Classification, histopathology and molecular pathology of thymic epithelial tumors: a review

Thymic epithelial tumors represent 0.2-1.5% among all malignant neoplasms. They are slow-growing tumors with an overall recurrence rate around 10% and 90% of them are located in the anterior mediastinum. In this review we focused on the classification, histopathology, molecular pathology and prognosis of thymic epithelial tumors, mainly thymoma and thymic carcinoma.

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

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

Thymoma: A Clinico-Pathologic Study Based on Newly Developed Morphologic Criteria

A retrospective study of 28 cases of thymoma classified according to Marino and Müller-Hermelink (cortical, medullary, mixed common, mixed with cortical predominance, mixed with medullary predominance thymoma) was undertaken to determine the existence of correlations between histology and clinical behavior. Cortical thymoma was observed in 11 cases (39.2%), mixed common thymoma in 9 (32.1%), mixed with cortical predominance in 5 (18%), and medullary thymoma in 3 (10.7%). In patients with cortical thymoma the tumor was always invasive (stages II and III according to Bergh), whereas medullary thymomas were noninvasive in 2 cases (stage I) and slightly invasive with a moderate infiltration of the capsule in the remaining case (stage II). Mixed common and mixed with cortical predominance thymomas displayed intermediate behavior. Twelve patients were affected by myasthenia gravis: 1 had medullary thymoma, 6 had mixed common thymoma, 3 had mixed thymoma with cortical predominance, and 2 had cortical thymoma. One patient with cortical thymoma had superior vena cava syndrome and 1 had erythroid hypoplasia; mixed common thymoma was associated with Cushing's syndrome in 1 patient. These data confirm previously reported observations (16) showing a higher degree of malignancy in patients with cortical thymoma.

Nephrotic Syndrome and a Retroperitoneal Mass: A Case Report of a Patient with Recurrent Invasive Thymoma

A 68-year-old man was admitted to our hospital to undergo an examination for nephrotic syndrome while concurrently complicated with recurrent thymoma in the parietal pleura and retroperitoneum. He had been diagnosed with invasive thymoma and had undergone thymo-thymectomy seven years previously. Based on the renal biopsy findings, his nephrotic syndrome was ascribed to minimal change disease. He was treated with corticosteroid monotherapy, which resulted in complete remission six months later, despite the fact that the recurrent thymoma remained. The role of thymoma in the pathogenesis of paraneoplastic glomerulopathy and the therapeutic concerns that emerged in this case are also discussed.

Ectopic Hamartomatous Thymoma: A Review Of The Literature With Report Of New Cases And Proposal Of A New Name: Biphenotypic Branchioma

Ectopic hamartomatous thymoma (EHT) is a rare benign neoplasm of the lower neck suggesting branchial origin. Despite use of the term thymoma in the nomenclature, there is no evidence of thymic origin or differentiation. It affects middle-aged adults with a remarkable male predominance. To date less than 80 cases have been reported in the English literature. We present here two additional cases of EHT. The first is a benign case in a 31-year-old man, showing typical histological features. The second is a malignant case in a 70-year-old woman, showing intraductal carcinoma arising in intimate association with an EHT. These cases are presented in the context of a review of cases reported in the English literature. The exact origin has not been identified, but is considered to be of branchial apparatus, creating a quandary about the best terminology. Recently, the designation "branchial anlage mixed tumor" or "thymic anlage tumor" were proposed, but do not quite reflect the true nature of the neoplasm. To avoid taxonomic confusion, international consensus on terminology is desired. As this entity is a neoplasm that shows dual mesoderm and endoderm derivation/differentiation, we propose a new name "biphenotypic branchioma."

Comparison of outcomes between neuroendocrine thymic tumours and other subtypes of thymic carcinomas: a joint analysis of the European Society of Thoracic Surgeons and the International Thymic Malignancy Interest Group

OBJECTIVES

The latest World Health Organization (WHO) histological classification divides thymic epithelial tumours in thymomas and thymic carcinomas (TCs), the latter also including the neuroendocrine thymic tumours (NETTs). NETTs and other TC histotypes have been described to have a significantly lower survival than thymomas, but these two groups of tumours have rarely been compared directly. Using the European Society of Thoracic Surgeons and the International Thymic Malignancy Interest Group datasets, we wanted to study this issue.

METHODS

This is a retrospective multicentre cohort study of patients operated for TC. Outcome measures were overall survival (OS) and recurrence-free survival (RFS). OS was analysed using the Kaplan-Meier method and RFS was assessed using competing risk analysis. The association with clinical and prognostic factors for OS and RFS was evaluated with log-rank test and Gray's test, respectively.

RESULTS

A total of 1247 tumours (1042 TCs) were collected between 1984 and 2012. A R0 resection was performed in 363 TCs and in 52 NETTs. The median follow-up was 4.4 years for TCs and 4.1 years for NETTs. Owing to the missing values for survival information, a total of 728 TC patients and 132 NETTs were included in the OS analysis. Among them, 262 TC and 39 NETT patients died. The median OS was 6.6 years for TC and 7.5 years for NETTs. The overall 5-year survival rates were 60% for TC and 68% for NETTs; 10-year survival rates were 40% for TCs and 39% for NETTs (P = 0.19). Five-year RFS was 0.35 and 0.34 for TCs and NETTs (P = 0.36). On multivariate analysis, histology did not influence either OS (P = 0.79) or RFS (P = 0.59).

CONCLUSIONS

This represents the largest clinical series of TCs and NETTs collected. Despite the biological aggressiveness of these rare neoplasms, the 5-year survival rate after resection is over 60% and TCs and NETT showed a similar rate of survival and recurrences after surgery.

[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.

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.

Value of Computerized 3D Shape Analysis in Differentiating Encapsulated from Invasive Thymomas

Objectives

To retrospectively investigate the added value of quantitative 3D shape analysis in differentiating encapsulated from invasive thymomas.

Materials and Methods

From February 2002 to October 2013, 53 patients (25 men and 28 women; mean age, 53.94 ± 13.13 years) with 53 pathologically-confirmed thymomas underwent preoperative chest CT scans (slice thicknesses ≤ 2.5 mm). Twenty-three tumors were encapsulated thymomas and 30 were invasive thymomas. Their clinical and CT characteristics were evaluated. In addition, each thymoma was manually-segmented from surrounding structures, and their 3D shape features were assessed using an in-house developed software program. To evaluate the added value of 3D shape features in differentiating encapsulated from invasive thymomas, logistic regression analysis and receiver-operating characteristics curve (ROC) analysis were performed.

Results

Significant differences were observed between encapsulated and invasive thymomas, in terms of cystic changes (p=0.004), sphericity (p=0.016), and discrete compactness (p=0.001). Subsequent binary logistic regression analysis revealed that absence of cystic change (adjusted odds ratio (OR) = 6.636; p=0.015) and higher discrete compactness (OR = 77.775; p=0.012) were significant differentiators of encapsulated from invasive thymomas. ROC analyses revealed that the addition of 3D shape analysis to clinical and CT features (AUC, 0.955; 95% CI, 0.935–0.975) provided significantly higher performance in differentiating encapsulated from invasive thymomas than clinical and CT features (AUC, 0.666; 95% CI, 0.626–0.707) (p<0.001).

Conclusion

Addition of 3D shape analysis, particularly discrete compactness, can improve differentiation of encapsulated thymomas from invasive thymomas.

The major prognostic factors of thymomas: about a Tunisian study of 100 cases

AIM

Thymomas are characterised by their rarity, histologic variability and peculiar patterns of recurrence. Herein, we present the experience of a single institution and aim to highlight the major prognostic factors of these tumours.

MATERIALS AND METHODS

We present a retrospective study on 100 thymomas diagnosed between 1994 and 2011. Statistical analyses were performed using version 18.0 SPSS. The Kaplan Meier method was used to estimate survival, and survival curves were compared using the Log-Rank test. A p < 0.05 was considered statistically significant.

RESULTS

50 men and 50 women underwent surgical resection for thymoma. Radiologic findings highlighted a diagnosis of thymoma in 51% of cases. The thymomas were classified as stage I in 25 cases, stage II in 47 cases, stage III in 25 cases and stage IV in 3 cases. According to the WHO classification, tumours were classified as type A in 14 cases, type AB in 24 cases, type B1 in 17 cases, type B2 in 20 cases, type B3 in 8 cases, B1/B2 in 8 cases and B2/B3 in 9 cases. The mean survival of patients was 136 months. Age, sex, tumour size, WHO classification and Masaoka stage were evaluated as prognostic factors. Univariate analysis showed that the major prognostic factors were WHO classification (p = 0.019) and Masaoka Stage (p = 0.0001).

CONCLUSION

Our results place emphasis on the prognostic value of WHO classification and Masaoka stage in thymomas; in addition, the necessity of improving reproducibility of microscopic classification to avoid discrepancies among prognostic groups is highlighted.

Corticomedullary differentiation and maturational arrest in thymomas

AIMS

Morphological complexity hampers the histological classification of thymomas. Our aim was to determine whether the use of novel differentiation and maturation markers of cortical and medullary thymic epithelial cells (cTECs and mTECs) might provide an approach to understanding the underlying biology of these tumours.

METHODS AND RESULTS

Fifty-seven thymomas were studied by immunohistochemistry. The cortical markers used were B5T, PRSS16, and cathepsin V. The medullary markers used were CD40, claudin-4, AIRE, and desmin. Involucrin and cytokeratin 10 were used to study terminal mTEC maturation. Irrespective of histological subtype, most thymomas contained distinct areas with cortical and medullary differentiation. Type B1, type B2 and type AB thymomas showed marked bi-lineage differentiation, with lack of terminal mTEC maturation in type AB. Type AB thymomas were unique in showing areas where cells with either cortical or medullary differentiation were intimately 'mixed' at the single-cell level. Type B3 and type A thymomas showed only abortive lineage differentiation and maturation.

CONCLUSIONS

Thymomas show highly characteristic patterns of bi-lineage TEC differentiation that reflect the histological subtypes recognized by the WHO classification. We hypothesize that thymomas arise from thymic precursor cells with different cortical and/or medullary maturation defects.

[Lack of uniformity in the treatment of thymomas]

Thymomas are the most frequently occurring tumours of the anterior mediastinum. However, they only constitue less than 1% of the total number of malignant diseases. The incidence in the USA is 0.15 per 100.000 persons per year, and the disease is most frequent in persons between 40 and 60 years of age. Because of the rarity of thymomas, lack of uniformity in treatment has been a major problem over the years. Therefore, international collaborations have been established, and national oncological centralisation of management has been arranged in order to improve the treatment and prognosis.

Thymoma: current concepts

Thymomas are unusual tumors, representing no more than 1% of all malignancies. However, thymomas are the most common epithelial tumors of the anterior mediastinum. Unfortunately, there is no general agreement regarding the best parameters to use to predict clinical behavior in these tumors.This review considers the status of the different histological classifications thus far presented for thymomas and offers an analysis of the association between histology and clinical behavior. It also emphasizes the importance of proper staging of thymomas, delineating the benefits and shortcomings of different proposed staging systems and offering thoughts on a better and more accurate staging stratification for patients with these tumors. All of the different parameters are presented in relation to survival rates. Based on current information, staging with proper stratification remains the most important parameter for predicting prognosis. For tumors limited to the mediastinal compartment, surgical resection is the most effective treatment, while induction therapy is a good alternative for patients in whom surgical resection is not possible.

Proteome analysis and tissue array for profiling protein markers associated with type B thymoma subclassification

BACKGROUND

The prognostic relevance of World Health Organization (WHO) subtypes within type B thymomas is still controversial. Understanding of the molecular characteristics of the different histologic types of thymomas will provide meaningful information for diagnosis and therapeutic management in type B thymoma.

METHODS

Proteins extracted from twelve type B thymoma tissue specimens (six type B1 and six type B2) were analyzed by two-dimensional electrophoresis (2-DE) coupled with MALDI-TOF-MS. Differentially expressed proteins were then assayed in sixty-nine type B thymoma tissues (including B1, B2 and B3) by tissue array analysis with immunohistochemistry staining. The relationship of their expression with clinicopathological parameters, such as tumor stage or WHO classification, was estimated by Spearman's Rank Correlation Test.

RESULTS

Sixteen differentially expressed proteins between type B1 and B2 thymoma tissues were identified. The differential levels of ezrin and glutathione S-transferase pi (GSTP1) were validated using immunohistochemistry staining. A statistically significant difference was observed in the positive rate of ezrin expression between type B1 thymoma and type B3 thymoma (Z = -2.963, P < 0.01). Ezrin showed a tendency to be expressed in higher classification tumors from type B1 to B3. A statistical analysis demonstrated that type B2 and B3 tumors had significantly higher positive expression of GSTP1 than the B1 group (type B2 vs. B1: Z = -2.582, P = 0.01; type B3 vs. B1: Z = -4.012, P ≤ 0.001). The results also showed a strong correlation between GSTP1 and WHO type staging of B1 to B3 tumors (Spearman's correlation coefficient: 0.633, P ≤ 0.001). Statistical analysis showed that there was close correlation between GSTP1 and ezrin expression with the clinical stage (Spearman's correlation coefficients, ezrin: 0.481, P < 0.05; GSTP1: 0.484, P < 0.01).

CONCLUSIONS

Differentially expressed proteins between type B1 and B2 thymoma tissues were analyzed by comparative proteomic analysis. The techniques of proteomic analysis and tissue array provide a potential tool for screening of key molecules in type B thymoma histological sub-classifications. The statistical analysis of ezrin and GSTP1 expression by immunohistochemistry, especially GSTP1, may be a useful approach for type B thymoma classification.

Classification of thymoma by fine needle aspiration biopsy according to WHO classification: a cytological algorithm for stepwise analysis in the classification of thymoma

OBJECTIVE

To evaluate the cytological characteristics of each type of thymoma and introduce an algorithm to classify thymoma using fine needle aspiration biopsy (FNAB).

STUDY DESIGN

We retrospectively reviewed the cytological characteristics of 15 cases of thymoma with three thymic carcinoma (1 type A thymoma, 6 type AB thymomas and 8 type B thymomas), which were confirmed by histology. Three major and one minor cytomorphologic parameter were adopted for classification: (1) number of lymphocytes in the smear background; (2) nuclear characteristics of thymic cells; (3) lymphocytes and crush artifacts in thymic cell clusters, and (4) nuclear arrangement of thymic cells.

RESULTS

An abundant lymphocytic smear background indicated type B thymomas in 87.5% of cases, contrary to the few lymphocytes in the remaining thymic tumors excluding type B thymomas (90%). Thymic cells contained no vesicular nuclei and inconspicuous nucleoli in 85.7% of type A thymoma and type AB thymoma cases. Type AB thymomas and type B thymomas showed more prominent crush artifacts in cell clusters than type A thymoma and thymic carcinoma. Thymic cells of type B thymomas and thymic carcinoma were arranged without whirling architecture in clusters. The proposed algorithm demonstrated a predictive rate of 88.8% for thymoma classification.

CONCLUSIONS

The stepwise classification of thymoma with FNAB may be useful in patients for whom an invasive diagnosis approach is not feasible.

[Correlation of amplification of chromosome 1 with histologic typing of thymic epithelial tumors]

OBJECTIVE

To study the correlation between amplification of chromosome 1 and histological typing and clinical staging of thymic epithelial tumors according to the WHO classification.

METHODS

Amplification of chromosome 1 was detected by interphase fluorescence in-situ hybridization (FISH) in 60 cases of thymic epithelial tumors, including type A thymoma (2 cases), type AB (19 cases), B1 (4 cases), B2 (14 cases), B3 (11 cases), metaplastic thymoma (2 cases), and thymic carcinoma (8 cases) and 11 samples of normal thymus.

RESULTS

Gain on chromosome 1 was found in 19 cases (31.7%) of thymic epithelial tumors, and none was detected in normal thymic tissues (P < 0.05). The positive rates of gain on chromosome 1 were statistically different among various histological subtypes of thymic epithelial tumors (P < 0.05), in which the highest rate of detection was in thymic carcinoma (6/8), the second, type B3 (6/11), followed by type A (1/2), type AB (4/19), type B2 (2/14) and type B1 (0). The positive rate of gain on chromosome 1 in type B3 had no statistical difference from thymic carcinoma (P > 0.05), but significantly higher than that in other types of thymoma (P < 0.05). In addition, the polysomy rate of chromosome 1 was significantly different among the thymic epithelial tumors at different clinical stages (P = 0.023), and that at stages III and IV was statistically higher than that in stages I and II (P = 0.003) but there was no significant difference between stage I and stage II tumors (P = 0.750).

CONCLUSIONS

Gain on chromosome 1 is more common in thymic carcinoma and type B3 thymoma than that in other subtypes of thymic epithelial tumors. Thymoma of type B3 may have different genetic features from other subtypes. Detection of gain on chromosome 1 by FISH is helpful in the differential diagnosis and prediction of prognosis in patients with thymic epithelium tumors.

Type A thymoma with generalised myasthenia gravis

Thymoma is a very rare tumour arising from thymus in the anterior mediastinum. A case of a spindle cell thymoma with Myasthenia gravis in a 34-year-old female who presented with difficulty in breathing and swallowing with shortness of breath is reported.

[Expression of CD20 in thymomas and its clinical implication]

OBJECTIVE

To study the expression of CD20 in thymomas and its clinical significance.

METHODS

One hundred and seventy-nine cases of thymoma were enrolled into the study. The histologic diagnosis was reviewed by two experienced pathologists on the basis of the 2004 WHO classification. One hundred and two cases were selected for immunohistochemical study for CD20, pancytokeratin, TdT, CD3, CD43, CD99 and S-100 protein. The cases were further categorized into two groups, according to the association with clinical evidence of myasthenia gravis. The immunostaining pattern was then statistically analyzed.

RESULTS

Amongst the 102 cases studied, 7 cases belonged to type A thymoma, 32 cases type AB thymoma, 17 cases type B1 thymoma, 15 cases type B2 thymoma, 17 cases type B3 thymoma and 14 cases thymic carcinoma. The expression rates of CD20 in neoplastic epithelial cells of type A, type AB, type B1, type B2 and type B3 thymomas and thymic carcinomas were 3/7, 84.4% (27/32), 1/17, 2/15, 0/17, 0/14, respectively. The proportions of CD20-positive lymphocytes in the background were 3/7, 18.8% (6/32), 14/17, 11/15, 11/17, 6/14, respectively. The proportion of CD20-positive intra-tumoral B lymphocytes in the group of thymomas with myasthenia gravis was 67.5% (22/40), in contrast to 35.5% (22/62) in those without myasthenia gravis.

CONCLUSIONS

The neoplastic epithelial cells in cases of type A and type AB thymoma, as well as few cases of type B1 and B2 thymoma, express CD20. The immunostain highlights the presence of oval, stellate or spindly cells. Thymomas associated with myasthenia gravis contain a significant population of CD20-positive intra-tumoral B lymphocytes. Type AB thymomas may be originated from different populations of cells, rather than a simple admixture of type A and B thymoma cells.

[Clinicopathologic analysis of 52 cases of thymic epithelial tumor]

OBJECTIVE

To study the clinicopathologic characteristics of thymic epithelial tumors and to evaluate the diagnostic reproducibility and clinical relevance of the 2004 WHO histologic classification system.

METHODS

The morphology and immunophenotype of 52 cases of thymic epithelial tumor were reviewed. The tumors were classified according to the new WHO classification system and the clinical data were analyzed.

RESULTS

Of the 52 cases studied, 45 were thymomas and 7 were thymic carcinomas. Amongst the 45 cases of thymoma, 6 (13.4%) were type A, 15 (33.3%) were type AB, 4 (8.9%) were type B1, 9 (20.0%) were type B2, 9 (20.0%) were type B3 and 2 (4.4%) were metaplastic thymoma. Amongst the 7 cases of thymic carcinoma, 6 were squamous cell carcinomas and 1 was neuroendocrine carcinoma. The commonest presentations were cough and chest pain. Some cases were incidentally discovered by routine physical examination. Thirteen cases (25.0%) of thymoma were associated with myasthenia gravis. CT scan showed that 49 cases (94.2%) were located in the anterior mediastinum. All cases of type A, AB and B1 thymoma and most cases of B2 thymoma appeared as well-defined homogeneous mass, whereas a few cases of type B2 thymoma and most cases of type B3 thymoma and thymic carcinoma were poorly demarcated and heterogeneous. According to Masaoka staging system, 20 cases (41.7%) belonged to stage I, 15 cases (31.3%) stage II, 11 cases (22.9%) stage III and 2 cases (4.1%) stage IV. The histologic subtypes of thymic epithelial tumors significantly correlated with the clinical stages (chi(2) = 32.5, P < 0.01).

CONCLUSIONS

The 2004 revision of WHO histologic classification system for thymic epithelial tumors shows a high degree of reproducibility. Correlation with the radiologic, clinical and prognostic parameters is helpful in determining the management strategy for individual patients.

[Histologic subtyping and prognosis of thymoma: a study of 108 cases]

OBJECTIVE

To study the prognostic and clinical relevance of histologic subtyping of thymoma according to the World Health Organization (WHO) classification.

METHODS

The clinicopathologic features of 108 patients with thymoma removed surgically were retrospectively reviewed. The histologic diagnosis of the tumors was made on the basis of 2004 WHO classification by two experienced pathologists. The correlation between Masaoka tumor stage, WHO histologic subtype, completeness of resection, presence of myasthenia gravis, other clinical parameters (including age, gender and tumor size) and survival was studied.

RESULTS

According to WHO classification, there were 7 cases (6.5%) of type A thymoma, 19 cases (17.6%) of type AB thymoma, 23 cases (21.3%) of type B1 thymoma, 19 cases (17.6%) of type B2 thymoma, 27 cases (25.0%) of type B3 thymoma and 13 cases (12.0%) of type C thymoma. According to Masaoka tumor staging, 36 cases (33.3%) were in stage I, 34 cases (31.5%) in stage II, 27 cases (25.0%) in stage III and 11 cases (10.2%) in stage IV(a). The association between histologic subtype and Masaoka tumor stage was statistically significant (P = 0.000). The 5-year survival rates of type A, AB, B1, B2 and B3 thymoma cases were 100%, 100%, 93%, 83% and 43%, respectively; while the 10-year survival rates were 100%, 100%, 81%, 70% and 33%, respectively. The median survival time of type C thymoma was 62.5 months. Type B2 and B3 thymoma cases had an intermediate prognostic ranking in comparison with type C thymoma and other groups (P = 0.000). The 5-year survival rates of tumors in stage I, II and III were 100%, 77% and 54%, respectively; while the 10-year survival rates were 100%, 70% and 27%, respectively. The median survival time of patients in stage IV(a) was 14.0 months. Masaoka tumor stage was highly significant in predicting survival of patients (P = 0.000). On multivariate analysis, Masaoka tumor stage was an independent predictive factor for survival (P = 0.027). On the other hand, the WHO subtype (type A to B1 versus type B2 to B3 versus type C) and completeness of resection could predict the tumor-related survival.

CONCLUSIONS

The Masaoka tumor stage is the single most important prognostic factor of thymoma. The WHO histologic subtype and completeness of resection affect mainly the post-operative survival. The classification of thymoma may also reflect the clinical behavior of the tumor. Type A, AB and B1 thymomas belong to the low-risk group, while type B2 and B3 thymomas have an intermediate prognostic ranking. Type C thymoma carries the worst prognosis.

Thymome - Inzidenz, Klassifikation und Therapie

Thymomas are a rare tumor entity. However, they represent 50 % of all tumors of the anterior mediastinum. There are no specific early symptoms. Overall in 10 - 15 % of patients with myasthenia gravis a thymoma is evident. Two major classifications are relevant in clinical practise: the Masaoka-classification and the WHO-classification. For their clinical and prognostic significance both classifications should be used for patients with thymomas. Additional, only resection status (RO) is known as a significant prognostic factor. Thymomas are compulsory malignant tumors. Distant metastasis is found as well as local recurrence in all stages of the disease. The 5-year-mortality rate constitutes about 80 %, not meaning any healing because local recurrences occur as late as five years after surgery. 60 % of all patients die from tumor-independent reasons making a clear prognostic statement difficult. Surgical treatment remains the gold standard and must be performed whenever possible. The most common approach is a median sternotomy. When dealing with a thymuscarcinoma, radical lymph node dissection is advisable. With respect of treatment only adjuvant radiation can possibly improve long term survival and reduces local recurrence rates for incomplete resected patients. There is no evidence for a benefit in patients with thymoma receiving adjuvant chemotherapy. A neo-adjuvant chemotherapy in combination with an adjuvant radiotherapy improves outcome after surgical resection in stage III and IV and goes along with better survival rates. Larger studies have not been performed so far. A multimodal therapy strategy is advised when dealing with thymomas in stage III and IV.

Clinical value of the WHO classification system of thymoma

Since the World Health Organization (WHO) histologic classification system for thymoma was introduced in 1999, several centers have published results using this system. This review of the published experience with the WHO system examines whether the classification is reproducible, whether the WHO system defines clinically distinct patient groups, assesses the independent prognostic value of the WHO type by multivariate analysis, and discusses the impact of the WHO system on clinical management decisions.

[Thymoma and thymic carcinoma--review of literature and clinical characteristics based on the Polish Paediatric Solid Tumours Study Group experience]

Thymomas and thymic carcinomas are rare neoplasms derived from the epithelial tissue of thymus, very infrequently developing in young adults and children. The estimation of thymomas' invasiveness has been the matter of discussion for many years reflected by numerous clinical and histological classifications. In 1999 the WHO classification was created, joining all the most important issues present in previously used systems. It is believed that histological structure is the most important prognostic factor in thymic carcinomas while in less aggressive types of thymomas the clinical stages influence the outcome. Staging of thymomas is most commonly based on the Masoka classification. Independent evaluation of the stage and histological aggressiveness are necessary to predict the clinical course and outcome in thymomas. Thus the term 'malignant thymoma' has been replaced by 'invasive thymoma' in clinical practice. The treatment strategy depends on the clinical stages of thymoma. Complete resection of the tumour is the treatment of choice with supplementing radiotherapy in more advanced clinical stages. Chemotherapy in invasive thymomas has been reported to play an increasingly important role as induction, supplementing and palliative therapy. It has been proved that combined treatment improves the outcome in invasive thymomas, especially in thymic carcinomas. This paper reviews the literature data concerning the histology, clinical issues and treatment of thymomas and thymic carcinomas. The clinical data on nine children with thymic carcinomas treated between 1992 and 2006 in the Polish oncological and surgical centres were also analysed and presented. Based on multicentre data we were able to conclude the following: 1. Thymic carcinomas in children are very rare and that is why early diagnosis is often difficult. 2. At diagnosis most cases are already inoperable, which results in poorer prognosis. 3. Complex adjuvant chemo- and radiotherapy in childhood thymic carcinomas seem to prolong overall survival. 4. Further detailed analysis in all the cases of thymic carcinomas in children is recommended in order to estimate the optimal strategy of treatment.

Expression of p63 in thymomas and normal thymus

The p63 gene, a member of the p53 family, is an epithelial marker expressed in embryonic ectoderm, breast myoepithelium, prostate, oral epithelium, epidermis, and urothelium. The DeltaN-p63 isoforms of p63, which are believed to behave as oncogenes, are expressed in squamous cell carcinoma, basal cell carcinoma, and transitional cell carcinoma. Only a few authors have looked for p63 expression in thymomas and normal thymus. We, therefore, thought of undergoing such a search by taking advantage of our archival material. We studied 66 cases of thymoma (1 type A, 8 type AB, 12 type B1, 19 type B2, 12 type B3, and 14 type C/thymic carcinoma) and 10 specimens of normal human thymus arranged in tissue microarrays. All thymomas (including thymic carcinomas) were positive for p63 regardless of type. Most of the epithelial cells of the normal thymus were also positive for this marker.

Outcome of surgical treatment for recurrent thymic epithelial tumors with reference to world health organization histologic classification system

BACKGROUND AND OBJECTIVES

The aim of this study was to clarify the significance of surgical treatment for recurrent thymic epithelial tumors with reference to the World Health Organization (WHO) histological classification system.

PATIENTS

Among 67 patients with tumor recurrence, 22 underwent a re-resection. There were 1 patient with a type AB tumor, 5 with type B1 tumors, 10 with type B2 tumors, 5 with type B3 tumors, and 1 with a carcinoma.

RESULTS

The 10-year survival rate following the initial resection was 70% in patients who underwent a re-resection and 35% in those who did not. The average intervals from the initial resection to re-resection were 10.3, 7.8, 6.0, 2.4, and 2.6 years for patients with type AB, B1, B2, B3 tumors, and carcinoma, respectively. The patient with a type AB tumor was alive at 2.4 years after re-resection, 12.7 years after the initial resection. The 5-year survival rates following re-resection in the patients with type B1, B2, and B3 tumors were 100, 56, and 60, respectively. The patient with a carcinoma died as a result of the tumor 2 years after re-resection.

CONCLUSION

WHO histological classification indicates the outcome of surgical treatment for recurrent thymic epithelial tumors.

Microscopic thymoma

Microscopic thymoma was first described in 1976 and remains in the latest WHO classification (2004). It defines an epithelial proliferation, with <1 mm in diameter, usually multifocal, that preferentially occurs in patients suffering from myasthenia gravis without a macroscopically evident tumour. A series of 87 thymectomies realised in myasthenic patients between 1992 and 2005 was reviewed. We describe three cases of microscopic thymoma: two male and one female with an average age of 41.6 years. All patients suffered from myasthenia gravis positive for acetylcholine receptor antibodies without any tumour detectable on chest tomodensitometric examination. Thymectomy was performed in all cases, enlarged to the mediastinal fat in one. Microscopic examination revealed three type-A microscopic thymoma, one multifocal, associated with lymphoid hyperplasia in two cases. After surgery, all patients had clinically improved. In summary, chest computed tomography is unable to detect microscopic thymoma. Histological examination of the entire specimen is indicated after thymectomy in myasthenic patients even if the thymus appears normal on radiographic examination. The role of microscopic thymoma as a predictor of clinical thymoma has not been proven.

Corpuscular thymoma: Entity or variant of organotypical thymomas WHO B2/B3?

Hassall's corpuscles are regular structures in the medulla of the normal thymus and in non-neoplastic thymic conditions, e.g. in multilocular thymic cysts. In thymomas, however, they are inconsistently found, and are believed to indicate medullary differentiation of WHO type B1-3 thymomas. We present five organotypical thymomas resembling WHO type B2 and B3 thymomas, but with an abundance of Hassall's corpuscles. We wonder whether this exceedingly rare observation might herald a distinct entity. Four tumors were asymptomatic, incidental findings and of low Masaoka stage (I or II) [20] . One patient suffered from myasthenia gravis which disappeared upon surgical removal of the thymus, while all other patients had no concomitant autoimmune disease. Two patients had a relapse-free follow-up of 12 and 2 years, respectively, upon curative surgery, and another tumor was an autopsy finding; follow-up data of two more recent cases was not yet available. The neoplastic epithelium other than Hassall's corpuscles was arranged either in a cortical type B2 pattern or in type B3 solid cords. In all examples, there was cyst formation, inflammatory reaction and repair, indicative of a long-standing condition. Immature T cells were present in all instances. "Corpuscular thymomas" morphologically resemble WHO type B2 and B3 thymomas, but appear biologically indolent and are rarely associated with myasthenia gravis. Whether they qualify for a separate entity has to be proven by larger series, including genetic studies.

Problem areas and inconsistencies in the WHO classification of thymoma

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

Recurrent thymoma: radiological (CT and FDG-PET) and histological (WHO criteria) features

A 66-year-old man, who had undergone surgical resection of a primary noninvasive thymoma (type B1) in the right anterolateral mediastinum 6 years before, underwent follow-up computed tomography (CT) scanning. The CT scan revealed a few nodules located at the posterior portion of the right thoracic base and just behind the right upper anterior chest wall. Subsequent fluorodeoxyglucose positron emission tomography (FDG-PET) scans showed multiple foci with high [standard uptake value (SUV) 4.3] and low (SUV 2.6) FDG uptake in the right lower posterior area and right upper anterior area of the chest, respectively. The fusion image of the CT and FDG-PET scans demonstrated that the areas of the increased FDG uptake corresponded to those of the nodules on the CT scan. All of the nodules were successfully removed surgically, and the histological features of the nodules indicated that they were type B1 or types B1 plus B2. We regarded the nodule located just behind the right upper anterior chest wall as a type B1 thymoma, whereas those in the posterior area of the right thoracic base as combined thymomas of types B1 plus B2. Our limited experience suggests that the degree of FDG uptake is a reflection of the subtype according to the World Health Organization (WHO) criteria. Furthermore, we showed the role of FDG-PET in the accurate assessment of recurrent thymoma and its therapeutic strategy.

Middle mediastinal thymoma of unusual pathologic type

Among the many sites of ectopic thymoma development, the middle mediastinum is the rarest in the English language literature we found only two case reports. We present a case of 69-year-old woman with slow-growing, ectopic middle mediastinum thymoma of an very unusual histological type, neither classified in the Müller-Hermelink nor the World Health Organization (WHO) classification.

Thymoma classification: current status and future trends

The classification of thymic epithelial neoplasms has been a controversial topic for many years. Recent advances in diagnostic methods and renewed interest in the biology of these tumors has led to efforts by investigators to shed new light on their biologic behavior and to offer novel perspectives on these unusual neoplasms. Several new classification schemes have been proposed, including the new World Health Organization schema for the histologic typing of tumors of the thymus. We review the current status of thymoma classification and comment on problem areas and future trends that may offer a more pragmatic approach to these tumors.

Diagnosis of thymoma

The diagnosis of thymic epithelial neoplasm has been a topic of controversy for many years. Reasons for this include the lack of predictive value associated with the morphology of these tumours and the multiplicity of classification schemes and terminologies proposed over the years. Recently, a new classification schema was introduced by the World Health Organization (WHO) in an attempt to standardise nomenclature and facilitate the diagnosis of primary thymic epithelial neoplasms. This schema, although not originally intended as a new histological classification, but rather as a means for translating equivalent terms from the various existing classifications, has represented a major step forward in this direction. However, problems still exist with the WHO schema, particularly with some of the criteria for the various histological subtypes as well as with issues of interobserver reproducibility. For this reason, we favour using a much more simplified approach to the morphological classification of thymic epithelial neoplasms. A personal approach to the morphological diagnosis of thymoma is described, with a brief explanation for the rationale for simplifying the existing diagnostic categories.

[A resected case of sclerosing thymoma]

An asymptomatic 47-year-old man was found to have an anterior mediastinal nodule on an annual chest X-ray. Chest CT showed a 2cm nodule in the left anterior mediastinum. Because thymoma was suspected, total thymectomy was performed. Histologically, the greater part of the nodule was composed of hyalinized fibrous tissues and there was a scattered, small aggregation of spindle to oval cells, showing positive for AE 1/3. Therefore this nodule was diagnosed as sclerosing thymoma, which is a subtype of thymoma first reported in 1994. Since few reports of this disease have been made so far, needless to say its clinical features or pathogenesis, even its very existence is not well known. Sclerosing thymoma should be taken into account, when only fibrous tissues are obtained by biopsy in patients with anterior mediastinal tumors.

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.

Thymomas: clinical-pathological correlations

AIM

Since World Health Organization (WHO) histologic typing of tumors of the thymus publication in 1999 only a few studies correlated this classification with the clinical features of the patients. We present the results of a retrospective analysis on patients, operated on for a thymoma, whose specimens were available, to compare the WHO thymoma histologic classification to the clinical behavior of the tumors.

METHODS

The specimens of 69 patients, who underwent surgical treatment between 1983 and 1998, were analyzed, comparing the clinical features of the patients and the hystological typing of the neoplasm, according to the WHO classification. A survival analysis of clinical and pathological prognostic factors was carried out.

RESULTS

The incidence of thymus-related syndrome was related to the histological subtype and increases progressively from A to B3, while in C subtype the incidence was nihl. With a mean follow-up of 108 months (range 54-239 months), we experienced 6 intrathoracic recurrencies, 3 of those were intrapleuric and 3 mediastinal. At the last follow-up, 52 patients were alive; 1 with disease. Five deaths were related to the tumor (2 mediastinal and 3 intrapleuric relapses). Actuarial five-year and ten-year survival was 95% and 88.9%. Because of the absence of deaths related to thymomas in most samples it was not possible to perform a comparison among different histological types and different clinical stages.

CONCLUSIONS

The WHO histologic classification seems to correlate with the incidence of thymus related syndromes and the clinical stage of Masaoka. Despite the higher incidence of recurrences in type B3 and C thymoma the WHO classification did not prove to be a prognostic factor.

[Correlation between MMP-2 activation and MT1-MMP mRNA expression in thymic epithelial tumors]

OBJECTIVE

To study the relationship between activation of pro-MMP-2 and expression of matrix metalloproteinases (MMP)-2, MT1-MMP and tissue inhibitor of metalloproteinases (TIMP)-2 mRNA in thymoma and thymic carcinoma; and to study the molecular mechanism of invasion and metastasis of thymic epithelial tumors.

METHODS

Fresh tissue specimens of thymoma, thymic carcinoma and normal thymus were included. The mRNA expression of MMP-2, MT1-MMP and TIMP-2 were analyzed by real-time reverse transcription polymerase chain reaction. The pro-MMP-2 activation ratio and its localization were determined by gelatin zymography and film in-situ gelatin-Zymography, respectively. Correlation of mRNA expression of MMP-2, MT1-MMP and TIMP-2 was investigated in tumors with different histological subtypes and clinical stages.

RESULTS

There were no significant differences in the expressions of MMP-2, MT1-MMP and TIMP-2 mRNA between I and II stage or III and IV stage thymomas (P > 0.05). However, significant differences of the expressions were observed between three tumor groups: I-II stage, III-IV stage and thymic carcinomas (P < 0.005), and between three histological subtypes: AB-B1 (lymphocyte-rich and mixed types), B2-B3 (cortical and predominantly polygonal cells types) and thymic carcinomas (P < 0.05). Expression levels of MT1-MMP and TIMP-2 mRNA were correlated with pro-MMP-2 activation ratio (Spearman rank correlation: r = 0.7235, r = 0.7647, P < 0.005). The expression of MMP-9 did not show significant differences between thymomas and thymic carcinomas.

CONCLUSIONS

MMP-2, MT1-MMP and TIMP-2 mRNA expression levels are correlated with the histologic subtypes and clinical stages of thymoma. The mRNA expressions of MT1-MMP and TIMP-2 are correlated with the activation ratio of pro-MMP-2. It is speculated that upregulation of MT1-MMP gene expression may induce an activation of pro-MMP-2 through TIMP-2.

Clinical usefulness of the WHO histological classification of thymoma

PURPOSE

Rosai et al. published the World Health Organization (WHO) classification of thymic epithelial tumors in 1999, and its clinical usefulness seems to be established. It is our purpose to find the clinically relevant diagnostic points in the WHO Histological Classification of Thymoma.

METHODS

Thymomas surgically removed from 100 consecutive patients at Juntendo University Hospital between October 1983 and February 2002 were classified according to the WHO histological classification. We assessed overall survival and recurrence-free rate calculated for each tumor type in the WHO classification compared with those of tumors classified by the Masaoka system.

RESULTS

The thymic epithelial tumors in this series comprised 10 type A, 15 type AB, 18 type B1, 21 type B2, 33 type B3, and 3 type C tumors according to the WHO classification. Based on the Masaoka system, the disease was stage I in 53 patients, stage II in 30, stage III in 15, and stage IV in 2. The 15-year recurrence-free rate was 100% for type A, AB and B1, while the rates for types B2 and B3 were 66.7% and 54.5%, respectively. The 10-year recurrence-free rate was 66.7% for type C. The 15-year recurrence-free rate of the 64 patients with type A, AB, B1, and B2 thymomas was significantly higher from that of the 33 patients with type B3 thymoma (p=0.0026).

CONCLUSION

When using the WHO classification, it is critical to distinguish type B3 thymoma from other tumor types.

[Correlations of novel histological classification of 82 thymoma patients to their clinical characteristics and prognosis]

BACKGROUND & OBJECTIVE

The World Health Organization (WHO) histological classification of thymoma was published in 1999. This study was to investigate the correlations of WHO histological classification of thymoma to its clinical characteristics and prognosis.

METHODS

Records of 82 thymoma patients treated with surgery were reviewed retrospectively. Histological diagnosis based on WHO classification system was made by an experienced pathologist. The correlations of WHO histological classification of thymoma to its clinical characteristics and prognosis were analyzed.

RESULTS

Of the 82 cases, 5 (6.1%) were type A, 21 (25.6%) were type AB, 14 (17.1%) were type B1, 12 (14.6%) were type B2, 14 (17.1%) were type B3, and 16 (19.5%) were type C; according to Masaoka clinical staging system, 29 (35.4%) were in stage I, 13 (15.8%) in stage II , 32 (39%) in stage III , and 8 (9.8%) in stage IVa. The histological subtype of thymoma was significantly correlated with clinical stage (chi2 = 47.29, P < 0.001) and tumor invasive degree (chi2 = 30.78, P < 0.001). Complete resection rate was significantly higher in patients with type A, AB, B1 or B2 tumors than in patients with type B3 or C tumors (84.6% vs. 50.0%, chi2 = 11.29, P = 0.002). The 5-year survival rates of patients with stage I, II, III , and IVa were 100%, 100%, 69.5%, and 37.5%, respectively; the 10-57.1%, year survival rates were 88.1%, 47.5, and 0, respectively. The difference of survival rates among different clinical stages (log-rank = 40.31, P < 0.001) and histological subtypes (log-rank = 16.0, P = 0.007) were significant.

CONCLUSION

To some extent, the WHO histological classification reflects the biological behavior and clinical characteristics of thymoma, and may be helpful in diagnosing and treating thymoma.

Immunohistochemical staining of hedgehog pathway-related proteins in human thymomas

The thymus plays an essential role in the maturing of progenitor cells to functional T cells. Recent studies suggest that the Hedgehog (Hh) signaling pathway contributes to this differentiation process. However, there is limited information concerning the expression of Hh pathway-related proteins (Hh proteins) in the human thymus. The staining of Hh proteins in the thymic epithelium of 26 surgically resected thymoma tissues was examined by immunohistochemistry. The staining of sonic Hh (Shh) correlated relatively well with the World Health Organization histological classification of thymoma. The higher the grade, the fainter the staining. However, no significant difference in Shh staining was found between normal and neoplastic epithelia. Interestingly, Gli1 staining in thymomas was significantly greater than that in normal thymus (p < 0.0001). Thus, some members of the Hh signaling pathway may contribute to the development of thymoma.

World Health Organization histologic classification: An independent prognostic factor in resected thymomas

The histologic classification of thymoma remained controversial since 1999, when the World Health Organization (WHO) Consensus Committee published a histologic typing system for tumours of thymus. Clinical features, postoperative relapsing rates, and survival of patients with thymoma were evaluated with reference to the WHO histologic classification, based on a series of 178 patients, submitted to surgery between 1988 and 2000. There were 21 type A, 49 type AB, 45 type B1, 50 type B2 and 13 type B3 tumours. The invasiveness of tumours was 23.8%, 51%, 73.3%, 82% and 100% for types A, AB, B1, B2 and B3 tumours, respectively. The frequency of invasion of the great vessels increased according to the tumour type in the order A (0%), AB (4%), B1 (6.6%), B2 (22%), and B3 (23%). The 10-year disease-free survival was 95%, 90%, 85%, 71% and 40% for types A, AB, B1, B2 and B3, respectively. According to the Masaoka staging system, the disease-free survival rates were 94%, 88% and 66% for stages I, II and III, respectively, at 10 years. No stage IVA thymomas reached 10 years follow-up. Overall survival at 10 years were 88% and 25% when complete and incomplete resection were considered. By multivariate analysis, Masaoka staging system, WHO histologic classification and complete resection were significant independent prognostic factors, whereas age- and sex-associated myasthenia gravis were not. The present study demonstrated the World Health Organization histologic classification a good prognostic factor, such as completeness of surgical resection and Masaoka staging system.

Stage IV Thymic Carcinoma: A Study of 20 Patients

BACKGROUND

This study was performed to investigate the clinical factors, tumor characteristics, treatment approach, and prognosis of patients with Stage IV thymic carcinoma (WHO type C).

METHODS

The records of 20 patients with histologically confirmed thymic carcinoma treated between 1988 and 2002 at the Division of Oncology at Taipei Veterans General Hospital were reviewed.

RESULTS

Therapy consisted of surgical debulking, adjuvant radiotherapy, and chemotherapy in six patients (30%), surgical debulking with adjuvant chemotherapy in two patients (10%), surgical debulking with adjuvant radiotherapy in one patient (5%), radiotherapy with adjuvant chemotherapy in eight patients (40%), and chemotherapy alone in three patients (15%). After a median follow-up of 22 months (range, 5-72 months), three patients (15%) were alive. Eighteen patients (90%) experienced disease recurrence after a median of 9 months (range, 2-41 months); 12 (66%) of these patients initially had stage IVa disease, and 6 (33%) had stage IV b disease. Five patients had an undifferentiated type of histology. The median time to progression was 5 months. However, none of these patients was able to receive salvage therapy due to their poor performance status. For those patients with a lymphoepithelioma-like histology, the median survival was 36 months; there was tumor recurrence in five patients and they all received salvage chemotherapy. The median survival time for these five patients was 51 months. For patients with squamous cell type, the median time to progression was 10 months. Five patients received salvage chemotherapy and the median survival was 28 months. There was a significant difference (P < 0.0001) in the median survival between those who received chemotherapy (18 months) after tumor relapse and those who did not (1 month).

CONCLUSIONS

Our results indicate that multidisciplinary treatment, including surgery, radiotherapy, and chemotherapy, is beneficial in treating primary thymic carcinoma. Chemotherapy plays an important role in both primary and relapsed stage IV thymic carcinoma in terms of prolonging the disease-free survival and median survival of patients with lymphoepithelioma-like or squamous cell histology types. For patients with an undifferentiated histology, multidisciplinary treatment or chemotherapy might not be helpful in either primary or relapsed stage IV thymic carcinoma.

Thymoma and Thymic Carcinoma: An Update of the WHO Classification 2004

When dealing with tumors of the thymus and mediastinum, both the surgeon and the pathologist are confronted with a vast variety of different pathohistologic entities, among which epithelial tumors, namely thymomas and thymic carcinomas, are the most frequent. Intimate knowledge of the different entities and their anticipated clinical outcome is required to meet diagnostic and therapeutic challenges. We herein briefly update the reader with the most important new changes in the 2004 WHO classification of tumors of the thymus and to important new trends in the treatment of some of these tumors.

Thymoma

Thymoma is a rare epithelial tumor of the thymus, but the most common malignancy in the anterior mediastinum. A unique feature is its association with paraneoplastic syndromes, in particular myasthenia gravis. According to the WHO classification 6 histologic types of thymic epithelial tumors can be discriminated. Tumor stage according to MASAOKA is the most important prognostic factor. Non-invasive tumors (stage I) are usually completely resected and no further therapy is warranted. For incompletely resected tumors and locally advanced invasive thymomas (stage Ill-IV) postoperative radiotherapy with 50-60 Gy is advisable. Chemotherapy, preferably with Cisplatinum, is indicated with inoperable thymomas or metastatic disease. In general thymomas have a fair prognosis even in advanced stage. Long term follow-up is mandatory up to 10 years.

Thymus and thymoma: what's new?

The thymus is the prototype of lymphoid and epithelial organ that consists of lymphoid and epithelial cells. In spite of remarkable progresses made in the field of the immunohistochemical characterisation of the thymus parenchyma, the diagnosis of thymoma largely depends on the interpretation of conventional morphologic aspects. Histogenesis of this organ is a multi-step process, and many stages reproduce lesions and changes found in the adult thymus. The normal structure and its variants are extremely helpful to differentiate normal from pathologic aspects. Particular aspects of the thymus structures were shown in myasthenia gravis, despite the behaviour of thymoma in these patients is not clearly understood. Authors performed a detailed description of the conventional pathology of the thymoma, based on the new classifications, recently adopted. The immunohistochemical profile could be helpful in the diagnosis of many cases, and also seems to be useful in prediction of invasion that is the most important criterion in prognosis.

[Our strategy in the therapy of myasthenia gravis]

Surgical treatment of myasthenia gravis has at the 3 (rd) Department of Surgery, 1 (st) Medicine Faculty of Charles University in Prague a multiyear tradition which has originated in the 60's of the 20 (th) century. Since that time we carried out over 1 000 operations on the thymus, especially thymectomy for myasthenia gravis (MG) and with lesser frequency for thymomas. Thymectomy combined with exenteration of fatty tissue from the front mediastinum belongs to basic MG surgery. According to our experience an optimal approach to the thymus is given by partial sternotomy. A jugular approach is not regarded as enough radical. Videothoracoscopic approach and operation are possible but take more time, however they are the method of choice at some workplaces. The combined conservative and surgical treatment brings in 80 % of the cases an obvious improvement or deletion of the symptoms of the disease.