of local recurrence (SUVmax, 11.65 vs 3.48, p< 0.0001; TBR, 12.93 vs 2.94, p< 0.0001), lymph node metastasis (SUVmax, 13.45 vs 3.05, p=0.003875; TBR, 12.43 vs 2.21, p=0.001661), and distant metastasis (SUVmax, 11.89 vs 2.96, p < 0.0001; TBR, 13.32 vs 2.32, p< 0.0001). Despite no statistical comparison was made with [18F]FDG, [18F]AlF-NOTA-FAPI-04 imaging exhibited high levels of sensitivity, specificity, PPV, NPV, and accuracy for detecting postoperative local recurrence, lymph node metastasis, and distant metastasis in patients with gastric cancer.

Conclusion

[18F]AlF-NOTA-FAPI-04 has demonstrated potential for more accurate tumor re-evaluation in GC, thus enhancing treatment decision-making.

Automated Radiosynthesis of [18F]FluoFAPI and Its Dosimetry and Single Acute Dose Toxicological Evaluation

BACKGROUND

Cancer-associated fibroblasts have become a new target for therapy. Fibroblasts present within malignancies express the fibroblast activation protein (FAP). Inhibitors to FAP (FAPI) are small molecules recently developed as a theranostic agents for imaging and radiotherapy. All currently used FAPI rely on a linker-chelator complex attached to the 'inhibitor'. We describe a new automated method of the direct attachment of the radioisotope to the inhibitor, resulting in a >50% MW reduction with the hope of an improved tumor-to-background ratio and tumor uptake.

METHODS

[18F]FluroFAPI was developed from a Sn precursor. This allowed for subsequent automated radioflourination. We obtained the biodistribution of [18F]FluroFAPI in rats, performed estimated human radiation dosimetry, and performed a 100× expected single dose toxicology analysis for eventual first-in-human experiments.

RESULTS

The synthesis of the Sn precursor for FluorFAPI and the automated synthesis of [18F]FluroFAPI was demonstrated. [18F]FluroFAPI had favorable estimated human radiation dosimetry, and demonstrated no adverse effects when injected at a dose of 100× that planned for [18F]FluroFAPI.

CONCLUSIONS

With the successful development of an automated synthesis of [18F]FluroFAPI, first-in-human testing can be planned with the hope of an improved tumor-to-background performance compared to other FAPI agents.

Clinical value of [18F]AlF-NOTA-FAPI-04 PET/CT for assessing early-stage liver fibrosis in adult liver transplantation recipients compared with chronic HBV patients

AIMS

To investigate the clinical value and performance of [18F]AlF-NOTA-FAPI-04 PET/CT in assessing early-stage liver fibrosis in liver transplantation (LT) recipients.

METHODS

A prospective study including 17 LT recipients and 12 chronic Hepatitis B (CHB) patients was conducted. All patients received liver biopsy, transient elastography (TE), and [18F]AlF-NOTA-FAPI-04 PET/CT. On [18F]AlF-NOTA-FAPI-04 PET/CT scans, the liver parenchyma's maximum standardized uptake values (SUVmax) were measured. The receiver operating characteristic (ROC) curve analysis was applied to determine the diagnostic efficacy of [18F]AlF-NOTA-FAPI-04 PET/CT in early-stage liver fibrosis (S1-S2) compared with the diagnostic performance of TE.

RESULTS

Among those 29 patients enrolled in this study, 15(51.7%) had fibrosis S0, 10(34.5%) had S1, and 4(13.8%) had S2, respectively. The SUVmax of patients with early-stage liver fibrosis was significantly higher than those without liver fibrosis in LT recipients and CHB patients (P = 0.004, P = 0.02). In LT recipients, a SUVmax cut-off value of 2.0 detected early-stage liver fibrosis with an AUROC of 0.92 (P = 0.006), and a liver stiffness measurements (LSM) score cut-off value of 8.2 kPa diagnosed early-stage liver fibrosis with an AUROC of 0.80 (P = 0.012). In CHB patients, a SUVmax cut-off value of 2.7 detected early-stage liver fibrosis with an AUROC of 0.94 (P < 0.001) and an LSM scores cut-off value of 8.4 kPa diagnosed early-stage liver fibrosis with an AUROC of 0.91 (P < 0.001).

CONCLUSION

[18F]AlF-NOTA-FAPI-04 PET/CT could be applied to evaluate early-stage liver fibrosis in LT recipients and CHB patients properly, with the potential additional advantages in monitoring and predicting complications after LT.

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.

Performance of [18F]FDG PET/CT versus FAPI PET/CT for lung cancer assessment: a systematic review and meta-analysis

PURPOSE

This article aims to compare the diagnostic performance of 18-fluorodeoxyglucose ([18F]FDG) PET/CT and fibroblast activating protein inhibitor (FAPI) PET/CT in the assessment of primary tumors, lymph nodes, and distant metastases in lung cancer patients.

METHODS

A systematic search was conducted on the Cochrane Library, Embase, and PubMed/MEDLINE databases from inception until November 1, 2022. Included studies assessed the use of FAPI PET/CT and [18F]FDG PET/CT in patients with lung cancer. The Quality Assessment of Diagnostic Accuracy Studies-2 (QUADAS-2) tool was used to evaluate the risk of bias. A random variable model was used to analyze the diagnostic tests of the two imaging modalities.

RESULTS

The sensitivity of FAPI PET/CT in detecting primary lung cancer lesions was 0.98 (95% CI: 0.88-1.00), while the sensitivity of [18F]FDG PET/CT was 0.99 (95% CI: 0.74-1.00). For the detection of metastatic lesions (lymph node metastases and distant metastases), FAPI PET/CT had a sensitivity of 0.99 (95% CI: 0.90-1.00), while the sensitivity of [18F]FDG PET/CT was 0.77 (95% CI: 0.66-0.85). However, the specificity of the two imaging modalities could not be assessed due to the lack of sufficient information on pertinent true negatives.

CONCLUSION

In the diagnosis of metastatic lung cancer lesions, FAPI PET/CT demonstrated a higher sensitivity compared to [18F]FDG PET/CT. Therefore, FAPI PET/CT may be considered an alternative imaging modality for the assessment of primary lung cancer tumors, lymph node metastases, and distant metastases.

CLINICAL RELEVANCE STATEMENT

FAPI may be an alternative to [18F]FDG in the assessment of primary lung cancer tumors, lymph node metastases, and distant metastases, which plays a very important role in treatment.

KEY POINTS

• This article is to compare the performance of [18F]FDG PET/CT with FAPI PET/CT in the assessment of primary tumors, lymph nodes, and distant metastases in lung cancer. • However, FAPI PET/CT has a higher sensitivity for the diagnostic assessment of metastatic lung cancer lesions.

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

Purpose

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

Patients and methods

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

Results

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

Conclusion

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

A Head-to-Head Comparison of 68Ga-LNC1007 and 2-18F-FDG/68Ga-FAPI-02 PET/CT in Patients With Various Cancers

OBJECTIVES

This head-to-head comparison study was designed to investigate the radiotracer uptake and clinical feasibility of using 68Ga-LNC1007, to detect the primary and metastatic lesions in patients with various types of cancer, and to compare the results with those of 2-18F-FDG PET/CT and 68Ga-FAPI-02 PET/CT.

PATIENTS AND METHODS

Sixty-one patients with 10 different kinds of cancers were enrolled in this study. Among them, 50 patients underwent paired 68Ga-LNC1007 and 2-18F-FDG PET/CT, and the other 11 patients underwent paired 68Ga-LNC1007 and 68Ga-FAPI-02 PET/CT. The final diagnosis was based on histopathological results and diagnostic radiology. Immunohistochemistry for FAP and integrin αvβ3 was performed in 24 primary tumors.

RESULTS

68Ga-LNC1007 PET/CT detected all 55 primary tumors, whereas 2-18F-FDG PET/CT was visually positive for 45 primary tumors (P = 0.002). Furthermore, subgroup analysis showed that 68Ga-LNC1007 PET/CT was superior to 2-18F-FDG PET/CT in diagnosing renal cell carcinomas and hepatocellular carcinomas. For metastatic tumors, 68Ga-LNC1007 PET/CT revealed more PET-positive lesions and higher SUVmax for skeletal metastases and peritoneal metastases compared with 2-18F-FDG. The SUVmax and tumor-to-background ratio of primary tumors on 68Ga-LNC1007 PET/CT were much higher than those on 68Ga-FAPI-02 PET/CT, the same was also observed for metastatic tumors. Immunohistochemical results showed that the SUVmean quantified from 68Ga-LNC1007 PET was correlated with FAP expression level (r = 0.564, P = 0.005).

CONCLUSIONS

68Ga-LNC1007 is a promising new diagnostic PET tracer for imaging of various kinds of malignant lesions. It may be a better alternative to 2-18F-FDG for diagnosing renal cell carcinoma, hepatocellular carcinoma, skeletal metastases, and peritoneal metastases.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

FAPI Compared with FDG PET/CT for Diagnosis of Primary and Metastatic Lung Cancer

Background The radiotracer fluorine 18 (18F)-labeled fibroblast activation protein inhibitor (FAPI) has shown promise for visualizing several types of cancer, but the accuracy of 18F-FAPI compared with 18F-fluorodeoxyglucose (FDG) for the detection of lung cancer remains uncertain. Purpose To evaluate the effectiveness of 18F-FAPI-based PET/CT imaging for the diagnosis of primary and metastatic lung cancer lesions as compared with 18F-FDG PET/CT. Materials and Methods In this secondary analysis of a prospective trial, consecutively recruited patients from a single center with pathologically confirmed lung cancer were prospectively enrolled from December 2020 to April 2022 and underwent paired 18F-FAPI and 18F-FDG PET/CT examinations at intervals of more than 20 hours and within 7 days of each other. Histopathologic and clinical follow-up results were used as reference standards for final diagnoses. 18F-FAPI and 18F-FDG uptake were compared using the McNemar test or paired Student t test. Diagnostic accuracy was compared between the two techniques by using the McNemar χ2 test. Results Sixty-eight participants (median age, 63 years [IQR, 58-68 years; range, 42-79 years]; 46 male [68%]) were evaluated. Compared with the mean tumor-to-background ratio (TBR) for FDG uptake, TBR for FAPI uptake was lower in primary lung tumors (25.3 ± 14.0 [SD] vs 32.1 ± 21.1; P < .001) but higher in metastatic lymph nodes (7.5 ± 6.6 vs 5.9 ± 8.6; P < .001) and bone metastases (8.6 ± 5.4 vs 4.3 ± 2.3; P < .001). For diagnostic accuracy in a total of 548 lesions in 68 participants, compared with 18F-FDG PET/CT, 18F-FAPI PET/CT demonstrated a higher sensitivity (99% [392 of 397 lesions] vs 87% [346 of 397]; P < .001), specificity (93% [141 of 151 lesions] vs 79% [120 of 151]; P = .004), accuracy (97% [533 of 548 lesions] vs 85% [466 of 548]; P < .001), and negative predictive value (97% [141 of 146 lesions] vs 70% [120 of 171 lesions]; P < .001), but there was no evidence of a difference for positive predictive value (98% [392 of 402 lesions] vs 92% [346 of 377 lesions]; P = .57). Conclusion 18F-FAPI PET/CT may be superior to 18F-FDG PET/CT for detecting lung cancer. © RSNA, 2023 Supplemental material is available for this article. See also the editorial by Zukotynski and Gerbaudo in this issue.

Increased 68 Ga-FAPI Activity in Benign Pulmonary Nodules

ABSTRACT

A 68-year-old man who had recently been diagnosed with pulmonary nodules underwent both 18 F-FDG and 68 Ga-FAPI PET/CT. Both studies showed increased uptake in pulmonary nodules, which are suspected to be malignant. However, based on the histopathological findings after surgery, this is ultimately diagnosed as a benign pulmonary nodule. Our case suggests that pulmonary nodules with intense 68 Ga-FAPI uptake may be benign as well.

Synthesis and Preclinical Evaluation of a Novel FAPI-04 Dimer for Cancer Theranostics

Overexpression of fibroblast activation protein (FAP) in cancer-associated fibroblasts in a wide variety of tumors enables a highly selective targeting strategy using FAP inhibitors (FAPIs). Quinoline-based FAPIs labeled with radionuclides have been widely developed for tumor-targeted nuclear medicine imaging. However, the short retention time of FAPIs at the tumor site limits their application in radionuclide therapy. In this study, a novel FAPI-04 dimer was synthesized and labeled with radionuclides to prolong the retention time in tumors for imaging and therapy. To prepare the FAPI-04 dimer complex, DOTA-Suc-Lys-(FAPI-04)₂, we used Fmoc-Lys(Boc)-OH as the linker to conjugate two FAPI-04 structures by an amide reaction. The resulting product was further modified by DOTA groups to allow for conjugation with radioactive metals. Both [⁶⁸Ga]Ga-(FAPI-04)₂ and [¹⁷⁷Lu]Lu-(FAPI-04)₂ showed a radiochemical purity of >99% and remained stable in vitro. In vivo, micro-PET images of SKOV3, A431, and H1299 xenografts revealed that the tumor uptake of [⁶⁸Ga]Ga-(FAPI-04)₂ was about twice that of [⁶⁸Ga]Ga-FAPI-04 and that the accumulation of [⁶⁸Ga]Ga-(FAPI-04)₂ at the tumor site did not significantly decrease even 3h after injection. The tumor-abdomen ratio of [⁶⁸Ga]Ga-(FAPI-04)₂ images was significantly higher than that of [¹⁸F]F-FDG images. For radionuclide therapy, [¹⁷⁷Lu]Lu-(FAPI-04)₂ effectively retarded tumor growth and displayed good tolerance. In conclusion, the DOTA-Suc-Lys-(FAPI-04)₂ design enhanced its uptake in FAP-expressing tumors, improved its retention time at the tumor site, and produced high-contrast imaging in xenografts after radionuclide labeling. Furthermore, it showed a noticeable antitumor effect. DOTA-Suc-Lys-(FAPI-04)₂ provides a new approach for applying FAPI derivatives in tumor theranostics.

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.

Early detection of radiation-induced myocardial damage by [18F]AlF-NOTA-FAPI-04 PET/CT imaging

PURPOSE

Retrospective analysis revealed increased [18F]AlF-NOTA-FAPI-04 uptake in the myocardium of patients with esophageal squamous cell cancer (ESCC) treated with concurrent chemoradiotherapy (CCRT). This study investigated and verified the feasibility of [18F]AlF-NOTA-FAPI-04 PET/CT for detecting radiation-induced myocardial damage (RIMD).

METHODS

Myocardial FAPI uptake was analyzed before and during radiotherapy in thirteen ESCC patients treated with CCRT. In the animal study, a single dose of 50 Gy was delivered to the cardiac apex of Wistar rats (24 rats, including 16 RIMD model rats and 8 control model rats). RIMD model rats were scanned with [18F]AlF-NOTA-FAPI-04 PET/CT weekly for 12 weeks, and left ventricular ejection fraction (LVEF) was measured by magnetic resonance imaging. Dynamic, blocking, and [18F]FDG PET/CT studies (4 rats/group) were performed on RIMD rats at 5 weeks post-radiation, and histopathological analyses were conducted.

RESULTS

Increased FAPI uptake in the myocardium was found after CCRT (1.53 ± 0.53 vs 1.88 ± 0.70, P = 0.015). In RIMD rats, significantly increased FAPI uptake in the damaged myocardium was observed from the 2nd week post-radiation exposure and peaked in the 5th week. Significantly more intense tracer accumulation was observed in the damaged myocardium than in the remote myocardium, as identified by decreased [18F]FDG uptake and confirmed by autoradiography, hematoxylin-eosin, Masson's trichrome, and immunohistochemical staining. The LVEF remained unchanged at the 3rd week post-radiation exposure but was remarkably decreased compared with that in the control group at the 8th week.

CONCLUSION

Through clinical phenomena and animal experimental studies, this study indicated that [18F]AlF-NOTA-FAPI-04 PET/CT imaging can detect RIMD noninvasively and before a decrease in LVEF, indicating the clinical potential of [18F]AlF-NOTA-FAPI-04 as a PET/CT tracer for early monitoring of RIMD.

Performance and Prospects of [68Ga]Ga-FAPI PET/CT Scans in Lung Cancer

Fibroblast activation protein (FAP) could be a promising target for tumor imaging and therapy, as it is expressed in >90% of epithelial cancers. A high level of FAP-expression might be associated with worse prognosis in several cancer types, including lung cancer. FAPI binds this protein and allows for labelling to Gallium-68, as well as several therapeutic radiopharmaceuticals. As FAP is only expressed at insignificant levels in adult normal tissue, FAPI provides a highly specific tumor-marker for many epithelial cancers. In this review, current information on the use of [68Ga]Ga-FAPI PET/CT in lung cancer is presented. [68Ga]Ga-FAPI shows a high uptake (standardized uptake value = SUVmax) and tumor-to-background ratio (TBR) in primary lung cancer lesions, as well as in metastatic lesions of other tumor types located in the lung and in lung cancer metastases located throughout the body. Where a comparison was made to [18F]FDG PET/CT, [68Ga]Ga-FAPI showed a similar or higher SUVmax and TBR. In brain and bone metastases, [68Ga]Ga-FAPI PET/CT outperformed [18F]FDG PET/CT. In addition to this strong diagnostic performance, a possible prognostic value of [68Ga]Ga-FAPI PET/CT in lung cancer is proposed.

Comparison of 18 F-FDG PET/CT and 68 Ga-FAPI-04 PET/CT in patients with non-small cell lung cancer

AIM

In this study, we aimed to compare the diagnostic accuracy of 18 F-fluorodeoxyglucose ( 18 F-FDG) and Gallium-68 labeled fibroblast activator protein inhibitor ( 68 Ga-FAPI)-04 PET/CT in the tumor-node-metastasis (TNM) staging of patients with nonsmall cell lung cancer (NSCLC) and investigate whether adenocarcinoma (ADC) and squamous cell cancer (SCC) exhibit different uptake patterns on 68 Ga-FAPI-04 PET/CT.

MATERIALS AND METHOD

Twenty-nine patients with a histopathologically-confirmed diagnosis of NSCLC, who had no history of previous radiation therapy or chemotherapy and underwent 18 F-FDG PET/CT and 68 Ga-FAPI-04 PET/CT imaging between January 2021 and December 2021 were included in this retrospective study. Staging was performed using the 8th edition of the TNM staging system on both 18 F-FDG PET/CT and 68 Ga-FAPI-04 PET/CT images. Standardized uptake value (SUV) max and tumor-to-background ratios (TBR) were calculated on primary lesions and metastases.

RESULTS

There was no statistically significant difference in primary lesions in terms of SUV max and TBR values. However, 68 Ga-FAPI-04 PET/CT was significantly superior to 18 F-FDG PET/CT in terms of the number of lymph nodes and bone metastases revealed. The SUV max and TBR values of lymph nodes, hepatic lesions and bone lesions were significantly higher on 68 Ga-FAPI-04 PET/CT than on 18 F-FDG PET/CT. 68 Ga-FAPI-04 PET/CT changed the disease stage of three patients (10.9%). The diagnostic accuracy of 68 Ga-FAPI-04 PET/CT was 100%, whereas the diagnostic accuracy of 18 F-FDG PET/CT was 89.6% ( P  = 0.250).

CONCLUSION

Although 68 Ga-FAPI-04 PET/CT detected more lesions and higher diagnostic accuracy than 18 F-FDG PET/CT in NSCLC, neither method was statistically superior to each other in terms of diagnostic accuracy in TNM staging.

From Automated Synthesis to In Vivo Application in Multiple Types of Cancer-Clinical Results with [68Ga]Ga-DATA5m.SA.FAPi

Radiolabeled FAPI (fibroblast activation protein inhibitors) recently gained attention as widely applicable imaging and potential therapeutic compounds targeting CAF (cancer-associated fibroblasts) or DAF (disease-associated fibroblasts in benign disorders). Moreover, the use of FAPI has distinct advantages compared to FDG (e.g., increased sensitivity in regions with high glucose metabolism, no need for fasting, and rapid imaging). In this study, we wanted to evaluate the radiochemical synthesis and the clinical properties of the new CAF-targeting tracer [68Ga]Ga-DATA5m.SA.FAPi. The compound consists of a (radio)chemically easy to use hybrid chelate DATA.SA, which can be labeled at low temperatures, making it an interesting molecule for 'instant kit-type' labeling, and a squaric acid moiety that provides distinct advantages for synthesis and radiolabeling. Our work demonstrates that automatic synthesis of the FAP inhibitor [68Ga]Ga-DATA5m.SA.FAPi is feasible and reproducible, providing convenient access to this new hybrid chelator-based tracer. Our studies demonstrated the diagnostic usability of [68Ga]Ga-DATA5m.SA.FAPi for the unambiguous detection of cancer-associated fibroblasts of various carcinomas and their metastases (NSCLC, liposarcoma, parotid tumors, prostate cancer, and pancreas adenocarcinoma), while physiological uptake in brain, liver, intestine, bone, and lungs was very low.

Comparison of 68Ga-FAPI and 18F-FDG PET/CT in the Evaluation of Patients With Newly Diagnosed Non-Small Cell Lung Cancer

Purpose

Several studies have demonstrated that ⁶⁸Ga-FAPI PET/CT shows high intratumoral tracer uptake and low normal tissue uptake, allowing for excellent visualization of cancer. The purpose of this study was to compare the ability of ⁶⁸Ga-FAPI and ¹⁸F-FDG PET/CT for the evaluation of newly diagnosed NSCLC.

Materials and Methods

A prospective analysis of 28 individuals with histopathologically newly confirmed NSCLC that underwent ⁶⁸Ga-FAPI and ¹⁸F-FDG PET/CT was conducted. The performance of two imaging modalities was compared based upon visual assessment, rates of cancer detection, and semi-quantitative parameters (target-to-background ratio [TBR], maximum standard uptake value [SUVmax]) for both primary tumors and metastases.

Results

In total, this study enrolled 28 participants (13 male, 15 female; median age: 60.5 years, range: 34 – 78 years. <u>For primary tumors, ⁶⁸Ga-FAPI and ¹⁸F-FDG PET/CT have similar detection performance (28 vs. 27). However, ⁶⁸Ga-FAPI PET/CT was found to more effectively evaluate most metastases as compared to ¹⁸F-FDG PET/CT. ⁶⁸Ga-FAPI PET/CT detecting more metastases present within the lymph nodes (53 vs. 49), pleura (8 vs. 7), liver (4 vs. 1), and bone (41 vs. 35).</u> The SUVmax and TBR values for ⁶⁸Ga-FAPI were substantially superior to those for ¹⁸F-FDG in lymph node, pleural, and bone metastases. While the SUVmax for these two imaging approaches was comparable for hepatic metastases, ⁶⁸Ga-FAPI exhibited a significantly higher TBR in relation to that of ¹⁸F-FDG. In addition, ⁶⁸Ga-FAPI PET/CT demonstrates excellent N (80% [8/10]) and M (92.9% [26/28]) staging accuracy in NSCLC patients.

Conclusions

⁶⁸Ga-FAPI PET/CT as an examination modality is excellent for evaluation of newly diagnosed NSCLC. ⁶⁸Ga-FAPI PET/CT improves the detection rates of most metastases and facilitating the superior staging of patients with newly diagnosed NSCLC, relative to that achieved by ¹⁸F-FDG PET/CT.

New PET Tracers: Current Knowledge and Perspectives in Lung Cancer

PET/CT with the tracer 2-[¹⁸F]fluoro-2-deoxy-D-glucose ([¹⁸F]FDG) has improved diagnostic imaging in cancer and is routinely used for diagnosing, staging and treatment planning in lung cancer patients. However, pitfalls of [¹⁸F]FDG-PET/CT limit the use in specific settings. Additionally, lung cancer is still the leading cause of cancer associated death and has high risk of recurrence after curative treatment. These circumstances have led to the continuous search for more sensitive and specific PET tracers to optimize lung cancer diagnosis, staging, treatment planning and evaluation. The objective of this review is to present and discuss current knowledge and perspectives of new PET tracers for use in lung cancer. A literature search was performed on PubMed and clinicaltrials.gov, limited to the past decade, excluding case reports, preclinical studies and studies on established tracers such as [¹⁸F]FDG and DOTATE. The most relevant papers from the search were evaluated. Several tracers have been developed targeting specific tumor characteristics and hallmarks of cancer. A small number of tracers have been studied extensively and evaluated head-to-head with [¹⁸F]FDG-PET/CT, whereas others need further investigation and validation in larger clinical trials. At this moment, none of the tracers can replace [¹⁸F]FDG-PET/CT. However, they might serve as supplementary imaging methods to provide more knowledge about biological tumor characteristics and visualize intra- and inter-tumoral heterogeneity.

The value of the Standardized Uptake Value (SUV) and Metabolic Tumor Volume (MTV) in lung cancer

The diagnosis, staging and therapeutic monitoring of lung cancer were amongst the first applications for which the utility of FDG PET was documented and FDG PET/CT is now a routine diagnostic tool for clinical decision-making. As well as having high sensitivity for detection of disease sites, which provides critical information about stage, the intensity of uptake provides deeper biological characterization, while the burden of disease also has potential clinical significance. These disease characteristics can easily be quantified on delayed whole-body imaging as the maximum standardized uptake value (SUV_max) and metabolic tumor volume (MTV), respectively. There have been significant efforts to harmonize the measurement of these features, particularly within the context of clinical trials. Nevertheless, however calculated, in general, a high SUV_max and large MTV have been shown to have an adverse prognostic significance. Nevertheless, the use of these parameters in the interpretation and reporting of clinical scans remains inconsistent and somewhat controversial. This review details the current status of semi-quantitative FDG PET/CT in the evaluation of lung cancer.

Higher accuracy of [68 Ga]Ga-DOTA-FAPI-04 PET/CT comparing with 2-[18F]FDG PET/CT in clinical staging of NSCLC

PURPOSE

This study aimed to explore the clinical staging performance of [⁶⁸ Ga]Ga-DOTA-FAPI-04 PET/CT compared with that of 2-[¹⁸F]FDG PET/CT in non-small cell lung cancer (NSCLC) patients lesion by lesion.

METHODS

A total of 134 diagnosed or suspected NSCLC patients were enrolled in the prospective study (ChiCTR2000038080); they received paired 2-[¹⁸F]FDG PET/CT and [⁶⁸ Ga]Ga-DOTA-FAPI-04 PET/CT. Of these patients, the retrospective analysis of 74 NSCLC patients with pathological results was conducted from primary tumor (T) diagnosis, lymph node (N), and metastatic lesion (M) staging. The imaging characteristics of the lung nodules and suspected metastases were obtained and analyzed, and the staging performance of 2-[¹⁸F]FDG PET/CT and [⁶⁸ Ga]Ga-DOTA-FAPI-04 PET/CT was compared.

RESULTS

For T diagnosis, [⁶⁸ Ga]Ga-DOTA-FAPI-04 showed better diagnostic performance than 2-[¹⁸F]FDG in 79 lung nodules of 72 patients, especially for nonsolid and small-dimension adenocarcinoma nodules. For N staging, 98 lymph nodes (LNs) with pathological results in 37 patients were analyzed. The SUV_max of [⁶⁸ Ga]Ga-DOTA-FAPI-04 in the nonmetastatic LNs was significantly lower than that in the metastatic LNs. Regarding metastatic LN identification, the calculated optimum cut-off value of [⁶⁸ Ga]Ga-DOTA-FAPI-04 SUV_max was 5.5, and the diagnostic accuracy using [⁶⁸ Ga]Ga-DOTA-FAPI-04 and 2-[¹⁸F]FDG criteria was 94% and 30%, respectively (P < 0.001). For M staging, [⁶⁸ Ga]Ga-DOTA-FAPI-04 identified more lesions than 2-[¹⁸F]FDG (257 vs. 139 lesions) in 14 patients with multiple metastases. Overall, the staging accuracy of [⁶⁸ Ga]Ga-DOTA-FAPI-04 was better than that of 2-[¹⁸F]FDG in 52 patients with different pathological stages [43/52 (82.7%) vs. 27/52 (51.9%), P = 0.001].

CONCLUSION

Compared with 2-[¹⁸F]FDG PET/CT, [⁶⁸ Ga]Ga-DOTA-FAPI-04 PET/CT demonstrated better staging performance in NSCLC patients with different pathological stages, especially those with localized disease.

Characteristics of tumour stroma in regional lymph node metastases in colorectal cancer patients: a theoretical framework for future diagnostic imaging with FAPI PET/CT

Purpose

The recently developed fibroblast activation protein inhibitor (FAPI) tracer for PET/CT, binding tumour-stromal cancer-associated fibroblasts, is a promising tool for detection of positive lymph nodes. This study provides an overview of features, including sizes and tumour-stromal content, of lymph nodes and their respective lymph node metastases (LNM) in colorectal cancer (CRC), since literature lacks on whether LNMs contain sufficient stroma to potentially allow FAPI-based tumour detection.

Methods

Haematoxylin and eosin-stained tissue slides from 73 stage III colon cancer patients were included. Diameters and areas of all lymph nodes and their LNMs were assessed, the amount of stroma by measuring the stromal compartment area, the conventional and total tumour-stroma ratios (TSR-c and TSR-t, respectively), as well as correlations between these parameters. Also, subgroup analysis using a minimal diameter cut off of 5.0 mm was performed.

Results

In total, 126 lymph nodes were analysed. Although positive correlations were observed between node and LNM for diameter and area (r = 0.852, p < 0.001 and r = 0.960, p < 0.001, respectively), and also between the LNM stromal compartment area and nodal diameter (r = 0.612, p < 0.001), nodal area (r = 0.747, p < 0.001) and LNM area (r = 0.746, p < 0.001), novel insight was that nearly all (98%) LNMs contained stroma, with median TSR-c scores of 35% (IQR 20–60%) and TSR-t of 20% (IQR 10–30%). Moreover, a total of 32 (25%) positive lymph nodes had a diameter of < 5.0 mm.

Conclusion

In LNMs, stroma is abundantly present, independent of size, suggesting a role for FAPI PET/CT in improved lymph node detection in CRC.

[18F]AlF-NOTA-FAPI-04: FAP-targeting specificity, biodistribution, and PET/CT imaging of various cancers

PURPOSE

In this pilot study, we developed a new tracer, [¹⁸F]AlF-labeled FAPI-04 chelated with NOTA, denoted as [¹⁸F]AlF-NOTA-FAPI-04, and tested the specificity, biodistribution, and clinical application for PET/computed tomography (CT) imaging of various types of cancers in patients.

METHODS

In vitro binding specificity of FAPI-04 to FAP was verified in U87 cells confocal of a fluorescence-labeled variant. In vivo imaging, competition, and dynamic scanning analyses were conducted to evaluate [¹⁸F]AlF-NOTA-FAPI-04 imaging in xenograft mouse model using small-animal PET/CT. The application of [¹⁸F]AlF-NOTA-FAPI-04 was analyzed by imaging different types of cancers in patients.

RESULTS

Both in vitro and in vivo results showed high binding specificity of FAPI-04 to FAP. High intratumoral uptake and fast body clearance of the tracer were observed in the xenograft mouse model and cancer patients. High-contrast images and negligible radiation exposure to normal tissue were observed on [¹⁸F]AlF-NOTA-FAPI-04 PET/CT in 28 patients with 8 different types of cancers. Five of 28 patients underwent PET/CT scanning at 1 h, 2 h, and 4 h after intravenous injection of [¹⁸F]AlF-NOTA-FAPI-04. Seven patients with advanced lung cancer underwent dual-tracer imaging, and 44 and 37 metastatic lesions were detected by [¹⁸F]AlF-NOTA-FAPI-04 PET/CT and [¹⁸F]F-FDG PET/CT, respectively. Overall, 80.0% of metastatic lesions was identified by both [¹⁸F]AlF-NOTA-FAPI-04 and ¹⁸F-FDG, 17.8% by [¹⁸F]AlF-NOTA-FAPI-04 PET/CT only, and 2.2% by [¹⁸F]FDG PET/CT only.

CONCLUSION

[¹⁸F]AlF-NOTA-FAPI-04 offers high specificity as a tracer for FAP imaging and allows fast imaging with high contrast in tumors. [¹⁸F]AlF-NOTA-FAPI-04 is better at identifying metastatic lesions in patients with advanced lung cancer than [¹⁸F]FDG, and its use may facilitate tumor staging.

Expression of fibroblast activation protein in lung cancer and its correlation with tumor glucose metabolism and histopathology

PURPOSE

To explore the expression of fibroblast activation protein (FAP) in lung cancer (LC) and its correlation with tumor glucose metabolism and histopathology.

METHODS

From June 2018 to November 2020, 73 patients with newly diagnosed LC were included. Immunohistochemical staining was used to quantify FAP expression in tumors. The histopathological type and tumor grade were determined via histopathological examination. The tumor glucose metabolism parameters and tumor maximal diameter were measured via [¹⁸F] F-FDG PET/CT. Univariate and multivariate analysis were performed to study the correlation of FAP expression levels with glucose metabolism variables and tumor histopathology.

RESULTS

Positive FAP expression was observed in 97.3% (71/73) LC lesions, which was significantly higher than 87.7% (64/73) of [¹⁸F] F-FDG positivity observed on PET/CT (χ² = 4.818, P = 0.028). In 12 early adenocarcinomas (ADCs), only three lesions (25%) were positive for [¹⁸F] F-FDG on PET/CT; however, 10 lesions (83.3%) were positive for FAP. When FAP expression was classified into low level (scores ≤ 3) and high level (scores > 4), high FAP level was found in 80.8% tumors and low FAP level in the other 19.2% tumors. High FAP level was identified in 100.0% of squamous cell carcinomas (SCCs), 85.7% of ADCs, 66.7% (4/6) of large cell neuroendocrine carcinomas (LCNCs), and 40.0% (4/10) of small cell lung cancers (SCLCs) (P < 0.05). In non-mucinous ADC lesions, on univariate analysis, FAP expression level showed a close relationship with tumor metabolism parameters (maximal standard uptake value (SUVmax), mean standard uptake value (SUVmean), and total lesion glycolysis (TLG)), tumor diameter, tumor grade, and lesion attenuation (P < 0.05).

CONCLUSION

The present study demonstrates that FAP is widely expressed in LC and shows great variation in different histopathological types. A high positive rate of FAP expression implies that FAP-targeted imaging may be a sensitive modality for diagnosing LC, especially in early ADCs. Further validation with such probes is warranted.