Thymoma--morphologic subclassification correlates with invasiveness and immunohistologic features: a study of 122 cases

Mark Wick contributions to pathology of the mediastinum

Mark Wick made a wide range of contributions to the field of mediastinal pathology. Early papers amplified the spectrum of neuroendocrine carcinomas of the thymus and brought attention to the aggressive nature of this tumor, also highlighting the occurrence of coexisting carcinoid tumor and small cell carcinoma of this organ. The controversial issue of thymoma classification was addressed in several papers and editorial comments, while also reporting a case of metastatic thymoma. A series of thymic carcinomas as well a report on the unusual clear cell variant bear his name as one of the authors. He summarized the topic of mediastinal cyst in a review published in 2005. Sarcomas arising in mediastinal germ cell tumors were also within the purview of his interests, with a publication of series of seven cases. He reviewed the topic of inflammatory myofibroblastic tumor of the heart and added a case to the existing literature. Two books dedicated to different aspect of mediastinal pathology also carry his name in the front cover in association with Drs Taazelar in one and Marchevsky in the other.

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.

Expression patterns for Bcl-2, EMA, β-catenin, E-cadherin, PAX8, and MIB1 in thymomas

The expression of immunohistochemical markers has been extensively investigated in thymomas to assist in the differential diagnosis. We have studied six select markers to determine their utility in the evaluation of these tumors. A series of 126 thymomas including 33 type A, 27 type AB, 20 type B1, 22 type B2, and 24 type B3, were examined utilizing a tissue microarray (TMA) technique with antibodies to e-cadherin, β-catenin, PAX8, bcl-2, EMA, and MIB-1. Keratin AE1/AE3 and p63 were used for quality control. A significant finding was strong and consistent positivity for bcl-2 in type A (90%) and type AB (88.8%) thymoma, while 100% of B1, B2, and B3 were negative. The distribution of e-cadherin and β-catenin was not useful for differential diagnosis. E-cadherin and β-catenin were expressed in a high proportion of all the tumors (92-100%), except for B2 thymoma which showed only 45% expression. A significant increase in the expression of the MIB-1 proliferation marker (mean: 12.8% nuclear positivity) was also observed in B3 thymoma compared with the other histologic types. Statistical significance was confirmed using Kruskal's non-parameterized test for distribution. EMA was generally negative except for spindle cells in the fibrous septa in types A and AB thymoma. PAX8 showed less consistent nuclear staining than p63 and was only widely expressed in 55.7% of cases. Bcl-2 may serve as a useful marker to separate spindle cell thymomas (Type A and AB) from the other types, and the MIB1 proliferation index may be of use to differentiate type B2 from type B3 thymoma.

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

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

Epidemiology of thymic epithelial tumors: 22-years experience from a single-institution

Background

To assess the correlation of WHO histological classification and Masaoka–Koga staging system of thymic epithelial tumors (TETs) with prognosis.

Methods

We retrospectively analyzed 83 patients with TETs in the Instituto Nacional de Enfermedades Neoplasicas between 1996 to 2018. We analyzed the clinical stages, histological types and treatment modalities and attempted to determine the impact on overall survival. The data was retrieved from clinical files and reviewed by a pathologist who reclassificated according to the 2004 WHO classification system. The staging was performed with the Masaoka–Koga staging system. Survival curves were constructed with Kaplan‐Meir method.

Results

There was a total of 83 patients with a median age of 55 years old included in the study. The histological type corresponded to thymoma (T) in 63.8% (n = 53) and to thymic carcinoma (TC) in 36.1%. T were type A, AB, B1, B2 and B3 in 14.4%, 18%, 12%, 3.6%, 7.4% of cases, respectively. The proportion of advanced disease (Masaoka stage III–IV) was high (65%). With a median follow‐up of 88.4 months, median overall survival (OS) was 81.6 months for T and 12.3 months for TC (P = 0.01). Univariate analysis showed that sex, histological type, clinical stage and surgery (P = 0.01) were significant independent prognostic factors. On multivariate analysis, histology type and Masaoka–Koga staging had an effect on survival.

Conclusions

The results indicates a clear association between the WHO histological classification and Masaoka–Koga staging system with survival. We found a higher proportion of TETs with advanced disease at diagnosis. Further research are required and collaboration is important to foster knowledge focused on classification and treatment.

Key points

Significant findings of the study

The WHO histological classification, the Masaoka–Koga system and surgery treatment were associated with overall survival.

What this study adds

To determine prognosis factors in TETs.

Genome‑wide DNA methylation profile of thymomas and potential epigenetic regulation of thymoma subtypes

The aim of the present study was to examine the whole-genome DNA methylation status of thymomas and identify differences in thymoma DNA methylation profiles. DNA methylation profiles of tissues (n=12) were studied using the Infinium MethylationEPIC BeadChip microarray (850K) and analyzed in relation to gene expression data. Functional annotation analysis of DNA methylation between the different groups was performed using the online tool GeneCodis3. In order to assess the diagnostic value of candidate DNA methylation markers, receiver operation characteristic (ROC) analysis was performed using the pROC package. A total of 10,014 CpGs were found to be differentially methylated (Δβ>0.2) between two thymoma types (type A and B). Combination analysis showed that 36 genes had differentially methylated CpG sites in their promoter region. ‘Pathways in cancer’, ‘focal adhesion’ and ‘regulation of actin cytoskeleton’ were the most enriched KEGG pathways of differentially methylated genes between tumor and controls. Among the 29 genes that were hypomethylated with a high expression, zinc finger protein 396 and Fraser extracellular matrix complex subunit 1 had the largest area under the curve. The present results may provide useful insights into the tumorigenesis of thymomas and a strong basis for future research on the molecular subtyping of epigenetic regulation in thymomas.

Robotic-assisted thymectomy: current perspectives

Thymectomy is the cornerstone in the treatment of thymic tumors and an accepted option for the management of myasthenia gravis. Different surgical approaches have been described, but the gold standard is represented by median sternotomy. In the last two decades, the development of minimally invasive surgery has led to an increased acceptance of thymectomy, especially for benign diseases. Robotic thymectomy seems a further step in the development and evolution of minimally invasive approaches. Since its introduction, different authors described their experience with robotic thymectomy, both for nonthymomatous myasthenia gravis and for thymic tumors. Available data show that robotic thymectomy may be considered a safe and feasible operation. In patients with nonthymomatous myasthenia, robotic thymectomy is effective and the long-term results are encouraging. The role of robotic thymectomy in patients affected by thymoma is still under evaluation, but the intermediate results seem promising both in terms of surgical and oncologic outcomes.

KI-67 Antigen Expression Predicts Survival and Correlates with Histologic Subtype in the WHO Classification of Thymic Epithelial Tumors

We performed an immunohistochemical study with monoclonal antibodies to Ki-67 antigen and p53 protein on 45 cases of thymic epithelial tumors classified according to the recent World Health Organization (WHO) classification system to evaluate whether there is correlation between the expression of these markers and prognosis, histologic subtype, and myasthenia gravis (MG). We also correlated histologic subtype with sex, age, MG, and survival. Ki-67 and p53 labeling indices (LIs) were expressed as a percentage of positive nuclear immunostaining by counting 1,000 epithelial tumor cells. Statistically significant differences were found between Ki-67 LI and survival (p = 0.007), whereas the prognostic implication of p53 could not be demonstrated, although there appeared a trend that patients with tumors of higher LIs had worse survival. Significant correlations were also found between Ki-67 (p < 0.0005) and p53 (p < 0.0005) LIs and histologic subtypes. No correlation was found between these parameters and MG. Histologic subtypes of the WHO classification also correlated with survival (p = 0.01), whereas no correlation was found with sex, age, and MG. In conclusion, our results indicate that the proliferative activity, assessed by Ki-67 LI, and the histologic pattern, according to WHO classification system, seems to represent reliable parameters in the prognosis of thymic epithelial tumors.

Multi-institutional European experience of robotic thymectomy for thymoma

BACKGROUND

Robotic thymectomy for early-stage thymomas has been recently suggested as a technically sound and safe approach. However, due to a lack of data on long term results, controversy still exists regarding its oncological efficacy. In this multi-institutional series collected from four European Centres with high volumes of robotic procedures, we evaluate the results after robot-assisted thoracoscopic thymectomy for thymoma.

METHODS

Between 2002 and 2014, 134 patients (61 males and 73 females, median age 59 years) with a clinical diagnosis of thymoma were operated on using a left-sided (38%), right-sided (59.8%) or bilateral (2.2%) robotic approach. Seventy (52%) patients had associated myasthenia gravis (MG).

RESULTS

The average operative time was 146 minutes (range, 60-353 minutes). Twelve (8.9%) patients needed open conversion: in one case, a standard thoracoscopy was performed after robotic system breakdown, and in six cases, an additional access was required. Neither vascular and nerve injuries, nor perioperative mortality occurred. A total of 23 (17.1%) patients experienced postoperative complications. Median hospital stay was 4 days (range, 2-35 days). Mean diameter of resected tumors was 4.4 cm (range, 1-10 cm), Masaoka stage was I in 46 (34.4%) patients, II in 71 (52.9%), III in 11 (8.3%) and IVa/b in 6 (4.4%) cases. At last follow up, 131 patients were alive, three died (all from non-thymoma related causes) with a 5-year survival rate of 97%. One (0.7%) patient experienced a pleural recurrence.

CONCLUSIONS

Our data suggest that robotic thymectomy for thymoma is a technically feasible and safe procedure with low complication rates and short hospital stays. Oncological outcome appears to be good, particularly for early-stage tumors, but a longer follow-up period and more cases are necessary in order to consider this as a standard approach. Indications for robotic thymectomy for stage III or IVa thymomas are rare and should be carefully evaluated.

Cervical type AB thymoma (Mixed) tumour diagnosis in a mynah as a model to study human: clinicohistological, immunohistochemical and cytohistopathological study

Abstract

Thymoma is a primary mediastinal neoplasm arising from or exhibiting differentiation towards thymic epithelial cells, typically with the presence of non-neoplastic lymphocytes. A 13-year-old male Mynah bird (acridotheres tristis) was presented for evaluation of a 2.3 × 1.5 × 1.0 cm mass in the left ventrolateral cervical region. The clinical signs, radiology, cytohistopathology and immunohistochimy findings related to the thymoma are presented. These findings indicated that the tumor was a type AB thymoma according to the World Health Organization (WHO) and veterinary classification. Thymomas are rarely reported in avian species and this is the first report in a Mynah bird.

Virtual slides

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1159525819982779.

Expression of podoplanin in thymoma: its correlation with tumor invasion, nodal metastasis, and poor clinical outcome

Recent studies have shown that podoplanin overexpression is associated with lymph node metastasis and poor clinical outcome in several malignant tumors. To investigate the role of podoplanin in thymoma, we examined 111 thymomas by immunohistochemistry using monoclonal antibody D2-40, which recognizes podoplanin. The tumors consisted of 8 type A, 40 type AB, 15 type B1, 23 type B2, 15 type B3, and 10 combined thymomas according to the World Health Organization histological classification system and of 41 stage I, 28 stage II, 16 stage III, 20 stage IVa, and 6 stage IVb thymomas according to the Masaoka staging system. We have found podoplanin expression in 0 (0%) type A, 4 (10%) type AB, 4 (27%) type B1, 16 (70%) type B2, 10 (67%) type B3, and 7 (70%) combined thymomas and in 5 (12%) cases of stage I, 7 (25%) of stage II, 11 (69%) of stage III, 12 (60%) of stage IVa, and all (100%) of stage IVb thymomas. Podoplanin was significantly expressed in B2/B3/combined thymomas and advanced stage thymomas (P < .0001). On survival analysis, podoplanin expression was significantly associated with an increased risk of death for the whole group of thymomas (P = .0002), although it was not identified as an independent prognostic factor in multivariate analysis. The significant survival curve differences of podoplanin expression were also seen for stage III/IVa/IVb thymomas (P = .0409) and B2/B3/combined thymomas (P = .0478). In conclusion, D2-40 immunostaining seems to be valuable for predicting the aggressive and metastatic potential of thymomas and the prognosis of the patients.

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.

Ectopic (mediastinal) parathyroid adenoma with prominent lymphocytic infiltration

Parathyroid adenoma with prominent lymphocytic infiltrates is very rare, with only 8 previously reported cases in the English scientific literature. Cases with prominent lymphocytic infiltrates of ectopic (mediastinal) parathyroid adenomas have not been reported. The prominent lymphocytic infiltration may make the diagnosis difficult on frozen sections, even on permanent histologic sections. We herein describe a case of ectopic (mediastinal) parathyroid adenoma with prominent lymphocytic infiltration in a 29-year-old man with hyperparathyroidism for 4 years. Immunohistochemical studies were important in making such a diagnosis.

Genome-wide genetic aberrations of thymoma using cDNA microarray based comparative genomic hybridization

Background

Thymoma is a heterogeneous group of tumors in biology and clinical behavior. Even though thymoma is divided into five subgroups following the World Health Organization classification, the nature of the disease is mixed within the subgroups.

Results

We investigated the molecular characteristics of genetic changes variation of thymoma using cDNA microarray based-comparative genomic hybridization (CGH) with a 17 K cDNA microarray in an indirect, sex-matched design. Genomic DNA from the paraffin embedded 39 thymoma tissues (A 6, AB 11, B1 7, B2 7, B3 8) labeled with Cy-3 was co-hybridized with the reference placenta gDNA labeled with Cy-5. Using the CAMVS software, we investigated the deletions on chromosomes 1, 2, 3, 4, 5, 6, 8, 12, 13 and 18 throughout the thymoma. Then, we evaluated the genetic variations of thymoma based on the subgroups and the clinical behavior. First, the 36 significant genes differentiating five subgroups were selected by Significance Analysis of Microarray. Based on these genes, type AB was suggested to be heterogeneous at the molecular level as well as histologically. Next, we observed that the thymoma was divided into A, B (1, 2) and B3 subgroups with 33 significant genes. In addition, we selected 70 genes differentiating types A and B3, which differ largely in clinical behaviors. Finally, the 11 heterogeneous AB subtypes were able to correctly assign into A and B (1, 2) types based on their genetic characteristics.

Conclusion

In our study, we observed the genome-wide chromosomal aberrations of thymoma and identified significant gene sets with genetic variations related to thymoma subgroups, which might provide useful information for thymoma pathobiology.

MR imaging of thymic epithelial tumors: correlation with World Health Organization classification

PURPOSE

The aim of this study was to determine magnetic resonance imaging (MRI) features of various subtypes of thymic epithelial tumors based on the World Health Organization classification.

MATERIALS AND METHODS

The study included 64 patients with histologically proven thymic epithelial tumors. Two observers evaluated the MRI findings in terms of tumor size, contour, lobulation, shape, homogeneity, the presence of intratumor high- and low-signal foci, enhancement degree and pattern, the presence of capsule and septum, and associated mediastinal lymphadenopathy and pleural effusion.

RESULTS

Type A tumors were more likely to have a smooth contour, round shape, distinct capsule, and smaller size compared to any other type of thymic epithelial tumor. Thymic carcinomas demonstrated a higher prevalence of low-signal foci within the mass on T2-weighted images and mediastinal lymphadenopathy than any other types. The frequency of heterogeneous intensity on T2-weighted images increased from type A tumors to thymic carcinomas.

CONCLUSION

The presence of a smooth contour, round shape, and capsule is highly suggestive of a type A tumor. Foci of low signal intensity in the mass on T2-weighted images and mediastinal lymphadenopathy are highly suggestive of thymic carcinomas.

The Thymus: A Comprehensive Review

Since first being described as such by Galen of Pergamum (130-200 ad), the thymus has remained an "organ of mystery" throughout the 2000-year history of medicine. The thymus reaches its maximum weight in puberty and subsequently undergoes involution, and thus is hardly an eye-catching structure on imaging studies performed in healthy adults. However, once there has been involvement of the thymus by a disease process, the gland demonstrates a variety of clinical and radiologic manifestations that require comprehensive understanding of each entity. Furthermore, it is important for radiologists to be familiar with the current World Health Organization histologic classification scheme for thymic epithelial tumors and to understand its clinical-pathologic, radiologic, and prognostic features.

Glia maturation factor-beta is produced by thymoma and may promote intratumoral T-cell differentiation

AIMS

To investigate whether Glia maturation factor-beta (GMFB) is expressed in thymomas and is associated with T-cell development.

METHODS AND RESULTS

We investigated the expression of GMFB by immunohistochemistry in 86 cases of thymoma classified into five type A, 35 type AB, 11 type B1, 26 type B2, and nine type B3 thymomas according to the World Health Organization classification system. Immunoblotting and in situ hybridization (ISH) studies were also performed in selected cases. The results of the immunoblot analysis were in accordance with those of immunohistochemical scoring. The ISH study ascertained the tumour cells producing the protein. Immunohistochemically, GMFB expression was observed in one (20%) of type A, 32 (80%) of type AB, all (100%) of type B1 and B2, and eight (89%) of type B3 thymoma with statistically significant differences between type A and type AB, type B1, or type B2 thymoma, and between type B3 and type AB or type B2 thymoma. There was a significant correlation between GMFB expression and the amount of accompanying non-neoplastic T cells. GMFB promoted T-cell differentiation into CD4-/CD8+ cells when analysed by two-colour flow cytometry.

CONCLUSIONS

The present study suggests that T-cell development in thymoma may be maintained partly by GMFB produced by the tumour cells.

Pathology of thymic tumors

As the thymus is composed of heterogeneous admixture of lymphoid and epithelial elements, tumors originating in the thymus may be of varied histologic types. Thymomas are the most common thymic tumor in adults. Thymoma classification has historically been controversial, but a system put forth by the World Health Organization (WHO) in 2004 has been generally accepted as a reproducible and clinically relevant classification. In addition to histologic subtype, tumor stage and resection status are important factors in determining outcome in thymomas. Thymic lymphomas typically occur in younger patients than thymomas. The most common thymic lymphomas are precursor T-lymphoblastic lymphoma, Hodgkin lymphoma, and primary mediastinal large B-cell lymphoma. Thorough histologic sampling and, in some cases, the appropriate use of ancillary studies such as immunohistochemistry, flow cytometry, and molecular studies, are important in proper pathologic evaluation of thymic tumors.

Protein expression and gene amplification of epidermal growth factor receptor in thymomas

BACKGROUND

Epidermal growth factor receptor (EGFR) overexpression and amplification are important prognostic factors in many solid tumors and anti-EGFR antibody-based therapy is now available as a promising therapeutic modality. There is little information in the literature regarding the biologic role of EGFR in thymomas that are characterized by variable clinical presentations, histologic heterogeneity, and unpredictable behavior.

METHODS

Protein expression and gene amplification of EGFR were investigated in 32 thymomas (9 World Health Organization [WHO] type A, 5 type AB, 7 type B2, 7 type B3, 4 type C) using immunohistochemistry and fluorescence in situ hybridization (FISH). FISH analysis included assessment of the average number of copies of the EGFR gene per cell, the average ratio of the EGFR gene to chromosome 7 copy numbers, and ploidy.

RESULTS

The results of FISH analysis showed statistically significant correlation with WHO histologic type, invasion, advanced clinical stage, but not with tumor size and outcome. Thymomas associated with myasthenia gravis more frequently showed hyperploidy when compared with sporadic tumors, but there was no difference in EGFR gene amplification. EGFR protein expression assessed by immunohistochemistry did not correlate with any studied clinicopathologic variables. There was poor correlation between the protein expression and gene amplification, only 7 of 23 specimens (30%).

CONCLUSIONS

The potential role of EGFR in the pathogenesis of advanced-stage thymomas indicated that evolving anti-EGFR antibody therapy may be considered as a treatment option.

Does CT of Thymic Epithelial Tumors Enable Us to Differentiate Histologic Subtypes and Predict Prognosis?

OBJECTIVE

The aims of our study were to describe the CT findings of thymic epithelial tumors and to correlate these findings with the histopathologic subtypes and prognosis.

MATERIALS AND METHODS

The CT findings of thymic epithelial tumors were analyzed in 91 patients who had undergone surgery between May 1995 and June 2002. Two observers, who were unaware of the histopathologic classification made in accordance with World Health Organization (WHO) recommendations and the prognosis of the tumors, retrospectively reviewed the initial CT findings in terms of the contours and shapes of the tumors and the presence of necrosis, calcification, mediastinal fat or great vessel invasion, pleural seeding, contrast enhancement, and lymph node enlargement. These findings were compared with the simplified subgroups of WHO histologic classification (low-risk thymomas [types A, AB, and B1], high-risk thymomas [types B2 and B3], and thymic carcinomas [type C]) and with postoperative recurrence.

RESULTS

The study found 31 low-risk thymomas (eight type A, 16 type AB, and seven type B1 tumors), 45 high-risk thymomas (25 type B2 and 20 type B3), and 15 thymic carcinomas (type C). Lobulated contour was more often seen in high-risk thymomas (26/45, 58%; p = 0.0456) and thymic carcinomas (10/15, 67%; p = 0.033) than in low-risk thymomas (9/31, 29%). Mediastinal fat invasion was more often seen in thymic carcinomas (5/15, 33%; p = 0.0133) than in low-risk thymomas (1/31, 3%). Great vessel invasion was seen only in thymic carcinomas (2/15, 13%; p = 0.0244). Tumors with a lobulated or irregular contour, an oval shape, mediastinal fat or great vessel invasion, and pleural seeding showed significantly more frequent recurrence and metastasis (all, p < 0.05).

CONCLUSION

Although CT is of limited value in differentiating histologic subtypes according to the WHO classification, CT findings may serve as predictors of postoperative recurrence or metastasis for the thymic epithelial tumors.

Thymoma Presenting with Infarction

Thymomas are the most common tumours of the anterior mediastinum with most patients presenting incidentally. We present a case of thymoma presenting with sudden onset severe chest pain and raised plasma aminotransaminases secondarily to spontaneous infarction. We discuss the presence of these aminotransaminases in this highly unusual presentation of thymoma and believe our case demonstrates the inherent limitations of plasma enzymes due to their lack of specificity and sensitivity.

Thymoma: a clinicopathologic study based on the new World Health Organization classification

OBJECTIVE

This study explored the relationship between the histologic subtype of thymoma according to the new World Health Organization histologic classification and the clinical findings, as well as the prognostic significance of the classification.

METHODS

A total of 130 patients with thymoma, who underwent resection at the National Cancer Center Hospital, Tokyo, from 1962 to 2000, were studied retrospectively. The histologic subtype of thymoma was determined according to the new World Health Organization histologic classification. The stage was also determined according to a modified Masaoka's classification as stage I, II, III, IVa, or IVb. To determine the factors that may affect the prognosis of thymoma, a multivariate analysis with Cox's proportional hazards regression model was performed.

RESULTS

The distribution of histologic subtype was type A (n = 18), type AB (n = 56), type B1 (n = 15), type B2 (n = 29), and type B3 (n = 12). A close correlation was seen between the histologic subtype and stage (P =.000). The overall survivals at 5 and 10 years were 92% and 91%, respectively. The 5- and 10-year survivals according to stage were 100% and 100% (stage I, n = 40; stage II, n = 54), 81% and 76% (stage III, n = 25), and 47% and 47% (stage IV, n = 11), respectively. The difference in survival between stage III and stage IV was significant (P =.000). Patients with type A or AB thymoma demonstrated a 100% survival at both 5 and 10 years. Recurrences were seen in 12 patients with complete resection. According to a multivariate analysis, tumor size (P =.001), completeness of resection (P =.002), histologic subtype (P =.011), and stage (P =.00) were significant prognostic factors.

CONCLUSION

The World Health Organization histologic classification significantly correlated with the clinical stage. Tumor size, completeness of resection, histologic subtype, and stage predicted the prognosis of thymoma.

Using the World Health Organization Classification of thymic epithelial neoplasms to describe CT findings

OBJECTIVE

Our purpose was to assess the CT features of various subtypes of thymic epithelial neoplasms on the basis of the 1999 World Health Organization classification.

MATERIALS AND METHODS

Thymic epithelial neoplasms in 53 patients who underwent thymectomy were retrospectively assessed histologically according to the 1999 World Health Organization classification. Type A and B neoplasms correspond to thymomas and type C, to thymic carcinoma. The study included four patients with type A, 14 with type AB, nine with type B1, 14 with type B2, four with type B3, and eight with type C epithelial tumors. Two observers independently assessed the CT scans without knowledge of the histologic findings.

RESULTS

Type A tumors were more likely to have smooth contours on CT (4/4, 100%) and round shapes (3.5/4, 88%) than any other type of thymic epithelial tumor (all, p < 0.05). Type C tumors had a higher prevalence of irregular contours (6/8, 75%) than any other type of thymic epithelial tumor (all, p < 0.05). Calcification was more frequently seen in type B1 (4/9, 44%), type B2 (8.5/14, 61%), and type B3 (3/4, 75%) tumors than in type AB (2/14, 14%) and type C (0.5/8, 6%) tumors (all, p < 0.05).

CONCLUSION

Smooth contours and a round shape are most suggestive of type A thymic epithelial tumor, whereas irregular contours are most suggestive of type C tumor. Calcification is suggestive of type B tumors. CT is of limited value, however, in differentiating type AB, B1, B2, and B3 tumors.

Histologic classification of thymic epithelial tumors: comparison of established classification schemes

The object of our multicenter retrospective study was to compare the new histologic World Health Organization (WHO) classification and the classical histologic Bernatz classification in terms of interobserver agreement and prognostic importance. The influence of coexisting diseases was also analyzed using the Charlson score. We evaluated 218 patients from 5 different hospitals who were treated between 1967 and 1998. The statistical methods of analysis included Kaplan-Meier estimates of survival curves and the application of Cox proportional hazards models to identify sets of prognostic factors for survival. Interobserver agreement was assessed by kappa coefficients. For both WHO and Bernatz classifications, interobserver agreement was good (weighted kappa > 0.87). However, the subdiversification of the "bioactive" WHO subgroup (B1, B2, B3) resulted in an interobserver agreement of only 0.49 within this group. In multivariable models, both the WHO classification and the Bernatz classification including carcinomas showed similar prognostic capabilities. The B3 type in the WHO classification and the predominantly epithelial type in the Bernatz classification had an intermediate prognostic ranking in comparison with the carcinomas and with the other subgroups. For both classifications, further simplification and subclassification into 3 subgroups led to classes with good discriminative power in respect to survival. In addition, very good interobserver agreement was observed in the simplified classifications. Comorbidity, sex, age of the patient and lymphofollicular hyperplasia had no major influence on overall survival. Both classifications showed similar prognostic power. Interobserver agreement of the type B subgroups was only moderate. By simplification of the classifications, subgroups with distinct survival could be identified.

Thymic epithelial tumors can develop along two different pathogenetic pathways

To investigate genetic abnormalities associated with the development of thymic epithelial tumors, we performed microsatellite analysis of 26 thymomas belonging to three different World Health Organization types (A, B3, and C) using 48 repeats. The most frequent aberration seen was loss of heterozygosity (LOH) in the region 6q23.3-25.3 detected in 11 tumors (45.8% of informative cases). Further consistent LOHs were detected in regions 3p22-24.2, 3p14.2 (FHIT gene locus), 5q21 (APC), 6p21, 6q21-22.1, 7p21-22, 8q11.21-23, 13q14 (RB), and 17p13.1 (p53). Microsatellite instability was extremely rare, occurring in one type B3 thymoma only, although, at 12.5% of the analyzed loci. Comparing the allelotypes of the analyzed thymomas, we were able to identify two pathogenetic pathways these tumors develop along, characterized by the 6q23.3-25.3 and 5q21 LOHs, respectively. The APC aberration on 5q21 showed significant associations with LOH in the 3p22-24.2, 13q14, and 17p13.1 regions. Interestingly, type A thymomas presented with consistent LOH in the region 6q23.3-25.5 only, they did not reveal any aberrations in the APC, RB, and p53 gene loci or regions 3p22-24.2 and 8q11.21-23. The absence of these aberrations might be the reason for the well-known benign behavior of type A thymomas as compared to types B3 and C tumors.

Classification of thymic epithelial neoplasms: a controversial issue coming to an end?

The classification of thymic epithelial neoplasms has been one of the most controversial issues in tumor pathology. There are two opposing schools of pathologists holding different views regarding the classification of thymic epithelial neoplasms. One school of pathologists believe that histological classification of thymomas is not possible or useful. Another school of pathologists believe that thymomas can be histologically subclassified despite their complex histomorphology and that these histological subtypes correlate with their aggressiveness and clinical behavior. A compromised histological classification has been established by World Health Organization (WHO) to designate thymic epithelial neoplasms with letters and numbers. This classification should be adopted internationally to facilitate the communication among concerned pathologists and oncologists. A simple histological classification of thymomas based on cytomorphology and supported by cytokeratin expressions is proposed and compared to the WHO and Müller-Hermelink's histogenetic classifications.

Thymoma with prominent cystic and hemorrhagic changes and areas of necrosis and infarction: a clinicopathologic study of 25 cases

Twenty-five cases of thymoma with prominent cystic and hemorrhagic changes and areas of necrosis and infarction are presented. The patients were 11 women and 14 men between the ages of 18 and 73 years (median 45.5 years). Clinically, nine patients were asymptomatic and their mediastinal tumor was discovered on routine chest radiograph. Sixteen patients presented with symptoms of chest pain and cough. All patients underwent surgical resection of their tumor. Grossly, the tumors were described as well circumscribed and encapsulated, with the exception of two that showed infiltration of pleura and pericardium. The tumors measured from 4 to 13 cm in greatest dimension. On cut surface they showed prominent cystic areas and foci of hemorrhage and necrosis. Histologically, the tumors contained solid areas showing an admixture of round to oval epithelial cells devoid of atypia admixed with small lymphocytes in varying proportions. Cystic changes with areas of necrosis, infarction, and hemorrhage were present in all cases and comprised extensive areas of the tumors. The areas of infarction showed features of ischemic necrosis and were always intimately associated with vaso-occlusive and thrombotic phenomena and with cystic and hyperplastic changes of adjacent thymic epithelium. Clinical follow-up in 14 patients showed that 11 were alive and well from 1 to 18 years after surgery (median follow-up 9 years). Three patients died: one of complications during the immediate postoperative period, one because of colonic adenocarcinoma 9 years after diagnosis of the mediastinal tumor, and one because of pneumonia 6 years later. The two patients with invasive tumors were lost to follow-up. The present study appears to indicate that areas of hemorrhage and necrosis in well encapsulated, noninvasive thymomas do not portend an adverse prognosis.

Thymoma: trends over time

BACKGROUND

This is a review of a series of patients who presented with thymoma over the most recent 20-year period. Changes and trends in disease patterns were documented.

METHODS

Data were collated retrospectively but all pathology slides were reviewed. Survival functions were estimated using the Kaplan-Meier method.

RESULTS

Seventy-one patients had a partial or total thymectomy during this period for a thymoma. Average age was 55 years. Twenty-three patients (32%) had myaesthenia gravis. Eighteen patients (25%) were asymptomatic. Thirty-three patients (47%) had stage 1 disease. Complete resection was achieved in 60 patients (85%). Five-year survival was 88%. Fifty percent of patients with myesthenia gravis showed improvement in symptoms.

CONCLUSIONS

Five- and 10-year survival rates in this study are better than in other series. We attribute this to an increasing number of patients with stage 1 and stage 2 disease, particularly those with myasthenia gravis who now have screening computer tomography, and also to the surgical intent of aiming to achieve complete resection even if excision of adjacent tissue is required.

Spindle cell and mixed spindle/lymphocytic thymomas: an integrated clinicopathologic and immunohistochemical study of 81 cases

Forty-three cases of spindle cell thymoma (medullary, WHO type A) and 38 cases of mixed spindle/lymphocytic thymoma (WHO type AB) were studied for their clinicopathologic and immunohistochemical characteristics. Three histologic patterns of spindle cell thymoma were observed: short-spindled (57%), long-spindled (31%), and micronodular (12%). The short-spindled variant was composed of oval to short spindle cells commonly arranged in a hemangiopericytic or microcystic pattern. The long-spindled variant chiefly consisted of fibroblast-like epithelial cells mimicking fibrohistiocytic neoplasms. The micronodular variant was characterized by small nests of short spindle cells dispersed among a lymphoid stroma with frequent germinal centers. All kinds of spindle cell could be admixed with lymphocyte-rich "cortex"-like areas to constitute mixed spindle/lymphocytic thymomas. Immunohistochemically, the epithelial cells in up to 70% of the short-spindled and long-spindled variants of spindle cell thymoma and 90% of mixed spindle/lymphocytic thymomas were positive for CD20, whereas the epithelial cells in all micronodular spindle cell thymomas were negative. All of the spindle cell thymomas and most of the mixed spindle/lymphocytic thymomas in this study were found in stages I and II. Follow up of the patients did not disclose relapse or mortality directly resulting from the tumors. However, the prognosis of stage I and II spindle cell and mixed spindle/lymphocytic thymomas did not significantly differ from those of stage I and II thymomas of other types by a stage-matched survival analysis. Our data showed that spindle cell and mixed spindle/lymphocytic thymomas are distinctive in histologic pattern and immunohistochemical profile. When interpreted within the context of staging, spindle cell and mixed spindle/lymphocytic thymomas presenting in stages I and II most likely behave in an indolent fashion.

Clinical and functional significance of WHO classification on human thymic epithelial neoplasms: a study of 146 consecutive tumors

We examined the clinical and functional significance of histologic classification of thymic epithelial neoplasms proposed by the World Health Organization (WHO), based on an analysis of 146 consecutive tumors derived from 141 patients and 47 normal thymuses derived from children ranging in age from 1 to 9 years. Invasive tumors were seen in 12.5%, 38.6%, 40.0%, 69.4%, 80.0%, and 100% of type A, AB, B1, B2, B3, and C primary tumors, respectively. All of six recurrent or metastatic lesions were type B2 tumors. Myasthenia gravis was associated in 0%, 6.8%, 40.0%, 55.6%, 10.0%, and 0% in patients with type A, AB, B1, B2, B3, and C tumors, respectively. The average number (x10(6)) of tumor-associated CD4+CD8+ cells present in 1 g of tumor tissue was 1.5, 391.1, 1041.7, 333.9, 24.5, and 0.2 in type A, AB, B1, B2, B3, and C, respectively, and it was 1168.2 in the normal thymuses. Thus, type B1 tumor retained the function to induce CD4+CD8+ double-positive cells at a level comparable to that of the normal thymic cortical epithelial cells, followed by type AB and type B2 tumors. Type A and B3 tumors had this function at a barely detectable level, and type C tumor was nonfunctional. WHO histologic classification was shown to reflect the clinical features and the T-cell-inducing function of thymic epithelial tumors.

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

Six hundred thirty cases of thymomas were evaluated to determine morphologic heterogeneity. The thymomas were grouped in 4 categories using previous terminology. Stratification according to the number of sections available for examination revealed a marked difference in distribution by histopathologic type. A cutoff number of 5 sections appears to provide a difference in subgrouping these tumors. In addition, the proportion of invasive tumors increases with the number of sections examined. Final classification may be affected by the extent of sampling. Histopathologic classification of thymoma, although of academic interest, may have limited practical relevance for assessment of prognosis in limited biopsy tissue. Proper evaluation of histology and aggressive potential in thymoma should be based on ample sampling and assessment of capsular integrity, which is best accomplished on thoroughly sampled resection specimens rather than incomplete or limited biopsy samples.

Cytogenetic profile of a thymoma. A case report and review of the literature

Cytogenetic analysis of mixed lymphocyte and epithelial thymoma in a nonmyasthenic female patient revealed deletion of part of the short arm of chromosome 6. To our knowledge, this cytogenetic abnormality in a benign thymoma has not been previously described in the literature, which is reviewed.

Current status of the diagnosis and treatment of thymoma

Although thymomas are rare neoplasms, they are the most common tumor of the anterior mediastinum in adults. Preferred therapy for these neoplasms is complete surgical resection. If a thymoma cannot be completely resected, postoperative radiotherapy may produce satisfactory results in controlling the tumor. Significant 5- and 10-year survival rates have been recorded for patients with advanced thymomas who have been treated by radiation therapy alone. Chemotherapy may be used in patients with unresectable thymomas as well, but the results are less promising than with radiotherapy. Combinations of radiotherapy and chemotherapy used on patients with unresectable thymomas have produced encouraging results. Surveillance of patients with thymoma should be prolonged because late recurrence (more than 5 years after initial therapy) can be expected in a significant minority of patients. Aggressive therapy of late recurrence, including resection of new tumor masses and pleural metastases, has yielded successive disease-free intervals that validate persistent treatment.

Different age-related effects of thymectomy in myasthenia gravis: role of thymoma, zinc, thymulin, IL-2 and IL-6

Different age-related immune pathogenetic mechanisms in myasthenia gravis (MG) have been suggested because of restoration after thymectomy (Tx) of altered zinc, thymulin (TH) and T-cell subsets exclusively in early-onset patients (younger <50 years), not in late-onset patients (older >50 years). In this context interleukin-2 (IL-2), interleukin-6 (IL-6) and thymoma are crucial because both involved in MG pathogenesis and correlated with acetylcholine receptors (AchRs) Ab production. Moreover, IL-2 and IL-6 are zinc-dependent, are altered in aging and related with zinc and TH age-dependent declines. Moreover, zinc is relevant for immune efficiency. In order to confirm these different age-related pathogenetic mechanisms further, the role of thymoma, zinc, TH, IL-2 and IL-6 is studied in MG patients with generalized MG with and without thymoma before and 1 month and 1 year after Tx. The high IL-2, IL-6, zinc, and AChR Ab levels observed before Tx are significantly correlated each other in younger MG patients (<50 years) independently by thymoma and in older MG patients (>50 years) with thymoma. No correlations exist in older MG patients without thymoma. Thymulin is not correlated with other parameters considered to be both in younger and older MG patients independently by the thymoma. Thymectomy restores zinc; immune parameters and AChR Ab are exclusively in the younger group, not in the older one. These findings suggest that IL-2 and IL-6, via zinc, rather than TH, may be involved in different age-related pathogenetic mechanisms mainly in early-onset MG. By contrast, thymoma may be involved in MG etiology in late-onset representing, as such, a useful discriminant tool for MG etiology between early and late-onset MG patients. Because autoimmune phenomena may rise in aging, a parallelism with altered immune functions during aging is discussed.

Recurrent genetic aberrations in thymoma and thymic carcinoma

Apart from single reported aberrant karyotypes, genetic alterations in thymic epithelial neoplasms have not been investigated so far. In this study, 12 World Health Organization classification type A thymomas (medullary thymomas), 16 type B3 thymomas (well-differentiated thymic carcinomas), and nine type C thymomas, all of them primary thymic squamous cell carcinomas, were analyzed by comparative genomic hybridization and fluorescence in situ hybridization. With the exception of one single case, type A thymomas did not reveal chromosomal gains or losses in comparative genomic hybridization. In contrast, all type B3 thymomas showed chromosomal imbalances, with gain of 1q, loss of chromosome 6, and loss of 13q occurring in 11 (69%), six (38%), and five (31%) of 16 cases, respectively. In primary thymic squamous cell carcinoma, the most frequent chromosomal losses were observed for 16q (six of nine cases, 67%), 6 (4 of 9, 44%), and 3p and 17p (three of nine each, 33%), whereas recurrent gains of chromosomal material were gains of 1q (5 of 9, 56%), 17q, and 18 (three of nine each, 33%). This study shows that the distinct histological thymoma types A and B3 exhibit distinct genetic phenotypes, whereas type B3 thymoma and primary thymic squamous cell carcinoma partially share genetic aberrations. In addition to the possible tumorigenic role, the deletion in type B3 thymoma of chromosome 6, harboring the HLA locus, might play a role in the pathogenesis of paraneoplastic autoimmunity characteristic of thymoma.

DNA-ploidy analysis correlates with the histogenetic classification of thymic epithelial tumours

The ploidy values of the epithelial component were determined in a series of thymomas and organotypic thymic carcinomas using image cytometry and the results were compared with the histological tumour subtypes according to the histogenetic classification introduced by Marino, Müller Hermelink, and Kirchner (MMHK). Forty-six cases of thymic epithelial tumours were included in the study. After reclassification according to the MMHK classification, the distribution among the subtypes was as follows: three medullary, nine mixed type, five predominantly cortical (organoid), 16 cortical thymomas, and 13 well-differentiated thymic carcinomas. Single cell preparations were made from paraffin-embedded tumour tissue and stained according to Feulgen. Ploidy analysis was performed using an automated image analysis system. In five cases, DNA cytometry could not be performed, for technical reasons. The remaining 41 cases consisted of 11 diploid and 30 non-diploid tumours. The percentage of aneuploid tumours in the different subtypes increased from medullary (0 per cent) through mixed type (44.4 per cent), predominantly cortical (75 per cent), cortical (83.3 per cent) to well-differentiated thymic carcinomas (100 per cent). DNA-ploidy determination using image cytometry correlates with the concept of the MMHK classification of thymomas.

Clinical and pathologic predictors of survival in patients with thymoma

OBJECTIVE

To evaluate the Johns Hopkins Hospital experience with 136 thymomas over the past 40 years. This number of patients allowed quantitative estimation of the independent influence of common clinicopathologic risk factors using multivariate analysis.

SUMMARY BACKGROUND DATA

Thymomas vary widely in terms of recurrence and influence on overall survival. Several series have indicated the importance of initial tumor invasion, as well as the extent of surgical resection, as predictors of recurrence and survival after thymoma resection. However, findings have been equivocal when other predictors of prognosis were examined.

METHODS

The authors evaluated 136 patients seen at the Johns Hopkins Hospital between 1957 and 1997 with a pathologic diagnosis of thymoma. Demographic information, clinical staging data, surgical and adjuvant treatment details, and patient follow-up data were obtained from the patient record and from detailed patient or family interviews. Microscopic sections of all 136 patients were reviewed by two pathologists blinded to the clinical data. All data were analyzed by multivariate Cox regression analysis, which allowed the quantification of the independent predictive value of 12 putative clinicopathologic prognostic indicators.

RESULTS

Completeness of follow-up was 99%, 99%, and 98% of eligible patients at 5, 10, and 15 years, respectively. Forty percent of the patients had associated myasthenia gravis and 27% had a secondary primary malignancy. Overall patient survival rates were 71%, 56%, 44%, 38%, and 33% at 5, 10, 15, 20, and 25 years, respectively. Overall, the thymoma-related mortality rate was 14%; the nonthymoma-related mortality rate was 26%. Incomplete resection, preoperative absence of myasthenia gravis, and advanced Lattes/Bernatz pathologic class were found to be independent predictors of poorer overall survival.

CONCLUSIONS

These findings support a policy of aggressive, complete surgical resection of all thymomas when feasible. Thymoma behaves as a rather indolent tumor, with most deaths from causes unrelated to thymoma or its direct treatment. Clinicians should have an increased awareness of the possibility of second primary malignancies in patients with thymoma.

From basic immunobiology to the upcoming WHO-classification of tumors of the thymus. The Second Conference on Biological and Clinical Aspects of Thymic Epithelial Tumors and related recent developments

The Second Conference on Biological and Clinical Aspects of Thymic Epithelial Tumors in Leiden, The Netherlands, 1998, set the stage for an interdisciplinary meeting of immunologists, pathologists and members of various clinical disciplines to exchange their recent findings in the field of thymus-related biology, pathology, and medicine. The contributions covered such diverse subjects as the role of transcription factors and cytokines in the development of the thymic microenvironment, thymic T, B and NK cell development, the pathogenesis of myasthenia gravis and other thymoma-associated autoimmunities, the pathology of thymic epithelial tumors and germ cell neoplasms, and new approaches to their diagnosis and treatment. This editorial will briefly sum up the data presented at the Conference and will comment on related novel findings that have been reported since then. Because it was also at the Leiden Conference, that the proposal of the WHO committee for the classification of thymic tumors was discussed for the first time, a description of the upcoming WHO Classification of Tumors of the Thymus is given with emphasis on the diagnostic criteria of thymic epithelial tumors, that should now be termed as type A, AB, B1-3 and type C thymomas, to make pathological and clinical studies comparable in the future.

Thymoma: state of the art

Thymoma is the most common tumor of the anterior mediastinum. This tumor is associated with unique paraneoplastic syndromes, such as myasthenia gravis, hypogammaglobulinemia, and pure red cell aplasia. The rarity of this tumor, however, has somewhat obscured the optimal treatment for this disease. For the majority of patients who present with localized tumor, surgical extirpation remains the standard of choice. Adjuvant radiotherapy seems to improve local control and survival. In more advanced disease, systemic therapy has been demonstrated to produce a 50% to 80% objective response rate. These observations have led to the development of multimodality therapy for the treatment of patients with advanced thymoma. In this article, we will review the current perspectives on the management of early stage and advanced thymoma.