Correlations between histological type, clinical behaviour, and prognosis in 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 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.

Stiff-person syndrome associated with invasive thymoma: a case report

We report a case of a 40-year-old female with continuous muscle stiffness and painful muscle spasms. The symptoms worsened over a two-week period after onset. Electrophysiological examinations revealed continuous muscle discharge, which was markedly reduced by intravenous administration of diazepam. High levels of anti-glutamic acid decarboxylase (GAD) antibodies were detected in both serum and cerebrospinal fluid, suggesting that the patient suffered from stiff-person syndrome. Steroid pulse therapy and immunoadsorption therapy alleviated the clinical symptoms and decreased the anti-GAD antibody titer. A chest CT revealed the presence of an invasive thymoma. Neither anti-acetylcholine receptor (AChR) antibodies nor symptoms of myasthenia gravis (MG) were observed. The patient underwent a thymectomy and postoperative radiotherapy. These treatments further alleviated the clinical symptoms. The present case is the first that associates stiff-person syndrome with invasive thymoma, and not accompanied by MG. The autoimmune mechanism, in this case, may be triggered by the invasive thymoma.

Thymoma: update for the new millennium

Thymomas are relatively common tumors of the anterior superior mediastinum. They are usually relatively slowly growing tumors and their prognosis depends on the macroscopic and microscopic invasion of surrounding tissues. Surgery is the mainstay treatment of thymomas, and complete resection represents one of the most important prognostic factors in this disease. Other important prognostic indicators include the tumor stage and size and the presence of symptoms. Postoperative radiotherapy is indicated in tumors with invasion of surrounding tissues, even if resection was radical, since it improves local control and survival. Cytotoxic chemotherapy has been employed in several relatively small phase II studies and in advanced disease has been demonstrated to produce a 50%-80% objective response rate. Neoadjuvant cytotoxic chemotherapy and/or external beam radiotherapy has been used with some success in patients with tumors which are not readily resectable. Novel antiproliferative systemic agents, with both cytotoxic and cytostatic mechanisms of action, are being tested in ongoing prospective clinical trials.

Invasive medullary thymoma associated with Myasthenia gravis: an unusual case

Thymomas are tumors characterized by a remarkable morphological heterogeneity and variable clinical behavior. This tumor has unique clinical associations, most notably with hematological abnormalities and myasthenia gravis. According with the Müller-Hermelink criteria, there are significant differences between the histological types of thymomas and the association with myasthenia gravis. Among the different histological types, medullary thymoma is the least frequent variant associated with this autoimmune disease. In this report we describe a case of medullary thymoma presenting in a 71-year- old woman with a myasthenic syndrome.

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.

Clinical and pathologic predictors of survival in patients with thymoma

OBJECTIVE

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

SUMMARY BACKGROUND DATA

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

[Association of thymoma and severe intestinal strongyloidiasis]

A 59-years-old man with thymoma and severe intestinal strongyloidiasis is reported. The authors pointed out a possible influence of immunological response related with thymoma in the development of hyperinfection by Strongyloides stercoralis.

Prognostic importance of histomorphologic subclassification for epithelial thymic tumors

BACKGROUND

The prognostic importance of various clinical variables (age, sex, association with myasthenia gravis), staging according to Masaoka, histologic type according to the Marino/Kirchner/Müller-Hermelink (MKM-H) classification, and residual tumor category (R category) was evaluated in a retrospective analysis.

METHODS

Eighty-two patients with epithelial thymic tumors (ETTs) treated in the period 1969-1993 were evaluated, and archived specimens were histologically reclassified according to the classification of MKM-H.

RESULTS

Age, sex, and association with myasthenia gravis were of no prognostic importance. The R category is of significant prognostic importance, with 5- and 10-year survival rates of 93.6% and 87.3%, respectively, for R0 resections compared with 0% at 5 years for R1 and R2 resections (p < 0.001). Staging (Masaoka) proved to be a prognostic factor (5-/10-year survival: stage I, 100%/90.9%; II, 95%/88.2%; III, 55.9%/46.6%; and IV, 10.8%/ 10.8%; p < 0.001). Histologic typing according to MKM-H is also of significant prognostic importance (5/10 year survival: thymomas: medullary, 100%/100%; mixed, 100%/100%, predominantly cortical, 68.6%/68.6%; cortical, 65.8%/65.8%; thymic carcinomas: well-differentiated type, 62.3%/44.5%; thymic carcinomas other than well-differentiated type, 33.6%/26.9%; p < 0.001). Multivariate analysis demonstrated that staging (p < 0.001), R category (p < 0.026), and MKM-H classification (p < 0.028) have an independent impact on survival.

CONCLUSIONS

Staging (Masaoka), R category, and histologic classification (MKM-H) are important independent prognostic factors for patients with epithelial thymic tumors. Complete (R0) surgical resections should be the ultimate goal in the clinical management of patients with epithelial thymic tumors.

Prognostic factors of patients with thymoma

OBJECTIVES

To analyze the prognostic factors influencing the survival of patients with thymoma, clinical characteristics, treatment modalities and survival of patients were evaluated. The efficacy of chemotherapy was also determined.

METHODS

Retrospective study was done on one hundred patients whose diagnosis was confirmed pathologically at Seoul National University Hospital from 1981 to 1994. The staging was carried out according to the Masaoka system. Survival rate was calculated by the Kaplan-Meier method and prognostic factors were analyzed by a multivariate analysis (Weibull model).

RESULTS

The stage of 100 patients was as follows: Stage I-50, II-6, III-27, IV A-10, IV B-7. The overall survival rates at 5 and 10 years after diagnosis were 73.1% and 58.7%, respectively. The 5-year survival differences, according to various prognostic factors, were as follows: 1) Stage: I-92.8%, II-100%, III-71.6%, IVA-25.9% and IVB-32.9% (p = 0.0029). 2) Age: < 60 years-79.5% and > or = 60 years-41.5% (p = 0.0489). 3) Extent of resection: Total patients: complete resection-87.6% and incomplete resection-50.5% (p > 0.05) Stage III: complete resection-66.7% and incomplete resection-75.5% (p > 0.05) 4) Myasthenia gravis: present-71.6% and absent-74.9% (p > 0.05) Seventeen patients were treated with a combination chemotherapy of Cyclophosphamide, Adriamycin and cisplatin(CAP). Two complete responses and seven partial responses (overall response rate of 53%) were observed with a median response duration of fourteen months. Combination chemotherapy with CAP was effective.

CONCLUSIONS

Stage and age were the independent prognostic factors in patients with thymoma. However, the presence of myasthenia gravis or the extent of resection in stage III patients was not associated with the survival time.

Recurrent thymoma: evidence for histological progression

The clinicopathological features of nine cases of recurrent thymomas have been studied. At presentation, all cases were histologically classified as thymomas with cortical differentiation, including predominantly cortical thymoma, cortical thymoma and well-differentiated thymic carcinoma. In five cases the morphological features of the recurrence(s) were suggestive of a histological progression of the tumour from predominantly cortical thymoma to cortical thymoma and/or well-differentiated thymic carcinoma, usually associated with a more advanced clinical stage, the latter indicating a clinical progression. These findings suggest that all types of thymoma with cortical differentiation are histologically and histogenetically related neoplasms, associated with a more aggressive clinical behaviour and a significant risk of recurrence. The overall outcome of patients with recurrent thymoma in this series was poor, since six patients (66.6%) died due to the disease, 2-14 years after the first diagnosis. The clinical implication of our findings is that thymomas with cortical differentiation always need careful follow-up, even in those cases which are not obviously invasive at onset.

Immunohistochemical detection of bcl-2 protein in thymoma

The protooncogene bcl-2 encodes a protein that inhibits apoptosis. The protein is expressed in most epithelial cells of the fetal thymic medulla but, to the best of our knowledge, no data are available on bcl-2 expression in thymoma. Expression of bcl-2 protein was analysed in 30 cases of thymoma by immunohistological staining of paraffin-embedded tissue. All cases were examined and classified according to the Salyer and Eggleston and the Müller-Hermelink classification. In four cases, the protooncogene bcl-2 was abnormally expressed in spindle cells of pure medullary thymoma, whereas the non-spindle cells in mixed and in cortical thymoma were negative. All the lymphocytes were also strongly positive in medullary thymoma while a few lymphocytes showed light staining in other thymomas.

Radiotherapy and chemotherapy for invasive thymomas: a multicentric retrospective review of 90 cases. The FNCLCC trialists. Fédération Nationale des Centres de Lutte Contre le Cancer

PURPOSE

Thymoma is a rare disease. The treatment of patients with invasive thymoma remains controversial. The prognosis of such patients is poor, even with the use of postoperative radiation therapy and chemotherapy. We retrospectively reviewed the outcome and prognostic factors in a series of 90 patients presenting with an invasive thymoma treated by partial resection or biopsy and radiation therapy.

METHODS AND MATERIALS

From 1979-1990, 163 patients with the diagnosis of lymphoepithelial thymoma were treated in 10 French cancer centers. Patients were staged using the postoperative "GETT" classification derived from that of Masaoka. Ninety patients who presented with an invasive thymoma, 58 Stage III (21 IIIA: partial resection and 37 IIIB: biopsy) and 32 Stage IVA (intrathoracic thymoma spread), are the subject of this report. Treatment combined surgery and radiation therapy (+/- chemotherapy), with curative intent. Surgery consisted of partial resection in 31 patients (21 Stage III), and biopsy in 55 patients (37 Stage III). The median radiation dose to the tumor was 50 Gy (30-70 Gy). Supraclavicular radiation was performed in 59 patients (median dose 40 Gy). Chemotherapy, combined with radiation in 59 patients, consisted of multidrug regimens, mainly platinum based.

RESULTS

The median follow-up is 105 months (20-165 months). The 5- and 10-year overall survival rates are 51 and 39%, respectively. There is a great impact of the extent of surgery on survival: the 5- and 10-year survival rates were 64% and 43%, respectively, after partial resection, compared to 39% and 31% after biopsy (p < 0.02). Local control at 8.5 years was obtained in 59 of 90 patients (66%): 40 Stage III, 19 Stage IVA. There is a significant relationship between the extent of surgery and the local control (16% of relapse after partial resection vs. 45% after biopsy, p < 0.05). Seven patients developed significant (grades 3-4 WHO grading system) treatment-induced side effects. Stage, histologic type, and chemotherapy were not prognostic factors.

CONCLUSION

In this large multicentric retrospective study of invasive thymomas (Stage III-IVA) treated by surgery and radiation, results show the importance of loco-regional treatments, such as surgery and radiation therapy. There is also a great impact of radiation on local control. However, the rate of local recurrence (34%) justifies recommending a higher dose of radiation (> 50 Gy) than doses used in this study, for incompletely resected patients. The role of chemotherapy needs to be further assessed.

Thymoma--a study of 60 cases in Singapore

Of 60 cases of thymomas studied in Singapore between 1988 and 1992, the histogenetic classification proposed by Müller-Hermelink was successfully applied to subtype 58 cases. There were 20 (33%) cortical, six (10%) predominantly cortical, three (5%) medullary and 12 (20%) mixed thymomas. Twelve (20%) cases were well differentiated thymic carcinomas and five (8%) were classified as other thymic carcinomas. The pathological and clinical features are presented in detail. These subtypes showed significant correlation with invasive behaviour (stage) and myasthenia gravis. We conclude that the Müller-Hermelink classification has predictive utility and represents a major step towards the understanding of the biology of thymic epithelial tumours.

The clinicopathological correlation of epithelial subtyping in thymoma: a study of 112 consecutive cases

The clinicopathological features of 112 thymomas collected from the surgical pathological files of Taipei Veterans General Hospital from 1961 to 1991 were investigated to determinate the clinical efficacy of epithelial subtyping. All thymomas were categorized based on the Müller-Hermelink system into three subtypes: cortical thymoma, mixed thymoma, and medullary thymoma. The former was further subclassified into organoid thymoma, conventional cortical thymoma, and well differentiated thymic carcinoma (WDTC) according to the systems of Pescarmona and Kirchner. The association of each subtype with sex, age at diagnosis, clinical stage, presence of myasthenia gravis, and length of survival was studied. As classified by the Müller-Hermelink system, the cortical thymomas as a whole tended to occur in younger patients and were more frequently associated with myasthenia gravis than the medullary thymomas. The cortical thymomas also showed a propensity to be invasive in nature, whereas the medullary thymomas generally behaved as benign tumors. Further subclassification of cortical thymomas into organoid thymoma, conventional thymoma, and WDTC did not provide more information about clinical behavior. By Kaplan-Meier's actuarial survival analyses none of the epithelial subtypes displayed a statistically significant influence on prognosis. It is concluded that staging remains the most important factor affecting the patient's outcome. Because of the existence of many intermediate forms and the deficiency of clinical relevance, the subclassification of cortical thymomas should be interpreted as a morphological continuum rather than as distinct histological variants.

Thymoma. Histologic subclassification is an independent prognostic factor

BACKGROUND

Several histologic classifications of thymomas have been proposed, and attempts have been made to correlate the different histologic subtypes to clinical behavior and prognosis. Recently, Marino and Müller-Hermelink and Kirchner et al. proposed a new morphologic classification of thymomas based on the resemblance of the neoplastic cells to subtypes of the normal thymic epithelial cells. In this classification, six categories of thymic epithelial tumors are recognized. They define four categories of thymoma: medullary, mixed, organoid (predominantly cortical), and cortical, and two subgroups of thymic carcinomas: well differentiated thymic carcinoma and high grade carcinomas.

METHODS

The authors studied 116 patients with thymic epithelial tumors classified according to the proposals of Marino and Müller-Hermelink and Kirchner et al. to assess the effect of histologic classification and other factors (stage, size of tumor, lymphoid hyperplasia, myasthenia gravis, age, sex, and treatment) on survival, and freedom from relapse.

RESULTS

Eight cases (7%) were medullary, 32 cases (28%) mixed, 20 cases (17%) organoid (predominantly cortical), 21 cases (18%) cortical, 29 cases (25%) well differentiated carcinoma (WDTC), two cases (2%) high grade carcinoma, and four cases (3%) unclassifiable. Fifty-two patients were in stage I, 32 stage II (16 IIA, 16 IIB), 28 stage III, and four Stage IVA. Only stage (P = 0.0001; hazard ratio = 5.36) and histology (P = 0.0019; hazard ratio = 8.010) were significant in predicting recurrence. Histology was highly correlated with stage, but by multivariate analysis was an independent factor in predicting relapse (P = 0.0281; hazard ratio = 5.92). None of the medullary or mixed thymomas recurred, even though 30% were invasive. Patients with WDTC recurred more often and earlier than patients with organoid and cortical thymoma (log rank, P = 0.0001). The actuarial freedom from relapse for patients with WDTC was 58% at 5 years and 46% at 10 years compared with 100% for other subtypes. Both advanced stage (III and IV) and the WDTC histologic subtype significantly increased the risk of death from thymoma (log rank, P = 0.0001). The actuarial survival of patients with WDTC was 80% at 5 years and 54% at 10 years, whereas that of patients with the other subtypes was 100% at 5 and 10 years. Five of seven relapses and six of seven deaths from thymoma occurred in patients with WDTC. In Stage II patients, one of 16 minimally invasive (Stage IIA) tumors recurred, compared with 3 of 16 grossly invasive (Stage IIB) tumors, indicating that microscopic assessment of invasion is important in staging.

CONCLUSIONS

The histologic classification of Marino and Müller-Hermelink has prognostic significance, independent of tumor stage. Medullary and mixed thymomas were benign tumors with no risk of recurrence, even when capsular invasion was present. Organoid and cortical thymoma showed intermediate invasiveness and a low, but significant, risk of late relapse, even with minimal invasion. WDTC were always invasive and had a significantly increased risk of relapse and death, even for Stage II patients. Adjuvant therapy appears unnecessary for medullary and mixed thymomas, even when invasive.

Observer variation in the histopathological classification of thymoma: correlation with prognosis

AIMS

To assess the ability of three histopathologists, experienced in thoracic surgical reporting, consistently to classify thymomas as cortical, medullary, or mixed pattern tumours.

METHODS

Three histopathologists classified 74 thymomas (none frank carcinomas) as of either cortical, medullary, or mixed pattern, on two separate occasions. Kappa statistics were used to assess inter- and intra-observer agreement. Tumour type was compared with surgical stage as a predictor of biological behaviour.

RESULTS

Inter- and intra-observer agreement were only moderate (kappa 0.48 and 0.52, respectively). For only 26 of 74 tumours could a categorisation be consistently agreed on. Follow up information was obtained for 73 cases, with a mean follow up period of five years. The prognoses for those 26 of 74 cases appeared to be at variance from previously reported studies, and showed internal inconsistency, with the mixed pattern category showing a worse survival than the cortical category. For the group as a whole, however, stage at presentation was related to survival, with an overall five year survival of 78% (100% for stage I, 84% for stage II, 27% for stage III and 0% for stage IV).

CONCLUSIONS

The classification of thymomas into cortical, medullary, or mixed pattern tumours is difficult to apply. Surgical stage remains a better guide to prognosis.

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

We applied the classification system of Marino and Müller-Hermelink (Virchows Arch A Pathol Anat Histopathol 407:119-149, 1985) and Kirchner and Müller-Hermelink (Prog Surg Pathol 10: 167-189, 1989) to 122 thymic epithelial tumors to evaluate the utility of this classification and to determine its correlation with invasiveness, follicular lymphoid hyperplasia, myasthenia gravis, and immunophenotype. The majority of cases could be classified according to this scheme: eight cases (7%) were medullary thymoma, 34 cases (28%) were mixed thymoma, 20 cases (16%) were predominantly cortical (organoid) thymoma, 22 cases (18%) were cortical thymoma, 32 cases (26%) were well-differentiated carcinoma (WDC), two cases (2%) were high-grade carcinoma, and four cases (3%) were unclassifiable. We report a detailed histologic analysis of these subtypes, with criteria for diagnosis. We propose that the term "organoid thymoma" be replaced by "predominantly cortical thymoma." We also observed a previously unrecognized subtype of WDC with spindle-shaped epithelial cells, which must be distinguished from medullary thymoma. There was a strong correlation between histologic subtype and invasion (P < .0001). All medullary and mixed thymomas were either completely encapsulated (64%) or had only invasion through the capsule (36%). Organoid and cortical thymomas showed an intermediate degree of invasiveness, with 36% invasive into mediastinal fat and 14% into adjacent structures. All the cases of WDC were invasive either through the capsule (19%) or into adjacent structures (81%); five cases (16%) also showed distant spread in the form of pleural seeding (four cases) or lymph node metastasis (one case). Microscopic evaluation disclosed invasion in a substantial number of cases (28.5%) thought by the surgeon to be encapsulated. The presence of follicular lymphoid hyperplasia, either within the tumor, in the residual normal thymus, or in both, was a significant predictor of myasthenia gravis (P < .0015); there was an increased association of myasthenia gravis and thymomas with cortical type epithelium (organoid thymoma, cortical thymoma, and WDC). There was no correlation between epithelial cell morphology and antigen expression; however, the immunophenotype of the associated lymphocytes corresponded closely to the morphologic classification of the thymomas. The Müller-Hermelink morphologic classification can be applied to most cases of thymoma and strongly predicts invasive behavior. The correlation of lymphocyte immunophenotype with the morphologic classification of the epithelial cells suggests that it is biologically accurate.

Thymoma: a study of the pathologic classification of 71 cases with evaluation of the Muller-Hermelink system

A pathologic study of 71 consecutive cases of thymoma was conducted to determine the value of histologic classification for predicting the invasive potential of thymomas. The traditional and newly proposed Muller-Hermelink classification systems were studied for correlation with thymomas of the three clinicopathologic stages identified as noninvasive thymoma, microinvasive thymoma, and macroinvasive thymoma. None of the histologic types classified by the traditional system were correlated specifically with invasive growth. In contrast, the cortical-type thymoma of the Muller-Hermelink system correlated strongly with both microinvasive thymoma and macroinvasive thymoma (P < .001 for both). Although not all cortical thymomas manifested invasive growth and not all invasive thymomas were of the cortical type, the statistical data suggested that cortical thymomas should be regarded as potentially malignant tumors with the propensity for invasive growth. Spindle-cell thymoma of the traditional system or medullary thymoma of the Muller-Hermelink system, on the other hand, was not associated with invasiveness and behaved as a benign tumor. All other thymomas that were not purely spindle cell or medullary cell in nature had a potential for invasion and aggressive behavior, and this potential seemed to be inversely proportional to the percentage of fusiform cells in such neoplasms. Nevertheless, the results of this study support the usefulness of the Muller-Hermelink classification system in predicting the aggressive potential of thymomas. A group of microinvasive thymomas was identified as a separate group for analysis in this study. Although no recurrences were observed during the follow-up period, microinvasive thymomas deserve further study as a separate group because they correlated strongly with cortical thymoma. The association of thymoma with myasthenia gravis was rather high (63.4%) in this study. Both the mixed-type thymoma of the traditional classification system and the cortical-type thymoma of the Muller-Hermelink system showed statistically significant correlation with myasthenia gravis (P = .002 and .001, respectively).

Expression of epidermal and nerve growth factor receptors in human thymus and thymomas

The expression of epidermal growth factor (EGF) and nerve growth factor (NGF) receptors has been investigated by immunohistochemical analysis in eight normal human thymuses and in 15 thymomas. Thymomas were classified into five different histological types--medullary, mixed, predominantly cortical, cortical thymoma and well-differentiated thymic carcinoma. In fetal and paediatric normal thymus, EGF-receptor was expressed by subcapsular, cortical and medullary epithelial cells, whereas immunoreactivity for NGF-receptor was detected on only subcapsular and medullary epithelial cells. In thymomas, independent of their histological type, EGF-receptor was expressed by a large majority of epithelial cells. In contrast, the pattern of expression of NGF-receptor in thymomas was different for the various histological types. These findings indicate that the expression of both EGF and NGF receptors in human thymomas substantially reflects their expression in normal thymus, and suggest that EGF and NGF may play a role in the ontogenesis of the human thymus as well as in the histogenesis of thymomas.

Well-differentiated thymic carcinoma: a clinico-pathological study

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

'Organoid' thymoma: a well-differentiated variant with distinctive clinicopathological features

The present paper describes the clinical, histological and immunohistochemical features of five cases of 'organoid' thymoma. The histological hallmark of this lesion is the prominent and diffuse 'organoid' pattern, defined by the presence of several areas of medullary differentiation. These areas, which are strictly reminiscent of the medullary area of the normal thymus, are scattered within a neoplastic tissue resembling the thymus cortex, the overall appearance mimicking that of normal thymus. All cases shared common clinical features; they were non-invasive or minimally invasive tumours arising in young or middle-aged female patients. Although the incidence of 'organoid' thymoma is low (5.2% in our series), our morphological, immunohistochemical and clinical data suggest that this peculiar tumour may represent a well-differentiated variant of thymoma, with low-grade aggressiveness and a distinct clinicopathological profile.

Thymoma: results of 241 operated cases

Clinical and histopathological aspects of 241 thymomas were reviewed. One hundred sixty of the patients with thymoma had myasthenia gravis and 15 had other autoimmune diseases; 55% of the thymomas were encapsulated and 45% invasive. Operation was radical resection in 87.5% of the patients, subtotal resection with residual tumor in 8.7%, and simple biopsy in 3.7%. A tumor relapse was observed in 24 patients (10%): 2 (1.5%) of 133 with encapsulated thymomas and 22 (20.4%) of 108 with invasive thymomas; among these patients, a relapse was found in 20.6% of the patients who received radiotherapy postoperatively and in 24.6% who did not. Adverse prognostic factors were clinical stage IVa (multiple pleural nodes), not feasible resection (for technical reasons), inoperable tumor relapse, and association with one of the following autoimmune diseases: pure red cell aplasia, hypogammaglobulinemia, and lupus erythematosus. Conversely, myasthenia gravis is now a curable disease; it contributes to early discovery of associated thymoma, thus allowing a better survival for patients with thymoma who have myasthenia gravis compared with patients with thymoma but without myasthenia gravis (p less than 0.05). Postoperative radiotherapy does not seem necessary after removal of encapsulated thymomas, but it is advisable in case of invasive thymomas, regardless of the extent of the resection.

Role of radiation therapy in locally advanced thymoma

The records of all patients treated for thymoma in the Department of Radiotherapy of the University of Torino between 1970 and 1988 were reviewed. There were 77 patients in stage III or IVa (59 in stage III and 18 in stage IVa); 74 patients were operated upon before radiotherapy and 3 had a pre-operative irradiation followed by surgery and post-operative boost. Complete resection was possible in 55.9% of cases with stage III and in none with stage IVa. Subtotal resection was done in 35.6% of patients in stage III and 83.3% in stage IVa. 8 patients had only a biopsy: 5 in stage III (8.5%) and 3 in stage IVa (16.6%). Post-operative radiation doses ranged between 39.6 and 46 Gy to the whole mediastinum followed by a 10-16 Gy boost on smaller fields in cases presenting residual disease after surgery. The pre-operative dose was 30 Gy followed by a post-operative boost of 16-24 Gy. Conventional fraction sizes of 1.8-2 Gy were always used. The 10 years survival rate was 58.3%. There was a significant difference between stage III (70.9%) and stage IVa (26.3%) (p less than 0.0004). Survival of patients in stage III was not significantly affected by the type of surgery. No significant difference in survival or recurrence rate was observed in patients with different histologies and in patients with or without myasthenia. Thoracic relapses occurred in 15.2% of patients in stage III and in 50% of patients in stage IVa (p less than 0.01). Only 7 relapses (9.1%) were within the limits of the radiation field.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of prognostic factors and clinicopathological staging of thymoma

The prognostic value of four clinical variables (age and sex of patients, association with myasthenia gravis, and clinical stage) and histological type was analyzed in 83 consecutive patients with thymoma, histologically classified as cortical, medullary, and mixed. Age, sex, and association with myasthenia gravis did not prove to represent significant prognostic factors; clinical stage and histological type, on the contrary, had a highly significant prognostic value (p less than 0.001). A model of clinicopathological staging, based on both clinical stage and histological type, in which three major prognostic groups are considered is proposed. The degree of significance of this model is higher (p less than 0.0001) than that of clinical stage and histological type considered individually; its validity is further supported by the results of multivariate analysis according to the Cox regression model (p = 0.0001). We think it represents a prognostically valuable approach to the problem of management of thymoma.

Reoperation for thymoma: report of 23 cases

Twenty-three patients underwent reoperation for thymoma at intervals of 2 months to 17 years 10 months after the initial operation. There were no operative or hospital deaths. Myasthenia gravis occurred in 12 patients, but in only 2 was it a determinant for reoperation. The longest survival after reoperation is 12 years 9 months, and that patient is free from tumor. Four distinct surgical groups emerged, and their recognition provides an improved method of reporting and suggests a strategy for better overall management. Group 1 (n = 5) had completion of thymectomy (reoperation) after thymomectomy alone or after incomplete thymectomy. The interval was 2 months to 17 years 10 months. All 5 had myasthenia gravis. At reoperation, thymomas were found in 3 and a hyperplastic thymus in 2. Four are alive and tumor free 2 years to 8 years 2 months after reoperation. One died tumor free after 5 years. Group 2 (n = 8) had reoperation for recurrent thymoma after standard (presumably complete) resection. The interval was 2 years to 13 1/2 years. Four had myasthenia gravis. Four are alive 8 months to 5 years 8 months after reoperation, 3 without detectable tumor. Four died 3 years 3 months to 8 years 4 months after reoperation, 3 free from tumor. Group 3 (n = 8) underwent reoperation for initially unresectable thymoma after adjuvant treatment with chemotherapy, radiotherapy, or both. The interval was 3 months to 4 years 8 months. Three had myasthenia gravis. Six are alive 4 months to 4 years after reoperation, only 1 with tumor.(ABSTRACT TRUNCATED AT 250 WORDS)