On the histologic heterogeneity of thymic epithelial neoplasms. Impact of sampling in subtyping and classification of thymomas

Advanced three-dimensional X-ray imaging unravels structural development of the human thymus compartments

BACKGROUND

The thymus, responsible for T cell-mediated adaptive immune system, has a structural and functional complexity that is not yet fully understood. Until now, thymic anatomy has been studied using histological thin sections or confocal microscopy 3D reconstruction, necessarily for limited volumes.

METHODS

We used Phase Contrast X-Ray Computed Tomography to address the lack of whole-organ volumetric information on the microarchitecture of its structural components. We scanned 15 human thymi (9 foetal and 6 postnatal) with synchrotron radiation, and repeated scans using a conventional laboratory x-ray system. We used histology, immunofluorescence and flow cytometry to validate the x-ray findings.

RESULTS

Application to human thymi at pre- and post-natal stages allowed reliable tracking and quantification of the evolution of parameters such as size and distribution of Hassall's Bodies and medulla-to-cortex ratio, whose changes reflect adaptation of thymic activity. We show that Hassall's bodies can occupy 25% of the medulla volume, indicating they should be considered a third thymic compartment with possible implications on their role. Moreover, we demonstrate compatible results can be obtained with standard laboratory-based x-ray equipment, making this research tool accessible to a wider community.

CONCLUSIONS

Our study allows overcoming the resolution and/or volumetric limitations of existing approaches for the study of thymic disfunction in congenital and acquired disorders affecting the adaptive immune system.

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.

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.

Atypical thymoma (epithelial-rich thymoma, well-differentiated thymic carcinoma, WHO type B3 thymoma): A conundrum

Thymomas composed predominantly of epithelioid tumor cells with scattered lymphocytes have been well recognized in the literature. This subtype of thymoma has been variously termed epithelial-rich thymoma, well-differentiated thymic carcinoma, atypical thymoma, or World Health Organization (WHO) type B3 thymoma. Regardless of the designation however, these tumors are known to show a spectrum of histopathological growth patterns that may pose challenges in interpretation and diagnosis, particularly when dealing with small mediastinoscopic biopsies. Just like any other type of thymoma, those composed predominantly of epithelioid cells may present as encapsulated or invasive tumors. Nevertheless, compared to other subtypes of thymoma, they are uncommon neoplasms. Therefore, it becomes very important to sufficiently sample thymomas before making a diagnosis of a particular subtype, especially when the tumor is rich in epithelioid cells and only has a scant lymphocytic component. Because of the unusual occurrence of these tumors, there are only few large series of cases that attempt to highlight not only the more salient histopathological features but also the most important immunohistochemical and molecular characteristics.

Spindle cell thymoma (WHO type A) - Choriocarcinoma: An unusual association: A clinicopathological and immunohistochemical study of 3 cases

Three cases of an unusual association between spindle cell thymoma (WHO type A) and choriocarcinoma are presented. The patients are three men between the ages of 58 and 68 years. Clinically, all the patients presented with non-specific symptoms of cough, dyspnea, and chest pain. Clinical history and physical examination did not reveal the presence of any prior malignancy. Diagnostic imaging showed in the three patients the presence of a large anterior mediastinal mass. A core needle biopsy was obtained in the three patients. In two patients the biopsy showed the classic histology of a spindle cell thymoma while in one patient the biopsy showed the association of two tumors - spindle cell thymoma and choriocarcinoma. Surgical resection via thoracotomy was performed in the three patients. The mediastinal tumors measured between 9 and 17 cm in greatest diameter and were described as solid and lobulated with areas of hemorrhage. Histologically, all the tumors showed similar histological features of spindle cell thymoma (WHO type A) associated with a high-grade neoplasm composed of round and multinucleated giant cells compatible with choriocarcinoma. Immunohistochemical stains showed positive staining for keratin 5/6, and p40 in the spindle cell component, while the choriocarcinomatous component showed positive staining for human chorionic gonadotropin and human placental lactogen. The cases herein presented highlight not only the unusual association of spindle cell thymoma and choriocarcinoma but also raises some issues regarding the histogenesis of germ cell tumors, in this case choriocarcinoma.

An unusual huge thymoma composed of sclerosing thymoma and type AB thymoma: A case report

RATIONALE

Sclerosing thymoma (ST) is quite a rare disease, as denoted in previous literature. Less than 20 cases of ST have been reported to date. However, the combined thymoma, composed of both type AB thymoma and ST, has never been described before.

PATIENT CONCERNS

The subject, a 49-year-old woman, came in with the chief complaint of cough for 10 days.

DIAGNOSES

Both the contrast-enhanced computed tomography scan and the ultrasonography showed a huge mass located in the right thoracic cavity with inhomogeneous contrast accompanied by the invasion of the pericardium and pleura. Subsequently, computed tomography-guided core-needle biopsy revealed type B2 thymoma, and type AB thymoma could not be excluded. Based on postsurgical histopathology and immunohistochemical finding, this tumor was given the final diagnosis of ST and type AB thymoma.

INTERVENTIONS

After 6 months of adjuvant chemotherapy and local radiotherapy, total thymectomy was performed.

OUTCOMES

The patient has been duly followed up for 1 year without any tumor recurrence.

LESSONS

ST is a very rare mediastinal neoplasm. Moreover, ST in combination with AB thymoma and affecting a large area, is unprecedented. Whether radiotherapy and chemotherapy have a certain effect on ST requires further investigation. In addition, due to the unclear recurrence rate of ST, long-term follow-up evaluation seems necessary.

Diagnostic Challenges in Fine-Needle Aspiration Cytology of Mediastinal Tumors and Lesions

CONTEXT.—

Mediastinal tumors/lesions are frequently encountered in daily cytopathology practice. These lesions are accessible through endoscopic/endobronchial ultrasound-guided or computed tomography-guided fine-needle aspiration cytology and represent a wide range of primary and metastatic tumors. This often poses diagnostic challenges because of the complexity of the mediastinal anatomic structures. Tumors metastatic to mediastinal lymph nodes represent the most common mediastinal lesions and must be differentiated from primary lesions.

OBJECTIVE.—

To provide an updated review on the fine-needle aspiration cytology of mediastinal tumors/lesions, with an emphasis on diagnostic challenges. This review encompasses thymic epithelial neoplasms, mediastinal lymphoproliferative disorders, germ cell tumors, neuroendocrine tumors, soft tissue tumors, and metastatic tumors. Differential diagnoses; useful ancillary studies, including targeted immunohistochemical panels; and diagnostic pitfalls are discussed.

DATA SOURCES.—

Data were gathered from a PubMed search of peer-reviewed literature on mediastinal tumors. Data were also collected from the authors' own practices.

CONCLUSIONS.—

Fine-needle aspiration cytology plays a vital role in evaluation of mediastinal lesions. Being familiar with the clinical and cytomorphologic features of these lesions, appropriately triaging the diagnostic material for ancillary testing, and correlating with radiologic findings are important in arriving at correct diagnoses and guiding management.

Thymoma: Histologically a heterogenous group of tumors

Over the years the nomenclature of thymomas has been debated regarding the best manner in which these tumors should be grouped. In every schema presented thus far, the main issue has been the presence or lack of lymphocytes and accordingly, the tumors have been place into a specific category. However, even though this concept applies for most of the cases, there are numerous tumors that do not necessarily fit into those categories as either the thymomas show another cellular proliferation associated with the epithelial cells or the epithelial cell themselves are arranged in a pattern that departs from the conventional features of the classic thymoma. Herein we will emphasize those features, which in some circumstances, mainly with small mediastinoscopic biopsies may pose a considerable problem in interpretation. We do consider that the most important issue is to be familiar with the different growth pattern that these tumors may show in order to avoid misdiagnosis. In addition, we consider that regardless of the growth pattern or cellular composition of the tumor, it is highly recommended that these tumors just like any other be carefully sampled and properly stage. Although we are fully aware of the different growth pattern and specific cellular details that thymoma may show, the discussion of each one of those tumors is beyond the scope of this review. Therefore, we have placed more emphasis in those, which in our judgment are more commonly encountered in the daily practice.

Development and validation of a CT-texture analysis nomogram for preoperatively differentiating thymic epithelial tumor histologic subtypes

BACKGROUND

Thymic epithelial tumors (TETs) are the most common primary tumors in the anterior mediastinum, which have considerable histologic heterogeneity. This study aimed to develop and validate a nomogram based on computed tomography (CT) and texture analysis (TA) for preoperatively predicting the pathological classifications for TET patients.

METHODS

Totally TET 172 patients confirmed by postoperative pathology between January 2011 to April 2019 were retrospectively analyzed and randomly divided into training (n = 120) and validation (n = 52) cohorts. Preoperative clinical factors, CT signs and texture features of each patient were analyzed, and prediction models were developed using the least absolute shrinkage and selection operator (LASSO) regression. The performance of the models was evaluated and compared by the area under receiver-operator characteristic (ROC) curve (AUC) and the DeLong test. The clinical application value of the models was determined via the decision curve analysis (DCA). Then, a nomogram was developed based on the model with the best predictive efficiency and clinical utility and validated using the calibration plots.

RESULTS

Totally 87 patients with low-risk TET (LTET) (types A, AB, B1) and 85 patients with high-risk TET (HTET) (types B2, B3, C) were enrolled in this study. We separately constructed 4 prediction models for differentiating LTET from HTET using clinical, CT, texture features, and their combination. These 4 prediction models achieved AUCs of 0.66, 0.79, 0.82, 0.88 in the training cohort and 0.64, 0.82, 0.86, 0.94 in the validation cohort, respectively. The DeLong test and DCA showed that the Combined model, consisting of 2 CT signs and 2 texture parameters, held the highest predictive efficiency and clinical utility (p < 0.05). A prediction nomogram was subsequently developed using the 4 independently risk factors from the Combined model. The calibration curves indicated a good consistency between the actual observations and nomogram predictions for differentiating TET classifications.

CONCLUSION

A prediction nomogram incorporating both the CT and texture parameters was constructed and validated in our study, which can be conveniently used for the preoperative individualized prediction of the simplified histologic subtypes in TET patients.

Thymic Epithelial Tumors as a Model of Networking: Development of a Synergistic Strategy for Clinical and Translational Research Purposes

Among the group of thymic epithelial tumors (TET), thymomas often show either uncertain or explicit malignant biological behavior, local invasiveness, and intrathoracic relapse and are often difficult to manage. From the initial stages, thymic carcinomas tend to show aggressive behavior and extrathoracic spread. Moreover, the interplay of epithelial cells and thymocytes in thymomas causes complex immune derangement and related systemic autoimmune diseases. Due to their rare occurrence and to the limited funding opportunities available for rare tumors, it is challenging to make advances in clinical and translational research in TET. The authors of this paper are all members of a multidisciplinary clinical and research thoracic tumor team. Strong input was given to the team by long-standing expertise in TET in the Pathology Department. In addition, thanks to the collaboration between research units at our Institute as well as to national collaborations, over the last 10 years we were able to perform several tissue-based research studies. The most recent studies focused on microRNA and on functional studies on the thymic carcinoma cell line 1889c. The recent implementation of our biobank now provides us with a new tool for networking collaborative research activities. Moreover, the participation in a worldwide community such as ITMIG (International Thymic Malignancy Interest Group) has allowed us to significantly contribute toward fundamental projects/research both in tissue-based studies (The Cancer Genome Atlas) and in clinical studies (TNM staging of TET). Our achievements derive from constant commitment and long-standing experience in diagnosis and research in TET. New perspectives opened up due to the establishment of national [the Italian Collaborative Group for ThYmic MalignanciEs (TYME)] and European reference networks such as EURACAN, for an empowered joint clinical action in adult solid rare tumors. The challenge we face still lies in the advancement of clinical and basic science in thymic epithelial malignancies.

The role of needle core biopsies in the evaluation of thymic epithelial neoplasms

Thymic epithelial neoplasms are rare tumors derived from thymic epithelium that most often present as large anterior mediastinal masses. The vast majority of thymic epithelial neoplasms fall under the diagnostic category of thymoma, with a smaller percentage qualifying for a diagnosis of thymic carcinoma. The ability to render a definitive diagnosis on these tumors is generally hampered by their deep location and close proximity to vital structures, which makes biopsy sampling for histopathologic evaluation difficult. In recent years, the trend in medicine has been to opt for the least invasive procedure to obtain tissue samples that, by definition, implies also obtaining smaller and smaller biopsies, resulting in lesser amounts of tissue available for examination. In the mediastinum, the most common modalities for procuring biopsy samples from mass lesions include fine-needle aspiration, percutaneous core needle biopsy and video-assisted thoracoscopic biopsy. In this review, we will deal only with the role and limitations of percutaneous core biopsies in the interpretation of thymic epithelial neoplasms.

Sclerosing thymoma followed up for eight years as mediastinal goiter: A case report

INTRODUCTION

Sclerosing thymoma (ST) is an extremely rare disease with less than 20 cases ever been described. Here, we present a case of sclerosing thymoma that was followed up as mediastinal goiter for eight years.

PRESENTATION OF CASE

A 77-year-old man was presented with a superior mediastinal tumor. The patient was asymptomatic and not affected by myasthenia gravis. Computed tomography showed a well-defined superior mediastinal tumor whose size had regressed over time. Ultrasonography-guided core-needle biopsy revealed type B1 to B2 thymoma, and total-thymectomy was performed. Histopathologically, most of the tumor showed hyalinization and sclerosis, and slight signs of type AB thymoma were found at the tumor's periphery. The patient was diagnosed with ST. No evidence of recurrence was observed 12 months following surgery.

DISCUSSION

Since sclerosing thymoma is mostly composed of fibrous tissue, small specimens such as needle biopsies do not contain tumor cell nests and are difficult to confirm. Complete resection is currently the most common treatment for ST. Spontaneous regression of ST has been reported; however, the mechanisms involved have not yet been elucidated.

CONCLUSION

This rare case of sclerosing thymoma is an unusual case since it has follow up information for an eight year period due to the misdiagnosis of goiter. The follow up visits showed significant regression of the tumor over the eight year period without treatment; however, the etiology of sclerosis and regression remain unknown. The patient was treated by thymectomy with no recurrence after 12 months.

Sclerosing thymoma: A rare case report and brief review of literature

RATIONALE

Sclerosing thymoma is an extremely rare mediastinal neoplasm; it was recognized for the first time in 1994 and to date only 15 cases have been reported.

PATIENT CONCERNS

The present study report a case of a 65-year-old man who was incidentally found to have an anterior mediastinal nodule, without clinical symptoms including fever, chest pain, and myasthenia gravis.

DIAGNOSES

The chest computed tomography (CT) revealed the nodule was 4.9 × 4.2 × 3.0 cm in size. And the microscopic and immunohistochemical findings indicated that the final diagnosis was sclerosing thymoma.

INTERVENTIONS

The anterior mediastinal nodule was completely removed.

OUTCOMES

No evidence of recurrence or complication was found in the second year after surgery.

LESSONS

The biologic behavior of the rare sclerosing thymoma is still largely mysterious; it is utmost importance to classify the sclerosing thymoma from other mediastinal tumors. Its prognosis is favorable and thymectomy is currently the mainstay of treatment.

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 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]

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.

About thymic carcinomas: challenges in diagnosis and management

BACKGROUND

Thymic carcinomas are rare tumors with a challenging diagnosis. Our aim was to report our 17-year experience of these tumors and to highlight the challenges encountered and the main differential diagnoses ruled out.

METHODS

We studied 12 (92%) men and 1 (7.7%) woman with a mean age of 37 years (range 15-60 years). All patients were symptomatic, with chest pain representing the most frequent symptom. Radiology revealed anterior mediastinal masses in all cases, with either infiltration of the adjacent organs or pulmonary parenchymal metastases.

RESULTS

The diagnosis was made on surgical biopsies in 12 cases and a lymph node biopsy in one. Microscopic examination revealed squamous carcinoma in 3 cases, synovial sarcoma in 1, mucinous adenocarcinoma in 1, undifferentiated carcinoma in 2, clear cell carcinoma in 1, lymphoepithelioma-like carcinoma in 2, atypical carcinoid tumor in 2, and sarcomatoid carcinoma in 1. Total surgical resection was possible in one patient after neoadjuvant chemotherapy and radiotherapy. Follow-up was possible in only 6 patients, and the mean survival reached 13 months.

CONCLUSION

In spite of the lack of follow-up information, this study demonstrates the poor outcome associated with these tumors and the need for standardized treatment.

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.

ITMIG consensus statement on the use of the WHO histological classification of thymoma and thymic carcinoma: refined definitions, histological criteria, and reporting

INTRODUCTION

The 2004 version of the World Health Organization classification subdivides thymic epithelial tumors into A, AB, B1, B2, and B3 (and rare other) thymomas and thymic carcinomas (TC). Due to a morphological continuum between some thymoma subtypes and some morphological overlap between thymomas and TC, a variable proportion of cases may pose problems in classification, contributing to the poor interobserver reproducibility in some studies.

METHODS

To overcome this problem, hematoxylin-eosin-stained and immunohistochemically processed sections of prototypic, "borderland," and "combined" thymomas and TC (n = 72) were studied by 18 pathologists at an international consensus slide workshop supported by the International Thymic Malignancy Interest Group.

RESULTS

Consensus was achieved on refined criteria for decision making at the A/AB borderland, the distinction between B1, B2, and B3 thymomas and the separation of B3 thymomas from TCs. "Atypical type A thymoma" is tentatively proposed as a new type A thymoma variant. New reporting strategies for tumors with more than one histological pattern are proposed.

CONCLUSION

These guidelines can set the stage for reproducibility studies and the design of a clinically meaningful grading system for thymic epithelial tumors.

Characterization and management of cardiac involvement of thymic epithelial tumors

INTRODUCTION

Although thymic epithelial tumors (TETs) commonly infiltrate mediastinal structures, cardiac involvement is uncommon and has not been systematically studied. The purpose of this study was to describe our single-institution experience of the clinical presentation, treatment, and follow-up of cardiac involvement in patients with TETs.

METHODS

A single-institution retrospective review of cardiac involvement among patients with TETs from 2008 to 2012.

RESULTS

The frequency of cardiac involvement was 4%. All five patients with confirmed cardiac disease had left heart involvement. Only one patient was symptomatic. Myocardial invasion was the most common mode of involvement followed by transvenous spread. Surgical resection of the involved area was attempted in three patients: in one, surgery was aborted because of extensive myocardial involvement; in the other two patients, resection was incomplete. Surgery averted a potentially catastrophic hemodynamic complication in one patient. However, cardiac tumor recurred in both patients who underwent incomplete resection. One patient underwent radiation therapy resulting in complete regression of an aortic root mass.

CONCLUSIONS

This study represents the most comprehensive review of cardiac involvement in patients with TETs. In contrast to previous single-case reports, we found a preponderance of asymptomatic presentation, left heart involvement, and myocardial invasion. Dynamic cardiovascular magnetic resonance imaging should be considered in cases when cardiac involvement is suspected. Although immediate surgical resection is indicated for impending hemodynamic compromise, long-term palliation with surgery for myocardial involvement seems poor, especially when complete resection cannot be performed. Radiation therapy should be considered in selected patients.

When a thymic carcinoma "becomes" a GIST

Thymic carcinoma (TC) is a rare intrathoracic malignancy that it can be invasive and refractory to conventional treatment. Comprehensive genomic analysis evidenced a molecularly distinct subset of thymic carcinoma with high prevalence of c-kit mutation, which may behave as a gastrointestinal stromal tumor (GIST). Here, we present a case report of TC with c-Kit mutation, who has relapsed after exposure to multiple lines of combination chemotherapy, but he has shown an impressive and long lasting response to sunitinib after imatinib failure.

Extrathoracic metastases of thymic origin: a review of 35 cases

Thymic tumors are categorized as types A, AB, B1, B2, B3, and thymic carcinoma under the World Health Organization (WHO) classification. Thymomas are typically slow growing tumors that predominantly involve the surrounding structures through direct invasion, while thymic carcinomas tend to be more aggressive. A significant number of patients are asymptomatic and can present with metastases as the first presentation. The exact incidence of extrathoracic metastases from thymoma is not known. This study describes a series of 35 cases of histologically documented metastatic thymomas and thymic carcinomas at extrathoracic sites. These cases were classified according to the current World Health Organization (WHO) classification criteria, and we present their clinical data as well as discuss the differential diagnoses of these lesions. Our study shows that all types of thymic tumors, regardless of histologic type, can be associated with invasion and metastases to thoracic and extrathoracic sites.

Thymomas I: a clinicopathologic correlation of 250 cases with emphasis on the World Health Organization schema

We describe 250 cases of thymoma with emphasis on World Health Organization (WHO) histologic subtyping. The patients were 120 males and 130 females between the ages of 13 and 92 years. Surgical resection was performed, and histologic material was evaluated in every case. Macroscopically, the tumors varied in size from 3 to 20 cm in greatest diameter; about 12% were encapsulated, and about 88% were invasive tumors. A minimum of 5 sections of tumor was evaluated. Histologically, following the schema proposed by the WHO, 21.6% of thymomas were type A, 1.23% type B1, 3.2% type B2, and 9.2% type B3. More than 50% of tumors after subtyping fell into the mixed categories, which, in essence, diminishes the clinical impact of histologic subtyping over staging. The study herein described highlights that all thymomas had the potential to become invasive tumors.

Thymic malignancies: from clinical management to targeted therapies

PURPOSE

A key challenge in the treatment of thymoma and thymic carcinoma (TC) is in improving our understanding of the molecular biology of these relatively rare tumors. In recent years, significant efforts have been made to dissect the molecular pathways involved in their carcinogenesis. Here we discuss the results of large-scale genomic analyses conducted to date and review the most active chemotherapies and targeted treatments.

METHODS

We reviewed the literature for chemotherapeutic trials in the last 20 years and trials involving targeted therapies between 1999 and 2010. The search was supplemented by a review of abstracts presented at the annual meetings of the American Society of Clinical Oncology (from 1999 to 2010), at the first International Conference on Thymic Malignancies in 2009, and at a follow-up meeting of the newly formed International Thymic Malignancies Interest Group in 2010.

RESULTS

Surgery remains the treatment of choice for operable tumors, whereas chemotherapy is standard in locally advanced and metastatic disease. Thus far, targeted therapies have been developed empirically. Histone deacetylase inhibitors have shown some activity in thymoma whereas sunitinib may be active in TC. There are no data to support the use of HER2- or EGFR-targeted therapies in thymic malignancies.

CONCLUSION

Drug development for the treatment of thymic malignancies is difficult because of the rarity of these tumors. Ethnic differences are becoming apparent, with aggressive subtypes being observed in Asians and African Americans. Incremental improvements in our understanding of tumor biology suggest that molecular profiling-directed therapies may be the preferred route of investigation in the future.

Management of stage I and II thymoma

With a knowledgeable assessment of the clinical presentation and demographic and radiologic characteristics, most thymomas can be reliably identified preoperatively without the need for a biopsy. Surgery is the mainstay of treatment for stage I and II thymoma. The rate of complete resection is essentially 100% by open techniques, and recurrences are rare. A complete thymectomy via a sternotomy is the standard approach. Adjuvant radiotherapy after a complete resection does not appear to be of benefit. In the rare event of a recurrence, an aggressive approach should be taken with re-resection whenever possible.

Invasive spindle cell thymomas (WHO Type A): a clinicopathologic correlation of 41 cases

We report 41 cases of invasive spindle cell thymomas (World Health Organization type A). The patients were 16 women and 25 men between the ages of 38 and 80 years. Clinically, the patients had diverse symptomatology, including chest pain, cough, and dyspnea. None of the patients had a history of myasthenia gravis. According to the Mazaoka surgical staging system, 34 patients had stage II disease, 6 had stage III, and 1 had stage IV. Follow-up information showed that 30 patients were alive after a period ranging from 12 to 96 months; for 8 patients who are alive, the follow-up was less than 12 months; 1 patient died 10 months after initial diagnosis. For 2 patients, no follow-up information was obtained. This study stresses the fact that histologic features do not correlate with invasion or encapsulation because all thymomas, regardless of their histologic type, are capable of invasion.

A case of primary combined neuroendocrine carcinoma with squamous cell carcinoma in the upper gingiva

Neuroendocrine carcinoma is a rare neoplasm that occurs widely in various organs and tissues. The biological behavior of this tumor in the oral region remains poorly understood. We encountered an extremely rare case of combined neuroendocrine carcinoma with squamous cell carcinoma, occurring at the buccal gingiva in a 62-year-old woman. Left partial maxillectomy was performed. Histological examinations revealed solid nests with extensive necrosis and nuclear palisading at the periphery. The tumor also showed areas of stratified neoplastic squamous differentiation. Immunohistochemically, tumor nests stained positive for synaptophysin, chromogranin, N-CAM (CD56), and neuron-specific enolase. Strong positivity was seen for K14 and K17 in the squamous component and for K7 in the neuroendocrine component. Both components showed K19 staining. Cells with squamous differentiation and K14 staining occasionally expressed p63. The patient showed no evidence of disease as of 23 months postoperatively. Given the aggressive characteristics of neuroendocrine carcinoma, strict follow-up has been performed.

Histologic classification of thymoma: the World Health Organization and beyond

Thymoma classification has remained for many years a troubled and contentious field. In recent years, the World Health Organization (WHO) presented a proposal for the histopathologic classification of thymic epithelial neoplasms that has been adopted as the standard by many pathologists throughout the world. Yet, controversy still exists regarding its validity, accuracy, usefulness, and reproducibility in routine clinical practice. This article reviews the basic criteria of the current WHO classification of thymoma, along with its weaknesses and limitations, and presents alternate proposals for the histopathologic approach to the classification of thymic epithelial neoplasms.

Thymic epithelial tumours: a population-based study of the incidence, diagnostic procedures and therapy

The population-based incidence, diagnostic procedures, therapy and survival of thymic epithelial tumours were determined using the Netherlands National Pathological Archives and the Netherlands Cancer Registry. Excess mortality compared to the Netherlands standard population was estimated by relative survival analysis. Between 1994 and 2003, 537 thymic epithelial tumours were diagnosed. The incidence of all thymic epithelial tumours was 3.2/1,000,000. Diagnosis was obtained by primary resection in 56% of cases. Survival data were available for 232 cases. Not only thymic carcinomas (type C) but also thymomas (types B1-B3) were associated with excess mortality. Cases that underwent resection (78%) had a better survival than non-operated cases (median survival >10 years versus 1.1 years, p<0.001). Amongst the surgically treated cases (n=180), the completeness of resection did not predict survival (p=0.53). Thymic epithelial tumours are rare. Excess mortality was observed in the majority of tumours. Surgery offers the best perspectives, even if the resection is incomplete.

Problem areas and inconsistencies in the WHO classification of thymoma

The morphologic classification of thymoma has undergone numerous revisions in recent years and has been under continuous debate for the past several decades. With the introduction of the World Health Organization (WHO) schema for the classification of thymic epithelial neoplasms in 1999, a major step was taken toward achieving uniformity in the nomenclature of these tumors. A more recent iteration of the WHO morphologic classification of thymic epithelial neoplasms has now been published. Although these efforts have certainly contributed to clarifying many issues related to the pathology of thymoma, several problem areas and inconsistencies still remain surrounding this proposed schema. The purpose of this review is to address these problem areas, in particular as it relates to terminology, histopathologic criteria for diagnosis, and the prognostic significance for the various categories of the WHO schema.

Cytopathology of thymic epithelial neoplasms

A cytologic diagnosis of thymoma is extremely challenging. In part, this is because the tumor is uncommon and aspirates are infrequently encountered, a technically proficient interventional radiologist is needed, epithelial cells may be difficult to recognize in lymphoid rich aspirate smears, and there is inherent sampling error in a tumor that frequently displays heterogeneous histopathology. Critical to the cytologic diagnosis of most WHO Type B thymomas is the recognition of a distinct population of epithelial cells mixed with lymphocytes. This is more easily accomplished using Papanicolaou or H&E stains, and often requires a cytokeratin stain for verification (in the correct clinical-radiologic context) because these cells are cytologically bland and have a varying amount of cohesiveness. WHO Type A thymoma may contain only epithelial cells and thus mimic a spindle cell neoplasm, or mesothelial cell clusters. Limitations of the cytologic method include an unproven ability to definitively separate thymoma into specific WHO subtypes using cytology alone, and to determine capsular invasion. Non-neuroendocrine thymic carcinomas mimic their extra-thymic counterparts in cytologic aspirates, and their malignant nature is usually readily recognizable. Thymic neuroendocrine carcinomas (NEC) are also cytologically identical to their more common pulmonary sites of origin, but identification of moderately-differentiated NEC is generally not possible.