Difference in the distribution of tumor-infiltrating CD8+ T cells and FOXP3+ T cells between micronodular thymoma with lymphoid stroma and micronodular thymic carcinoma with lymphoid stroma

Micronodular thymoma with lymphoid stroma (MNT) is a rare thymic epithelial neoplasm subtype characterized by a micronodular tumor cell growth pattern and abundant lymphoid stroma. Micronodular thymic carcinoma with lymphoid stroma (MNCA) is considered as a malignant counterpart of MNT and exhibits a growth pattern similar to that of MNT but has histologic features reminiscent of thymic squamous cell carcinoma, such as cytologic atypia and CD5 and CD117 immunoexpression. Although both MNT and MNCA are characterized by abundant lymphoid stroma, it remains unknown whether there are differences in infiltrating lymphocytes between MNT and MNCA. We analyzed the immune microenvironment profile in eight MNT and three MNCA cases. The cell density of CD8-positive T cells was significantly higher in MNT than in MNCA, whereas that of FOXP3-positive T cells was significantly higher in MNCA than in MNT. There was no significant difference in the cell density of programmed death protein 1-positive T cells and programmed death ligand 1 expression between the MNT and MNCA cases. Our findings indicated that the immune microenvironment of MNCA differed from that of MNT and, compared with the T-cell profile of MNT, that of MNCA was more suppressive to patients′ antitumor immune response.     

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

The aetiology of primary B-cell lymphomas of the thymus is enigmatic. Although thymic follicular lymphoid hyperplasia (TFH) is commonly associated with myasthenia gravis (MG), lymphoma is not a complication of this condition. The present paper reports a high frequency of monoclonal B-cell populations (6 of 18 cases; 33%) in micronodular thymoma (MNT), a peculiar thymic epithelial neoplasm with a B-cell-rich stroma, while B cells were consistently polyclonal in TFH (25 cases) and other types of thymomas (15 cases) (p < 0.001). An intratumoural lymphoma could be identified in three of the six monoclonal MNTs. Sequencing of the monoclonal IgH chain revealed partially overlapping VDJ gene usage in MNT and thymic mucosa-associated lymphoid tissue (MALT) lymphomas. The neoplastic epithelium of MNTs, but not of TFH and other types of thymoma, expressed high levels of dendritic cell, T-cell, and B-cell chemoattractants, such as CCL18, CCR6, and CCL20. It is concluded that abnormal chemokine expression in an epithelial tumour, MNT, can promote the recruitment of MALT, the emergence of monoclonal B cells, and, eventually, the subsequent development of mediastinal lymphomas. More generally, the concept that expression of a 'high-risk' spectrum of chemokines due to local or genetic factors may interfere with B-cell homeostasis and may contribute to MALT lymphoma development in chronic inflammatory states is proposed.     

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.     

化生性胸腺瘤2例临床病理分析

目的：探讨化生性胸腺瘤的临床及病理学特征。方法：应用光镜及免疫组织化学方法观察2例化生性胸腺瘤的组织学特点及免疫学表型,并复习相关文献。结果：2例均为男性,年龄55岁及56岁。组织学肿瘤显示双相分化特点,上皮细胞区域与梭形细胞区域交错分布并相互移行。上皮细胞呈相互吻合的束状、岛状及宽大的梁状排列,细胞轻度异型,可见核沟及核内假包涵体,偶见核分裂像;梭形细胞呈短束状或席纹状排列,细胞温和,未见核分裂像。免疫表型：上皮细胞区域CK19和AE1/AE3呈强阳性表达,上皮膜抗原（epithelial membrane antigen,EMA）弱阳性;梭形细胞区域表达Vimentin、Bcl-2及CD99,AE1/AE3局灶阳性,EMA弱阳性。两种区域中Ki67指数均〈5%。间质淋巴细胞CD3、CD5、CD20阳性,不表达Td T和CD99。结论：化生性胸腺瘤是一种罕见的良性或低度恶性胸腺肿瘤,诊断依靠病理组织学和免疫组织化学标记,完整切除预后良好。     

Unusual thymoma subtypes

Thymomas are neoplastic proliferations of the epithelial cells of the thymus which are variably admixed with a non-neoplastic lymphoid component. Five common subtypes of thymoma are recognized in the current WHO classification. In addition to these five subtypes, three distinct unusual thymomas are currently listed as specific entities in the WHO scheme. These three subtypes, micronodular thymoma with lymphoid stroma, metaplastic thymoma and lipofibroadenoma, and their differential diagnostic consideration form the subject of this review. In addition, unusual variants of common thymomas are discussed.     

微结节性胸腺瘤伴淋巴样间质3例临床病理观察

目的:探讨微结节性胸腺瘤伴淋巴样间质(micronodular thymoma with lymphoid stroma,MNT)的临床病理特征.方法:通过组织学和免疫组织化学方法观察3例MNT,研究其临床病理特征,并复习文献.结果:肿瘤有纤维性假包膜,肿块内见多发性散在或局部融合的上皮性结节,由丰富淋巴细胞间质分隔,其中可见淋巴滤泡形成.上皮性结节由温和的细长形或卵圆形细胞组成,核仁不明显,结节内淋巴细胞稀少.免疫组织化学:上皮性结节内上皮细胞CKpan,CK5/6,CK19,CK8/18均阳性,Ki67约2%阳性,CD20,EMA阴性;间隔内淋巴细胞CD20,CD3,CD5,CD99,TdT均灶区阳性,p53,CD1α均散在阳性;淋巴细胞背景内CK5/6,C8/18,EMA均阴性.结论:MNT是一种罕见的胸腺肿瘤,目前WHO归于交界性,有特殊的发病部位和形态学表现,组织学及免疫组织化学有助于该肿瘤的诊断和鉴别诊断.     

Disseminated thymoma in pleural fluid: An unusual case

Thymic epithelial tumours show characteristic cytological features on fine-needle aspiration cytology, however the cytological features of thymoma in fluid cytology are not well described. We present the case of a 77 year-old-woman with known pleural dissemination of type B2/B3 thymoma presenting with shortness of breath and orthopnoea due to a pleural effusion. Cytological evaluation of the pleural fluid showed cellular smears composed of numerous small lymphocytes with small numbers of admixed mesothelial cells. There was no epithelial component. On immunohistochemical (IHC) staining the lymphocytes were T cells which were positive for CD3. CD1a and terminal deoxynucleotide transferase (TdT) were also positive, consistent with immature lymphocytes of thymic origin. Despite the lack of an epithelial component, this case was diagnosed as suspicious for recurrent/ metastatic thymoma. This is only the second published case of thymoma identified on pleural fluid cytology, and to our knowledge the first case describing thymoma in pleural fluid with no epithelial component, a potential pitfall with the more common differential diagnosis of a reactive lymphocytic effusion.     

Immunohistochemical metallothionein expression in thymoma: correlation with histological types and cellular origin

Metallothioneins (MTs) are low molecular weight and cysteine-rich intracellular proteins involved in metal homeostasis and detoxication. They are found in certain normal tissues, and are overexpressed in various tumours with correlation to more aggressive behaviour in certain tumours. Since the histopathological types of thymoma have unpredictable invasive potential, MT over-expression was investigated as a possible marker of the invasive potential of thymomas. We studied immunohistochemical MT expression in 27 non-invasive thymomas, 20 micro-invasive thymomas, and 23 macro-invasive thymomas with a mouse monoclonal anti-MT antibody E9 on formalin-fixed paraffin-embedded tissues. MT expression was significantly different among the three groups of thymomas ( P  = 0.02) with a stronger expression in invasive thymomas ( P  = 0.003). However, MT expression was not exclusively limited to invasive thymomas. Therefore, it could not be used as a marker of aggressive potential in individual thymomas. Analysis of MT expression according to the histological types of the thymomas revealed that eight of nine spindle cell thymomas, none of 10 small polygonal cell thymomas, four of 14 mixed thymomas, seven of 29 large polygonal cell thymomas, and seven of eight squamoid thymomas significantly expressed MT. There was a statistically significant difference in MT expression among different histological types of thymomas ( P  = 0.000). The strongest and most consistent expression was observed in spindle cell thymoma and squamoid thymoma. Since spindle cell thymoma was usually non-invasive and squamoid thymoma was more aggressive, MT expression does not correlate with the invasive potential of different histological types of thymomas. But because medullary epithelial cells of the thymus were positive for MT, our results suggest that both spindle cell thymoma and squamoid thymoma might derive from the medullary compartment of the thymus.     

Evaluation of a histogenetic classification for thymic epithelial tumours

We reviewed 87 thymic epithelial tumours from Chinese patients and typed them according to the Marino and Müller-Hermelink classification as updated by Kirschner and Müller-Hermelink in 1989. Related categories were grouped for statistical analyses; group 1, medullary thymoma and mixed thymoma; group 2, cortical predominant thymoma; group 3, cortical thymoma and well-differentiated thymic carcinoma; group 4, other thymic carcinomas; and group 5, unclassified. Group 3 tumours were more frequently associated with the myasthenia gravis syndrome compared with group 1 tumours ( P =0.001). They also presented at a more advanced stage. Groups 1 and 2 showed an excellent prognosis (100% survival at 10 years). The 10-year survival for groups 3 and 4 patients was 40% and 30% respectively. Pure medullary thymoma made up a higher proportion of our cases (10.3%) than those of a similar Caucasian study (5.3%). The eight thymic carcinomas (group 4) included two thymic lymphoepitheliomas. We conclude that the histogenetic classification evaluated shows a clear correlation with prognosis and clinical features, even when tested on separate geographic groups, where pathogenetic factors may be different. A common approach to classification of thymic epithelial tumours would greatly facilitate future studies on these possible differences.     

Thymoma with epithelial micronodules and lymphoid hyperplasia: six cases of a rare and equivocal subtype

Thymomas with the characteristic pattern of small epithelial nodules separated by an abundant lymphoid tissue have been recently described with divergent interpretations. These thymomas are not specified in currently used classification systems. We present six such thymomas, including three that represented 1.38% of a series of 217 consecutive cases. These thymomas were totally encapsulated (Masaoka stage I, n=1) or minimally invasive (stage II, n=5). The epithelial cells of the nodules were oval and bland-appearing. In one case, these cells formed rosettes. Cysts, that were present in four cases, showed a strong linear expression of EMA and were associated with foci of glandular differentiation. The lymphoid tissue was composed of large immature (CD1a and CD99-positive) T-cell areas (with epithelial cells restricted to small foci of residual thymus) and of B-cell (CD20-positive) areas with germinal centers. Mature T-cells were also present. Furthermore, one case, associated with myasthenia gravis, had an important WHO type B2 (cortical) component. Such a combined case has not been previously reported. Our study demonstrates that so-called micronodular thymomas are rare, usually have clinical and pathological features of WHO type A (medullary) thymomas, and that the lymphoid component is hyperplastic corresponding to both immature T-cell lymphoid tissue and B-cell lymphoid hyperplasia with germinal centers.     

Pigmented spindle cell carcinoid tumour of the thymus with ectopic adrenocorticotropic hormone secretion: report of a rare variant and differential diagnosis of mediastinal spindle cell neoplasms

AIMS: A variety of histological variants of thymic carcinoid tumour have been described. A rare case of pigmented spindle cell carcinoid tumour of the thymus is documented and compared with the reported cases of thymic pigmented carcinoid tumour in the literature, with a discussion of the differential diagnosis of spindle cell tumours of the mediastinum. METHODS AND RESULTS: A thymic tumour with ectopic adrenocorticotropic hormone (ACTH) secretion was resected from a 24-year-old man suffering from Cushing's syndrome. Histological, immunohistochemical, and ultrastructural studies revealed an ACTH-producing spindle cell carcinoid tumour harbouring pigmented melanocytes. Among four thymic pigmented carcinoid tumours reported before, only one was similar to the present case by being also an ACTH-secreting pigmented spindle cell thymic carcinoid tumour. The clinicopathological features of this tumour distinguish it from a spindle cell thymoma, spindle cell thymic carcinoma, and other mediastinal spindle cell tumours. CONCLUSIONS: This case illustrates an extremely rare variant of thymic carcinoid tumour exhibiting a spindle cell morphology and harbouring pigmented melanocytes. Awareness of this histological variant is important in the differential diagnosis of spindle cell tumours of the mediastinum.     

异位错构瘤性胸腺瘤1例及文献复习

目的探讨异位错构瘤性胸腺瘤(EHT)的临床及病理特征。方法复习1例EHT患者的临床病史、肿瘤组织的病理形态和免疫表型及相关文献。结果患者男性,56岁,以左胸锁关节下方皮下肿块为主要表现。肿瘤包膜完整,切面以灰白色实性为主。镜下表现复杂,以束状及平行排列的梭形细胞为主,混合有上皮成分及成熟的脂肪细胞等。瘤细胞均不具异型性,也缺乏坏死。免疫组化显示梭形细胞CK阳性,灶状细胞MSA阳性,S-100蛋白、desm in、vim entin和CD34均呈阴性。结论EHT有独特的发病部位和形态学表现,对梭形细胞上皮本质的认识是正确诊断的关键。     

Expression of the interferon-inducible chemokine IP-10 (CXCL10), a chemokine with proposed anti-neoplastic functions, in Hodgkin lymphoma and nasopharyngeal carcinoma

Hodgkin lymphoma (HL) and nasopharyngeal carcinoma (NPC) are characterized by their association with Epstein-Barr virus (EBV) and an abundant infiltrate of reactive lymphoid cells. The presence of this lymphoid stroma may influence the effect of anti-viral immunotherapy. The interferon-inducible chemokine IP-10 has anti-neoplastic effects in several model systems mediated by T-cells expressing the CXCR3 chemokine receptor. Using in situ hybridization, it is shown that IP-10 is expressed in neoplastic cells of HL and correlates both with the mixed cellularity histotype and with EBV infection. IP-10 expression was also detected in tumour cells of most NPCs as well as in EBV-negative squamous cell carcinomas of the tongue. Thus, in carcinomas, IP-10 expression showed no correlation with EBV infection. Numerous CXCR3-positive lymphocytes were detected in the lymphoid stroma of HL and NPC, raising the possibility of a Th1-predominant immune response in these cases. In view of the proposed anti-neoplastic functions of IP-10 and CXCR3-positive lymphocytes, these findings are unexpected and raise the possibility that endogenous IP-10 expression in the context of human tumours may not exert the anti-tumour effects ascribed to it by in vitro experiments.     

Neoplastic thymic epithelial cells of human thymoma support T cell development from CD4−CD8− cells to CD4+CD8+ cells in vitro

Human thymoma is a thymic epithelial cell tumour which often contains a large number of immature T cells and is frequently associated with autoimmune diseases. Since thymic epithelial cells play key roles in the development and selection of T cells in the normal thymus, we hypothesized that the neoplastic thymic epithelial cells of thymoma may support T cell differentiation in the tumour. We characterized CD4^?CD8^? cells in thymoma and applied an in vitro reconstitution culture system using the CD4^?CD8^? cells and the neoplastic epithelial cells isolated from thymoma. CD34, a stem cell marker, was expressed on 29.9 ± 12.2% of CD4^?CD8^? cells in thymoma. TCRγδ was expressed on 27.4 ± 15.1% of CD4^?CD8^? cells and CD19, a B cell marker, was expressed on 14.1 ± 23.1% of CD4^?CD8^? cells. CD4^?CD8^? cells expressed both IL-7R α-chain and common γ-chain. Purified CD4^?CD8^? cells from thymomas were cultured with the neoplastic epithelial cells, and their differentiation into CD4⁺CD8⁺ cells via CD4 single-positive intermediates was observed within 9 days' co-culture in the presence of recombinant IL-7. Furthermore, we examined the reconstitution culture using CD34⁺CD4^?CD8^? cells purified from normal infant thymus. The CD34⁺CD4^?CD8^? cells in normal thymus also differentiated to CD4⁺CD8⁺ cells in the allogeneic co-culture with the neoplastic epithelial cells of thymoma. These results indicate that the tumour cells of thymoma retain the function of thymic epithelial cells and can induce differentiation of T cells in thymoma.     

化生性胸腺瘤临床病理分析

目的探讨化生性胸腺瘤的临床病理特点。方法应用光镜、免疫组织化学(EnVision法)染色[单克隆抗体选用AE1/AE3、波形蛋白、上皮膜抗原(EMA)、CD3、CD5、CD20、CD34、CD57、CD99、末端脱氧核苷酸转移酶(TdT)、HMBE-1、calretinin、p53和Ki-67]和透射电镜观察3例化生性胸腺瘤的组织学特点、免疫学表型和超微结构。结果3例化生性胸腺瘤均为女性,年龄为33、58和45岁。组织学表现为双相分化特征,上皮细胞区域与梭形细胞区域交错分布并相互移行。上皮细胞区域的细胞轻度异型,有核沟和核内假包涵体,核分裂象罕见,呈岛状和条索状排列并相互吻合;梭形区域细胞形态温和,未见核分裂象,排列成束状或席纹状结构。免疫组织化学染色:上皮细胞区域AE1/AE3强阳性表达,不表达波形蛋白和CD5,Ki-67指数3%~5%;梭形细胞区域波形蛋白弥漫表达,EMA阳性,不表达CD5和CD20;间质淋巴细胞CD3阳性,不表达TdT和CD99。超微结构示上皮细胞区域细胞间有桥粒和半桥粒结构,而梭形细胞区域缺乏。结论化生性胸腺瘤是一类罕见的具有独特临床病理特征的良性或低度恶性胸腺上皮来源肿瘤。     

Expression of cortical and medullary thymic epithelial antigens in thymomas. An immunohistological study of 14 cases including a characterization of the lymphocytic compartment

Four monoclonal antibodies against antigens expressed differentially by the normal thymus epithelium, which define the cortical, medullary and subcapsular compartments, were used for immunohistological characterization of the epithelial cells in 14 thymomas. Furthermore, thymoma-associated lymphocytes were studied with monoclonal antibodies directed against T-lymphocyte differentiation antigens (CD1a, CD3, T-cell antigen receptor). Only four of the 14 thymomas could be classified into either medullary or cortical type thymoma based on the immunophenotype of epithelial cells. Ten cases escaped immunophenotypical classification due to co-expression of medullary and cortical antigens by the tumour cells. This aberration from the normal phenotype might indicate the failure of differentiation of such tumours. The immunophenotype of the associated lymphocytes, on the other hand, made it possible to classify the tumours as cortical (5 cases), mixed (2) and medullary (3) thymomas. Four thymomas escaped this classification scheme due to the absence of lymphocytes (2) or to a hybrid immunophenotype (2). Nevertheless, thymocytes of cortical type clearly predominated and were seen in all thymomas with associated lymphocytes. This feature may constitute a good diagnostic tool in differential diagnosis since, in 28 mediastinal or extramediastinal metastasis of tumours not derived from thymic epithelium and associated with various numbers of lymphocytes, none of them were found to contain CD1a positive lymphocytes.     

Well-differentiated thymic carcinoma: a clinico-pathological study

Summary Well-differentiated thymic carcinoma (WDTC) is a recently described epithelial tumour of the thymus previously classified as cortical or predominantly epithelial thymoma. The authors have reviewed a series of 15 cases of WDTC with the aim of further defining the clinicopathological features of this neoplasm. Histologically, the number of lymphocytes was always low; perivascular spaces and epithelial palisading around blood vessels and/or along fibrous septa were prominent features; 6 cases (40%) were associated with areas of typical cortical thymoma. All cases showed slight to moderate cytological atypia and nuclear grooving was frequently detected. Mitotic activity was variable but usually low. Clinically, all but 3 cases (80%) were invasive at surgery; myasthenia gravis was present in 9 cases (60%); 5 patients (33.3%) died due to disease and 2 additional patients (13.3%) had tumor recurrence. Our study indicates that WDTC has fairly distinctive clinicopathological features and that it is histologically and histogenetically related to cortical thymoma. The definition “well-differentiated carcinoma” is justified because of low-grade cytological atypia and retention of some organotypical histological features, in a tumour otherwise often displaying aggressive and sometimes clear-cut malignant clinical behaviour.     

Thymic carcinosarcoma associated with a spindle cell thymoma: an immunohistochemical study

A case of thymic carcinosarcoma associated with a spindle cell thymoma in a 71-year-old woman is reported. Histological and immunohistochemical studies of the carcinosarcoma showed two quite different components: the sarcomatous component included cells with myoid differentiation which stained for desmin and muscle specific actin, and some isolated cells which stained positively for low molecular weight cytokeratin, while the carcinomatous component, which formed less than 10% of the tumour, showed an epithelial phenotype, being positive for low and high molecular weight cytokeratin and epithelial membrane antigen. The thymoma cells showed epithelial markers, and a few cells were also positive for desmin and muscle specific actin. The rarity of this tumour and its possible histogenesis are discussed.