Expression of mesothelin in thymic carcinoma and its potential therapeutic significance

Immunotherapy for Thymomas and Thymic Carcinomas: Current Status and Future Directions

Thymic epithelial tumors are a histologically diverse group of cancers arising from the epithelial compartment of the thymus. These tumors are characterized by a low tumor mutation burden, a lack of actionable genomic changes, and, especially with thymomas, defects in immune tolerance. Surgery is the mainstay of the management of resectable disease, whereas advanced, unresectable tumors are treated with platinum-based chemotherapy. Disease recurrence can occur months to years after frontline treatment. Although several options are available for conventional treatment of recurrent thymic tumors, response rates are generally low, and treatment-related toxicity can affect quality of life. A subset of patients benefit from biologic therapies, but there remains an unmet need for the development of new treatments. Immune checkpoint inhibitors are safe, clinically active, and have contributed to an improvement in survival for patients with a wide variety of cancers. However, the application of these revolutionary treatments for thymic cancers is limited to their use for the management of recurrent thymic carcinoma because of the risk of immune toxicity. In this paper, we review the current uses of immunotherapy for the management of thymic epithelial tumors and highlight potential strategies to improve safety and broaden the application of these treatments for patients with thymic cancers.

Understanding the landscape of immunotherapy in thymic epithelial tumors

Thymic epithelial tumors (TETs) are a rare group of malignancies arising from the thymus. Surgery remains the foundation of treatment for patients with early-stage disease. Limited treatment options are available for the treatment of unresectable, metastatic, or recurrent TETs and are associated with modest clinical efficacy. The emergence of immunotherapies in the treatment of solid tumors has generated significant interest in understanding their role in TET treatment. However, the high rates of comorbid paraneoplastic autoimmune disorders, particularly in thymoma, have tempered expectations regarding the role of immune-based therapies. Clinical studies of immune checkpoint blockade (ICB) in thymoma and thymic carcinoma have revealed higher frequencies of immune-related adverse events (IRAEs) and limited efficacy. Despite these setbacks, the growing understanding of the thymic tumor microenvironment and systemic immune system has advanced the understanding of these diseases and provided opportunities for novel immunotherapy modalities. Ongoing studies are evaluating numerous immune-based treatments in TETs with the goal of improving clinical efficacy and mitigating IRAE risk. This review will provide insight into the current understanding of the thymic immune microenvironment, outcomes of previous ICB studies, and review treatments currently being explored for the management of TET.

Structural and Functional Thymic Biomarkers Are Involved in the Pathogenesis of Thymic Epithelial Tumors: An Overview

The normal human thymus originates from the third branchial cleft as two paired anlages that descend into the thorax and fuse on the midline of the anterior–superior mediastinum. Alongside the epithelial and lymphoid components, different types of lymphoid accessory cells, stromal mesenchymal and endothelial cells migrate to, or develop in, the thymus. After reaching maximum development during early postnatal life, the human thymus decreases in size and lymphocyte output drops with age. However, thymic immunological functions persist, although they deteriorate progressively. Several major techniques were fundamental to increasing the knowledge of thymic development and function during embryogenesis, postnatal and adult life; these include immunohistochemistry, immunofluorescence, flow cytometry, in vitro colony assays, transplantation in mice models, fetal organ cultures (FTOC), re-aggregated thymic organ cultures (RTOC), and whole-organ thymic scaffolds. The thymic morphological and functional characterization, first performed in the mouse, was then extended to humans. The purpose of this overview is to provide a report on selected structural and functional biomarkers of thymic epithelial cells (TEC) involved in thymus development and lymphoid cell maturation, and on the historical aspects of their characterization, with particular attention being paid to biomarkers also involved in Thymic Epithelial Tumor (TET) pathogenesis. Moreover, a short overview of targeted therapies in TET, based on currently available experimental and clinical data and on potential future advances will be proposed.

Thymic Carcinomas-A Concise Multidisciplinary Update on Recent Developments From the Thymic Carcinoma Working Group of the International Thymic Malignancy Interest Group

Thymic carcinomas are rare malignancies that in general arise in the prevascular (anterior) mediastinum. These tumors are usually invasive, often present at advanced stages, and typically behave aggressively. Studies are hampered by the paucity of these tumors, the large variety of carcinoma subtypes, and the lack of unique morphologic and immunophenotypic features. Despite these challenges, advances in diagnostic imaging, surgical approaches, systemic therapies, and radiation therapy techniques have been made. The WHO classification of thymic epithelial tumors has been updated in 2021, and the eighth tumor nodal metastasis staging by the American Joint Committee on Cancer/Union for International Cancer Control included thymic carcinomas in 2017. Molecular alterations that provide more insight into the pathogenesis of these tumors and that potentially permit use of novel targeted therapies are increasingly being identified. New approaches to radiation therapy, chemotherapy, and immunotherapy are under evaluation. International societies, including the International Thymic Malignancy Interest Group, European Society of Thoracic Surgeons, and Japanese, Chinese, and Korean thymic associations, have been critical in organizing and conducting multi-institutional clinical studies. Herein, we review contemporary multidisciplinary perspectives in diagnosis and management of thymic carcinoma.

Immunotherapy for Management of Thymic Epithelial Tumors: A Double-Edged Sword

Simple Summary

Immunotherapy has a rapidly expanding role for the treatment of several cancers due to durable clinical activity and favorable tolerability. However, the unique biology of thymic epithelial tumors (TETs) increases the risk of immune-mediated toxicity. In this paper we review the biology of thymic cancers and its impact on the potential benefits and risks of immunotherapy. We describe the results of completed clinical trials of immune checkpoint inhibitors for advanced TETs and provide an overview of potential biomarkers of response or toxicity of immunotherapy that might influence future development of immunotherapeutic modalities for the treatment of advanced thymoma and thymic carcinoma.

Abstract

Thymic epithelial tumors (TETs) are rare thoracic cancers that are broadly classified as thymomas and thymic carcinomas. Surgery is the cornerstone of management for early-stage disease. There are a limited number of effective treatment options for patients with advanced or recurrent disease. The occurrence of paraneoplastic autoimmune disorders in patients with TETs, especially thymomas, creates significant challenges for the development of immunotherapy, including immune checkpoint inhibitors, as a feasible treatment option. In addition, patients with TETs are at increased risk for the development of immune-mediated toxicity with a predilection for musculoskeletal and neuromuscular adverse events upon treatment with immunotherapy. The identification of biomarkers of response and toxicity is expected to play a key role in harnessing the benefits of immunotherapy for patients with TETs. In this paper we review the biology of TETs and the potential effects on the tolerability of immunotherapy. The results of clinical trials of immune checkpoint inhibitors for the treatment of advanced TETs are described to understand the potential risks and benefits of immunotherapy. We also provide an overview of future avenues for treatment with novel immunotherapeutic modalities and opportunities to develop biomarkers to improve the safety and tolerability of immunomodulatory treatments in patients with TETs.

Clinical Significance of Tumor Markers for Advanced Thymic Carcinoma: A Retrospective Analysis from the NEJ023 Study

Simple Summary

Advanced thymic carcinoma (ATC) is rare. Owing to its rarity, there is limited information on the prognostic factors, and the optimal serum tumor markers are also unknown. We conducted a multi-institutional retrospective study of patients with ATC. In this study, we collected data on patient characteristics, progression-free survival (PFS), overall survival (OS), and tumor marker values, and investigated the relationship between tumor marker values and PFS/OS. We found that the neuron-specific enolase (NSE) level may be a useful prognostic tumor marker for ATC, regardless of histology. The findings of the analysis limited to squamous cell carcinoma suggested that the NSE and squamous cell carcinoma antigen levels may be useful prognostic factors.

Abstract

The optimal tumor marker for predicting the prognosis of advanced thymic carcinoma (ATC) remains unclear. We conducted a multi-institutional retrospective study of patients with ATC. A total of 286 patients were treated with chemotherapy. Clinicopathological information, including serum tumor markers, was evaluated to determine the overall survival (OS) and progression-free survival (PFS). The carcinoembryonic antigen, cytokeratin-19 fragment, squamous cell carcinoma (SCC) antigen, progastrin-releasing peptide, neuron-specific enolase (NSE), and alpha-fetoprotein levels were evaluated. In the Kaplan–Meier analysis, the OS was significantly shorter in the patients with elevated NSE levels than in those with normal NSE levels (median, 20.3 vs. 36.8 months; log-rank test p = 0.029; hazard ratio (HR), 1.55; 95% confidence interval (CI), 1.05–2.31 (Cox proportional hazard model)); a similar tendency regarding the PFS was observed (median, 6.4 vs. 11.0 months; log-rank test p = 0.001; HR, 2.04; 95% CI, 1.31–3.18). No significant differences in the OS and PFS were observed among the other tumor markers. In both univariate and multivariate analyses of the patients with SCC only, the NSE level was associated with the OS and PFS. Thus, the NSE level may be a prognostic tumor marker for thymic carcinoma, regardless of histology.

Exploiting mesothelin in thymic carcinoma as a drug delivery target for anetumab ravtansine

BACKGROUND

Thymic epithelial tumours (TETs) are rare tumours comprised of thymomas and thymic carcinoma. Novel therapies are needed, especially in thymic carcinoma where the 5-year survival rate hovers at 30%. Mesothelin (MSLN), a surface glycoprotein that is cleaved to produce mature MSLN (mMSLN) and megakaryocyte potentiating factor (MPF), is expressed in limited tissues. However, its expression is present in various cancers, including thymic carcinoma, where it is expressed in 79% of cases.

METHODS

We utilised flow cytometry, in vitro cytotoxicity assays, and an in vivo xenograft model in order to demonstrate the ability of the MSLN targeting antibody-drug conjugate (ADC) anetumab ravtansine (ARav) in inhibiting the growth of thymic carcinoma.

RESULTS

Thymoma and thymic carcinoma cell lines express MSLN, and anetumab, the antibody moiety of ARav, was capable of binding MSLN expressing thymic carcinoma cells and internalising. ARav was effective at inhibiting the growth of thymic carcinoma cells stably transfected with mMSLN in vitro. In vivo, 15 mg/kg ARav inhibited T1889 xenograft tumour growth, while combining 7.5 mg/kg ARav with 4 mg/kg cisplatin yielded an additive effect on inhibiting tumour growth.

CONCLUSIONS

These data demonstrate that anetumab ravtansine inhibits the growth of MSLN positive thymic carcinoma cells in vitro and in vivo.

An Overview on Molecular Characterization of Thymic Tumors: Old and New Targets for Clinical Advances

Thymic tumors are a group of rare mediastinal malignancies that include three different histological subtypes with completely different clinical behavior: the thymic carcinomas, the thymomas, and the rarest thymic neuroendocrine tumors. Nowadays, few therapeutic options are available for relapsed and refractory thymic tumors after a first-line platinum-based chemotherapy. In the last years, the deepening of knowledge on thymus' biological characterization has opened possibilities for new treatment options. Several clinical trials have been conducted, the majority with disappointing results mainly due to inaccurate patient selection, but recently some encouraging results have been presented. In this review, we summarize the molecular alterations observed in thymic tumors, underlying the great biological differences among the different histology, and the promising targeted therapies for the future.

Relationship of possible biomarkers with malignancy of thymic tumors: a meta-analysis

Background

Role of biomarkers for promotion of tumor proliferation (BPTPs) and for promotion of apoptosis (BPAs) in thymic malignant tumors is still unclear. The purpose of this study was to evaluate the relationship between BPTPs and/or BPAs and malignancy of thymic malignant tumors.

Methods

Studies on thymic malignant tumors and biomarkers were searched in PubMed, ISI Web of Knowledge, and Embase databases, and all statistical analyses were conducted using Review Manager.

Results

Twelve articles related to biomarkers and thymic malignant tumors were selected and analyzed. A relationship between BPAs and Masaoka stage was demonstrated for four markers, namely Bax, p73, Casp-9 and Bcl-2, included 138 stage I/II patients and 74 stage III/IV patients, and BPAs were significantly correlated with high Masaoka staging (P = 0.03). We further found a relationship between BPAs and degree of malignancy for four markers, namely Bax, p73, Casp-9 and Bcl-2, included 176 thymoma patients and 36 thymic carcinoma patients, and BPAs were significantly correlated with thymic carcinoma (P = 0.010). In addition, a relationship between BPTP and Masaoka staging was demonstrated for seven markers, namely Podoplanin, Glut-1, Muc-1, Egfr, Igf1r, c-Jun, and n-Ras, included 373 patients with stage I/II and 212 patients with stage III/IV, and BPTPs were significantly correlated with high Masaoka staging (P < 0.001). We also found a relationship between BPTPs and degree of malignancy for ten markers, namely Mesothelin, c-Kit (CD117), Egfr, Lat-1, Muc-1,Ema, Glut-1, Igf1r, c-Jun, and n-Ras, included 748 thymoma patients and 280 thymic carcinoma patients, and BPTPs were significantly correlated with thymic carcinoma (P < 0.001).

Conclusion

These findings show that high levels of BPTPs or BPAs are more closely related to thymic carcinoma and Masaoka stage III/IV, suggesting that BPTPs and BPAs may play an important role in the occurrence and development of thymic malignant tumors.

Diagnostic Roles of Immunohistochemistry in Thymic Tumors: Differentiation between Thymic Carcinoma and Thymoma

Background: The present study aims to evaluate the diagnostic roles of various immunohistochemical (IHC) markers in thymic tumors, including thymic carcinoma (TC) and thymoma (TM). Methods: Eligible studies were obtained by searching the PubMed databases and screening the searched articles. Thirty-eight articles were used in the present meta-analysis and included 636 TCs and 1861 TMs. Besides, for IHC markers with statistical significance, a diagnostic test accuracy review was performed. Results: The comparison of various IHC expressions between TC and TM was performed for 32 IHC markers. Among these IHC markers, there were significant differences between TC and TM for beta-5t, B-cell lymphoma 2 (Bcl-2), calretinin, CD1a, CD5, carcinoembryonic antigen (CEA), cytokeratin19 (CK19), CD117, glucose transporter 1 (Glut-1), insulin-like growth factor 1 receptor (IGF-1R), mesothelin, MOC31, mucin1 (MUC1), p21, and terminal deoxynucleotidyl transferase (TdT). Markers with higher expressions in TCs were Bcl-2, calretinin, CD5, CEA, CD117, Glut-1, IGF-1R, mesothelin, MOC31, MUC1, and p21. Among these markers, there were no significant differences between TC and TM type B3 in immunohistochemistries for Bcl-2 and CK19. On the other hand, β-catenin and CD205 showed a considerable difference in IHC expressions between TC and TM type B3, but not between TC and overall TM. In diagnostic test accuracy review, MUC1 and beta-5t were the most useful markers for TC and TM, respectively. Conclusions: Taken together, our results showed that the expression rates for various IHC markers significantly differed between TC and TM. The IHC panel can be useful for differentiation from limited biopsied specimens in daily practice.

Diffuse mesothelin expression leads to worse prognosis through enhanced cellular proliferation in colorectal cancer

Mesothelin (MSLN) is a glycophosphatidylinositol (GPI)-linked cell surface protein that is highly expressed in several types of malignant tumor, including malignant pleural mesothelioma, ovarian cancer and pancreatic adenocarcinoma. Recently, a comprehensive immunohistochemical study using MN-1 monoclonal antibody identified a significant number of colorectal tumors in which MSLN was expressed. However, the clinicopathological profiles and survival of patients with MSLN-positive colorectal cancer have not been fully analyzed. In the current study, the expression of MSLN in 270 primary and 44 metastatic colorectal tumors was immunohistochemically analyzed to determine the clinical usefulness of MSLN immunohistochemistry and to identify potential candidates for future anti-MSLN therapy. In vitro experiments using colon cancer cell lines were performed to investigate the biological significance of MSLN expression in tumors. The results of univariate analyses identified a significant correlation between MSLN expression and females (P=0.0042). Furthermore, an inverse correlation between MSLN expression and solid/sheet-like proliferation (P=0.014) was also revealed. Additionally, overall survival was significantly shorter in patients with diffuse luminal/membranous expression of MSLN (P=0.018). Multivariable Cox hazards regression analysis revealed diffuse MSLN expression (hazard ratio, 2.26; 95% confidence interval, 1.04-4.91; P=0.039) as a potential risk factor. When comparing primary CRCs and the metastasis of each, a weakly positive correlation was identified for MSLN positivity (% positive cells; R=0.484; P<0.0001). The in vitro experiments revealed a positive role for MSLN in colon cancer cell proliferation. Thus, MSLN immunohistochemistry may be useful in the prognostication of patients with CRC. The results demonstrated that significant numbers of patients with MSLN-positive CRC exhibiting metastasis could be targeted by anti-MSLN therapies.

Deciphering the biology of thymic epithelial tumors

Thymic cancers arise from epithelial cells of the thymus and have a predilection for intrathoracic spread. Clinical behavior varies from relatively indolent to highly aggressive with a capacity to metastasize widely and adversely affect survival. Paraneoplastic autoimmune disorders are frequently observed in association with thymoma and have a significant impact on quality of life. Underlying immune deficits associated with thymic epithelial tumors (TETs) increase the risk for development of opportunistic infections and emergence of extrathymic malignancies. Advances in the molecular characterization of thymic tumors have revealed the lowest tumor mutation burden among all adult cancers and the occurrence of distinct molecular subtypes of these diseases. Mutations in general transcription factor IIi (GTF2I) are unique to TETs and are rarely observed in other malignancies. The infrequency of actionable mutations has created obstacles for the development of biologic therapies and has spurred research to uncover druggable genomic targets. Persistence of autoreactive T cells due to altered thymic function increases the risk for development of severe immune-related toxicity and limits opportunities for use of immune-based therapies, especially in patients with thymoma. In this paper we review emerging data on the molecular characterization and immunobiology of thymic tumors and highlight clinical implications of these discoveries.

Amatuximab and novel agents targeting mesothelin for solid tumors

Mesothelin (MSLN) is considered a promising target for cancer therapy. Originally extracted in 1992 after the immunization of mice with a human ovarian cancer (OC) cell line and cloned in 1996, MSLN seems to be involved in cell adhesion and metastasis. MSLN is prevalent in mesothelia tissues but is expressed in several human cancers, such as OC, pancreatic cancer, mesothelioma, and lung cancer. Amatuximab (MORAb-009) is a mouse-human chimeric monoclonal antibody with a selective affinity for MSLN. The principal mechanism of action comprises inhibition of binding of MSLN with the antigen CA125/MUC16. The highest phase of development is actually a Phase II trial (MORAb-009-201, Europe). In this review, we describe the mechanism of action of amatuximab and other MSLN-targeting novel drugs, along with a discussion about the expected efficacy, safety, and toxicity of this promising group of agents and implications for future research and clinical practice.

Chimeric Antigen Receptor (CAR) T-Cell Therapy for Thoracic Malignancies

Chimeric antigen receptor (CAR) T cells are patient T cells that are transduced with genetically engineered synthetic receptors to target a cancer cell surface antigen. The remarkable clinical response rates achieved by adoptive transfer of T cells that target CD19 in patients with leukemia and lymphoma have led to a growing number of clinical trials exploring CAR T-cell therapy for solid tumors. Herein, we review the evolution of adoptive T-cell therapy; highlight advances in CAR T-cell therapy for thoracic malignancies; and summarize the targets being investigated in clinical trials for patients with lung cancer, malignant pleural mesothelioma, and esophageal cancer. We further discuss the barriers to successfully translating CAR T-cell therapy for solid tumors and present strategies that have been investigated to overcome these hurdles.

Combining immunotherapy and radiation therapy for small cell lung cancer and thymic tumors

Recent work with immunotherapy has shown promising results with treatment of several solid malignancies, and there are several reports of good systemic responses with the combination of immunotherapy and radiation therapy (RT), most notably in advanced melanoma. Given the rapid increase in the use of checkpoint blockade as well as anti-tumor vaccines, we review here the preclinical rationale and ongoing clinical work in combining immunotherapy with RT for small cell lung cancer (SCLC) and thymic tumors. While there are several reports of promising results with the combination of immunotherapy and conventional systemic treatment, we focus here on the ongoing clinical studies that combine immunotherapy with RT, and highlight the emerging data for this multimodality approach as well as key preclinical and clinical issues that remain to be addressed. With regards to SCLC, trials exploring to the combination of immunotherapy and RT are already ongoing, but clinical studies for this combination in thymoma are lacking.