Micronodular thymoma: an epithelial tumour with abnormal chemokine expression setting the stage for lymphoma development

Autoimmunity in thymic epithelial tumors: a not yet clarified pathologic paradigm associated with several unmet clinical needs

Thymic epithelial tumors (TETs) are rare mediastinal cancers originating from the thymus, classified in two main histotypes: thymoma and thymic carcinoma (TC). TETs affect a primary lymphoid organ playing a critical role in keeping T-cell homeostasis and ensuring an adequate immunological tolerance against "self". In particular, thymomas and not TC are frequently associated with autoimmune diseases (ADs), with Myasthenia Gravis being the most common AD present in 30% of patients with thymoma. This comorbidity, in addition to negatively affecting the quality and duration of patients' life, reduces the spectrum of the available therapeutic options. Indeed, the presence of autoimmunity represents an exclusion criteria for the administration of the newest immunotherapeutic treatments with checkpoint inhibitors. The pathophysiological correlation between TETs and autoimmunity remains a mystery. Several studies have demonstrated the presence of a residual and active thymopoiesis in adult patients affected by thymomas, especially in mixed and lymphocytic-rich thymomas, currently known as type AB and B thymomas. The aim of this review is to provide the state of art in regard to the histological features of the different TET histotype, to the role of the different immune cells infiltrating tumor microenvironments and their impact in the break of central immunologic thymic tolerance in thymomas. We discuss here both cellular and molecular immunologic mechanisms inducing the onset of autoimmunity in TETs, limiting the portfolio of therapeutic strategies against TETs and greatly impacting the prognosis of associated autoimmune diseases.

GTF2I mutation in micronodular thymoma with lymphoid stroma

AIMS

Micronodular thymoma with lymphoid stroma is a rare subtype of thymoma with characteristic clinical and pathological features. Some of the features, such as indolent nature, principally spindle morphology and no significant association to myasthenia gravis, are shared with type A and AB thymoma, which is closely linked to GTF2I mutation. However, not much is known regarding the molecular genetics of this thymoma subtype. In this study, the GTF2I mutation status was investigated in 16 cases of micronodular thymoma.

METHODS

16 micronodular thymomas were retrieved and the GTF2I mutation was tested by Sanger sequencing. The clinicopathological findings were documented.

RESULTS

GTF2I c.1271T>A p.(Leu424His) mutation within exon 15 was detected in 14 out of 16 tumours (87.5%). Two patients died of other causes while all others remained alive with no evidence of recurrence during the follow-up period ranging from 19 to 188 months (median: 100 months).

CONCLUSIONS

GTF2I mutation status and presence of spindle cell morphology may indicate that type A and AB thymoma, and micronodular thymoma represent a group biologically distinct from type B thymomas, which generally lack this mutation.

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.

The Co-Existence of Micronodular Thymoma and Lymphoma: A Clinicopathological and Immunohistochemical Study of Two Cases

Two cases with the co-existence of micronodular thymoma and lymphoma are presented. The patients are two female patients 54 and 60 years of age who presented with symptoms of chest pain, general malaise, cough, and dyspnea. Diagnostic imaging demonstrated the presence of an anterior mediastinal mass. Initial biopsy was interpreted as an epithelial neoplasm compatible with thymoma. Surgical resection took place demonstrating the presence of micronodular thymoma in both cases. In addition, in both cases the lymphoid proliferation infiltrated surrounding adipose tissue. However, in one case the lymphoid proliferation was composed of atypical lymphocytes with irregular nuclei and increase mitotic activity positive for CD3 and TDT, while in the second case, the lymphoid proliferation was composed of more mature lymphocytes with a monocytoid appearance and positive for CD20. Both of these cases represent an unusual association and one that must be kept in the differential diagnosis especially in cases of micronodular thymoma.

Experimental model of micronodular thymic neoplasm with lymphoid stroma

BACKGROUND

Micronodular thymic neoplasm with lymphoid stroma (MNT), a subtype of thymic tumor, is histopathologically characterized by micronodular thymic epithelial cell nests with lymphoid stroma. Despite the distinct histopathology of MNT, its pathogenesis remains unclear.

METHODS

In this study, we aimed to examine a thymic tumor harboring thymic epithelial and lymphoid cells in a nonobese diabetic/severe combined immunodeficiency mouse.

RESULTS

The excised tumor cells were cultured in vitro and comprised epithelial tumor cells and lymphoid cells. During a three-dimensional cell culture, the epithelial tumor cells formed micronodular cell nests surrounded by lymphoid stroma. Notably, the lymphoid cells underwent apoptosis when they were separated from the epithelial tumor cells. Cutaneous transplantation of the cultured epithelial cells with splenocytes from BALB/c mice led to tumor formation, and these cells demonstrated a histopathology similar to that of human MNT in a nonobese diabetic/severe combined immunodeficiency mouse.

CONCLUSION

Given its overlapping features with human MNT, the transplanted tumor could serve as an experimental model of this disease.

Prognostic Model of Eleven Genes Based on the Immune Microenvironment in Patients With Thymoma

Purpose: The pathogenesis of thymoma (THYM) remains unclear, and there is no uniform measurement standard for the complexity of THYM derived from different thymic epithelial cells. Consequently, it is necessary to develop novel biomarkers of prognosis estimation for patients with THYM.

Methods: Consensus clustering and single-sample gene-set enrichment analysis were used to divide THYM samples into different immunotypes. Differentially expressed genes (DEGs) between those immunotypes were used to do the Kyoto Encyclopedia of Genes and Genomes analysis, Gene Ontology annotations, and protein-protein interaction network. Furthermore, the survival-related DEGs were used to construct prognostic model with lasso regression. The model was verified by survival analysis, receiver operating characteristic curve, and principal component analysis. Furthermore, the correlation coefficients of stemness index and riskscore, tumor mutation burden (TMB) and riskscore, drug sensitivity and gene expression were calculated with Spearman method.

Results: THYM samples were divided into immunotype A and immunotype B. A total of 707 DEGs were enriched in various cancer-related or immune-related pathways. An 11-genes signature prognostic model (CELF5, ODZ1, CD1C, DRP2, PTCRA, TSHR, HKDC1, KCTD19, RFX8, UGT3A2, and PRKCG) was constructed from 177 survival-related DEGs. The prognostic model was significantly related to overall survival, clinical features, immune cells, TMB, and stemness index. The expression of some genes were significantly related to drug sensitivity.

Conclusion: For the first time, a prognostic model of 11 genes was identified based on the immune microenvironment in patients with THYM, which may be helpful for diagnosis and prediction. The associated factors (immune microenvironment, mutation status, and stemness) may be useful for exploring the mechanisms of THYM.

Comparative clinicopathological and immunohistochemical study of micronodular thymoma and micronodular thymic carcinoma with lymphoid stroma

AIM

To elucidate the clinicopathological and immunohistochemical characteristics of micronodular thymomas (MNTs) and micronodular thymic carcinomas (MNCs) with lymphoid stroma.

METHODS

We examined four cases of MNTs and three cases of MNCs pathologically and immunohistochemically.

RESULTS

There were prominent cystic changes infive of the seven cases. The neoplasms contained epithelial tumour cells arranged in a micronodular growth pattern lined by cystic walls and separated by abundant lymphoid stroma. Only the tumour cell component of MNCs showed signs of malignancy characterised by cytological atypia and increased mitotic activity. Neoplastic MNC epithelial cells showed strong positivity for CD5 and CD117. However, no immature lymphocytes (TdT-positive and CD99-positive) were present in and around the tumour nodules. None of the patients died or suffered from disease due to MNTs or MNCs.

CONCLUSION

MNTs and MNCs are rare and less aggressive forms of thymic tumours and can be differentially diagnosed by immunohistochemistry.

Micronodular Thymoma With Lymphoid Stroma: A Trio of Cases, With Diverse-associated Histological Features

Introduction. Micronodular thymoma with lymphoid stroma (MNTLS) is a rare thymoma subtype characterized by distinctive histological appearance, unique clinical profile, and indolent course with good prognosis. In addition to its distinctive morphology, MNTLS may be associated with diverse histological features, such as thymic cysts and conventional thymoma, complicating the diagnostic picture further. Materials and methods. We report herein an account of 3 elderly patients (male-02; female-01), who presented with anterior mediastinal mass, and underwent robotic thymectomy. Microscopic examination revealed MNTLS in all 3 cases. In addition, 2 cases showed associated histological features in the form of a multilocular thymic cyst and conventional (type B2) thymoma, respectively. All 3 patients are doing well without recurrence or metastasis at 34, 28, and 19 months postsurgery. Conclusions. Awareness of this rare thymoma subtype is vital among pathologists to avoid misdiagnosis and ensure appropriate patient management. To date, only a few cases of this rare thymoma subtype have been reported in the literature, mostly as single case reports.

Thymic Hyperplasia with Lymphoepithelial Sialadenitis (LESA)-Like Features: Strong Association with Lymphomas and Non-Myasthenic Autoimmune Diseases

Thymic hyperplasia (TH) with lymphoepithelial sialadenitis (LESA)-like features (LESA-like TH) has been described as a tumor-like, benign proliferation of thymic epithelial cells and lymphoid follicles. We aimed to determine the frequency of lymphoma and autoimmunity in LESA-like TH and performed retrospective analysis of cases with LESA-like TH and/or thymic MALT-lymphoma. Among 36 patients (21 males) with LESA-like TH (age 52 years, 32-80; lesion diameter 7.0 cm, 1-14.5; median, range), five (14%) showed associated lymphomas, including four (11%) thymic MALT lymphomas and one (3%) diffuse large B-cell lymphoma. One additional case showed a clonal B-cell-receptor rearrangement without evidence of lymphoma. Twelve (33%) patients (7 women) suffered from partially overlapping autoimmune diseases: systemic lupus erythematosus (n = 4, 11%), rheumatoid arthritis (n = 3, 8%), myasthenia gravis (n = 2, 6%), asthma (n = 2, 6%), scleroderma, Sjögren syndrome, pure red cell aplasia, Grave's disease and anti-IgLON5 syndrome (each n = 1, 3%). Among 11 primary thymic MALT lymphomas, remnants of LESA-like TH were found in two cases (18%). In summary, LESA-like TH shows a striking association with autoimmunity and predisposes to lymphomas. Thus, a hematologic and rheumatologic workup should become standard in patients diagnosed with LESA-like TH. Radiologists and clinicians should be aware of LESA-like TH as a differential diagnosis for mediastinal mass lesions in patients with autoimmune diseases.

Micronodular Thymomas With Prominent Cystic Changes: A Clinicopathological and Immunohistochemical Study of 25 Cases

Twenty-five cases of micronodular thymomas with prominent cystic changes are presented. The patients are 13 men and 12 women between the ages of 38 and 69 years. Clinically, the majority of patients presented with nonspecific symptoms of cough, chest pain, and dyspnea. Four patients were asymptomatic. Diagnostic imaging showed the presence of an anterior mediastinal mass and surgical resection of the tumor mass was performed in all the patients. Histologically, all the tumors were characterized by the presence of cystic structures of varying sizes lined by different types of epithelium. In addition, the tumors were characterized by nodules of epithelial cells embedded in a lymphocyte-rich stroma with germinal centers. Twenty-one tumors were encapsulated while 4 tumors were minimally invasive. Immunohistochemical stains were positive for keratin in the nodular epithelial component while CD45 and CD20 were positive in the lymphoid component. Clinical follow-up ranging from 12 to 24 months was obtained in 19 patients. All the patients were alive and well without disease. No clinical follow-up was available in 6 patients. The cases presented in this article highlight the existence of cystic micronodular thymomas, which can be easily misdiagnosed as a multilocular thymic cyst.

Lymphomas of the Mediastinum and Their Differential Diagnosis

Lymphoma is the most common malignancy involving the mediastinum but can be challenging to diagnose on small biopsy specimens. This review provides a pattern-based approach to help triage small tissue samples for the diagnosis of mediastinal lymphoid proliferations, with focus on the main primary mediastinal lymphomas. The use of ancillary studies is highlighted, along with considerations to avoid misdiagnosis and scenarios to request additional tissue.

Micronodular thymoma with lymphoid stroma diagnosed 10 years after the first operation: a case report

INTRODUCTION

Micronodular thymoma with lymphoid stroma is a rare subtype of thymoma. Here we report a case of micronodular thymoma with lymphoid stroma that was completely resected after incomplete resection 10 years earlier.

CASE PRESENTATION

A 70-year-old Japanese woman who had undergone resection for a thymic cyst 10 years earlier was found to have a solid nodule with a multilocular lesion at the site of the previous operation. We suspected that the tumor was a malignant tumor and performed trans-sternal radical thymectomy and diagnosed the lesion as micronodular thymoma with lymphoid stroma pathologically. When we reassessed the thymic cyst that had been resected 10 years earlier, a few lesions of micronodular thymoma with lymphoid stroma were found in the cyst wall. Based on these findings, we concluded that only the cystic component of micronodular thymoma with lymphoid stroma had been removed, and that the residual lesion grew locally over the next 10 years before being completely resected by reoperation.

CONCLUSION

We experienced an unusual case of micronodular thymoma with lymphoid stroma, which is a rare subtype of thymoma. Greater care should be taken to exclude a thymoma with a cystic lesion, even if a thymic cyst is strongly suspected on computed tomography and magnetic resonance imaging.

Micronodular thymoma with lymphoid stroma: Two cases, one in a multilocular thymic cyst, and literature review

Micronodular thymoma with lymphoid stroma (MTWLS) is a rare type of thymoma that shows a similar pattern but varied morphology and immunophenotype of tumor cells. Because of the extremely limited number of cases reported, the pathology and biology of MTWLS are equivocal. Herein, we report two cases located in the anterior mediastinum: Case 1: a 58‐year‐old woman with a cystic mass measuring 5 × 3.0 × 2.5 cm in Mosaoka stage I; and Case 2: a 50‐year‐old man with a solid mass measuring 2.5 × 2.5 × 2.0 cm in stage IIb. Both patients were treated by thymectomy and are alive without recurrence or metastasis 15 and 17 months after surgery, respectively. Regardless of the spectrum of pathology and stage of MTWLS, this unique type of thymoma has a homogeneously favorable prognosis.

[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.

Ectopic micronodular thymoma with lymphoid stroma in the cervical region: a rare case associated with Langerhans cells proliferation

Micronodular thymoma (MNT) with lymphoid stroma is a rare thymic epithelial neoplasm with the characteristics of multiple nodules separated by abundant lymphoid stroma. MNTs mainly arise in the anterior mediastinum and thymus, while ectopic MNTs are extremely rarely seen. Here, we report an ectopic MNT that occurred in the neck of a 62-year-old woman. There were also scattered eosinophilic granulocytes and S100⁺/CD1a⁺ Langerhans cells within the tumor. This case provides a better understanding of such rare, poorly understood cases.

Micronodular thymic neoplasms: case series and literature review with emphasis on the spectrum of differentiation

We report nine cases of micronodular thymoma with lymphoid B-cell hyperplasia and one case of micronodular thymic carcinoma with lymphoid hyperplasia from our institution. For a better understanding of these rare tumors, clinical records, and histological features of these cases were reviewed, with detailed review of additional 64 literature cases of micronodular thymic neoplasms. The joint analysis identified 64 cases of micronodular thymoma with lymphoid B-cell hyperplasia and 9 cases of micronodular thymic carcinoma with lymphoid hyperplasia. Both groups revealed slight male predilection, with male:female ratio of 1.3:1 and 5:4, and occurred at >40 years of age, with a mean of 64 (41-83) and 62 (42-78) years, respectively. Myasthenia gravis was noted in 3/64 (5%) and 1/9 (11%) patients, respectively. Other systemic, disimmune, or hematologic disorders were noted in 6/64 (9%) and 1/9 (11%) patients, respectively. Components of conventional thymoma were reported in 11/64 (17%) micronodular thymomas with lymphoid B-cell hyperplasia, with transitional morphology between the two components in most of them. Cellular morphology was predominantly spindle in micronodular thymoma with lymphoid B-cell hyperplasia when specified (30/43), and epithelioid in micronodular thymic carcinoma with lymphoid hyperplasia (6/9), and cytological atypia was more encountered in the latter. Dedifferentiation/transformation from micronodular thymoma with lymphoid B-cell hyperplasia to micronodular thymic carcinoma with lymphoid hyperplasia seems to occur in a small subset of cases. Three cases of micronodular thymomas with lymphoid B-cell hyperplasia were described with co-existent low-grade B-cell lymphomas. Follow-up data were available for 30 micronodular thymomas with lymphoid B-cell hyperplasia and 6 micronodular thymic carcinomas with lymphoid hyperplasia, with a mean of 47 (0.2-180) months and 23 (3-39) months, respectively. Patients were alive without disease, except for five micronodular thymoma with lymphoid B-cell hyperplasia patients (dead from unrelated causes), and one micronodular thymic carcinoma with lymphoid hyperplasia patient (dead of disease).

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.

Micronodular thymoma with lymphoid stroma: an immunohistochemical study of the distribution of Langerhans cells and mature dendritic cells in six patients

AIMS

Micronodular thymoma with lymphoid stroma (MNT) is an uncommon variant of thymoma, characterized by multiple small nodules consisting of type A thymoma-like cells, which are separated by abundant B lymphocytes. The aim of the study was to elucidate the pathogenesis of the stromal lymphoid hyperplasia, which is currently unclear.

METHODS AND RESULTS

We retrieved six cases of MNT, and immunohistochemically examined the number and distribution of Langerhans cells (LCs) and mature dendritic cells (DCs), and compared them with those in type A and type AB thymomas. Many LCs were present within the small tumour nests, but LCs were rarely seen in the stroma (75.5/HPF versus 6.1/HPF, P < 0.0001). In contrast, mature DCs were present mainly in the surrounding stroma rather than within the tumour nodules (63.5/HPF versus 6.0/HPF, P < 0.0001), forming clusters with mature T lymphocytes adjacent to lymphoid follicles. In large nodules, as well as in type A and type AB thymomas, a few scattered LCs and DCs were identified. All patients were still alive and well.

CONCLUSIONS

Our results suggest that LCs take up tumour antigens and migrate to the stroma, where they mature and form clusters with T lymphocytes to activate them, resulting in lymphoid follicle formation. The favourable clinical behaviour may be attributable to the immune response induced by LCs.

Micronodular thymic carcinoma with lymphoid hyperplasia: a clinicopathological and immunohistochemical study of five cases

Five cases of an unusual variant of thymic carcinoma are described, which represent the counterpart of the so-called micronodular thymoma with lymphoid hyperplasia. The patients were three men and two women aged 42-78 years (mean 64 years). Three patients were asymptomatic and the tumors were found incidentally on chest radiographs performed for unrelated reasons. Two patients complained of dyspnea, chest pain and shortness of breath prompting further investigations. The tumors ranged in size from 3.2 to 10.0 cm and were described as infiltrative masses often invading adjacent structures. Prominent cystic changes were not identified. Histologically, the neoplasms were composed of epithelial tumor cells arranged in a micronodular growth pattern set in a stroma showing florid lymphoid hyperplasia. Contrary to micronodular thymoma, the epithelial cell component of the present cases showed unequivocal signs of malignancy characterized by cytological atypia and increased mitotic activity. Immunohistochemical studies showed the lymphoid component to be of mixed B- and T-cell lineage. None of the patients had a history of myasthenia gravis or other autoimmune disorder. Follow-up revealed that 4 patients were alive and well 3-26 months after diagnosis while 1 patient was dead of disease 21 months after diagnosis. The tumors in this series represent a distinct subtype of thymic carcinoma histologically strongly resembling micronodular thymoma with lymphoid hyperplasia. Awareness of this type of thymic carcinoma is important in order not to dismiss this tumor for a neoplasm of lower-grade malignancy.

Characterization of chromosomal aberrations in thymic MALT lymphoma

Mucosa-associated lymphoid tissue (MALT) lymphoma arising in the thymus is a rare disorder that shows a strong association with autoimmune disease. Several MALT-lymphoma-specific and -associated chromosomal abnormalities, including t(11;18), t(14;18), t(1;14), trisomy 3 and trisomy 18, are known to occur. The former translocation results in apoptosis inhibitor 2 gene (API2)-MALT lymphoma-associated translocation 1 (MALT1) fusion. In this study, we examined 14 cases of thymic MALT lymphomas for API2-MALT1 fusion using multiplex reverse transcription polymerase chain reaction and looked for trisomy 3, trisomy 18 and abnormalities of MALT1 and IGH genes using fluorescence in situ hybridization. Thymic MALT lymphoma cases had a high frequency of trisomy 3 (7/14 cases), a very low incidence of trisomy 18 (1/14) and no detectable MALT1-associated (0/13) or IGH-associated (0/13) gene abnormalities including t(11;18). A review of the literature showed that the pattern of chromosomal aberrations in thymic MALT lymphoma was similar to those of thyroid and salivary gland MALT lymphomas. Although frequently detected, trisomy 3 was not associated with any of the clinicopathological factors analyzed, suggesting that trisomy 3 may play a role in lymphoma development. In conclusion, the present study showed that thymic MALT lymphoma has a characteristic pattern of chromosomal aberrations that may be similar to those of other autoimmune-associated MALT lymphomas.

Thymic extranodal marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue: a clinicopathological and genetic analysis of six cases

We investigated six new cases of primary thymic extranodal marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue (MALT) to further characterize the clinicopathological and genetic features. The male to female ratio was 1:1. One female patient had suffered from systemic lupus erythematosus. Another female patient was diagnosed with rheumatoid arthritis after thymectomy. One patient had a concurrent tumor in the eyelid. Radiologically, all tumors were located in the prevascular space and presented as asymmetric heterogeneously enhanced cystic and solid masses. MALT1, BCL10 or IGH translocations and trisomy 18 were not observed in any cases by fluorescence in situ hybridization (FISH) analysis. Trisomy 3 was detected in one patient and another showed a TNFAIP3/A20 deletion. Meta-analysis (n = 51) including the present and previously reported cases revealed that the prevalence of autoimmunity was much lower in males with thymic MALT lymphoma compared to females (33% vs. 87%, p = 0.001). Additionally, the average age of females or patients with autoimmunity was about 10 years younger than that of males or patients without autoimmunity (p = 0.003 and p = 0.008, respectively). In summary, thymic MALT lymphoma arising without underlying autoimmunity frequently involves males or older patients. Trisomy 3 and an A20 deletion might play a role in the pathogenesis of thymic MALT lymphoma.

Two malignant tumours in the anterior mediastinum positive for CD5

To our knowledge, the simultaneous involvement of the anterior mediastinum by a thymic carcinoma and a B-cell chronic lymphocytic leukaemia has not been reported previously. The authors describe the case of a 62-year-old man, suffering from severe bronchitis. Chest x-ray and CT scan showed a mediastinal tumour, resected short-time after diagnosis. First, standard based histological examination revealed a thymic carcinoma admixed by a dense lymphatic infiltrate. Additional immunohistochemical staining for CD5-labelled epithelial thymic carcinoma cells as well as neoplastic B cells and led in combination with blood tests to confirm the diagnosis of the composite occurrence of a thymic carcinoma and a B-cell chronic lymphocytic leukaemia.

Mucosa associated lymphoid tissue (MALT) lymphoma of the thymus with trisomy 18

Extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma) of the thymus is rare and little is known about its karyotype abnormality. MALT lymphoma in general shows a good prognosis, but some reports suggest that the presence of trisomy 18 predicts recurrence. Here, we report a patient with MALT lymphoma of the thymus and the left parotid gland accompanied by Sjogren's syndrome. The karyotype analysis revealed that this is the first case of thymic MALT lymphoma with trisomy 18, which we believe is worth reporting. We also review cases with thymic MALT lymphoma previously reported in the literature.

Mucosa-associated lymphoid tissue lymphoma of the thymus associated with Sjögren's syndrome: report of a case

A 68-year-old Japanese man with Sjögren's syndrome was pointed out to have a nodular shadow in the anterior mediastinum. The tumor was resected under video-assisted thoracoscopy and it was pathologically diagnosed to be thymic mucosa-associated lymphoid tissue (MALT) lymphoma. There has been no recurrence for 17 months after surgery. Mucosa-associated lymphoid tissue lymphoma of the thymus is rare, and its pathological diagnosis requires sufficient knowledge and experience. Since thymic MALT lymphoma is distinct from MALT lymphoma of other sites in several ways, including gene abnormalities and geographic distribution, an alternative oncogenic pathway and the influence of racial and/or environmental factors must be considered to be involved. However, since the number of reported thymic MALT lymphomas is limited, these issues are still unclear. The accumulation of further similar cases will help to elucidate various issues concerning thymic MALT lymphoma associated with Sjögren's syndrome.

Thymomas: a cytological and immunohistochemical study, with emphasis on lymphoid and neuroendocrine markers

Background

The current study correlates cytologic morphology with histologic type and describes immunophenotypes with a focus on epithelial, neuroendocrine, and lymphoid characteristics in an institutional series of surgically excised thymomas.

Methods

Fine needle aspirates (FNAs) and surgical specimens were retrospectively analyzed, and immunohistochemical stains were performed for EMA, cytokeratin 7, cytokeratin 20, CD57 CD5, bcl-2, calretinin, vimentin, CD3, CD20, CD1a, CD99 and Ki67. Tumors were classified by WHO criteria.

Results

There were eleven male and six female patients with an age range of 41 to 84 years (mean, 61 years) and a male to female ratio of 1.8:1. Four thymomas (4/17, 23.5%) were associated with neuromuscular disease: myasthenia gravis (n = 3) and limbic encephalitis (n = 1). FNA, under CT guidance, was performed in 7 cases. The positive predictive value for thymoma by FNA cytology was 100% and the sensitivity was 71%. Thymomas associated with neuromuscular disorders were WHO types B2 (n = 1) and B3 (n = 3), and showed a strong expression of CD57 in the majority of neoplastic epithelial cells accompanied by large numbers of CD20+ intratumoral B lymphocytes. Two of seventeen (11.7%) thymomas (all sporadic B3 type) contained numerous neoplastic epithelial cells positive for CD5 and bcl-2.

Conclusion

Our results suggest that thymomas associated with autoimmune disorders contain a significant population of CD20+ intratumoral B lymphocytes. Strong CD57 positivity in thymomas may suggest a concomitant neuromuscular disorder, notably myasthenia gravis. CD5 expression is of limited value in the differential diagnosis of primary thymic epithelial neoplasms since both thymic carcinomas and thymomas may express CD5.

ImmunoglobulinVH genes in thymic MALT lymphoma are biased toward a restricted repertoire and are frequently unmutated

Thymic MALT lymphoma shows certain distinctive features among MALT lymphomas, such as expression of IgA isotype, consistent lack of API2-MALT1 gene fusion, and very strong association with autoimmune disease, especially Sjogren's syndrome. To help clarify the nature of the clonal lymphoid infiltrates, we analysed the usage and somatic hypermutation of the Ig heavy chain variable region (V(H)) genes in nine different cases. The V(H) rearrangement was potentially functional in all cases and was restricted to the V(H)3 family. V(H) usage was biased toward V(H)3-30 (five cases) and V(H)3-23 (three cases) segments, which have both been frequently expressed by autoimmune B cells. Somatic hypermutation was absent in five cases. Fewer than the expected replacement mutations were found in the framework regions in two cases, indicating a negative antigen selection pressure. Ongoing mutation was absent in all cases. D segment usage was varied, whereas J(H) segment usage was restricted to J(H)4. The observed patterns of V(H) usage and mutations suggested that specific antigens may play a pathologically relevant role in the genesis or progression of thymic MALT lymphoma.