Histologic classification of thymoma: a practical guide for routine cases

Making an accurate diagnosis of anterior mediastinal lesions: a proposal for a new diagnostic algorithm from the BTOG Thymic Malignancies Special Interest Group

Due to the rising demand in cross-sectional thoracic imaging, anterior mediastinal lesions are being identified with increasing frequency. Following iterative and multidisciplinary discussions, the BTOG Thymic Malignancies Special Interest Group have developed an algorithm to standardise the diagnostic approach for these relatively uncommon but important conditions which span from benign (thymic remnant, thymic hyperplasia and thymic cysts) to suspected localised thymomas to suspected more aggressive malignancy (thymic carcinoma, lymphoma and germ cell tumours). For each condition, we provide a brief description, an overview of the key radiological findings and a description of the proposed algorithm including the rationale behind the recommendations. We also highlight the role of magnetic resonance (MR) imaging for the characterisation of anterior mediastinal masses in specific indications when the necessary local resources and expertise exist. In addition, we hope this provides the rationale for service development in MR of the anterior mediastinum where current resource and expertise requires development. Through this standardised pathway, we hope to drive improvements in patient care by rationalising surveillance schedules, avoiding unnecessary resections of benign entities with their associated morbidity and optimising the diagnostic work-up prior to the appropriate treatment of anterior mediastinal malignancies.

Thymic epithelial tumours: histopathological classification and differential diagnosis

The epithelial and lymphoid compartments of the thymus can give rise to a wide variety of tumours, including thymomas, thymic carcinomas, lymphoreticular proliferations, germ cell tumours, and sarcomas. While some of these have close similarity to their counterparts in other organs, both in terms of histology and immunohistochemistry, as well as molecular features, others are unique to the thymus. The epithelial tumours, which can develop in the thymus, will be discussed in this review, with a particular emphasis on resolving differential diagnosis by means of morphology, immunohistochemical profiles, and molecular diagnostics.

Small molecule multitarget antiangiogenic inhibitor treatments for advanced thymic epithelial tumors: A retrospective study

BACKGROUND

Thymic epithelial tumors (TETs) are rare malignant tumors with limited treatment options. No established second-line treatment regimen is available following the preferred first-line chemotherapy, resulting in unsatisfactory efficacy and poor prognosis for patients with advanced TETs. This study aimed to evaluate the efficacy of small molecule multitarget antiangiogenic inhibitors as well as the prognostic factors for advanced TETs.

METHODS

A retrospective study was conducted using data from a real-world database. Clinical information and survival follow-up data were collected from 52 patients with advanced TETs who received small molecule multitarget antiangiogenic inhibitors at Zhejiang Cancer Hospital between August 10, 2016 and August 10, 2022. The short-term efficacy of the treatments, survival time of the patients, and relevant prognostic factors of advanced TETs were analyzed.

RESULTS

Out of the 52 patients included in this study, 16 had thymoma and 36 had thymic carcinoma. The 52 patients had an overall response rate of 21.1% and a disease control rate of 94.2%. In addition, the median progression-free survival (PFS) was 8.05 months, and the overall survival (OS) was 25.00 months. Apatinib was given to 33 patients, anlotinib to 15 patients, and sunitinib or lenvatinib to four patients. Only seven patients received antiangiogenic inhibitors as their first-line therapy, 27 patients as their second-line therapy, and 18 patients as third-line or subsequent therapy. Meanwhile, 42 patients received monotherapy with an antiangiogenesis inhibitor, while 10 patients received combination therapy. Univariate analysis indicated that the combined treatment was associated with a superior OS (p = 0.044); multivariate analysis indicated that the combined treatment was an independent prognostic factor for PFS (p = 0.014) and OS (p = 0.012).

CONCLUSION

The findings suggest that small molecule multitarget antiangiogenic inhibitors are efficacious as second or post-line treatments as a viable alternative treatment option for patients with advanced TETs.

PAX1 expression in thymic epithelial neoplasms and morphologic mimics

Thymic epithelial neoplasms are morphologically diverse and can pose a diagnostic challenge that is complicated by a lack of immunohistochemistry (IHC) markers that are entirely sensitive and specific for thymic epithelium. Polyclonal PAX8 is often used in this context, but it is not a specific marker. The PAX1 transcription factor shares significant homology with PAX8 and plays an integral role in thymic development in humans and murine models. This study evaluated the role of PAX1 IHC in differentiating thymic epithelial neoplasms from morphologic mimics on whole slide tissue sections. The PAX1 antibody stained all 74 thymoma cases; however, there was wide variability in staining intensity within each subtype. The antibody was less sensitive in thymic carcinomas and thymic neuroendocrine tumors compared to thymomas and demonstrated weak staining in a subset of morphologic mimics (21 squamous cell carcinomas, 6 pulmonary neuroendocrine tumors, 1 mesothelioma, 1 lymphoblastic lymphoma, and 1 granulosa cell tumor). With a H-score positive threshold of 75, the antibody had 100% specificity, and sensitivities of 92%, 56%, and 47% in thymomas, thymic neuroendocrine tumors, and thymic carcinomas respectively. The PAX1 antibody showed frequent geographic reduction in staining consistent with compromised antigenicity from variable formalin fixation. PAX1 IHC has a moderate-to-high sensitivity for thymic epithelial neoplasms; however, the wide staining variability and fixation effects may lead to difficulty with consistent interpretation. This marker is unlikely to supplant the role of PAX8 in diagnostic practice, but it may be a useful addition to immunohistochemistry panels when evaluating for thymic primary tumors.

Dataset for reporting of thymic epithelial tumours: recommendations from the International Collaboration on Cancer Reporting (ICCR)

AIMS

Thymic epithelial tumours (TET), including thymomas and thymic carcinomas and thymic neuroendocrine neoplasms, are malignant neoplasms that can be associated with morbidity and mortality. Recently, an updated version of the World Health Organization (WHO) Classification of Thoracic Tumours 5th Edition, 2021 has been released, which included various changes to the classification of these neoplasms. In addition, in 2017 the Union for International Cancer Control (UICC) / American Joint Committee on Cancer (AJCC) published the 8th Edition Staging Manual which, for the first time, includes a TNM staging that is applicable to thymomas, thymic carcinomas, and thymic neuroendocrine neoplasms.

METHODS AND RESULTS

To standardize reporting of resected TET and thymic neuroendocrine neoplasms the accrediting bodies updated their reporting protocols. The International Collaboration on Cancer Reporting (ICCR), which represents a collaboration between various National Associations of Pathology, updated its 2017 histopathology reporting guide on TET and thymic neuroendocrine neoplasms accordingly. This report will highlight important changes in the reporting of TET and thymic neuroendocrine neoplasms based on the 2021 WHO, emphasize the 2017 TNM staging, and also comment on the rigour and various uncertainties for the pathologist when trying to follow that staging.

CONCLUSION

The ICCR dataset provides a comprehensive, standardized template for reporting of resected TET and thymic neuroendocrine neoplasms.

Thymoma metastatic to the epidural thoracic spine

Background

Thymomas rarely metastasize to the spine. Here, we present a 69-year-old female diagnosed with stage IV thymoma, which subsequently developed a symptomatic epidural thoracic spinal lesion causing thoracic myelopathy.

Case Description

The patient initially presented with paraspinal rib pain, lower extremity weakness, and gait imbalance. The magnetic resonance revealed a T10 vertebral body lesion with epidural extension causing severe spinal cord compression. A T9-T10 hemilaminotomy for tumor resection was performed; this was followed by adjuvant chemotherapy and radiation. Gross total resection was achieved, and the final pathology was metastatic thymoma. Postoperatively, the patient significantly improved.

Conclusion

Metastatic thymomas to the thoracic spine are rare. For those presenting with epidural lesions causing myelopathy, surgical resection is beneficial and may be accompanied by adjunctive radiation and chemotherapy.

Proteomics analysis of serum from thymoma patients

Thymoma is the most common malignant tumor in thymic epithelial tumors (TETS). This study aimed to identify the changes in serum proteomics in patients with thymoma. Proteins were extracted from twenty patients with thymoma serum and nine healthy controls and prepared for mass spectrometry (MS) analysis. Data independent acquisition (DIA) quantitative proteomics technique was used to examine the serum proteome. Differential proteins of abundance changes in the serum were identified. Bioinformatics was used to examine the differential proteins. Functional tagging and enrichment analysis were conducted using the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. The string database was used to assess the interaction of different proteins. In all, 486 proteins were found in all samples. There were differences in 58 serum proteins between patients and healthy blood donors, 35 up-regulated and 23 down-regulated. These proteins are primarily exocrine and serum membrane proteins involved in controlling immunological responses and antigen binding, according to GO functional annotation. KEGG functional annotation showed that these proteins play a significant role in the complement and coagulation cascade and the phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) signal pathway. Notably, the KEGG pathway (complement and coagulation cascade) is enriched, and three key activators were up-regulated: von willebrand factor (VWF), coagulation factor v (F5) and vitamin k-dependent protein c (PC). Protein-protein interaction (PPI) analysis showed that six proteins ((VWF, F5, thrombin reactive protein 1 (THBS1), mannose-binding lectin-associated serine protease 2 (MASP2), apolipoprotein B (APOB), and apolipoprotein (a) (LPA)) were up-regulated and two proteins (Metalloproteinase inhibitor 1(TIMP1), ferritin light chain (FTL)) were down-regulated. The results of this study showed that several proteins involved in complement and coagulation cascades were up-regulated in the serum of patients.

Histomorphological Spectrum and Diagnostic Challenges in Thymic Epithelial Neoplasms with their Prognostic Significance: A Case Series of 33 Cases at a Regional Cancer Center in Western India

Objective Pathological diagnosis of thymic epithelial neoplasms is challenging due to multiple subtypes, tumor heterogeneity, and variations in inter-observer reproducibility. Very few studies are available on their spectrum in the Indian subcontinent. In this study, we aimed to explore the morphological spectrum and diagnostic difficulties in the classification and subtyping of thymic epithelial neoplasms along with their prognostic significance in the Indian population.

Material and Methods Retrospectively, all surgically resected thymectomy specimens operated at our institute as well as outside review cases during the period were included. Histomorphology and immunohistochemistry (IHC) slides were reviewed and correlated with clinicopathological variables.

Statistical Analysis Microsoft Excel 2019 and SPSS version 20 were used for data analysis.

Results Among the 33 thymic epithelial neoplasms operated during the study period, the commonest subtype was thymoma B2 type followed by AB, B1, A, and B3 types. A single case each of micronodular thymoma, microscopic thymoma, and thymic carcinoma were identified. Six cases of thymomas with more than one pattern (other than ‘A’) were noted. The male:female ratio was 2:1. Stage I in Modified Masaoka staging and pT1a in TNM staging were most common. Seven cases had metastasis, four during initial presentation and three during subsequent follow-up.

Discussion and Conclusion Thymic epithelial neoplasms show morphological overlapping of features. Thorough sampling, morphology, and IHC for exact subtyping of thymoma and diligent search and documenting of lymphovascular invasion (LVI) are vital as both are separate risk factors for metastasis/recurrence and help the clinician in a better follow-up of patients.

Investigational drugs for the treatment of thymic cancer: a focus on phase 1 and 2 clinical trials

INTRODUCTION

Thymic epithelial tumors (TETs) are rare tumors of thymic epithelial cells. Treatment options for advanced disease patients who failed standard platinum-based chemotherapy are limited.

AREAS COVERED

Phase I and II trials published in the last five years testing new systemic treatments for advanced TET patients are discussed, as well as ongoing trials. A PubMed database literature review was conducted for articles published between January 2016 and December 2021, and ongoing clinical trials were retrieved from ClinicalTrials.gov database.

EXPERT OPINION

The most promising classes of new drugs in TET patients are angiogenesis inhibitors and immune checkpoint antibodies (ICIs). Sunitinib and Lenvatinib showed response rates of 26% and 38%, respectively, and ICIs showed durable responses in 20-25% in thymic carcinoma patients (TCs). Both approaches are mainly active in TCs, therefore new treatment options for thymomas is an unmet medical need.Two major new therapeutic strategies are ICIs combinations with other drugs and drugs that target pathways that are dysregulated in TETs.Future challenges include the development of preclinical models to help identify novel targets and test new treatment strategies, and randomized clinical trials to provide reliable evidence based on survival endpoints.

Characterization of IL-10-producing regulatory B cells in thymoma

BACKGROUND

Regulatory B cells (Bregs) are a subset of B cells that secrete interleukin 10 (IL-10) and play a vital role in suppressing the immune response. The aim of this study was to evaluate the proportion of Bregs in patients with thymoma.

METHODS

The proportions of subgroups of Bregs in 23 patients with thymoma and 15 healthy controls were detected by flow cytometry. The serum IL-2, IL-4, IL-6, IL-10, IL-17A, IFN-γ, and TNF-α levels of the subjects were measured using a cytometric bead array (CBA).

RESULTS

The proportions of circulating IL-10⁺ B cells, IL-10⁺CD24^hiCD38^hi Bregs, and IL-10⁺CD24^hiCD27⁺ Bregs and the serum IL-10 level were significantly higher in patients with thymoma than in the control group and were negatively correlated with the Karnofsky Performance Scale (KPS) score. The serum levels of cytokines IL-2, IL-6, IFN-γ, and TNF-α were higher and serum IL-17A level was lower in patients with thymoma. Patients with advanced-stage thymoma exhibited significantly higher proportions of IL-10-producing Bregs and a higher serum IL-10 level. After tumour resection, the frequency of circulating IL-10⁺CD24^hiCD38^hi Bregs and the serum IL-10 level were significantly decreased in patients with thymoma. The serum IL-10 levels exhibited the best accuracy in assessing the risk of thymoma occurrence in this study.

CONCLUSIONS

The expression of IL-10 produced by Bregs is increased in patients with thymoma, particularly those with advanced-stage disease, which may suggest that Bregs are involved in the pathogenesis and progression of thymoma.

Juan Rosai as master of our comprehensive understanding of thymus and thymoma

In this study, the authors report on the activity of Juan Rosai, one of the pathologists most engaged in the definition of cells, diseases and tumors occurring in the thymus and in the mediastinum during the last 60 years. With his morphological skills and tireless interest in clarification of disease patterns, he contributed extraordinarily to expand our knowledge of the mediastinal diseases and to improve our diagnostic approach. He determined extraordinary advances also in trasmission electron microscopy and in immunohistochemistry as powerful diagnostic tools. Moreover, he proposed and promoted, together with an international panel of Pathologists, the World Health Classification of Thymic tumors as a definite progress in our comprehension and diagnostics of thymic epithelial tumors (TET). Our purpose is to review J. Rosai's achievements in thymic normal structure, in TET and particularly in the entity now definied as "thymoma", in distinction from the thymic carcinoma. To do this, our narrative will also be based on personal memories, longstanding collaborations and/or friendship with J. Rosai.

Diagnostic and prognostic values of 2-[18F]FDG PET/CT in resectable thymic epithelial tumour

OBJECTIVES

We aimed to evaluate the diagnostic ability for the prediction of histologic grades and prognostic values on recurrence and death of pretreatment 2-[¹⁸F]FDG PET/CT in patients with resectable thymic epithelial tumours (TETs).

METHODS

One hundred and fourteen patients with TETs who underwent pretreatment 2-[¹⁸F]FDG PET/CT between 2012 and 2018 were retrospectively evaluated. TETs were classified into three histologic subtypes: low-risk thymoma (LRT, WHO classification A/AB/B1), high-risk thymoma (HRT, B2/B3), and thymic carcinoma (TC). Area under the receiver operating characteristics curve (AUC) was used to assess the diagnostic performance of PET/CT variables (maximum standardised uptake value [SUVmax], metabolic tumour volume [MTV], total lesion glycolysis [TLG], maximum diameter). Cox proportional hazards models were built using PET/CT and clinical variables.

RESULTS

The tumours included 52 LRT, 33 HRT, and 29 TC. SUVmax showed good diagnostic ability for differentiating HRT/TC from LRT (AUC 0.84, 95% confidence interval [CI] 0.76 - 0.92) and excellent ability for differentiating TC from LRT/HRT (AUC 0.94, 95% CI 0.90 - 0.98), with significantly higher values than MTV, TLG, and maximum diameter. With an optimal cut-off value of 6.4, the sensitivity, specificity, and accuracy for differentiating TC from LRT/HRT were 69%, 96%, and 89%, respectively. In the multivariable Cox proportional hazards analyses for freedom-from-recurrence, SUVmax was an independent prognostic factor (p < 0.001), whereas MTV and TLG were not. SUVmax was a significant predictor for overall survival in conjunction with clinical stage and resection margin.

CONCLUSION

SUVmax showed excellent diagnostic performance for prediction of TC and significant prognostic value in terms of recurrence and survival.

KEY POINTS

• Maximum standardised uptake value (SUVmax) shows excellent performance in the differentiation of thymic carcinoma from low- and high-risk thymoma. • SUVmax is an independent prognostic factor for freedom-from-recurrence in the multivariable Cox proportional hazard model and a significant predictor for overall survival. • 2-[¹⁸F]FDG PET/CT can provide a useful diagnostic and prognostic imaging biomarker in conjunction with histologic classification and stage and help choose appropriate management for thymic epithelial tumours.

Correlation of clinical and computed tomography features of thymic epithelial tumours with World Health Organization classification and Masaoka-Koga staging

OBJECTIVES

Our goal was to investigate the correlation of clinical and computed tomography (CT) features of thymic epithelial tumours (TET) with the World Health Organization classification and the Masaoka-Koga staging system.

METHODS

Clinical and CT imaging data from 159 patients surgically and pathologically diagnosed with TET (82 men, 77 women; mean [± standard deviation] age, 52.08 ± 11.76 years) were retrospectively collected and reviewed. CT features were evaluated by radiologists. Tumour size, morphology, margin, density, calcification, cystic necrosis, density of the fat layer around the tumour, invasion of surrounding tissues, mediastinal lymph node enlargement, pleural/pericardial effusion, metastasis, plain CT scans and enhanced CT values were analysed.

RESULTS

Of the 159 patients with TET, 76 had low-risk thymoma, 55 had high-risk thymoma and 28 had thymic carcinomas. Age, maximum tumour diameter, myasthenia gravis, morphology, edges, density, fat around the lesion, mediastinal vascular, pericardial and lung tissue invasion, pleural/pericardial effusion, metastasis and arterial phase CT values were statistically different among the 3 groups (P < 0.05). Multivariate regression analysis revealed that edges, fat around the lesion, mediastinal vascular invasion and pericardial effusion were most relevant to TET classification. The 159 patients with TET were categorized into the non-invasion group (stage I; n = 58); the invasion of surrounding fat (stage II; n = 46); and the invasion of surrounding structures and metastasis group (stages III and IV; n = 55). Tumour diameter, morphology, margins, density, cystic degeneration and necrosis, invasion of surrounding fat and structure, pleural and pericardial effusion and lymph node enlargement were statistically different among the 3 groups (P < 0.05). Multivariate regression analysis revealed that edges, fat around the lesion, mediastinal vascular invasion and pleura invasion were the most relevant CT signs in relation to TET staging.

CONCLUSIONS

Analysis of clinical and CT features before surgery may facilitate the preliminary classification and stage diagnosis of TET.

Molecular landscape of thymic epithelial tumors

Thymic epithelial tumors (TETs) are extremely rare and represent the most frequent tumors of the anterior mediastinum originating from epithelial cells in the thymus. Thymic epithelial tumors include thymomas (TM), thymic carcinomas (TC) and thymic neuroendocrine neoplasms (TNEN). Thymomas are the most predominant and are associated with autoimmune diseases. The available data suggests that the different histological subtypes have specific molecular alterations. Thymic carcinoma shows recurrent gene mutations, but further investigations are needed to understand the role of those mutations in the pathogenetic of the TETs. Some of the new emerging identified molecular alterations have the potential to offer new targeted therapies opening new possibilities for the treatment of thymic epithelial tumors.

Identification of Molecular Characteristics and New Prognostic Targets for Thymoma by Multiomics Analysis

BACKGROUND

Thymoma is a heterogeneous tumor originated from thymic epithelial cells. The molecular mechanism of thymoma remains unclear.

METHODS

The expression profile, methylation, and mutation data of thymoma were obtained from TCGA database. The coexpression network was constructed using the variance of gene expression through WGCNA. Enrichment analysis using clusterProfiler R package and overall survival (OS) analysis by Kaplan-Meier method were carried out for the intersection of differential expression genes (DEGs) screened by limma R package and important module genes. PPI network was constructed based on STRING database for genes with significant impact on survival. The impact of key genes on the prognosis of thymoma was evaluated by ROC curve and Cox regression model. Finally, the immune cell infiltration, methylation modification, and gene mutation were calculated.

RESULTS

We obtained eleven coexpression modules, and three of them were higher positively correlated with thymoma. DEGs in these three modules mainly involved in MAPK cascade and PPAR pathway. LIPE, MYH6, ACTG2, KLF4, SULT4A1, and TF were identified as key genes through the PPI network. AUC values of LIPE were the highest. Cox regression analysis showed that low expression of LIPE was a prognostic risk factor for thymoma. In addition, there was a high correlation between LIPE and T cells. Importantly, the expression of LIPE was modified by methylation. Among all the mutated genes, GTF2I had the highest mutation frequency.

CONCLUSION

These results suggested that the molecular mechanism of thymoma may be related to immune inflammation. LIPE may be the key genes affecting prognosis of thymoma. Our findings will help to elucidate the pathogenesis and therapeutic targets of thymoma.

AB thymoma revealed by a huge intraparenchymal lung mass: a case report

Thymoma is an epithelial neoplasm of the thymus, which commonly lies in the anterior mediastinum. Unusually it can be found in other locations as well. Ectopic thymoma rarely presents as an intrathoracic tumor. We report a case of ectopic thymoma presenting as a giant right intrathoracic tumor, the patient was 51-year-old, and who was presented with heaviness in chest and breathlessness. Detailed investigation including chest computed tomography scan revealed a well-defined large solid tumor in the right thoracic cavity, in this case, immunohistochemical analysis demonstrated a thymome AB. The tumor was metastatic to the lung. Patient received a neoadjuvant chemotherapy, with favorable evolution.

Predicting Masaoka-Koga Clinical Stage of Thymic Epithelial Tumors Using Preoperative Spectral Computed Tomography Imaging

Objectives

To investigate the utility of spectral computed tomography (CT) parameters for the prediction of the preoperative Masaoka-Koga stage of thymic epithelial tumors (TETs).

Materials and Methods

Fifty-four patients with TETs, aged from 37 to 73 years old, an average age of 55.56 ± 9.79 years, were included in the study.According to the Masaoka-Koga staging method, there were 19 cases of stage I, 15 cases of stage II, 8 cases of stage III, and 12 cases of stage IV disease. All patients underwent dual-phase enhanced energy spectral CT scans. Regions of interest (ROIs) were defined in sections of the lesion with homogeneous density, the thoracic aorta at the same level as the lesion, the outer fat layer of the lesion, and the anterior chest wall fat layer. The single-energy CT value at 40-140 keV, iodine concentration, and energy spectrum curve of all lesion and thoracic aorta were obtained. The energy spectrum CT parameters of the lesions, extracapsular fat of the lesions, and anterior chest wall fat in stage I and stage II were obtained. The energy spectrum CT parameters of the lesions, enlarged lymph nodes and intravascular emboli in the 3 groups were obtained. The slope of the energy spectrum curve and the normalized iodine concentration were calculated.

Results

In stage I lesions, there was a statistically significant difference between the slope of the energy spectrum curve for the lesion and those of the fat outside the lesion and the anterior chest wall in the arteriovenous phase (P<0.001, P<0.001). The energy spectrum curve of the tumor parenchyma was the opposite of that of the extracapsular fat. In stage II lesions, there was a statistically significant difference between the slope of the energy spectrum curve for the anterior chest wall and those of the lesion and the fat outside the lesion in the arteriovenous phase(P<0.001, P<0.001). The energy spectrum curve of the tumor parenchyma was consistent with that of the extracapsular fat. Distinction between stage I and II tumors be evaluated by comparing the energy spectrum curves of the mass and the extracapsular fat of the mass. The accuracy rate of is 79.4%. For stages III and IV, there was no significant difference in the slope of the energy spectrum curve of the tumor parenchyma, metastatic lymph node, and intravascular embolism (P>0.05). The energy spectrum curve of the tumor parenchyma was consistent with that of the enlarged lymph nodes and intravascular emboli. The two radiologists have strong consistency in evaluating TETs Masaoka-Koga staging, The Kappa coefficient is 0.873,(95%CI:0.768-0.978).

Conclusion

Spectral CT parameters, especially the energy spectrum curve and slope, are valuable for preoperative TET and can be used in preoperative staging prediction.

Thymoma pathology and myasthenia gravis outcomes

INTRODUCTION

There is limited evidence regarding the impact of World Health Organization (WHO) subtype of thymoma on post-thymectomy outcome of thymoma-associated myasthenia gravis (TAMG). The objective was to determine if the pathological subtypes of thymoma were associated with post-thymectomy outcomes of myasthenia gravis (MG), in patients with TAMG.

METHODS

We performed a retrospective study of consecutive patients with TAMG who attended the neuromuscular clinic between January 2018 and December 2019 with a minimum follow-up of 1 y after thymectomy. Outcome measures were MG Impairment Index (MGII), single-simple question (SSQ), Myasthenia Gravis Foundation of America post-intervention status (MGFA PIS) and non-responder MG status at last assessment.

RESULTS

Ninety-five patients were included; mean age at onset was 48.1 ± 12.1 y; 54(56.8%) were females. Thirteen patients developed MG post-thymectomy. The most common thymoma was WHO type B2 in 39 (41.1%). Most patients (40, 42.1%) had Masaoka stage II thymoma. There was no association of thymoma subtypes or Masaoka stage of disease with age, gender, MG phenotype, serology, post-thymectomy onset, interval from onset to thymectomy, MGII, SSQ, MGFA PIS, or non-responder status. Associations were found between positive serology and lower MGII (11.1 ± 14.2 vs 23 ± 12.9, P = .050), thymic follicular hyperplasia (TFH) and higher SSQ (89.3 ± 11.7 vs 80.1 ± 20.2, P-.043), and lack of recurrence and higher SSQ (84.1 ± 18 vs 72.5 ± 20, P = .037).

DISCUSSION

The WHO pathological subtype of thymoma did not correlate with MG outcomes. However, positive acetylcholine antibody serology, presence of TFH, and non-recurrence of thymoma predict a favorable outcome.

Micronodular thymic carcinoma with lymphoid hyperplasia: relevance of immunohistochemistry with a small panel of antibodies for diagnosis-a RYTHMIC study

Micronodular thymic carcinoma with lymphoid hyperplasia (MNTCLH) is a rare form of thymic carcinoma. We present the experience of RYTHMIC, the French national network devoted to the treatment of thymic epithelial tumors through multidisciplinary tumor boards with a review of all tumors by pathologists for classification and staging. Six cases of MNTCLH were diagnosed during a review of 1007 thymic epithelial tumors. Histologically, epithelial cells with atypia and mitoses formed micronodules that were surrounded by an abundant lymphoid background with follicles. There was neither obvious fibro-inflammatory stroma nor necrosis. Spindle cells areas were common. Initial diagnosis was micronodular thymoma in two cases, cellular atypia being overlooked, eclipsed by the micronodular pattern. Immunohistochemistry with a panel of five antibodies showed that cytokeratins (AE1-AE3) and p63-positive epithelial cells also expressed CD5 and that there was no TdT-positive cells within the tumors. CD20 highlighted the lymphoid hyperplasia. Additionally epithelial cells also expressed CD117 and diffusely Glut 1. Twenty-seven micronodular thymomas with lymphoid stroma diagnosed during the same period did not show the CD5 and CD117 positivities seen in MNTCLH and contained TdT-positive lymphocytes. Three of the 6 patients with MNTCLH had adjuvant radiotherapy. Three patients with follow-up information were alive without recurrence at 38, 51, and 95 months. Our study shows that immunohistochemistry, such as that used in the RYTHMIC network with a small panel of antibodies, may easily help to confirm the correct diagnosis of MNTCLH, a rare and low-aggressive form of thymic carcinoma, and avoid the misdiagnosis of micronodular thymoma.

Old but gold: the role of drug combinations in improving response to immune check-point inhibitors in thoracic malignancies beyond NSCLC

The introduction of immune checkpoint inhibitors (ICIs) in non-oncogene addicted non-small cell lung cancer (NSCLC) has revolutionized the treatment scenario and led to a meaningful improvement in patient prognosis. Disappointingly, the success of ICI therapy in NSCLC has not been fully replicated in other thoracic malignancies as small cell lung cancer (SCLC), malignant pleural mesothelioma (MPM), and thymic epithelial tumors (TETs), due to the peculiar biological features of these disease and to the difficulties in the conduction of well-designed, biomarker-driven clinical trials. Therefore, combination strategies of ICIs plus conventional therapies (either chemotherapy, alternative ICIs or targeted agents) have been implemented. Although first approvals of ICI therapy have been recently granted in SCLC and MPM (in combination with chemotherapy and different ICIs), results remain somewhat modest and limited to a small proportion of patients. This work reviews the trial results of ICI therapy in mesothelioma, SCLC, and TETs and discusses the potential of combining ICIs with old drugs.

Thymic Epithelial Neoplasms: Radiologic-Pathologic Correlation

Thymic epithelial neoplasms, as classified by the World Health Organization, include thymoma, thymic carcinoma, and thymic carcinoid. They are a rare group of tumors and are often diagnosed incidentally in the work-up of parathymic syndrome, such as myasthenia gravis, or when mass effect or local invasion causes other symptoms. In each of these scenarios, understanding the radiologic-pathologic relationship of these tumors allows clinical imagers to contribute meaningfully to management decisions and overall patient care. Integrating important imaging features, such as local invasion, and pathologic features, such as necrosis and immunohistochemistry, ensures a meaningful contribution by clinical imagers to the care team.

Extracellular volume fraction measurement correlates with lymphocyte abundance in thymic epithelial tumors

Background

Recent advance in tissue characterization with parametric mapping imaging has the potential to be a novel biomarker for histopathologic correlation with thymic epithelial tumors (TETs). The purpose of our study is to evaluate MRI T1 mapping with the calculation of extracellular volume (ECV) fraction for histologic correlation with thymic epithelial tumor based on lymphocyte abundance.

Methods

A retrospective study including 31 consecutive patients (14 men and 17 women, median age, 56 years; interquartile range, 12 years) with TETs was performed. The T1 values and ECV were assessed by using quantitative MRI mapping techniques. Mann-Whitney U test, Kruskal-Wallis H test, and receiver operating characteristic curve analyses were used to assess discrimination between different types of TETs based on lymphocyte abundance.

Results

Extracellular volume was significantly higher in TETs with sparse lymphocyte, including type A, type B3, and thymic carcinoma, compared with those with abundant lymphocyte, including type B1, B2, and AB thymomas (42.5% vs 26.9%, respectively; p < 0.001). Extracellular volume was significantly higher in thymic carcinoma compared with low grade and high grade thymomas (48.6% vs 31.1% vs 27.6%, respectively; p = 0.002).

Conclusions

T1 mapping with the calculation of extracellular volume (ECV) fraction correlate with the WHO histologic classification of thymic epithelial tumor based on lymphocyte abundance.

Expression of cathepsins B, D and K in thymic epithelial tumours

AIM

Cathepsins are proteases that regulate a wide range of physiological processes, including protein turnover, cell signalling and antigen presentation. Recent studies have shown that cathepsins are highly upregulated in many types of tumours. Of the 15 cathepsins in humans, cathepsins V and S are abundantly expressed in the thymus, and we previously showed that the immunostaining of these cathepsins could serve as diagnostic markers for thymic epithelial tumours. However, little is known about the expression of other cathepsins in thymic epithelial tumours. To determine the diagnostic implications of cathepsins, we performed immunohistochemical analysis of cathepsin B (CTB), cathepsin D (CTD) and cathepsin K (CTK), all of which have been reported to correlate with the progression of squamous cell carcinoma.

METHODS

The association between cathepsin expression and clinicopathological features was evaluated in 122 cases of thymoma and thymic carcinoma.

RESULTS

CTB and CTD were frequently expressed in type A and type AB thymomas. In contrast, CTB and CTD were significantly less common in type B thymomas than in type A or AB thymomas. In type AB thymomas, the expression of CTB correlated with histological features, and was found predominantly in the type A component. Notably, CTK was expressed most commonly in thymic carcinomas, and patients who died of the disease showed increased expression of CTK.

CONCLUSIONS

The expression of CTB and CTD correlated with the histological subtype of thymoma. In addition, the expression of CTK appears to be useful for the diagnosis of thymic carcinomas and as a prognostic marker.

Histotyping of Indian thymomas: A clinicopathologic study from north India

Background & objectives:

Thymomas are rare, but most common anterior mediastinal lesions. The histomorphologic spectrum of thymic epithelial tumours (TETs) in Indian population has not been explored in depth. This study was aimed to assess the histomorphology of TETs in the Indian patients and correlate clinical parameters with pathological features.

Methods:

It was a retrospective study conducted in a tertiary referral hospital in north India. All morphologically confirmed cases of TETs since 2009 were included. Clinical details and histology slides were reviewed using the Modified Masaoka-Koga staging system and WHO 2015 classification. Clinicopathological correlation and survival analysis were done. A comparative review from other published Indian studies was performed.

Results:

A total of 219 cases of TETs (138 resections and 81 biopsies) were identified. The most common histomorphologic type was B2, and the most frequent stage was I. Types A/AB were common in older age (P<0.01). Clinically, higher stage tumours were found mostly in men (P<0.01), and these were Type B thymomas (P<0.01). Myasthenia gravis was more common in women (P<0.02) and in lower stages (P<0.05). Survival analysis revealed significant association between recurrence and tumour stage. Although thymic carcinoma was diagnosed on biopsy, no resectable case was identified.

Interpretation & conclusions:

Our findings showed that the thymomas in Indian patients were most commonly Stage I tumours of B2 and AB histotypes. Resected thymic carcinomas were conspicuously absent in our study. More studies need to be done to establish the frequency and biology of TETs from India.

Thymic epithelial tumors: From biology to treatment

In the last few years, meaningful advances have been made in the knowledge of the biology of Thymic Epithelial Tumors (TETs). Data available suggest that in most cases, the different histological subtypes could be distinct biological entities, characterized by specific molecular aberrations, rather than representing a histological continuum of diseases. Recurrent gene mutations in Thymomas and Thymic Carcinoma have been identified, but we still do not know the exact role played by these mutations in TETs pathogenesis. Relevant new data are now available on the pathogenetic mechanisms underlying the association between TETs and autoimmune diseases that warrant further investigations for the potential therapeutic implications. The progress in knowledge of the molecular pathways involved in TETs pathogenesis, allowed to identify and to test target therapies potentially active in such diseases. Platinum-based chemotherapy remains the standard first line treatment for patients with advanced or metastatic TETs. However, some promising data have been reported on the activity of new target therapies, including anti-angiogenic drugs, Cycline Dependent Kinases and PI3K/mTOR inhibitors, as well as of Immune-checkpoint inhibitors. A number of new drugs and combinations are currently under evaluation. The efficacy of new drugs should be balanced with their toxicity profiles, in such complex patients that seem to be more susceptible to develop drug-related toxicities, in particular with immunotherapies.

Deciphering tissue-based proteome signatures revealed novel subtyping and prognostic markers for thymic epithelial tumors

Thymic epithelial tumors (TETs) belong to a group of tumors that rarely occur, but have unresolved mechanisms and heterogeneous clinical behaviors. Current care of TET patients demands biomarkers of high sensitivity and specificity for accurate histological classification and prognosis management. In this study, 134 fresh‐frozen tissue samples (84 tumor, 40 tumor adjacent, and 10 normal thymus) were recruited to generate a quantitative and systematic view of proteomic landscape of TETs. Among them, 90 samples were analyzed by data‐independent acquisition mass spectrometry (DIA‐MS) leading to discovery of novel classifying molecules among different TET subtypes. The correlation between clinical outcome and the identified molecules was probed, and the prioritized proteins of interest were further validated on the remaining samples (n = 44) via parallel reaction monitoring (PRM) as well as immunohistochemical and confocal imaging analysis. In particular, two proteins, the cellular mRNA deadenylase CCR4 (carbon catabolite repressor 4)‐NOT (negative on TATA) complex subunit 2/9 (CNOT2/9) and the serine hydroxymethyltransferase that catalyzes the reversible interconversions of serine and glycine (SHMT1), were found at dramatic low levels in the thymic epithelia of more malignant subtype, thymic squamous cell carcinoma (TSCC). Interestingly, the mRNA levels of these two genes were shown to be closely correlated with prognosis of the TET patients. These results extended the existing human tissue proteome atlas and allowed us to identify several new protein classifiers for TET subtyping. Newly identified subtyping and prognosis markers, CNOT2/9 and SHMT1, will expand current diagnostic arsenal in terms of higher specificity and prognostic insights for TET diagnosis and management.

A case of thymoma in myasthenia gravis: Successful outcome after thymectomy

INTRODUCTION

Thymic abnormalities occur as hyperplasia and thymoma. Myasthenia gravis is commonly present in thymoma. Thymectomy possesses risk due to anatomical proximity with vital thoracic structures and myasthenia crisis.

PRESENTATION OF CASE

Forty five years female with complaints of difficulty swallowing and weakness of upper limb muscles upon investigation showed mass in mediastinum and antibody test for myasthenia gravis positive. Medical management was done for a month followed by thymectomy. There were no intra and postoperative complications. Medical management was stopped one month after surgery and she is symptom free.

DISCUSSION

Thymectomy is the standard of care where median sternotomy is the mainstay approach to surgery. Various other surgical approaches and complications revolving around surgery has been discussed.

CONCLUSION

Surgical removal of thymoma cured myasthenia gravis in our case. We focused on proper preoperative optimization of myasthenia gravis symptoms before thymectomy.

Aetiology and pathogenesis of paraneoplastic autoimmune disorders

Paraneoplastic autoimmune disorders (PAD) represent a group of autoimmune diseases associated with neoplasms. As a consequence of a remote autoimmunity-mediated effect, PAD are found in multiple organs or tissues, including the skin, blood and nervous system. Compared with non-paraneoplastic autoimmune diseases, PAD have different aetiologies, pathologies, disease symptoms and treatment responses. There are two main origins of autoimmunity in PAD: neoplasm-mediated dysregulated homeostasis in immune cells/organs and in autoantigens. Pathologically, PAD are mediated predominantly by either autoantibodies or autoreactive T-cells. In the past decade, significant progress has been achieved in increasing our understanding of the aetiology and pathology of PAD. In this review article, we aim to provide a comprehensive overview of the recent advances in this field.

Using proteomic profiling to characterize protein signatures of different thymoma subtypes

Background

Histology is a traditional way to classify subtypes of thymoma, because of low cost and convenience. Yet, due to the diverse morphology of thymoma, this method increases the complexity of histopathologic classification, and requires experienced experts to perform correct diagnosis. Therefore, in this study, we developed an alternative method by identifying protein biomarkers in order to assist clinical practitioners to make right classification of thymoma subtypes.

Methods

In total, 204 differentially expressed proteins in three subtypes of thymoma, AB, B2, and B3, were identified using mass spectrometry. Pathway analysis showed that the differentially expressed proteins in the three subtypes were involved in activation-related, signaling transduction-related and complement system-related pathways. To predict the subtypes of thymoma using the identified protein signatures, a support vector machine algorithm was used. Leave-one-out cross validation methods and receiver operating characteristic analysis were used to evaluate the predictive performance.

Results

The mean accuracy rates were > 80% and areas under the curve were ≧0.93 across these three subtypes. Especially, subtype B3 had the highest accuracy rate (96%) and subtype AB had the greatest area under the curve (0.99). One of the differentially expressed proteins COL17A2 was further validated using immunohistochemistry.

Conclusions

In summary, we identified specific protein signatures for accurately classifying subtypes of thymoma, which could facilitate accurate diagnosis of thymoma patients.

Pathological discrepancies in the diagnosis of thymic epithelial tumors: the Tallinn-Lyon experience

Background

Thymic epithelial tumors are rare thoracic tumors for which pathological diagnosis is challenging due to the definition of multiple subtypes, tumor heterogeneity, and variations in interobserver reproducibility. In this study, we aimed at analyzing the quality of pathological reporting in line with the consistency between initial diagnosis and final diagnosis after expert review through a collaboration between the largest thoracic oncology center in Estonia, and one expert center in France.

Methods

Hospital electronic database and pathology databases from the Tallinn North Estonia Medical Centre were searched for thymic and mediastinal tumors from 2010 to 2017. Pathology specimens were referred to the Pathology Department of the Lyon University hospital. Overall, 55 tissue specimens from 49 patients were included.

Results

From pathology reports, tumor size, diagnosis, and invasion had been mentioned in ≥80% of cases, while resection status and staging were assessed in only 48% and 17% of cases, respectively. The initial diagnosis was consistent with that of the review in 60% of cases. Diagnostic concordance for thymoma subtypes was low (Cohen's kappa 0.34, 95% CI: 0.16-0.52). Overall, a major change in the management of 8 (16%) patients had to be made after pathological review: 3 patients had a normal thymus according to the reference centre, while thymoma B1 or B2 had been diagnosed locally; 5 additional patients had a final diagnosis of non-thymic tumor.

Conclusions

Implementing structured pathology reports may help to decrease discrepancies in the diagnosis of thymic epithelial tumors. The development of expert networks is an opportunity to improve diagnosis and patient care, particularly in regard to rare cancers.

Aplastic Anemia as an Immune-mediated Complication of Thymoma: A Case Report

Thymomas are the most common masses located in the anterior mediastinum, and they are often associated with autoimmune disorders including myasthenia gravis, polymyositis, and aplastic anemia (AA). Autoreactive T-cell clones generated by the thymoma may lead to autoimmune disorders. We report the case of a 14-year-old boy who was examined for AA, and the underlying cause was determined to be an immune-mediated complication of thymoma. He had no matched sibling donors. He underwent thymectomy, and 3 months later he was treated with immunosuppressive therapy (IST), consisting of antithymocyte globulin and cyclosporine A. The duration of the IST was determined to be a period of 12 months. He has recently been in complete response condition for 6 months since IST stopped. IST is a successful treatment choice for thymomas associated with AA in childhood.

D2-40 Antibody is a Specific Marker for B2 Thymomas

The correlation between the worse outcome of thymomas and expression of podoplanin (D2-40 antibody) in neoplastic cells has been proved in recent studies. We investigated the expression of podoplanin in thymic epithelial tumors of different histologic types and stages resected in our institution. The presence and type of reaction (membranous or cytoplasmic) with D2-40 antibody were assessed. Analyzed group consisted of 72 tumors: 3 type A, 19 type AB, 5 type B1, 24 type B2, 4 type B3, 2 micronodular, 1 metaplastic, and 9 combined B2B3 thymomas and 5 thymic carcinomas. Positive reaction with D2-40 was detected in 7 cases (37%) of AB type, 2 (40%) of B1, 28 (85%) of B2, 3 (23%) of B3, and 1 case (100%) of metaplastic thymoma. All positive B2 and 2 cases of B3 thymomas revealed membranous type of reaction, whereas other subtypes showed less conspicuous cytoplasmic reactivity. A correlation between B2 thymoma and membranous type of reaction was statistically significant (P<0.0001). There was also a slight relationship between cytoplasmic type of reaction and AB or B1 thymomas (P=0.0256). No correlation was detected between D2-40-reactivity and stage (P=0.4) or myasthenic symptoms (P=0.21). In conclusion, membranous type of reaction with D2-40 antibody in thymomas is highly specific for B2 subtype, but antipodoplanin immunoreactivity has no relationship with the tumor stage.

High CTLA-4 expression correlates with poor prognosis in thymoma patients

Thymomas, tumors that arise from epithelial cells of the thymus gland, are the most common neoplasms of the anterior mediastinum, with an incidence rate of approximately 2.5 per million/year. Cytotoxic T Lymphocyte Antigen 4 (CTLA-4 or CD152) exerts inhibitory activity on T cells, and since its oncogenic role in the progression of different types of tumors, it has emerged as a potential therapeutic target in cancer patients.

In this study, we assessed the expression of CTLA-4 both at mRNA and protein levels in paraffin embedded-tissues from patients with thymomas. Furthermore, we evaluated the relationship between CTLA-4 expression and the clinical-pathologic characteristics and prognosis in patients with thymomas. Sixty-eight patients with median age corresponding to 62 years were included in this analysis. Thymomas were classified accordingly to the WHO and Masaoka-Koga for histochemical analysis and for prognostic significance.

A statistical difference was found between CTLA-4 mRNA levels in human normal thymus compared with thymoma specimens. CTLA-4 expression was statistically found to progressively increase in A, B1, B2, AB and it was maximal in B3 thymomas. According to Masaoka-Koga pathological classification, CTLA-4 expression was lower in I, IIA and IIB, and higher in invasive III and IV stages. By confocal microscopy analysis we identified the expression of CTLA-4 both in tumor cells and in CD45⁺ tumor-infiltrating leukocytes, mainly in B3 and AB thymomas.

Finally, CTLA-4 overexpression significantly correlates with reduced overall survival in thymoma patients and in atypical thymoma subgroup, suggesting that it represents a negative prognostic factor.

Seronegative Paraneoplastic Limbic Encephalitis Associated with Thymoma

Paraneoplastic limbic encephalitis is an autoimmune syndrome characterized by the acute or subacute onset of encephalopathy, memory loss, confusion, temporal lobe seizures, and behavioral and mood changes. Although most patients with paraneoplastic limbic encephalitis have antineuronal antibodies, advances in the field now permit the diagnosis without autoantibody test results. In this case illustrating the new diagnostic criteria, we report a 70-year-old woman who was brought to the emergency room after the acute onset of cognitive impairment, altered mental status, and choreoathetoid movements. Brain magnetic resonance imaging showed hyperintense signals in both temporal lobes, and a chest computed tomogram revealed a thymoma. Because the patient met current diagnostic criteria for autoimmune limbic encephalitis, we were able to start treatment before her antibody tests were processed. The patient received immunotherapy and her tumor was resected. Her choreoathetoid movements disappeared and her other neurologic symptoms improved. Her cerebrospinal fluid proved to be negative for paraneoplastic limbic encephalitis antibodies. Most but not all patients with paraneoplastic limbic encephalitis associated with thymoma have evidence of paraneoplastic antibodies. Prompt management of the underlying malignancy determines whether patients survive and may minimize future cognitive and functional impairment. Practicing neurologists and psychiatrists should be aware of this diagnosis.

Can 18F-FDG PET predict the grade of malignancy in thymic epithelial tumors? An evaluation of only resected tumors

Objective

Although 18-fluorine fluorodeoxyglucose positron emission tomography (¹⁸F-FDG PET) is thought to be useful for predicting the histological grade of thymic epithelial tumors (TETs), it remains controversial. To date, just a few of many previous studies have included only resected cases. Therefore, we investigated ¹⁸F-FDG PET findings only in patients with resected TETs.

Patients and methods

A total of 112 patients with TETs consisting of 92 thymomas and 20 thymic carcinomas (TCs), resected at two institutes (Shizuoka Cancer Center [Shizuoka] and National Cancer Center Hospital [Tokyo]) between October 2002 and December 2015, were evaluated. Spearman rank correlation coefficient was used to assess the association between the maximum standardized uptake value (SUVmax) in the tumor and both the histological subtype and tumor stage. The cutoff value of SUVmax for differentiating thymoma from TC was calculated.

Results

The SUVmax was strongly related to both the World Health Organization (WHO) histological subtype and tumor stage based on the eighth edition of the tumor-node-metastasis (TNM) classification (Spearman rank correlation coefficient =0.485 and 0.432; p = 0.000 and 0.000, respectively). There was a significant difference between thymoma and TC. The optimal SUVmax cutoff value for differentiating thymoma from TC was 4.58 (sensitivity: 80% and specificity: 78.3%). In contrast, there was no significant difference between low-risk (type A, AB, and B1) and high-risk (type B2 and B3) thymoma, or between type B3 thymoma and the other subtypes.

Conclusion

Our results suggest that ¹⁸F-FDG PET is useful for differentiating thymoma from TC, but not for predicting the histologic grade of thymoma.

Decreased Wnt4 expression inhibits thymoma development through downregulation of FoxN1

BACKGROUND

The Wnt signaling pathway controls the development of thymic epithelial cells by regulating the expression of FoxN1. Thymoma is a type of malignant tumor arising from the thymic epithelial cells. To determine whether Wnt4 and FoxN1 are involved in the pathogenesis of thymoma, this study determined the mRNA and protein levels of Wnt4 and Foxn1 in thymoma, and analyzed the effect of thymoma cell apoptosis and tumor growth in nude mice after Wnt4 and FoxN1 downregulation.

METHODS

Wnt4 and FoxN1 mRNA and protein levels in thymoma tissues were analyzed by RT-qPCR and immunohistochemistry, respectively. Thymoma cells were cultured and transfected with siRNA targeting the Wnt4, JNK, and FoxN1 genes. Apoptosis of thymoma cells were analyzed after Wnt4 and FoxN1 downregulation. In addition, thymoma cells were inoculated into nude mice and tumor growth was analyzed.

RESULTS

The rates of expression of Wnt4 and FoxN1 protein were 64.3% and 58.9%, while the levels of mRNA expression were 2.56±0.04 and 1.83±0.11, respectively. With increasing malignancy of thymoma, the rates of positivity for Wnt4 and FoxN1 mRNA and protein expression gradually increased. Upon interfering with Wnt4, JNK, and FoxN1 gene expression by using siRNA technology, the inhibition rates were 56.7%, 72.6%, and 63.2%, respectively. The expression of FoxN1 mRNA and protein was decreased after Wnt4 and JNK downregulation. After downregulation of Wnt4 and FoxN1 gene expression, the apoptosis rate of thymoma cells increased and the tumor volume decreased in nude mice.

CONCLUSIONS

High expression of Wnt4 and FoxN1 may play an important role in the generation and development of thymoma. The FoxN1 gene produced a marked downstream effect through the regulation of Wnt4. Determining the positivity for both Wnt4 and FoxN1 can help us to evaluate the level of malignancy of thymoma.

Dataset for reporting of thymic epithelial tumours: recommendations from the International Collaboration on Cancer Reporting (ICCR)

AIMS

The International Collaboration on Cancer Reporting (ICCR) is a not-for-profit organization formed by the Royal Colleges of Pathologists of Australasia and the United Kingdom, the College of American Pathologists, the Canadian Association of Pathologists-Association Canadienne des Pathologists in association with the Canadian Partnership Against Cancer, and the European Society of Pathology. Its goal is to produce standardized, internationally agreed, evidence-based datasets for use throughout the world.

METHODS AND RESULTS

This article describes the development of a cancer dataset by the multidisciplinary ICCR expert panel for the reporting of thymic epithelial tumours. The dataset includes 'required' (mandatory) and 'recommended' (non-mandatory) elements, which are validated by a review of current evidence and supported by explanatory text. Seven required elements and 12 recommended elements were agreed by the international dataset authoring committee to represent the essential information for the reporting of thymic epithelial tumours.

CONCLUSIONS

The use of an internationally agreed, structured pathology dataset for reporting thymic tumours provides all of the necessary information for optimal patient management, facilitates consistent and accurate data collection, and provides valuable data for research and international benchmarking. The dataset also provides a valuable resource for those countries and institutions that are not in a position to develop their own datasets.

Expression of cathepsins V and S in thymic epithelial tumors

Cathepsins are a group of proteolytic enzymes of the endosomal/lysosomal pathway involved in the thymic development of T cells restricted by major histocompatibility complex class II molecules. In the normal thymus, cathepsin V (CTV) and cathepsin S (CTS) are expressed in cortical and medullary epithelial cells, respectively. To investigate whether cathepsins could serve as a diagnostic marker, we performed immunohistochemical analysis for CTV and CTS in 77 cases of thymic epithelial tumors. Almost all cases (59/60) of thymoma expressed CTV, whereas 28 of 60 cases of thymoma expressed CTS. Notably, CTS was expressed in most cases of type A and type AB thymomas, but not in type B thymoma. The expression of cathepsins in type AB thymoma showed a clear correlation with histologic features; CTV was found predominantly in the type B component, and CTS was frequently expressed in the type A component. In thymic carcinoma, CTV was expressed in less than half cases (7/17), and the ratio of CTS-positive cases was equivalent to that of thymoma (8/17). Cases of CTV-negative thymic carcinoma tended to have a higher incidence of recurrence than did CTV-positive cases. Although further studies with a larger number of cases are required to confirm the utility of cathepsin immunostaining, CTV and CTS appear to serve as auxiliary diagnostic and/or prognostic markers in thymic epithelial tumors.

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.

State of the art: diagnostic tools and innovative therapies for treatment of advanced thymoma and thymic carcinoma

In this review article, state-of-the-art diagnostic tools and innovative treatments of thymoma and thymic carcinoma (TC) are described with special respect to advanced tumour stages. Complete surgical resection (R0) remains the standard therapeutic approach for almost all a priori resectable mediastinal tumours as defined by preoperative standard computed tomography (CT). If lymphoma or germ-cell tumours are differential diagnostic considerations, biopsy may be indicated. Resection status is the most important prognostic factor in thymoma and TC, followed by tumour stage. Advanced (Masaoka-Koga stage III and IVa) tumours require interdisciplinary therapy decisions based on distinctive findings of preoperative CT scan and ancillary investigations [magnetic resonance imaging (MRI)] to select cases for primary surgery or neoadjuvant strategies with optional secondary resection. In neoadjuvant settings, octreotide scans and histological evaluation of pretherapeutic needle biopsies may help to choose between somatostatin agonist/prednisolone regimens and neoadjuvant chemotherapy as first-line treatment. Finally, a multimodality treatment regime is recommended for advanced and unresectable thymic tumours. In conclusion, advanced stage thymoma and TC should preferably be treated in experienced centres in order to provide all modern diagnostic tools (imaging, histology) and innovative therapy techniques. Systemic and local (hyperthermic intrathoracic chemotherapy) medical treatments together with extended surgical resections have increased the therapeutic options in patients with advanced or recurrent thymoma and TC.

Thymoma related myasthenia gravis in humans and potential animal models

Thymoma-associated Myasthenia gravis (TAMG) is one of the anti-acetylcholine receptor MG (AChR-MG) subtypes. The clinico-pathological features of TAMG and its pathogenesis are described here in comparison with pathogenetic models suggested for the more common non-thymoma AChR-MG subtypes, early onset MG and late onset MG. Emphasis is put on the role of abnormal intratumorous T cell selection and activation, lack of intratumorous myoid cells and regulatory T cells as well as deficient expression of the autoimmune regulator (AIRE) by neoplastic thymic epithelial cells. We review spontaneous and genetically engineered thymoma models in a spectrum of animals and the extensive clinical and immunological overlap between canine, feline and human TAMG. Finally, limitations and perspectives of the transplantation of human and murine thymoma tissue into nude mice, as potential models for TAMG, are addressed.