Establishment and characterization of a novel cell line derived from human thymoma AB tumor

The Way Ahead: Lessons Learned from Decades of Cancer Research on Thymomas and Thymic Carcinomas

The history of thymoma (TH) research begins in the early 20th century, when Bell first recognized the epithelial nature of these tumors and their association with myasthenia gravis (MG) [...].

Histogenetic and disease-relevant phenotypes in thymic epithelial tumors (TETs): The potential significance for future TET classification

Thymic epithelial tumors (TETs) encompass morphologically various subtypes. Thus, it would be meaningful to explore the expression phenotypes that delineate each TET subtype or overarching multiple subtypes. If these profiles are related to thymic physiology, they will improve our biological understanding of TETs and may contribute to the establishment of a more rational TET classification. Against this background, pathologists have attempted to identify histogenetic features in TETs for a long time. As part of this work, our group has reported several TET expression profiles that are histotype-dependent and related to the nature of thymic epithelial cells (TECs). For example, we found that beta5t, a constituent of thymoproteasome unique to cortical TECs, is expressed mainly in type B thymomas, for which the nomenclature of cortical thymoma was once considered. Another example is the discovery that most thymic carcinomas, especially thymic squamous cell carcinomas, exhibit expression profiles similar to tuft cells, a recently discovered special type of medullary TEC. This review outlines the currently reported histogenetic phenotypes of TETs, including those related to thymoma-associated myasthenia gravis, summarizes their genetic signatures, and provides a perspective for the future direction of TET classification.

The immune landscape of human thymic epithelial tumors

Human thymic epithelial tumors (TET) are common malignancies in the anterior mediastinum with limited biological understanding. Here we show, by single cell analysis of the immune landscape, that the developmental pattern of intra-tumoral T-cells identify three types within TETs. We characterize the developmental alterations and TCR repertoires of tumor-infiltrating T cells in the context of the distinguishing epithelial tumor cell types. We demonstrate that a subset of tumor cells, featuring medullary thymic epithelial cell (TEC) phenotype and marked by KRT14/GNB3 expression, accumulate in type 1 TETs, while T-cell positive selection is inhibited. Type 2 TETs are dominated by CCL25⁺ cortical TEC-like cells that appear to promote T-cell positive selection. Interestingly, the CHI3L1⁺ medullary TEC-like cells that are the characteristic feature of type 3 TETs don’t seem to support T-cell development, however, they may induce a tissue-resident CD8⁺ T cell response. In summary, our work suggests that the molecular subtype of epithelial tumour cells in TETs determine their tumour immune microenvironment, thus GNB3 and CHI3L1 might predict the immunological behavior and hence prognosis of these tumours.

Thymic epithelial tumours represent a heterogenous group of malignancies with varied immune cell infiltration and prognosis. Here authors systematically analyze the phenotypes of both epithelial and immune cells that form these tumours, and identify three major subtypes with different T cell involvement that might affect prognosis.

Functional apoptosis profiling identifies MCL-1 and BCL-xL as prognostic markers and therapeutic targets in advanced thymomas and thymic carcinomas

BACKGROUND

Multi-omics studies have shown a high and lack of common driver mutations in most thymomas (TH) and thymic carcinomas (TC) that hamper the development of novel treatment approaches. However, deregulation of apoptosis has been proposed as a common hallmark of TH and TC. BH3 profiling can be utilized to study the readiness of living cancer cells to undergo apoptosis and their dependency on pro-survival BCL-2 family proteins.

METHODS

We screened a cohort of 62 TH and TC patient samples for expression of BCL-2 family proteins and used the TC cell line 1889c and native TH for dynamic BH3 profiling and treatment with BH3 mimetics.

RESULTS

Immunohistochemical overexpression of MCL-1 and BCL-xL was a strong prognostic marker of TH and TC, and BH3 profiling indicated a strong dependency on MCL-1 and BCL-xL in TH. Single inhibition of MCL-1 resulted in increased binding of BIM to BCL-xL as an escape mechanism that the combined inhibition of both factors could overcome. Indeed, the inhibition of MCL-1 and BCL-xL in combination induced apoptosis in a caspase-dependent manner in untreated and MCL-1-resistant 1889c cells.

CONCLUSION

TH and TC are exquisitely dependent on the pro-survival factors MCL-1 and BCL-xL, making them ideal candidates for co-inhibition by BH3 mimetics. Since TH show a heterogeneous dependency on BCL-2 family proteins, upfront BH3 profiling could select patients and tailor the optimal therapy with the least possible toxicity.

The 2021 WHO Classification of Tumors of the Thymus and Mediastinum: What Is New in Thymic Epithelial, Germ Cell, and Mesenchymal Tumors?

This overview of the fifth edition of the WHO classification of thymic epithelial tumors (including thymomas, thymic carcinomas, and thymic neuroendocrine tumors [NETs]), mediastinal germ cell tumors, and mesenchymal neoplasms aims to (1) list established and new tumor entities and subtypes and (2) focus on diagnostic, molecular, and conceptual advances since publication of the fourth edition in 2015. Diagnostic advances are best exemplified by the immunohistochemical characterization of adenocarcinomas and the recognition of genetic translocations in metaplastic thymomas, rare B2 and B3 thymomas, and hyalinizing clear cell carcinomas. Advancements at the molecular and tumor biological levels of utmost oncological relevance are the findings that thymomas and most thymic carcinomas lack currently targetable mutations, have an extraordinarily low tumor mutational burden, but typically have a programmed death-ligand 1^high phenotype. Finally, data underpinning a conceptual advance are illustrated for the future classification of thymic NETs that may fit into the classification scheme of extrathoracic NETs. Endowed with updated clinical information and state-of-the-art positron emission tomography and computed tomography images, the fifth edition of the WHO classification of thymic epithelial tumors, germ cell tumors, and mesenchymal neoplasms with its wealth of new diagnostic and molecular insights will be a valuable source for pathologists, radiologists, surgeons, and oncologists alike. Therapeutic perspectives and research challenges will be addressed as well.

Genomic clustering analysis identifies molecular subtypes of thymic epithelial tumors independent of World Health Organization histologic type

Further characterization of thymic epithelial tumors (TETs) is needed. Genomic information from 102 evaluable TETs from The Cancer Genome Atlas (TCGA) dataset and from the IU-TAB-1 cell line (type AB thymoma) underwent clustering analysis to identify molecular subtypes of TETs. Six novel molecular subtypes (TH1-TH6) of TETs from the TCGA were identified, and there was no association with WHO histologic subtype. The IU-TAB-1 cell line clustered into the TH4 molecular subtype and in vitro testing of candidate therapeutics was performed. The IU-TAB-1 cell line was noted to be resistant to everolimus (mTORC1 inhibitor) and sensitive to nelfinavir (AKT1 inhibitor) across the endpoints measured. Sensitivity to nelfinavir was due to the IU-TAB-1 cell line’s gain-of function (GOF) mutation in PIK3CA and amplification of genes observed from array comparative genomic hybridization (aCGH), including AURKA, ERBB2, KIT, PDGFRA and PDGFB, that are known upregulate AKT, while resistance to everolimus was primarily driven by upregulation of downstream signaling of KIT, PDGFRA and PDGFB in the presence of mTORC1 inhibition. We present a novel molecular classification of TETs independent of WHO histologic subtype, which may be used for preclinical validation studies of potential candidate therapeutics of interest for this rare disease.

Small interfering-high mobility group A2 attenuates epithelial-mesenchymal transition in thymic cancer cells via the Wnt/β-catenin pathway

Thymus carcinoma is one of the thymic epithelial neoplasms with high metastasis, which does not have any good treatment at present. High mobility group A2 (HMGA2) is highly expressed in a variety of malignant tumors, such as lung cancer, colon cancer and ovarian cancer and is closely related to tumor invasion and metastasis. The present study aimed to investigate the effect and mechanism of HMGA2 on epithelial-mesenchymal transition (EMT) in thymic cancer cells. IU-TAB-1, A549, HCT-116 and 293T cells were screened by testing the protein expression level of HMGA2 though western blotting and subjected to HMGA2 interference [small interfering (si)-HMGA2]. Cell proliferation was evaluated using the Cell Counting Kit-8 assay. Cell migration and invasion were detected using the Transwell assay. Cell apoptosis was examined using flow cytometry and β-catenin expression was observed by immunofluorescence. The levels of E-cadherin, vimentin, Wnt3a, Wnt5a and β-catenin proteins were determined by western blotting. Among the four cell lines tested, IU-TAB-1 cells demonstrated the highest expression of HMGA2 (P<0.05) and were hence selected for subsequent experiments. Compared with the control group (untransfected cells), si-HMGA2 resulted in significantly decreased proliferation, migration and invasion of IU-TAB-1 cells, whereas apoptosis was increased (P<0.05). The protein expression of vimentin, Wnt3a, Wnt5a and β-catenin was significantly decreased by si-HMGA2 compared with the control group (P<0.05), whereas E-cadherin expression was increased (P<0.05). After treatment with si-HMGA2 in combination with Wnt/β-catenin agonists (SKL2001) or inhibitors (XAV-939), EMT was respectively enhanced or inhibited in IU-TAB-1 cells. Overall, si-HMGA2 may attenuate EMT in thymic cancer cells and the mechanism may be related to the Wnt/β-catenin pathway.

A Tuft Cell-Like Signature Is Highly Prevalent in Thymic Squamous Cell Carcinoma and Delineates New Molecular Subsets Among the Major Lung Cancer Histotypes

INTRODUCTION

In-depth genomic characterization of thymic epithelial tumors (TETs), comprising thymomas and thymic carcinomas (TCs), failed to identify targetable mutations and suggested unique biology of TETs, including KIT expression in most TCs. Recently, tuft cell-like medullary thymic epithelial cells were identified in the murine thymus, and our reanalysis of the published gene expression data revealed that these cells express KIT. In addition, recently, a minor subset of SCLCs with tuft cell-like features was described.

METHODS

We interrogated mRNA expression data from our tumor cohorts (N = 60) and publicly available, independent data sets from TETs and NSCLC (N = 1199) for expression of tuft cell genes and KIT. Expression of KIT and of POU2F3 protein, the master regulator of tuft cells, was analyzed in cancer tissue (N = 344) by immunohistochemistry.

RESULTS

Normal human thymic tuft cells and most TCs coexpressed KIT and known tuft cell genes, particularly POU2F3 and GFI1B. Unexpectedly, small subsets of tuft cell-like tumors coexpressing POU2F3, GFI1B, and KIT were also identified among pulmonary squamous cell carcinomas, adenocarcinomas, and large cell neuroendocrine carcinoma and clustered together in each histologic cohort. In addition to the tuft cell-like signature, both thymic and lung tuft cell-like carcinomas had distinct genetic, pathologic, and clinical features in each cohort.

CONCLUSIONS

We suggest that the tuft cell-like phenotype defines novel subsets of thymic and pulmonary carcinoma. Its high prevalence in thymic squamous cell carcinomas that have no known toxic or viral etiologies suggests a new mechanism of carcinogenesis that may lead to specific drug susceptibilities.

Downregulation of CYLD promotes IFN-γ mediated PD-L1 expression in thymic epithelial tumors

OBJECTIVES

Recent genomic studies suggest the biological significance of the　cylindromatosis (CYLD) gene in thymic epithelial tumors (TETs). CYLD is a crucial regulator of immune response, and we previously reported that CYLD mutation is associated with high PD-L1 expression in thymic carcinoma. Therefore, we wanted to explore the role and mechanism of CYLD in regulating PD-L1 expression in TETs.

MATERIALS AND METHODS

The role of CYLD in PD-L1 expression was assessed by knockdown of CYLD in TET cells upon stimulation with interferon gamma (IFN-γ), tumor necrosis factor-α (TNF-α) or polyinosinic-polycytidylic acid (poly I:C). The molecular mechanism was investigated through analysis of downstream molecules in the STAT1/IRF1 pathway. Moreover, the clinical correlation between low CYLD and high PD-L1 expression, and the clinical impact of CYLD expression were evaluated in tissue microarrays of 105 TET cases.

RESULTS

CYLD knockdown significantly enhanced the expression of PD-L1 in presence of IFN-γ stimulation in most TET cell lines. However, this phenomenon was not observed in presence of TNF-α stimulation. CYLD knockdown upregulated IFN-γ mediated activation of the STAT1/IRF1 axis, which in turn induced PD-L1 expression. Interestingly, we found a significant association between low CYLD expression and ≥ 50 % PD-L1 expression (p = 0.001). In addition, the average proportion of tumor cells exhibiting PD-L1 staining was significantly higher in the low CYLD expression group (24.7 %) than in the high CYLD expression group (5.2 %) (p = 0.005). There was no correlation between CYLD expression and the frequency of pre-existing paraneoplastic auto-immune diseases. In advanced stages (III/IV), the low CYLD expressing group had numerically worse survival than the high CYLD group (log-rank p = 0.089).

CONCLUSIONS

Our findings provide insight into the mechanism of regulation of PD-L1 expression by CYLD in TET cells. Tumors with low CYLD expression could be potential targets for PD-1/PD-L1 inhibitors.

Activation of the mTOR/ Akt pathway in thymic epithelial cells derived from thymomas

The pathogenesis of thymic epithelial tumors remains poorly elucidated. The PIK3/Akt/mTOR pathway plays a key role in various cancers; interestingly, several phase I/II studies have reported a positive effect of mTOR inhibitors in disease control in thymoma patients. A major limit for deciphering cellular and molecular events leading to the transformation of thymic epithelial cells or for testing drug candidates is the lack of reliable in vitro cell system. We analyzed protein expression and activation of key players of the Akt/ mTOR pathway namely Akt, mTOR, and P70S6K in eleven A, B and AB thymomas as well as in normal thymuses. While only Akt and phospho-Akt were expressed in normal thymuses, both Akt and mTOR were activated in thymomas. Phospho-P70S6K was expressed in all thymic tumors whatever their subtypes, and absent in normal thymus. Interestingly, we report the activation of Akt, mTOR and P70S6 proteins in primary thymic epithelial cells maintained for short period of time after their derivation from seven AB and B thymomas. Finally, we showed that rapamycin (100 nM) significantly reduced proliferation of thymoma- derived epithelial cells without inducing cell death. Our results suggest that the activation of the Akt/ mTOR pathway might participate to the cell proliferation associated with tumor growth. Ultimately, our data enhance the potential role of thymic epithelial cells derived from tissue specimens for in vitro exploration of molecular abnormalities in rare thymic tumors.

Therapeutic Effects of XPO1 Inhibition in Thymic Epithelial Tumors

Exportin 1 (XPO1) mediates nuclear export of many cellular factors known to play critical roles in malignant processes, and selinexor (KPT-330) is the first XPO1-selective inhibitor of nuclear export compound in advanced clinical development phase for cancer treatment. We demonstrated here that inhibition of XPO1 drives nuclear accumulation of important cargo tumor suppressor proteins, including transcription factor FOXO3a and p53 in thymic epithelial tumor (TET) cells, and induces p53-dependent and -independent antitumor activity in vitro Selinexor suppressed the growth of TET xenograft tumors in athymic nude mice via inhibition of cell proliferation and induction of apoptosis. Loss of p53 activity or amplification of XPO1 may contribute to resistance to XPO1 inhibitor in TET. Using mass spectrometry-based proteomics analysis, we identified a number of proteins whose abundances in the nucleus and cytoplasm shifted significantly following selinexor treatment in the TET cells. Furthermore, we found that XPO1 was highly expressed in aggressive histotypes and advanced stages of human TET, and high XPO1 expression was associated with poorer patient survival. These results underscore an important role of XPO1 in the pathogenesis of TET and support clinical development of the XPO1 inhibitor for the treatment of patients with this type of tumors. Cancer Res; 77(20); 5614-27. ©2017 AACR.

The 2015 World Health Organization Classification of Tumors of the Thymus: Continuity and Changes

This overview of the 4th edition of the World Health Organization (WHO) Classification of thymic tumors has two aims. First, to comprehensively list the established and new tumor entities and variants that are described in the new WHO Classification of thymic epithelial tumors, germ cell tumors, lymphomas, dendritic cell and myeloid neoplasms, and soft-tissue tumors of the thymus and mediastinum; second, to highlight major differences in the new WHO Classification that result from the progress that has been made since the 3rd edition in 2004 at immunohistochemical, genetic and conceptual levels. Refined diagnostic criteria for type A, AB, B1-B3 thymomas and thymic squamous cell carcinoma are given, and it is hoped that these criteria will improve the reproducibility of the classification and its clinical relevance. The clinical perspective of the classification has been strengthened by involving experts from radiology, thoracic surgery, and oncology; by incorporating state-of-the-art positron emission tomography/computed tomography images; and by depicting prototypic cytological specimens. This makes the thymus section of the new WHO Classification of Tumours of the Lung, Pleura, Thymus and Heart a valuable tool for pathologists, cytologists, and clinicians alike. The impact of the new WHO Classification on therapeutic decisions is exemplified in this overview for thymic epithelial tumors and mediastinal lymphomas, and future perspectives and challenges are discussed.

99mTc MIBI THYMIC SCINTIGRAPHY IN DIAGNOSIS AND THERAPEUTIC DECISION MAKING: WHAT IS BEHIND THE IMAGE?

CONTEXT

Despite CT being generally used in thymic pathology, in the case of regions with the same tissue density, only functional radioisotopic imaging can hint towards malignity.

OBJECTIVES

To assess the usefulness of 99mTc MIBI scintigraphy for diagnosis and treatment planning in thymoma, in relation with the radiotracer uptake mechanism.

PATIENTS AND METHODS

99mTc MIBI thymic scans for 19 patients diagnosed with thymic disorders were assessed using tumor uptake ratio (UR). Specimens of thymectomies were examined and cytological assessments were correlated with the UR.

RESULTS

The UR of all surgical patients was higher than 1.2, with a 1.5 cutoff between lymphoid hyperplasia and thymoma. The UR values were correlated with the histopathologic diagnosis (Pearson correlation 0.91, significant at p<0.01). The highest UR was 3.24, found in the case of an AB thymoma where the rate lymphocytes/epithelial cells (L/E) was 1.6. In B1 thymoma UR was 1.14 and L/E was 2.46.

CONCLUSION

Phenotype differences between thymoma types correlate with 99mTc MIBI cellular uptake: lower rate L/E corresponds to higher UR, higher malignity potential and invasiveness. A thymic 99mTc MIBI UR higher than 1.5, corresponding to a CT tumoral image, is suggestive for a thymoma, requiring surgical treatment first.

PI3K as a Potential Therapeutic Target in Thymic Epithelial Tumors

INTRODUCTION

Thymic epithelial tumors (TETs) are rare tumors originating from the epithelium of the thymus with limited therapeutic options beyond surgery. The pathogenesis of TETs is poorly understood, and the scarcity of model systems for these rare tumors makes the study of their biology very challenging.

METHODS

A new cell line (MP57) was established from a thymic carcinoma specimen and characterized using standard biomarker analysis, as well as next-generation sequencing (NGS) and functional assays. Sanger sequencing was used to confirm the mutations identified by NGS.

RESULTS

MP57 possesses all the tested thymic epithelial markers and is deemed a bona fide thymic carcinoma cell line. NGS analysis of MP57 identified a mutation in the gene PIK3R2, which encodes a regulatory subunit of PI3K. Further analysis identified different mutations in multiple PI3K subunit genes in another cell line and several primary thymic carcinoma samples, including two catalytic subunits (PIK3CA and PIK3CG) and another regulatory subunit (PIK3R4). Inhibiting PI3K with GDC-0941 resulted in in vitro antitumor activity in TET cells carrying mutant PI3K subunits.

CONCLUSIONS

Alterations of PI3K due to mutations in its catalytic or regulatory subunits are observed in a subgroup of TETs, in particular, thymic carcinomas. Targeting PI3K may be an effective strategy to treat these tumors.

A large microRNA cluster on chromosome 19 is a transcriptional hallmark of WHO type A and AB thymomas

Background:

Thymomas are one of the most rarely diagnosed malignancies. To better understand its biology and to identify therapeutic targets, we performed next-generation RNA sequencing.

Methods:

The RNA was sequenced from 13 thymic malignancies and 3 normal thymus glands. Validation of microRNA expression was performed on a separate set of 35 thymic malignancies. For cell-based studies, a thymoma cell line was used.

Results:

Hierarchical clustering revealed 100% concordance between gene expression clusters and WHO subtype. A substantial differentiator was a large microRNA cluster on chr19q13.42 that was significantly overexpressed in all A and AB tumours and whose expression was virtually absent in the other thymomas and normal tissues. Overexpression of this microRNA cluster activates the PI3K/AKT/mTOR pathway. Treatment of a thymoma AB cell line with a panel of PI3K/AKT/mTOR inhibitors resulted in marked reduction of cell viability.

Conclusions:

A large microRNA cluster on chr19q13.42 is a transcriptional hallmark of type A and AB thymomas. Furthermore, this cluster activates the PI3K pathway, suggesting the possible exploration of PI3K inhibitors in patients with these subtypes of tumour. This work has led to the initiation of a phase II clinical trial of PI3K inhibition in relapsed or refractory thymomas (http://clinicaltrials.gov/ct2/show/NCT02220855).

Establishment and characterization of a novel cell line derived from thymoma with myasthenia gravis patients

Background

Thymoma is a cancer with rare incidence, but it is a major malignancy in adult anterior mediastinum, occurring in about 40% of patients with myasthenia gravis. Because of the lack of thymic epithelial tumor cell lines, thymoma has lagged far behind other tumors in cytological studies. It is, therefore, quite necessary to establish a new thymic epithelial tumor cell line from Chinese patients to study the pathogenic mechanism and therapeutic methods.

Methods

Twenty-three samples of tumor tissues were collected from thymoma and thymic carcinoma patients for primary culture by tissue explant, suspension cell culture method, and collagenase digestion. We detected the biological characteristics and origin of the cell line after the establishment of a novel thymoma cell line.

Results

A novel cell line, designed as Thy0517, was established from thymoma type AB with myasthenia gravis patients by tissue explant. As an immortalized cell line, it always has a stable growth cycle, and there is no change in characteristics and morphology after culturing for 18 months and passing 160 generations in vitro. The experimental data demonstrate that the cell line exhibits the growth characteristics of tumor cells, the doubling time of 37 hours, with tumorigenicity in vitro and chromosome abnormality. Immunocytochemistry indicated that the cell line positive expression of CK7, CK8/18, CK19, CK-pan, CD24, BCL-2, P63, Vimentin, epithelial membrane antigen and epidermal growth factor receptor, lymphocyte related antigen CD99, and TdT were negatively expressed.

Conclusions

The newly established thymic epithelial tumor cell line from Chinese patients provides a model in the study of thymoma and molecularly targeted therapies.

Type AB thymoma is not a mixed tumor of type A and type B thymomas, but a distinct type of thymoma

Type AB thymoma is generally regarded to be a mixture of type A and type B thymomas, but has not been studied extensively. In this study, we precisely investigated the characteristics of type AB thymoma immunohistochemically and compared it with other types of thymoma, including type A, metaplastic, and type B1 thymoma. In type A thymoma, the tumor cells were composed solely of pan-cytokeratin (CK-AE1/AE3)(+) claudin-1(+) vimentin(-) epithelial membrane antigen (EMA)(-) short spindle cells. Metaplastic thymoma exhibited biphasic architecture of epithelial islands of short spindle cells, which were phenotypically almost identical to the tumor cells in type A thymoma, and anastomosing bundles of CK-AE1/AE3(-) claudin-1(-) vimentin(+) EMA(+) fibroblast-like long spindle-shaped epithelial cells. Interestingly, we found that there were two distinctive subtypes of cell in type AB thymoma: the conventional subtype and the metaplastic subtype. The conventional subtype is characterized by type A-like components resembling type A thymoma. The metaplastic subtype is characterized by type A-like components extensively resembling the anastomosing bundles of fibroblast-like long spindle epithelial cells. Interestingly, the metaplastic subtype was a major subtype (14/19 cases), while the conventional subtype was a minor one (5/19 cases). In contrast to the rarity of metaplastic thymoma, the metaplastic subtype of type AB thymoma appears to be a major subtype of type AB thymoma.

A gene signature to determine metastatic behavior in thymomas

Purpose

Thymoma represents one of the rarest of all malignancies. Stage and completeness of resection have been used to ascertain postoperative therapeutic strategies albeit with limited prognostic accuracy. A molecular classifier would be useful to improve the assessment of metastatic behaviour and optimize patient management.

Methods

qRT-PCR assay for 23 genes (19 test and four reference genes) was performed on multi-institutional archival primary thymomas (n = 36). Gene expression levels were used to compute a signature, classifying tumors into classes 1 and 2, corresponding to low or high likelihood for metastases. The signature was validated in an independent multi-institutional cohort of patients (n = 75).

Results

A nine-gene signature that can predict metastatic behavior of thymomas was developed and validated. Using radial basis machine modeling in the training set, 5-year and 10-year metastasis-free survival rates were 77% and 26% for predicted low (class 1) and high (class 2) risk of metastasis (P = 0.0047, log-rank), respectively. For the validation set, 5-year metastasis-free survival rates were 97% and 30% for predicted low- and high-risk patients (P = 0.0004, log-rank), respectively. The 5-year metastasis-free survival rates for the validation set were 49% and 41% for Masaoka stages I/II and III/IV (P = 0.0537, log-rank), respectively. In univariate and multivariate Cox models evaluating common prognostic factors for thymoma metastasis, the nine-gene signature was the only independent indicator of metastases (P = 0.036).

Conclusion

A nine-gene signature was established and validated which predicts the likelihood of metastasis more accurately than traditional staging. This further underscores the biologic determinants of the clinical course of thymoma and may improve patient management.

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.