Clinical significance of FAP-α on microvessel and lymphatic vessel density in lung squamous cell carcinoma

Association of future cancer metastases with fibroblast activation protein-α: a systematic review and meta-analysis

Introduction

Fibroblast activation protein-α (FAP-α) is a vital surface marker of cancer-associated fibroblasts, and its high expression is associated with a higher tumor grade and metastasis. A systematic review and a meta-analysis were performed to associate future metastasis with FAP-α expression in cancer.

Methods

In our meta-analysis, relevant studies published before 20 February 2024 were systematically searched through online databases that included PubMed, Scopus, and Web of Science. The association between FAP-α expression and metastasis, including distant metastasis, lymph node metastasis, blood vessel invasion, vascular invasion, and neural invasion, was evaluated. A pooled odds ratio (OR) with 95% confidence intervals (CI) was reported as the measure of association.

Results

A total of 28meta-analysis. The random-effects model for five parameters showed that a high FAP-α expression was associated with blood vessel invasion (OR: 3.04, 95% CI: 1.54-5.99, I 2 = 63%, P = 0.001), lymphovascular invasion (OR: 3.56, 95% CI: 2.14-5.93, I 2 = 0.00%, P < 0.001), lymph node metastasis (OR: 2.73, 95% CI: 1.96-3.81, I 2 = 65%, P < 0.001), and distant metastasis (OR: 2.59; 95% CI: 1.16-5.79, I 2 = 81%, P < 0.001). However, our analysis showed no statistically significant association between high FAP-α expression and neural invasion (OR: 1.57, 95% CI: 0.84-2.93, I 2 = 38%, P = 0.161).

Conclusions

This meta-analysis indicated that cancer cells with a high FAP-α expression have a higher risk of metastasis than those with a low FAP-α expression. These findings support the potential importance of FAP-α as a biomarker for cancer metastasis prediction.

PET/CT FAPI: Procedure and evidence review in oncology

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

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.

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

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

High expression of fibroblast-activating protein is a prognostic marker in non-small cell lung carcinoma

Background

Fibroblast‐activating protein (FAP) is expressed in cancer‐associated fibroblasts (CAFs) in many human carcinomas and in some types of carcinoma cells. Here, we examined the proportion of FAP protein expression in non‐small cell lung carcinoma (NSCLC) and investigated the correlation of FAP expression with clinicopathological background.

Methods

In total, 344 NSCLC tissues were examined. Tissue microarrays were constructed, and FAP expression was analyzed using immunohistochemistry. The status of FAP expression in tumor cells and CAFs was correlated with clinicopathological background, molecular features, and patient outcomes.

Results

A total of 280 patients (81.4%) had low FAP expression, and 64 patients (18.6%) had high FAP expression in tumor cells. In CAFs, 230 patients (66.9%) had low FAP expression, and 114 patients (33.1%) had high FAP expression. In multivariate analyses, high FAP expression in tumor cells was an independent predictive factor of both overall survival (OS; hazard ratio [HR] = 2.57, 95% confidence interval [CI]: 1.49–4.42, p < 0.001) and recurrence‐free survival (RFS; HR = 2.13, 95% CI: 1.38–3.29, p < 0.001). Based on combinations of FAP expression in tumor cells and CAFs, patients with Low^T/Low^CAFs had better OS and RFS than did those in the other subgroups. By contrast, patients with High^T/High^CAFs had poor OS and RFS compared with those in the other subgroups.

Conclusions

Overall, FAP expression in tumor cells and the combination FAP expression in tumor cells and CAFs were strongly associated with patient survival and may be useful predictive biomarkers for patient outcomes in NSCLC.

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.

Correlation of tumor microenvironment-related markers with clinical outcomes in patients with squamous cell carcinoma of the lung

Background

Squamous cell carcinoma (SCC) is the major histological type in lung cancer (LC). The tumor microenvironment (TME) drives tumor progression and metastasis. In the TME, cancer-associated fibroblasts (CAFs) play key roles in carcinogenesis. However, the roles of CAFs in lung SCC remain unknown. In this study, we evaluated whether the CAF phenotype was determined by various CAF-related proteins and whether CAF-related protein expression contributed to clinical outcomes in patients with lung SCC.

Methods

We examined the associations of CAF- and epithelial-mesenchymal transition (EMT)-related markers expressed in CAFs, including α-smooth muscle actin (α-SMA), CD10, podoplanin, fibroblast-specific protein 1 (FSP1), platelet-derived growth factor receptor (PDGFR) α, PDGFRβ, adipocyte enhancer-binding protein 1 (AEBP1), fibroblast activation protein (FAP), tenascin-C, Zinc finger E-box binding homeobox 1 (ZEB1), and twist homolog 1 gene (TWIST1), in 108 lung SCC tissues using immunohistochemistry. In addition, cluster analysis was used to identify objective expression patterns of immunohistochemical markers. Finally, the CD3/CD8 ratio was evaluated in order to identify the associations of CAF-related proteins with the CD3/CD8 ratio using immunohistochemistry.

Results

SCC samples were classified into two subgroups (CAF-phenotype), which were significantly correlated with disease-free and overall survival using univariate and multivariate analyses. Moreover, high AEBP1 expression was identified as an independent prognostic marker in this cohort by univariate and multivariate analyses. The CD3/CD8 ratio was not correlated with the CAF-phenotype.

Conclusions

The presence of a specific subgroup defined by multiple markers could be used for prediction of prognosis in patients with lung SCC. In addition, AEBP1 overexpression played key roles in prediction of a poor prognosis in patients with lung SCC.

Fibroblast Activation Protein-α as a Target in the Bench-to-Bedside Diagnosis and Treatment of Tumors: A Narrative Review

Fibroblast activation protein-α (FAP) is a type II integral serine protease that is specifically expressed by activated fibroblasts. Cancer-associated fibroblasts (CAFs) in the tumor stroma have an abundant and stable expression of FAP, which plays an important role in promoting tumor growth, invasion, metastasis, and immunosuppression. For example, in females with a high incidence of breast cancer, CAFs account for 50–70% of the cells in the tumor’s microenvironment. CAF overexpression of FAP promotes tumor development and metastasis by influencing extracellular matrix remodeling, intracellular signaling, angiogenesis, epithelial-to-mesenchymal transition, and immunosuppression. This review discusses the basic biological characteristics of FAP and its applications in the diagnosis and treatment of various cancers. We review the emerging basic and clinical research data regarding the use of nanomaterials that target FAP.

Characterising cancer-associated fibroblast heterogeneity in non-small cell lung cancer: a systematic review and meta-analysis

Cancer-associated fibroblasts (CAFs) are a key component of the tumour microenvironment with evidence suggesting they represent a heterogeneous population. This study summarises the prognostic role of all proteins characterised in CAFs with immunohistochemistry in non-small cell lung cancer thus far. The functions of these proteins in cellular processes crucial to CAFs are also analysed. Five databases were searched to extract survival outcomes from published studies and statistical techniques, including a novel method, used to capture missing values from the literature. A total of 26 proteins were identified, 21 of which were combined into 7 common cellular processes key to CAFs. Quality assessments for sensitivity analyses were carried out for each study using the REMARK criteria whilst publication bias was assessed using funnel plots. Random effects models consistently identified the expression of podoplanin (Overall Survival (OS)/Disease-specific Survival (DSS), univariate analysis HR 2.25, 95% CIs 1.80-2.82) and α-SMA (OS/DSS, univariate analysis HR 2.11, 95% CIs 1.18-3.77) in CAFs as highly prognostic regardless of outcome measure or analysis method. Moreover, proteins involved in maintaining and generating the CAF phenotype (α-SMA, TGF-β and p-Smad2) proved highly significant after sensitivity analysis (HR 2.74, 95% CIs 1.74-4.33) supporting attempts at targeting this pathway for therapeutic benefit.

Impact of the Tumor Microenvironment on Tumor Heterogeneity and Consequences for Cancer Cell Plasticity and Stemness

Tumor heterogeneity is considered the major cause of treatment failure in current cancer therapies. This feature of solid tumors is not only the result of clonal outgrowth of cells with genetic mutations, but also of epigenetic alterations induced by physical and chemical signals from the tumor microenvironment (TME). Besides fibroblasts, endothelial and immune cells, mesenchymal stroma/stem-like cells (MSCs) and tumor-associated macrophages (TAMs) intimately crosstalk with cancer cells and can exhibit both anti- and pro-tumorigenic effects. MSCs can alter cancer cellular phenotypes to increase cancer cell plasticity, eventually resulting in the generation of cancer stem cells (CSCs). The shift between different phenotypic states (phenotype switching) of CSCs is controlled via both genetic programs, such as epithelial-mesenchymal transdifferentiation or retrodifferentiation, and epigenetic alterations triggered by signals from the TME, like hypoxia, spatial heterogeneity or stromal cell-derived chemokines. Finally, we highlight the role of spontaneous cancer cell fusion with various types of stromal cells. i.e., MSCs in shaping CSC plasticity. A better understanding of cell plasticity and phenotype shifting in CSCs is a prerequisite for exploiting this phenomenon to reduce tumor heterogeneity, thereby improving the chance for therapy success.

Endothelial, pericyte and tumor cell expression in glioblastoma identifies fibroblast activation protein (FAP) as an excellent target for immunotherapy

Objectives

Targeted immunotherapies such as chimeric antigen receptor (CAR)-T cells are emerging as attractive treatment options for glioblastoma, but rely on identification of a suitable tumor antigen. We validated a new target antigen for glioblastoma, fibroblast activation protein (FAP), by undertaking a detailed expression study of human samples.

Methods

Glioblastoma and normal tissues were assessed using immunostaining, supported by analyses of published transcriptomic datasets. Short-term cultures of glioma neural stem (GNS) cells were compared to cultures of healthy astrocytes and neurons using flow cytometry. Glioblastoma tissues were dissociated and analysed by high-parameter flow cytometry and single-cell transcriptomics (scRNAseq).

Results

Compared to normal brain, FAP was overexpressed at the gene and protein level in a large percentage of glioblastoma tissues, with highest levels of expression associated with poorer prognosis. FAP was also overexpressed in several paediatric brain cancers. FAP was commonly expressed by cultured GNS cells but absent from normal neurons and astrocytes. Within glioblastoma tissues, the strongest expression of FAP was around blood vessels. In fact, almost every tumor vessel was highlighted by FAP expression, whereas normal tissue vessels and cultured endothelial cells (ECs) lacked expression. Single-cell analyses of dissociated tumors facilitated a detailed characterisation of the main cellular components of the glioblastoma microenvironment and revealed that vessel-localised FAP is because of expression on both ECs and pericytes.

Conclusion

Fibroblast activation protein is expressed by multiple cell types within glioblastoma, highlighting it as an ideal immunotherapy antigen to target destruction of both tumor cells and their supporting vascular network.

Fibroblast Activation Protein-α Expressing Fibroblasts Promote Lymph Node Metastasis in Esophageal Squamous Cell Carcinoma

Background and Objectives

Esophageal squamous cell carcinoma (ESCC) remains one of the most common malignancies in China and has a high metastasis rate and poor prognosis. Fibroblast activation protein-α (FAP-α) is a serine peptidase the expression of which in cancer-associated fibroblasts has been associated with a higher risk of metastases and poor survival. This study aimed to analyze the correlation of FAP-α expression with the lymph node metastasis and prognostic significance in ESCC.

Methods

FAP-α expression was examined in 121 resected ESCC specimens and 10 adjacent normal tissue using immunohistochemistry. FAP-α expression was scored in the stromal fibroblasts adjacent to neoplastic nests. A chi-square test was used to analyze the correlation between FAP-α expression in tumors stromal and lymph node metastasis of ESCC. The association between FAP-α expression and prognosis was evaluated using univariable and multivariable statistical modeling.

Results

FAP-α expression was absent in the benign controls. FAP-α expression was evident in the stromal 37% (45/121) of ESCC. Expression of FAP-α level is significantly associated with lymph node metastasis (p=0.023), but it is not correlated to age, gender, and tumor location in ESCC patients. Stromal FAP-α expression was significantly associated with poor survival in univariable (HR 2.009; 95% CI 1.259–3.205; p=0.003) and multivariable analysis (HR 1.833; 95% CI 1.144–2.937; p=0.012).

Conclusion

FAP-α may be an important regulator in lymph node metastasis of ESCC and may provide a novel therapeutic target in ESCC.

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The prognostic significance of fibroblast activation protein-α in human lung adenocarcinoma

Background

Fibroblast activation protein (FAP) is a type II cell surface-bound integral serine protease, which is an important biomarker of cancer-associated fibroblasts. FAP-α performs several biological activities, including remolding extracellular matrix and acting as an immunosuppressor in the tumor microenvironment. However, the proliferation role of FAP-α in human lung adenocarcinoma has not been fully elucidated.

Methods

The expression of FAP-α in 94-paired human lung adenocarcinoma tissues was identified by immunohistochemistry test. The effect of FAP on cell proliferation was examined by CCK-8 assay. RNA-sequencing and bioinformatics analysis were utilized to investigate the underlying mechanism. Western blot analysis, quantitative polymerase chain reaction (qPCR), and nude mice experiments, were also conducted for further validation.

Results

The proliferation rates of human fibroblast strains FAP-HFF and FAP-BJ, and human lung adenocarcinoma cell line FAP-SPC-A-1 were higher than those of controls. The nude mice experiment also showed that FAP could promote the proliferation of SPC-A-1 cell line in vivo. qPCR and Western blot analysis indicated that CCNB1 was upregulated by the overexpression of FAP in the lung adenocarcinoma cell line. The expression of FAP-α was higher in both the cytoplasm and stroma of lung adenocarcinoma than in adjacent normal tissues. Survival analysis indicated that patients with higher expression of FAP-α in tumor stroma had a poor prognosis (P=0.019). The Cancer Genome Atlas Program (TCGA) data also showed that the expression of FAP within tumor tissues was higher (in both cytoplasm and stroma) compared with that in normal tissues (P<0.05).

Conclusions

Our study indicates that FAP-α could facilitate the proliferation of lung adenocarcinoma cells and can be a prognostic marker in human lung adenocarcinoma.

Clinical significance of cancer-associated fibroblasts and their correlation with microvessel and lymphatic vessel density in lung adenocarcinoma

Background

To determine whether cancer‐associated fibroblasts (CAFs) are associated with microvessel density (MVD) and lymphatic vessel density (LVD) in lung adenocarcinoma (ADC) or are not prognostic.

Methods

Ninety‐three lung adenocarcinoma patients without adjuvant therapy between January 2010 and June 2011 were enrolled. CAFs, MVD, and LVD were identified by α‐smooth muscle actin (α‐SMA), CD34 and D2‐40 staining via immunohistochemistry. Staining intensities were assessed and quantified. For statistics, Pearson's chi‐square test, logistic regression, Kaplan‐Meier, and log‐rank tests were applied. In addition, the Cox proportional hazards model was used for multifactor analysis to predict survival.

Results

CAFs abundance in lung adenocarcinoma is associated with higher MVD and LVD. In addition, a correlation was demonstrated between MVD and LVD (P < 0.05). CAFs, MVD, and LVD are significantly correlating with age, tumor size, differentiation grade, clinical stage, and lymph node metastasis (P < 0.05), but not influenced by gender, tumor location, and smoking history. Three‐year overall survival in the CAFs‐poor group is 64.5%, which is significant higher than that in the CAFs‐rich cohort (41.9%). Further, we found that age, clinical stage, α‐SMA, CD34, D2‐40 positivity, tumor size, differentiation grade, and lymph node metastasis significantly correlate with overall survival of patients with lung adenocarcinoma. However, sex, smoking history, and tumor location have no association with 3‐year survival. The clinical stage is an independent prognostic factor in overall survival (P < 0.05).

Conclusions

The density of CAFs identified by α‐SMA staining is associated with progression and metastasis of lung adenocarcinoma and affects the patient's disease outcome.