The International Association for the Study of Lung Cancer Thymic Epithelial Tumor Staging Project: Unresolved Issues to be Addressed for the Next Ninth Edition of the TNM Classification of Malignant Tumors.

Thymic epithelial tumors are presently staged using a consistent TNM classification developed by the International Association for the Study of Lung Cancer (IASLC) and approved by the Union for International Cancer Control and the American Joint Committee on Cancer. The stage classification is incorporated in the eight edition of the TNM classification of thoracic malignancies. The IASLC Staging and Prognostic Factors Committee (SPFC)-Thymic Domain (TD) is in charge for the next (ninth) edition expected in 2024. The present article represents the midterm report of the SPFC-TD: in particular, it describes the unresolved issues identified by the group in the current stage classification which are worth being addressed and discussed for the ninth edition of the TNM classification on the basis of the available data collected in the central thymic database which will be managed and analyzed by Cancer Research And Biostatistics. These issues are grouped into issues of general importance and those specifically related to T, N, and M categories. Each issue is described in reference to the most recent reports on the subject, and the priority assigned by the IASLC SPFC-TD for the discussion of the ninth edition is provided.

Classification, histopathology and molecular pathology of thymic epithelial tumors: a review.

Thymic epithelial tumors represent 0.2-1.5% among all malignant neoplasms. They are slow-growing tumors with an overall recurrence rate around 10% and 90% of them are located in the anterior mediastinum. In this review we focused on the classification, histopathology, molecular pathology and prognosis of thymic epithelial tumors, mainly thymoma and thymic carcinoma.

Recent advances and conceptual changes in the classification of neuroendocrine tumors of the thymus.

Neuroendocrine tumors of the thymus (TNET) are exceedingly rare neoplasms. Their histomorphology is identical to neuroendocrine tumors elsewhere in the body (in particular the lungs) and bears no similarity with thymomas and thymic carcinomas. Recent molecular findings have profoundly changed our perception of these tumors and may impact future histological classification systems.

Thymic Malignancy-Updates in Staging and Management.

Thymomas are relatively indolent tumors that present with locally advanced disease in 30% of the patients. Thymic carcinoma is a more aggressive histology with shorter disease-free and overall survival. Early-stage tumors are managed best with complete resection. Multimodal therapy is the standard of care for locally advanced tumors and neoadjuvant therapy may help improve respectability. Stage and complete resection are the strongest prognostic factors for long-term survival. Based on early experience, targeted and immunotherapies have shown limited promise in advanced disease.

Interobserver variation in the classification of thymic lesions including biopsies and resection specimens in an international digital microscopy panel.

AIMS: Thymic tumours are rare in routine pathology practice. Although the World Health Organization (WHO) classification describes a number of well-defined categories, the classification remains challenging. The aim of this study was to investigate the reproducibility of the WHO classification among a large group of international pathologists with expertise in thymic pathology and by using whole slide imaging to facilitate rapid diagnostic turnover. METHODS AND RESULTS: Three hundred and five tumours, consisting of 90 biopsies and 215 resection specimens, were reviewed with a panel-based virtual microscopy approach by a group of 13 pathologists with expertise in thymic tumours over a period of 6 years. The specimens were classified according to the WHO 2015 classification. The data were subjected to statistical analysis, and interobserver concordance (Fleiss kappa) was calculated. All cases were diagnosed within a time frame of 2 weeks. The overall level of agreement was substantial (κ = 0.6762), and differed slightly between resection specimens (κ = 0.7281) and biopsies (κ = 0.5955). When analysis was limited to thymomas only, and they were grouped according to the European Society for Medical Oncology Clinical Practice Guidelines into B2, B3 versus A, AB, B1 and B3 versus A, AB, B1, B2, the level of agreement decreased slightly (κ = 0.5506 and κ = 0.4929, respectively). Difficulties arose in distinguishing thymoma from thymic carcinoma. Within the thymoma subgroup, difficulties in distinction were seen within the B group. CONCLUSIONS: Agreement in diagnosing thymic lesions is substantial when they are assessed by pathologists with experience of these rare tumours. Digital pathology decreases the turnaround time and facilitates access to what is essentially a multinational resource. This platform provides a template for dealing with rare tumours for which expertise is sparse.

Atypical Type A Thymoma Variant Manifesting Polymyalgia Rheumatica.

We report a case of atypical type A thymoma variant manifesting polymyalgia rheumatica. A 68-year-old man underwent extended thymectomy with concomitant resection of the pericardium and right lung for an anterior mediastinal tumor. He was diagnosed with atypical type A thymoma variant with pericardial invasion. He developed pain in his extremities 1 year and 2 months after surgery. Detailed examinations resulted in a diagnosis of polymyalgia rheumatica and bone metastasis of thymoma. He was treated with oral prednisolone for polymyalgia rheumatica. His symptoms and bone lesion have been stable up to the present time of 3.5 years post-surgery.

Lymph node metastasis in thymic malignancies: A Chinese multicenter prospective observational study.

OBJECTIVES: To study the incidence and pattern of lymph node metastases in thymic malignancies. METHODS: This multicenter prospective observational trial with intentional lymph node dissection was carried out by the Chinese Alliance for Research in Thymomas (ChART). Data on patients with thymic tumors without pretreatment were collected prospectively. Results from this prospective study were then compared with those from a previously reported ChART retrospective study. RESULTS: Among 275 patients, metastasis was detected in 41 nodes (3.04%) in 15 patients (5.5%). The rate of lymph node metastasis was 2.1% (5/238) in patients with thymomas, 25% (6/24) in those with thymic carcinomas, and 50% (4/8) in those with neuroendocrine tumors (P < .001). The rate of lymph node metastasis in category T1 to T4 tumors was 2.7% (6/222) in T1, 7.7% (1/13) in T2, 18.4% (7/38) in T3, and 50% (1/2) in T4 (P < .001). Nodal involvement was significantly higher compared with the ChART retrospective study (5.5% vs 2.2%; P = .002), although the 2 groups were comparable in terms of tumor stage and histology. Metastasis was found in N1 nodes in 13 patients (86.7%) and in N2 nodes in 8 patients (53.3%); 6 patients (40%) had simultaneous N1/N2 diseases and 6 (40%) had multistation involvement. Based on World Health Organization histological classification and Union for International Cancer Control T category, patients were divided into a low-risk group (1/192; 0.5%) with T1-2 and type A-B2 diseases and a high-risk group (14/83; 16.9%) of category T3 and above or histology B3 and above tumors for nodal metastasis (P < .001). On multivariate analysis, type B3/thymic carcinoma/neuroendocrine tumors, category T3 or above, and N2 dissection predicted a greater likelihood of finding nodal metastasis. CONCLUSIONS: Lymph node involvement in thymic malignancies is more common than previously recognized, especially in tumors with aggressive histology and advanced T category. Intentional lymph node dissection increases the detection of nodal involvement and improves accuracy of staging. In selected high-risk patients, systemic dissection of both N1and N2 nodes should be considered for accurate tumor staging.

Diagnosis of thymic epithelial tumor subtypes by a quantitative proteomic approach.

The histological typing of thymic epithelial tumours (TETs) still remains a challenge for surgical pathologists, especially when encountering borderline cases mainly focused on spindle cell types (including type A, atypical type A (aA), AB, and B3). A systematic proteomics analysis of TETs was performed using isobaric tags for relative and absolute quantification (iTRAQ) labeling coupled with two-dimensional liquid chromatography-tandem mass spectrometry (2D-LC-MS/MS). In total, 6479 and 6305 proteins were identified and quantified, respectively. After Gene Ontology (GO) annotation and Ingenuity Pathway Analysis (IPA), six differentially expressed proteins were validated by tissue microarray or multiple reaction monitoring (MRM) quantification. ABCE1 and CLIC2 are promising to be diagnostic candidate biomarkers in thymic carcinomas (TCs). CHD1L was up-regulated in type AB and type B thymomas compared with type A thymoma. Both CLIC2 and MAP7 were negatively detected in type B1 and B2 thymomas. SMAD4 was overexpressed in type aA thymomas and TCs. CDC42 was significantly down-regulated in type B2 thymomas compared with other subtypes. Six novel candidate biomarkers were found to be useful in differentiating subtypes of TETs. SMAD4 may play a specific role in tumorigenesis and the development of aA thymomas and thymic carcinomas.

Thymoma: a clinicopathological correlation of 1470 cases.

We present 1470 surgical resections for thymoma identified in the pathology files of 14 institutions from 11 countries with the purpose of determining and correlating a simplified histological classification of thymoma and pathological staging with clinical outcome. The study population was composed of 720 men and 750 women between the ages of 12 and 86 years (average, 54.8 years). Clinically, 137 patients (17%) had a history of myasthenia gravis, 31 patients (3.8%) of other autoimmune disease, and 55 (6.8%) patients of another neoplastic process. Surgical resection was performed in all patients. Histologically, 1284 (87.13%) cases were thymomas (World Health Organization types A, B1, and B2, and mixed histologies), and 186 (12.7%) were atypical thymomas (World Health Organization type B3). Of the entire group, 630 (42.9%) were encapsulated thymomas, and 840 (57.9%) were invasive thymomas in different stages. Follow-up information was obtained in 1339 (91%) patients, who subsequently were analyzed by univariate and multivariate statistical analysis. Follow-up ranging from 1 to 384 months was obtained (mean, 69.2 months) showing tumor recurrence in 136 patients (10.1%), whereas 227 died: 64 (28.2%) due to tumor and 163 (71.8%) due to other causes. Statistical analysis shows that separation of these tumors into thymoma and atypical thymoma is statistically significant (P = .001), whereas tumor staging into categories of encapsulated, minimally invasive, and invasion into adjacent organs offers a meaningful clinical assessment with a P = .038. Our findings suggest that our simplified histological schema and pathological staging system are excellent predictors of clinical outcome.

Evaluation of the new TNM-staging system for thymic malignancies: impact on indication and survival.

BACKGROUND: The objective of this study is the evaluation of the Masaoka-Koga and the International Association for the Study of Lung Cancer (IASLC)/International Thymic Malignancy Interest Group (ITMIG) proposal for the new TNM-staging system on clinical implementation and prognosis of thymic malignancies. METHODS: A retrospective study of 76 patients who underwent surgery between January 2005 and December 2015 for thymoma. Kaplan-Meier survival analysis was used to determine overall and recurrence-free survival rates. RESULTS: Indication for surgery was primary mediastinal tumor (n = 55), pleural manifestation (n = 17), or mediastinal recurrence (n = 4) after surgery for thymoma. Early Masaoka-Koga stages I (n = 9) and II (n = 14) shifted to the new stage I (n = 23). Advanced stages III (Masaoka-Koga: n = 20; ITMIG/IASLC: n = 17) and IV (Masaoka-Koga: n = 33; ITMIG/IASLC: n = 35) remained nearly similar and were associated with higher levels of WHO stages. Within each staging system, the survival curves differed significantly with the best 5-year survival in early stages I and II (91%). Survival for stage IV (70 to 77%) was significantly better compared to stage III (49 to 54%). Early stages had a significant longer recurrence-free survival (86 to 90%) than advanced stages III and IV (55 to 56%). CONCLUSIONS: The proportion of patients with IASLC/ITMIG stage I increased remarkably, whereas the distribution in advanced stages III and IV was nearly similar. The new TNM-staging system presents a clinically useful and applicable system, which can be used for indication, stage-adapted therapy, and prediction of prognosis for overall and recurrence-free survival.

JOURNAL CLUB: Doubling Time of Thymic Epithelial Tumors Correlates With World Health Organization Histopathologic Classification.

OBJECTIVE: Awareness of volume doubling times (VDTs) of different thymic epithelial tumors (TETs), including low- and high-grade thymomas and thymic carcinomas, is important for their management. The purpose of this study was to evaluate the VDTs of incidentally found TETs using 3D volumetry (3D-VDT) and longest diameter (LD-VDT). MATERIALS AND METHODS: This retrospective study included 50 patients (30 men, 20 women) who had histologically proven TETs and who underwent at least two serial CT studies at greater than 2-month intervals. TETs were classified into World Health Organization subtypes and further divided into low-grade (group A [A-B1]) and high-grade (group B [B2, B3]) thymoma and thymic carcinoma (group C). Tumor volumetry was performed by either manual segmentation (3D-VDT) or longest diameter measurement (LD-VDT). RESULTS: Groups A, B, and C accounted for 15, 26, and nine tumors. The median LDVDT in group A was 703.6 days (range, 286.7-1855.9 days); group B, 412.1 days (range, 130.9-716.9 days), and group C, 146.3 days (range, 68.9-448.3 days) (p < 0.01). The median 3D-VDTs were 1138.8 days (range, 350.1-3915.3 days), 711.0 days (range, 145.5-7209.5 days), and 203.1 days (range, 58.9-766.9 days) (p < 0.01). In ROC analysis, both LD-VDT (AUC, 0.873; p < 0.01; optimal cutoff value, 222.6 days; 90.2% sensitivity, 77.8% specificity) and 3DVDT (AUC, 0.859; p < 0.01; optimal cutoff value, 218.0 days; 92.7% sensitivity; 66.7% specificity) differentiated group C from groups A and B. CONCLUSION: VDTs differ among TETs according to tumor grade. Measurement of either LD-VDT or 3D-VDT is sensitive for differentiating carcinomas from thymomas (cutoff value, ≈ 220 days).

Assessment of the ITMIG Statement on the WHO Histological Classification and of the Eighth TNM Staging of Thymic Epithelial Tumors of a Series of 188 Thymic Epithelial Tumors.

INTRODUCTION: Thymic epithelial tumors (TETs) are rare intrathoracic malignancies that are categorized histologically according to the WHO classification, which was recently updated in 2015 on the basis of a consensus statement of the International Thymic Malignancy Interest Group (ITMIG); at the same time, the standard Masaoka-Koga staging system is scheduled to be replaced by the eighth edition of the TNM staging classification by the American Joint Committee on Cancer/Union for International Cancer Control consortium. Our objectives were to analyze the feasibility of assessing ITMIG consensus major and minor morphological and immunohistochemical criteria and the eighth edition of the TNM staging classification in a routine practice setting. METHODS: This is a single-center study conducted at the Louis-Pradel Hospital of Lyon University, one of the largest centers for TETs in France. Overall, a large surgical series of 188 TETs diagnosed in 181 patients between 2000 and 2014 at our center were analyzed. RESULTS: There were 89 men (49%) and 92 women (51%); 57 patients (31%) presented with myasthenia gravis at time of diagnosis. According to the WHO classification, there were nine type A thymomas (5%), 67 type AB thymomas (36%), 19 type B1 thymomas (10%), 46 type B2 thymomas (24%), 27 type B3 thymomas (14%), and 20 thymic carcinomas (11%). ITMIG consensus major criteria were identified in 100% of type A, AB, B1, and B2 thymomas. After restaging according to the eighth edition of the TNM staging classification, there were 127 stage I (84%), three stage II (2%), 17 stage IIIa (11%), no stage IIIb, two stage IVa (1%), and three stage IVb (2%) thymomas. Significant correlation between histological type and stage at diagnosis was maintained after restaging according the TNM classification. CONCLUSION: Comprehensive analysis of our well-characterized surgical series of 188 TETs indicates the feasibility and the diagnostic value of the ITMIG consensus statement on WHO histological classification and highlights the major switch in staging when the eighth edition of the TNM staging classification is applied.

Genomic Analysis of Thymic Epithelial Tumors Identifies Novel Subtypes Associated with Distinct Clinical Features.

Purpose: To reconcile the heterogeneity of thymic epithelial tumors (TET) and gain deeper understanding of the molecular determinants of TETs, we set out to establish a clinically relevant molecular classification system for these tumors.Experimental Design: Molecular subgrouping of TETs was performed in 120 patients from The Cancer Genome Atlas using a multidimensional approach incorporating analyses of DNA mutations, mRNA expression, and somatic copy number alterations (SCNA), and validated in two independent cohorts.Results: Four distinct molecular subtypes of TETs were identified. The most commonly identified gene mutation was a missense mutation in General Transcription Factor II-I (GTF2I group), which was present in 38% of patients. The next group was identified by unsupervised mRNA clustering of GTF2I wild-type tumors and represented TETs enriched in expression of genes associated with T-cell signaling (TS group; 33%). The remaining two groups were distinguished by their degree of chromosomal stability (CS group; 8%) or instability (CIN group; 21%) based upon SCNA analyses. Disease-free survival and overall survival were favorable in the GTF2I group and unfavorable in the CIN group. These molecular subgroups were associated with TET histology and clinical features including disease-free survival. Finally, we demonstrate high expression of PD1 mRNA and correlation of PD1 and CD8A in the TS subgroup.Conclusions: Molecular subtyping of TETs is associated with disease-free and overall survival. Classification of TETs by a molecular framework could aid in the refinement of staging and in the discovery and development of rational treatment options for patients with TETs. Clin Cancer Res; 23(16); 4855-64. ©2017 AACR.

Diagnostic Value of Dual-time-point F-18 FDG PET/CT and Chest CT for the Prediction of Thymic Epithelial Neoplasms.

We retrospectively assessed the dual-time-point (DTP) F-18 FDG PET/CT findings of thymic epithelial neoplasms (TENs) and investigated the diagnostic capacity of PET/CT compared to that of CT for predicting carcinoma. We calculated the ratio of the standardized uptake value of the tumor and that of the aortic arch (T/M ratio) for both the 90-min early scan and the 2-h delayed scan in 56 TEN patients. We used a multivariate logistic regression (MLR) analysis to estimate the CT features of carcinoma. We compared the diagnostic capacities of PET/CT and chest CT using receiver operating characteristic (ROC) analyses. The ROC curve revealed that the appropriate cut-off T/M ratio value for the highest accuracy was 2.39 with 75.0% accuracy. The area under the curve (AUC) was 0.855. The statistical analyses for DTP scans of 35 TEN patients demonstrated 74.3% accuracy and 0.838 AUC for the early scan versus 82.9% and 0.825 for the delayed scan. The MLR analysis indicated that mediastinal fat infiltration was a predictor of carcinoma. The ROC curve obtained for the model yielded an AUC of 0.853. Delayed scanning could improve the diagnostic capacity for carcinoma. The T/M ratio and mediastinal fat infiltration are predictive of carcinoma with moderate diagnostic accuracy.

Thymic Neuroendocrine Neoplasms: Biological Behaviour and Therapy.

Thymic neuroendocrine neoplasms are rare tumours, but their management can often be highly problematic. While previously assumed to be essentially variants of bronchopulmonary (lung) carcinoids, they are generally more aggressive and more difficult to treat. Some 25% are associated with multiple endocrine neoplasia-1, while a higher proportion are associated with the ectopic ACTH syndrome, and occasionally both. We discuss the classification of these tumours, their biology as far as is known, and their clinical, biochemical and imaging features. We also review possible management options and suggest stratagems to optimise their treatment, which even today is far from optimal.

Evolution of Classification of Thymic Epithelial Tumors in the Era of Dr Thomas V. Colby.

CONTEXT: -Numerous histomorphologic and staging classifications of thymic epithelial tumors (TETs) have been proposed during the last century, suggesting that the classification of these tumors is challenging and controversial. Difficulties of classifying TETs include various combinations of epithelial cells and lymphocytes and the paucity of these tumors. The prognostic significance, specifically of the histomorphologic classifications, has been debated. Early classifications were also challenged by the uncertainty of the neoplastic component(s) of the tumor. OBJECTIVE: -To discuss the evolution of the histomorphologic classification and the staging system of TET. Controversies and problems of some classifications and their importance for therapeutic management and prognosis will be reviewed. Classifications that incorporated new concepts and approaches at the time or outcome studies will be highlighted. Current classifications will be discussed and the staging system that was recently proposed for the upcoming eighth American Joint Committee on Cancer staging will be described. DATA SOURCES: -Search of literature database (PubMed) and current (2015) World Health Organization classification. CONCLUSIONS: -Histomorphologic and staging classifications of TET have evolved during the last century and especially during the era of Thomas V. Colby, MD. Evidence supports that the staging system has prognostic implications independent of and superior to the histomorphologic classification. Histomorphology appears to be important for biologic features of TET.

Vascular architecture as a diagnostic marker for differentiation of World Health Organization thymoma subtypes and thymic carcinoma.

AIMS: Thymomas and thymic squamous cell carcinomas (TSQCCs) are rare thymic epithelial tumours. Data on angiogenesis and vascular phenotype in these tumours are limited, and no study has taken histological World Health Organization (WHO) subtypes into account. The aim of this study was to compare vascularization, pericytes coverage and expression of angiogenic growth factors in different WHO-defined subtypes of thymoma METHODS AND RESULTS: Vascular density, diameter and architecture and expression of α-smooth muscle actin (SMA), platelet-derived growth factor (PDGF) receptor-ß (PDGFRß), vascular endothelial growth factor (VEGF) receptor 1 (VEGFR1) and VEGF receptor 2 (VEGFR2) were investigated in WHO type A, AB, B1, B2 and B3 thymomas and TSQCCs, by the use of immunostaining, quantitative morphometry, and tumour vessel isolation by trypsin digestion. Expression levels of angiopoietin 1 (Ang-1), angiopoietin 2 (Ang-2), VEGF-A, PDGF-B and Hif-1α were examined by quantitative reverse transcription polymerase chain reaction. A and AB thymomas were characterized by a dense network of capillary-like vessels with tight pericyte coverage, whereas B thymomas showed a loose vascular network with increasing vascular diameters and increasing expression of SMA and PDGFRß from B1 to B3 thymomas and TSQCCs. VEGFR1 and VEGFR2 were expressed in vessels of all analysed tumour entities, and at higher levels in epithelial cells of A and B3 thymomas and TSQCCs. mRNA of Ang-2, but not of Ang-1, was significantly up-regulated in all thymoma subtypes, with the highest levels being found in A thymomas. In TSQCCs, Ang-1 and VEGF were the predominantly up-regulated growth factors. Hif-1α was only up-regulated in B3 thymomas and TSQCCs. CONCLUSION: Thymomas and TSQCCs differ significantly in their vascular architecture and expression of key angiogenic growth factors. The findings could help to improve the differential diagnosis of difficult-to-classify thymic epithelial tumours, and indicate different mechanisms of tumour angiogenesis and functional differences of tumour vessels of major thymoma subtypes and TSQCCs.

Expression of mesothelin in thymic carcinoma and its potential therapeutic significance.

OBJECTIVES: Advanced thymic epithelial tumors (TETs) lack adequate treatment options in part due to absence of well characterized tumor-specific antigens. Mesothelin, a cell surface antigen, has been used successfully as a target for tumor-directed therapy. We sought to determine tumor expression and serum levels of mesothelin in patients with TETs. PATIENTS AND METHODS: Tissue samples were obtained from 71 patients with histologically confirmed, unresectable advanced TETs and evaluated for mesothelin expression by immunohistochemistry. The evaluation was blinded for clinical data and outcome. Mesothelin expression and its association with clinico-pathological parameters and survival were assessed. RESULTS: Thymic carcinoma, thymoma, and thymic neuroendocrine tumors (NETs) accounted for 34 (48%), 29 (41%), and 8 (11%) cases respectively. Mesothelin expression was seen in a significantly larger proportion of thymic carcinoma (27/34, 79%) than thymoma (3/29, 10%) (P<0.0001) and was absent in thymic NETs. Among thymic carcinomas 13/34 (38%) showed expression in nearly all tumor cells. Immunoreactivity was membranous, strong, and homogenous. Patients with thymic carcinoma and high mesothelin expression (in >50% of tumor cells) had significantly improved overall survival (median not reached, n=19) compared to patients with no or low mesothelin expression (1.60 years; 95% CI: 1.24-4.94 years; n=15; HR=4.46, 95% CI: 1.55-12.80; p=0.0026). CONCLUSION: Mesothelin expression is frequently observed in advanced thymic carcinomas, infrequently in thymomas and is absent in thymic NETs. Due to strong, membranous expression mesothelin is a potential therapeutic target in thymic carcinoma.

[Thymomas]. / Thymome.

Thymomas are rare tumors but are one of the most common mediastinal neoplasms in adults and exhibit an enormous variability in histological, biological and genetic features. The morphological spectrum within a given entity is enormous and some tumors with histological patterns of more than one entity are more common than pure histological subtypes. Due to a lack of subtype-specific markers classification of thymomas often requires complex diagnostic algorithms. The refined presentation including the definition of obligatory and optional features and of diagnostic immunohistochemical profiles, is the focus of the new World Health Organization (WHO) classification of thymomas, aiming at improving diagnostic reproducibility. This review highlights novel aspects of the WHO classification of thymomas and addresses typical differential diagnostic challenges with a focus on diagnostic pitfalls.