Thymoma: a clinical and pathological study of 65 cases

Thymic epithelial tumours: histopathological classification and differential diagnosis

The epithelial and lymphoid compartments of the thymus can give rise to a wide variety of tumours, including thymomas, thymic carcinomas, lymphoreticular proliferations, germ cell tumours, and sarcomas. While some of these have close similarity to their counterparts in other organs, both in terms of histology and immunohistochemistry, as well as molecular features, others are unique to the thymus. The epithelial tumours, which can develop in the thymus, will be discussed in this review, with a particular emphasis on resolving differential diagnosis by means of morphology, immunohistochemical profiles, and molecular diagnostics.

On the Histologic Classification of Thymoma

The classification of thymoma continues to be a source of controversy in pathology. The difficulties in histologic classification are evident from the number of proposals that have been offered over the years, as well as for the continuous changes and modifications introduced by the World Health Organization to their classification system over the past 20 years. We analyze here some of the issues involved in the classification of these tumors and the difficulties encountered for practicing pathologists in deciphering the "letters and numbers" system devised by the World Health Organization. We would like to propose an alternate approach to thymoma histologic classification that capitalizes on the basic observation of their cytologic features and incorporates the pattern of growth resulting from the interplay of the tumor cells with other cellular constituents as a secondary characteristic. The proposed histologic classification provides a simplified, reproducible means of histologically categorizing these tumors and can be easily understood by most practicing pathologists in simple and clear morphologic terms.

Clinicodemographic characteristics and prognostic role of myasthenia gravis in thymoma: Experience from a Saudi population

OBJECTIVES

The objectives of the study were to determine the clinicodemographic characteristics and the prognostic role of myasthenia gravis (MG) in thymoma.

METHODS

The records of patients who underwent surgical resection of thymoma at King Faisal Specialist Hospital and Research Center in the past 23 years were reviewed. Seventy thymoma patients were finally included and were then categorized based on MG status into the MG group (39 patients) and the non-MG group (31 patients). Collected data included patients' demographic characteristics, tumor characteristics, and postoperative clinical outcomes. All analyses were conducted using SPSS. The comparison between both groups was tested using the Student t-test and Chi-square test for continuous and categorical variables, respectively. A P = 0.05 or less indicated statistical significance.

RESULTS

Patients' age ranged from 11 to 76 years, and female predominance was observed (55.7%). Compared to the non-MG group, no difference in patients' gender was observed (P = 0.058); however, MG patients had a younger age (39.30 vs. 48.77, P = 0.0095). No difference was noted between both groups based on the World Health Organization classification (P = 0.398), but MG patients tended to present with less-advanced tumors based on the TNM classification (P = 0.039) and lower stage based on the MASAOKA staging system (P = 0.017). No significant change in tumor size (P = 0.077), resectability (P = 0.507), and adjuvant therapy (P = 0.075) were observed. MG was not significantly associated with postoperative complications, morbidity, or mortality. However, it exhibited a prognostic protective role in terms of lower recurrence (2.56% vs. 35.48%, P = 0.0001) and longer survival duration (18.62 vs. 10.21 years, P < 0.001) as compared to non-MG patients.

CONCLUSIONS

MG occurrence in thymoma patients is more likely to occur at a younger age, higher TNM classification, and advanced MASAOKA stage. Although no significant association was noted between MG and complications and mortality, MG exhibited a protective role in thymoma by providing a lower recurrence rate and longer survival duration.

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.

Thymoma: Challenges and Pitfalls in Biopsy Interpretation

The interpretation of biopsy specimens in the diagnosis of thymoma is a subject that is generally not addressed in the literature. Even though the diagnosis of thymoma may seem to be an easy step in the assessment of these tumors, in reality, it is the biopsy specimen interpretation that will be use to determine course of action in any particular patient. It may determine whether a patient is a surgical candidate or on the contrary whether a patient may be benefited the most by medical therapy. In addition, there may be conditions in which all that is required is surgical resection without any further treatment, and that the evaluation of those conditions does not necessarily required the careful pathologic staging that thymomas need. In addition, it is important to highlight that in small biopsies, there are limitations not only in terms of the cellularity and other features that may not be present in such biopsy but also the limitation in term of immunohistochemical interpretation. Herein we have attempted to highlight numerous tumoral conditions that are frequently encountered in the daily practice of mediastinal pathology, some of them pose significant problems in separating them from thymomas. Needles to say, the entire spectrum of mediastinal pathology that may at any given time mimic thymoma is well beyond the scope of this review. Furthermore, we also herein emphasize the need for proper clinical and radiologic information and correlation in order to lead to a better interpretation of the biopsy specimen. The emphasis in this review is on thymoma and their possible pitfall and shortcomings while evaluating small biopsy specimens.

Adrenal crisis and acute exacerbation of interstitial lung disease after thymoma needle biopsy: a case report and literature review

Thymoma is the most common paraneoplastic syndrome–associated tumor. It is related to a variety of autoimmune diseases including myasthenia gravis, systemic lupus erythematosus, and hypogammaglobulinemia. Only a few reports of thymoma associated with Addison’s disease have been reported to date. Herein, we report a novel case of thymoma complicated with autoimmune Addison’s disease and interstitial lung disease. The patient developed adrenal crisis with persistent hypotensive shock and heart block after needle biopsy. Acute exacerbation of the interstitial lung disease was also observed, accompanied by severe respiratory failure. After treatment with glucocorticoids, somatostatin, and temporary pacemaker implantation, the patient’s condition improved, and the thymoma had shrunk in size. Finally, he underwent transsternal extended thymectomy and lymph node dissection. Hydrocortisone was given intravenously before surgery, on the operation day and after the surgery. The operation was uneventful, and no hypotension or fever occurred. Cortisol and ACTH were still obviously abnormal at 1 month post-surgery. The clinical manifestations of Addison’s disease and interstitial lung disease are hidden and can be easily overlooked. However, in the postoperative period, Addison’s disease can lead to adrenal crisis developing, which can progress to life-threatening shock, arrhythmia, and acute respiratory failure. Therefore, clinicians should be aware of this phenomenon and consider a regimen combining proactive glucocorticoid replacement therapy with somatostatin to preserve the life of such patients.

Myasthenia Gravis Is Not an Independent Prognostic Factor of Thymoma: Results of a Propensity Score Matching Trial of 470 Patients

Objective

The association between the prognosis of thymoma and MG remains controversial. Differences in clinical characteristics and treatments between patients with and without MG may affect the findings of those studies. We designed this propensity score matching trial to investigate whether MG is an independent prognostic predictor in thymoma.

Methods

Patients with pathologically diagnosed thymoma and MG were enrolled in the MG group. Moreover, the propensity score matching method was used to select patients who were diagnosed with thymoma without MG from the database of two participating centers. Matched factors included sex, age, Masaoka stage, pathological subtypes, and treatments. Matched patients were enrolled in the non-MG group. Chi-squared test was used to compare the characteristics of the two groups. Overall survival, local-regional relapse-free survival, distant metastasis-free survival, progression-free survival, and cancer-specific survival were calculated from the diagnosis of thymoma using the Kaplan–Meier method.

Results

Between April 1992 and October 2018, 235 patients each were enrolled in the MG and non-MG groups (1:1 ratio). The median ages of patients in the MG and non-MG groups were 46 years old. The World Health Organization pathological subtypes were well balanced between the two groups (B2 + B3: MG vs. non-MG group, 63.0 vs. 63.4%, p = 0.924). Most patients in both groups had Masaoka stages I–III (MG vs. non-MG group, 90.2 vs. 91.5%, p = 0.631). R0 resections were performed in 86.8 and 90.2% of the MG and non-MG groups, respectively (p = 0.247). The median follow-up time of the two groups was 70.00 months (MG vs. non-MG group, 73.63 months vs. 68.00 months). Five-year overall survivals were 92.5 and 90.3%, 8-year overall survivals were 84.2 and 84.2%, and 10-year overall survivals were 80.2 and 81.4% (p = 0.632) in the MG and non-MG groups, respectively. No differences were found in the progression-free survival, distant metastasis-free survival, and local-regional relapse-free survival between the two groups.

Conclusion

MG is not an independent or direct prognostic factor of thymoma, although it might be helpful in diagnosis thymoma at an early stage, leading indirectly to better prognosis.

Molecular profiling of thymoma with myasthenia gravis: Risk factors of developing myasthenia gravis in thymoma patients

OBJECTIVE

Thymoma is a rare epithelial tumor arising from the thymus in the anterior mediastinum. Nearly 50% of patients with thymoma develop myasthenia gravis, which is an indication of a poor long-term prognosis. Here, we identified specific and effective molecular markers for predicting in the development of myasthenia gravis patients with thymoma.

MATERIAL AND METHODS

We investigated molecular profiling based on RNA-sequencing (RNA-seq) for myasthenia gravis development in patients with thymoma. RNA was extracted from 34 patients with thymoma, 16 of whom had myasthenic and 18 of whom did not, and transcriptome profiles were analyzed through next-generation sequencing.

RESULTS

We discovered 140 differential expressed genes associated with myasthenia gravis in thymoma patients. The four genes, hypoxia-inducible factor 3 alpha (HIF3A), insulin-like growth factor-binding protein 1, pyruvate dehydrogenase kinase, and Krüppel-like factor 15 were differentially expressed in patients with thymoma who has myasthenia gravis and were validated by quantitative polymerase chain reaction. HIF3A expression was significantly higher in patients with myasthenia gravis than in those without.

CONCLUSION

HIF3A is aberrantly expressed in patient with thymoma who has myasthenia gravis and may be involved in the development of myasthenia gravis in thymoma patient.

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.

Efficacy of computed tomography features in predicting stage III thymic tumors

Accurate assessment of the invasion of intrathoracic structures by stage III thymic tumors assists their appropriate management. The present study aimed to evaluate the efficacy of computed tomography (CT) features for the prediction of stage III thymoma invasion. The pre-operative CT images of 66 patients with confirmed stage III thymic tumors were reviewed retrospectively. The CT features of invasion into the mediastinal pleura, lungs, pericardium and great vessels were analyzed, and their sensitivity, specificity, positive predictive value (PPV), negative predictive value and accuracy were calculated. For mediastinal pleural and pericardial invasion, an absence of space between the tumor and the mediastinal pleura/pericardium with mediastinal pleural/pericardial thickening and pleural/pericardial effusion exhibited a specificity and PPV of 100%, respectively. For lung invasion, a multi-lobular tumor convex to the lung with adjacent lung abnormalities exhibited a specificity and PPV of 91.2 and 81.3%, respectively. For vessel invasion, the specificity and PPV were each 100% for tumors abutting ≥50% of the vessel circumference, and for tumor oppression, deformation and occlusion of the vessel. In conclusion, recognition of the appropriate CT features can serve as a guide to invasion by stage III thymic tumors, and can facilitate the selection of appropriate pre-operative treatment.

Computed Tomography of Anterior Mediastinal Tumors

Computed tomographic (CT) features in 10 patients with germ cell tumor of the mediastinum and 15 with thymoma were compared with surgically resected specimens. The CT findings of the internal structure of tumors were the most important factor for specific diagnosis. Germ cell tumors showed a round mass without distinct lobulation, frequently with calcification appearing as a globular shape, and especially in benign tumors as an arched shape along the wall. Homogeneous low density masses (near-water) with a thick wall were benign and non-homogeneous density masses (a mixture of near-water and soft tissue) were malignant. Thymoma usually showed a solid mass with lobulation and sometimes had an eggshell type of calcification in the tumor. Therefore, CT is of importance in the diagnosis of anterior mediastinal masses.

Thymoma and thymic carcinomas

Thymomas (Ts) and thymic carcinomas (TCs) are rare tumours of the mediastinum with an incidence rate of 1.7/million per year in Europe. Histological classification is based on rate of non-malignant-appearing thymic epithelial cells and proportions of lymphocytes (A, AB, B1, B2, B3, and C), while staging system concerns localisation of the involved areas. Surgery is the mainstay of treatment with a 10-year survival of 80%, 78%, 75%, and 42% for stages I, II, III and IV, respectively, with an R0 resection. Radiotherapy has a role in selected cases (stage III patients or R1-2 residual) and platinum-based chemotherapy remains the standard of care for patients with advanced disease. A multimodality approach would be advisable when surgery is not recommended. Since molecular aberrations are poorly understood and few responses are reported, targeted therapies are yet being studied. In this review, we describe key aspects of clinical management for Ts and TCs.

Outcomes of Thymoma Treated with Multimodality Approach: A Tertiary Cancer Center Experience of 71 Patients

Aims

To explore the demographics and clinical outcome of patients with thymoma treated with a multimodality approach at our institute.

Methods

A total of 71 patients with thymoma (Masaoka stage II-IV and WHO subtype AB-B3) treated from 1999-2013 were included in this retrospective analysis. Age, stage, WHO subtypes, details of surgery, radiotherapy, and chemotherapy were noted. Progression-free survival (PFS) was estimated using Kaplan-Meier method and SPSS (version 21.0) was used for statistical analysis.

Results

Male:female ratio was 56:15 with median age at presentation of 41 years. Stage-wise distribution was 6:46:19 for stage II, stage III, and stage IV, respectively. A total of 31 patients (44%) had associated myasthenia gravis and 3 had pure red cell aplasia. A total of 57 patients (80%) underwent radical thymectomy and all of these patients received adjuvant radiotherapy. A total of 15 patients and 7 patients received adjuvant chemotherapy and neoadjuvant chemotherapy, respectively. At median follow-up of 19.3 months (range 7.9-72.3 months), 2-year and 3-year PFS rate for the entire cohort was 78.3% and 57.1%, respectively. On univariate analysis, surgery (hazard ratio [HR] 3.881; 95% confidence interval [CI] 1.784-19.220; p = 0.006) and stage (HR 5.457; 95% CI 1.567-18.996; p = 0.0001) were significant prognostic factors and association with myasthenia gravis (HR 0.404; 95% CI 0.151-1.078; p = 0.078) trended towards better PFS. Stage retained its prognostic significance (HR 5.501; 95% CI 2.076-14.573; p = 0.0006) on multivariate analysis.

Conclusions

Multimodality management of locally advanced thymoma yields decent survival outcomes. Masaoka stage is an independent prognostic factor for survival and radical surgery should be contemplated in all cases of locoregionally limited thymoma.

Thymic neoplasm: a rare disease with a complex clinical presentation

Thymic neoplasms constitute a broad category of rare lesions with a wide spectrum of pathologic characteristics and clinical presentations which therefore require a high index of suspicion to diagnose. The natural history of the disease is seldom predictable, anywhere from an indolent to an aggressively malignant course. Although the classification and staging of these lesions are complex and controversial, complete radical surgical resection remains the gold standard of therapy. Radiation and chemotherapy are important elements of the multimodality approach to treating these patients and it is important for thoracic surgeons to work closely with their colleagues in other disciplines in the management of and future research endeavors in thymic neoplasm. In this review, we discuss the evaluation of the patient with an anterior mediastinal mass, the classification and staging of thymic neoplasms, the role of surgery, radiation and chemotherapy in treating this disease, as well as future directions in research for novel targeted therapies.

Invasive thymoma with venous intraluminal extension: CT and MRI findings

We herein report an unusual case of invasive thymoma with venous intraluminal extension. The thymoma extended into the superior vena cava, the left brachiocephalic vein, and the proximal portion of the left jugular and subclavian veins intraluminally. It was suggested that the tumor had a discrete intravascular growth via the thymic vein into the left brachiocephalic vein and extended into the proximal portion of the left jugular and subclavian veins in the opposite direction of the venous stream.

Thymic neoplasms: a clinical update

Thymoma is a unique neoplasm of the anterior mediastinum that is frequently associated with indolent growth and a variety of paraneoplastic syndromes. One third of cases are detected during the evaluation of myasthenia gravis. Classification systems of thymoma have limited ability in accurately predicting prognosis and course of disease. Thus, staging is the only way to predict clinical behavior. Encapsulated tumors that are surgically resected carry the best prognosis. Adjuvant radiotherapy is recommended for incompletely excised and most invasive thymomas. Chemotherapy in anthracycline-based chemotherapy remains the most effective chemotherapy for neoadjuvant, adjuvant or palliative treatment.

Thymomas II: a clinicopathologic correlation of 250 cases with a proposed staging system with emphasis on pathologic assessment

We present 250 cases of thymomas with emphasis on their clinical staging and follow-up. The patients were 120 males and 130 females between the ages of 13 and 92 years. Surgical resection was performed and histopathologic material evaluated in every case. Grossly, the tumors resected varied in size from 3 to 20 cm in greatest diameter. According to our proposed staging system, 31 cases were stage 0, 128 were stage I, 70 stage II, and 21 stage III at the time of resection. Histologically, approximately 53% of thymomas were of mixed histologic types. Follow-up information ranging from 1 to 16 years was obtained, showing significant statistical P values of .044 and .016 for overall and recurrence-free survival, respectively. We consider that our proposed staging system offers better stratification of cases and improved histologic definitions for proper staging of cases of thymoma.

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

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

Epidemiology of thymoma and associated malignancies

BACKGROUND

Thymoma is a rare malignancy of unknown etiology.

METHODS

The author examined patterns in thymoma incidence in the US general population using data from Surveillance, Epidemiology, and End Results (SEER) cancer registries. Prior studies concerning the risk of additional malignancies in thymoma patients were reviewed.

RESULTS

Based on cancer registry data, the overall incidence of thymoma in the US is 0.13 per 100,000 person-years. Thymoma is exceedingly uncommon in children and young adults, rises in incidence in middle age, and peaks in the seventh decade of life. Thymoma incidence is especially high among Asians and Pacific Islanders in the US. While several studies based at single treatment centers have suggested that thymoma patients have a broadly increased risk for other malignancies, follow up data from US cancer registries support a more limited spectrum of cancer risk. In particular, thymoma patients have a subsequently elevated risk for developing B-cell non-Hodgkin's lymphoma. Based on limited data, thymoma patients may also have an elevated risk for developing soft tissue sarcomas.

DISCUSSION

Thymoma is a rare malignancy. The excess risk for non-Hodgkin's lymphoma is consistent with an effect of immune disturbance arising from the thymoma or its treatment. While descriptive epidemiologic data may yield clues to the etiology of thymoma, large multi-center case-control studies will be required to formally evaluate environmental and genetic risk factors.

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.

Myasthenia gravis and autoimmune Addison disease in a patient with thymoma

The association of thymoma with myasthenia gravis has been well documented. However, the relationship between these two syndromes and Addison disease are very rarely encountered in clinical practice. We report on a 32-year-old man who underwent a resection for thymoma 48 months ago. The diagnosis of Addison disease was made followed by a diagnosis of myasthenia gravis on the basis of a high titer of acetylcholine receptor levels. The treatment of oral prednisolone 7.5 mg/day and oral prostigmine 180 mg/day was initiated. His symptoms and physical signs were improved after this treatment. To our knowledge, this is the fourth reported case of thymoma synchronously associated with myasthenia gravis and Addison disease.

Histologic classification of thymoma: the World Health Organization and beyond

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

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.

Proposal of a Novel System for the Staging of Thymic Epithelial Tumors

BACKGROUND

We designed and assessed a new TNM staging system (herein called the INT [Istituto Nazionale Tumori] system) for thymic epithelial tumors in order to overcome the perceived drawbacks of Masaoka's system, which represents the current standard.

METHODS

In all, 123 cases were evaluated. The histologic types according to the World Health Organization (WHO) classification were as follows: subtype A: 5 cases; AB: 40; B1: 16; B2: 29; B3: 16; and C: 17 cases. There were 45 Masaoka's stage I, 33 stage II, 26 stage III, and 19 stage IV cases. A total of 11 INT definitions were grouped into three stages: locally restricted disease (75 cases), which included Masaoka's stage I and selected stage II cases (no pleural invasion); locally advanced disease (37 cases), which included Masaoka's stage III cases plus those staged II owing to pleural invasion and those staged IV owing to intrathoracic nodal or limited pleuropericardial involvement; and systemic disease (11 cases), which included the remaining Masaoka's stage IV cases.

RESULTS

Completeness of resection, WHO types, and both staging systems were significant prognostic factors (p < 0.0001) on univariate analysis. The 95-month progression-free survival rates according to Masaoka's system were stage I: 100%; II: 93.6%; III: 46.3%; and IV: 23.2%. The INT system corresponding figures were as follows: locally restricted disease: 98.6%; locally advanced disease: 46.9%; and systemic disease: 11.7%. The INT system was the prognostic factor with the greatest impact (p = 0.0218) on multivariate analysis (Masaoka's system: p = 0.2012; completeness of resection: p = 0.6855; histology: p = 0.9386).

CONCLUSIONS

The INT system allows finer disease descriptions than Masaoka's system, resulting in a stage grouping with higher prognostic distinctiveness.

Malignant thymoma associated with mixed connective tissue disease: a case report

Many autoimmune diseases have been reported to be associated with malignancy. Mixed connective tissue disease (MCTD), however, has rarely been associated with malignancy. Thymoma is one of the neoplasms often reported to be related to various immunological disorders. Among the types of thymoma defined by WHO, malignant thymoma (thymoma type C) is the one least reported to be associated with autoimmune disease. Here, we report a case of malignant thymoma with concurrent MCTD, which manifested with acrosclerosis, Raynaud's phenomenon, arthritis (synovitis), and a high titer of anti-ribonucleoprotein antibody.

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.

Thymoma and Myasthenia Gravis: A Clinical Study of 1,089 Patients From Japan

BACKGROUND

The thymus or thymoma plays a role in the pathogenesis of myasthenia gravis (MG). Although previous studies have reported that the presence of MG in thymoma patients is an indicator of poor prognosis, recent reports have shown that the presence of MG no longer influences the prognosis or indicates a more favorable prognosis in thymoma patients.

METHODS

To clarify the difference in tumor behavior between thymoma with MG and that without MG, we compiled 1,089 thymomas treated between 1990 and 1994 from 115 institutes in Japan and analyzed the clinical characteristics of thymoma with MG compared with thymoma without MG.

RESULTS

MG was associated with 270 cases (24.8%) of thymoma. The total resection cases comprised 94.6% and 91.4%, and the recurrent cases comprised 6.4% and 8.3% in the groups with and without MG, respectively. The 5-year survival rates for thymoma with and without MG in stage III were 85.7% and 89.3%, respectively; and those in stage IV were 85.1% and 63.9%, respectively. The prognosis of thymoma with MG in stage IV tended to be better than that of thymoma without MG (p = 0.0523). The thymoma with MG group had fewer stage IVb thymomas than did the thymoma without MG group (15% vs 34%). The resectability rate in the thymoma with MG group was higher than that in the thymoma without MG group (60% vs 38%).

CONCLUSIONS

Thymoma with MG is equally or less malignant than that without MG. The infrequency of stage IVb thymomas and the high resectability rate had an influence on the favorable prognosis of stage IV thymoma with MG.

Paraneoplastic Neurologie Syndrome and Autoimmune Addison Disease in a Patient with Thymoma

A 48-year-old man with autoimmune Addison disease developed the following paraneoplastic neurologic syndromes (PNNS): limbic encephalitis, opsoclonus/myoclonus, and sensorimotor and autonomic neuropathies. An anterior mediastinal mass detected on a chest computed tomographic scan was found on resection to be a noninvasive lymphocytic thymoma. The PNNS went into remission 1 year after the thymectomy. This is the first case of thymoma associated with autoimmune Addison disease and PNNS to be described in the literature.

Pericardial ectopic thymoma

Primary intrapericardial thymoma is an unusual localization. We report a case of a patient with an isolated and primary pericardial thymoma. This 72-year-old woman presented with dyspnea, dysphony and myalgia. The radiological evaluation revealed an intrapericardial mass. Surgical exploration showed a hemorrhagic and infiltrative tumor in the pericardial sac, while the mediastinum was free of tumor. Surgical biopsies and, later, an ablation of pericardial mass were done. The tumor was a thymoma, composed of large epithelial cells and immature T lymphocytes and was classified B2 according to the World Health Organization classification (1999). Clinically, a myasthenia gravis was revealed. We discuss the few cases reported in the literature.

Malignant thymoma in the United States: demographic patterns in incidence and associations with subsequent malignancies

The cause of thymoma is unknown. No population-based study has described demographic patterns of thymoma incidence. Previous reports have linked thymoma with diverse subsequent malignancies, but these associations are uncertain. We used Surveillance, Epidemiology and End Results (SEER) data to study the incidence of malignant thymoma by sex, age and race in the United States (1973-1998). Incidence was modeled with joinpoint regression (for age) and Poisson regression. We also used SEER data to compare malignancies following thymoma diagnosis with those expected from general population rates, calculating the standardized incidence ratio (SIR, observed/expected cases) to measure risk. The overall incidence of malignant thymoma was 0.15 per 100000 person-years (849 cases). Thymoma incidence increased into the 8th decade of age and then decreased. Incidence was higher in males than females (p=0.007) and was highest among Asians/Pacific Islanders (0.49 per 100000 person-years). Following thymoma, there were 66 malignancies (SIR 1.5, 95%CI 1.2-1.9). The most notable excess risk for subsequent malignancy was for non-Hodgkin's lymphoma (B immunophenotype) where the SIR was 4.7 (95%CI 1.9-9.6, 7 cases). There were also excess digestive system cancers (SIR 1.8, 95%CI 1.1-2.9) and soft tissue sarcomas (SIR 11.1, 1.3-40.1). No other cancers were increased after thymoma. In conclusion, malignant thymoma is extremely rare. The peak in late adulthood deserves further study. Variation in incidence by race suggests a role for genetic factors. Our study did not demonstrate broadly increased risk for malignancies following thymoma.

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.

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.

Thymic malignancies

Thymomas and thymic carcinomas are unique tumors of the anterior mediastinum. The association of a variety of different paraneoplastic syndromes with such lesions has fascinated physicians and researchers for years. Most recently, it has been demonstrated by numerous authors that thymomas are chemosensitive tumors. Their indolent nature and relative rarity have made evaluation through prospective randomized clinical trials extremely difficult. Further information regarding the molecular nature of these neoplasms and immunologic aspects is needed in future investigation.

Invasive and Noninvasive Thymoma: Distinctive CT Features

PURPOSE

The purpose of this work was to evaluate the CT features of thymoma and to determine the most helpful findings in differentiating invasive from noninvasive thymoma.

METHOD

The CT scans from 27 patients with invasive thymoma and 23 with noninvasive thymoma were independently assessed by two observers without knowledge of their invasiveness. The presence and distribution of various CT findings were independently analyzed.

RESULTS

Invasive thymomas were more likely to have lobulated (16/27, 59%) or irregular (6/27, 22%) contours than noninvasive thymomas (8/23, 35% and 1.5/23, 6%, respectively) (p < 0.05). Invasive thymomas had a higher prevalence of low attenuation areas within the tumor (16/27, 60%) than noninvasive thymomas (5/23, 22%) (p < 0.001) as well as foci of calcification (14.5/27, 54% vs. 6/23, 26%; p < 0.01).

CONCLUSION

The presence of lobulated or irregular contour, areas of low attenuation, and multifocal calcification is suggestive of invasive thymoma.

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.

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.

Thymoma--the usefulness of some prognostic factors for diagnosis and surgical treatment

AIMS

The aim of the study was to identify prognostic factors which could help evaluate both the treatment offered to patients with thymoma and late results.

METHODS

Forty patients were treated for mediastinal thymoma. The patients were staged clinico-pathologically (according to Masaoka) on the basis of the retrospective analysis of their operation protocols as follows: seven (17.5%)-stage I, 19 (22. 5%)-stage II, 17 (42.5%)-stage III, seven (17.5%)-stage IV. Analysis of DNA contents in cell nuclei of 23 thymomas was performed by the flow cytofluorometric method.

RESULTS

From the whole group of patients, 65% survived for 5 years, 55% survived for 10 years and 43% survived for 15 years. We noted significant differences in survival time between stage I and stage IV (P<0.0012); stage II and stage IV (P<0.0006), as well as between stage III and stage IV (P<0. 005). Significantly worse prognosis was observed in the case of cortical thymomas as compared with medullary or mixed types (P<0. 0001 P<0.002). Analysis of DNA content showed signficantly higher probability of survival for the patients who had DI=1.0 (diploid), as compared with DNA >1.0 (aneuploid) (P<0.006). Of the 11 patients with diploid tumours, 91% survived for 5 years, but of the 12 aneuploid, only 23% survived.

CONCLUSION

The most important positive prognostic factors influencing survival rate in patients with thymoma are: lower stage, medullary type (according to Muller-Hermelink classification), possibility of performing complete resection, diploidal nature of the tumour. Multivariate analysis of survival revealed clinico-pathological stage (according to Masaoka) and histological type (according to Salyer) as significantly independent prognostic factors.