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

Prognostic and Clinical Relevance of the World Health Organization Schema for the Classification of Thymic Epithelial Tumors

STUDY OBJECTIVES

Controversy has ensued about the prognostic relevance of the new World Health Organization (WHO) schema for the classification of thymoma. In this study, we present the clinical and histologic features of 108 thymomas and evaluate the usefulness of this histologic schema in view of the prognosis.

DESIGN

Retrospective, clinicopathologic analysis of our experience and a review of recent literature.

SETTING

Department of Thoracic and Cardiovascular Surgery of a university hospital.

METHODS

A series of 108 thymomas were reviewed and classified by the new WHO schema. The clinical characteristics and the survival outcome were investigated in reference to the WHO subtypes. The Cox proportional hazards model was applied to determine the factors affecting the tumor-related survival. Recent literature on the prognostic relevance of the WHO schema was reviewed.

RESULTS

There were 7 type A tumors, 25 type AB tumors, 12 type B1 tumors, 32 type B2 tumors, 20 type B3 tumors, and 12 type C tumors. The histologic subtype closely correlated with the Masaoka stage (p = 0.00). The tumor-related survivals at 5 years and 10 years were 88.0% and 77.9%, respectively. Stage III and IV tumors had a significantly worse prognosis than stage I or II tumors (p < 0.05). Type B3 tumors had an intermediate prognostic ranking in comparison with the carcinomas and with the other groups. On multivariate analysis, the WHO subtype (A-B2 vs B3 vs C) could predict the tumor-related survival, but the Masaoka stage was the most important prognostic factor affecting the postoperative survival (p = 0.026).

CONCLUSION

The Masaoka stage is the most important determinant of survival in surgically resected cases of thymoma. To clarify the prognostic relevance and clinical usefulness of the WHO schema, consistent parameters reflecting the surgical outcome and development of the diagnostic tools that could improve the interobserver agreement within type B are needed.

Chromosomal imbalances in sporadic neuroendocrine tumours of the thymus

Neuroendocrine (carcinoid) tumours of the thymus are rare neoplasms characterized by a highly malignant clinical behavior. Some of these tumors are associated with MEN1. In this study we evaluated 10 cases of sporadic thymic neuroendocrine tumours using immunohistochemistry and comparative genomic hybridization (CGH). All tumours showed a diffuse expression of neuron specific enolase (NSE) and synaptophysin. Chromosomal imbalances were detected in 8/10 cases, the most frequent gains were seen on chromosome Xp (3/10 cases), 7p, 7q, 11q, 12q, and 20q (2/10 each), losses were most frequently detected at 6q (5/10 each), 6p (3/10 each), 4q (3/10 each), 3p, 10q, 11q and 13 q (2/10 each). These CGH data show a degree of overlap with chromosomal imbalances commonly observed in advanced thymomas.

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

OBJECTIVE

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSION

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

[Primary non-lymphoid thymic neoplasms. A study of 58 cases]

BACKGROUND AND OBJECTIVE

Primary non-lymphoid thymus tumors (PNLTT) are an uncommon though quite varied pathology. Our objective was to identify the clinical, therapeutic and histologic variables with a prognostic value in these neoplasms.

PATIENTS AND METHOD

We studied 58 PNLTT cases, corresponding to 52 epithelial neoplams (PTEN), 4 thymolipomas (7%) and 2 neuroendocrine tumors (3%). Commonest clinical manifestations were myasthenia gravis (41%) and dyspnea (21%). Three patients were symptom-free (24%). We used Kaplan-Meier survival curves and Cox regression model.

RESULTS

All patients underwent surgery which consisted of thymectomy. Four patients underwent a biopsy procedure alone. Perioperative mortality was 3% (n = 2) and morbidity was 31% (n = 18), mainly because of respiratory and wound problems. 24 patients with PTEN, Masaoka degrees III and IV, and a patient with a lymphoepithelial carcinoma received adjuvant chemotherapy and/or radiotherapy. With a follow-up of 13 + 5 years, 12 PTEN patients and one patient with a neuroendrocrine tumor died as a consequence of the evolution of the disease. Cumulative survival was 80% at 5 years, 71% at 7 years and 63% at 10 years. There are currently two local relapses in two PTEN cases after 9 and 8 years of follow-up, respectively. Main prognostic factors are the histologic type and subtype and the clinical stage (p < 0.001).

CONCLUSIONS

In PNLTT early diagnosis is crucial in order to administer a correct treatment before the clinical stage is more advanced. Main prognostic factors are the histologic type and subtype and the clinical stage.

Tumor recurrence and survival in patients treated for thymomas and thymic squamous cell carcinomas: a retrospective analysis

PURPOSE

Thymic epithelial tumors (TET) are rare epithelial neoplasms of the thymus with considerable histologic heterogeneity. This retrospective study focused on the correlation of WHO-defined TET histotypes with survival and tumor recurrence in a large cohort of patients receiving different modes of treatment.

PATIENTS AND METHODS

Two hundred twenty-eight patients were followed for up to 21 years (median, 60 months; range, 1 to 252 months) after primary surgery. Forty-two patients received adjuvant radiotherapy (mean dose, 53 Gy), and 33 patients received adjuvant chemotherapy.

RESULTS

Seventy-six (88%) of 86 patients with WHO type A, AB, and B1 thymomas were treated by surgery alone, with three tumor relapses after 3 to 10 years (median, 3.4 years). Twelve of 67 patients with WHO type B2 and B3 thymomas in Masaoka stages I and II were treated by adjuvant radiotherapy without evidence of tumor recurrence after 1 to 12 years (median, 4 years). Among 75 patients with B2 and B3 thymomas with incomplete resection or a tumor stage III or higher, the recurrence rate was 34% (n = 23) after 0.5 to 17 years (median, 5 years) in patients receiving adjuvant radiochemotherapy, compared to 78% (seven of nine patients) in patients without adjuvant radiochemotherapy. Incomplete tumor resection was associated with a high recurrence rate (65%) and a poor prognosis (P <.01).

CONCLUSION

The long-term outcome of TET patients is related to tumor stage, WHO histotype, completeness of surgical removal, and type of treatment. Prospective trials are warranted to formally address the efficacy of adjuvant therapy in the treatment of localized and advanced malignant TETs.

Clusters of chromosomal imbalances in thymic epithelial tumours are associated with the WHO classification and the staging system according to Masaoka

Using comparative genomic hybridisation, we investigated chromosomal imbalances in 28 cases of thymic epithelial neoplasms including type A, B2, B3, the A component of type AB and different subtypes of type C thymoma. To identify different patterns of chromosomal aberrations associated with the biological behaviour and the histological diversity of thymomas, a hierarchical cluster analysis of 65 cases was performed. The here-reported Comparative Genomic Hybridisation (CGH) data (28 cases) of partly uninvestigated tumour subtypes were pooled with previously published data of chromosomal imbalances of 37 thymomas (Zettl et al. [Am J Pathol 2000;157:257-66]). The analysis of 278 chromosomal subbands yielded 2 main clusters. The first main cluster was characterised by gains of the chromosomal arm 1q, consisted only of type C and B3 thymomas and was further subdivided into 2 subgroups. To the first subgroup only thymomas were attributed, which, in addition to gains of the chromosomal arm 1q, showed losses on 6q and 16q, whereas tumours belonging to the second subgroup exhibited no further recurrent chromosomal alterations. The second main cluster was formed by a heterogeneous group of thymoma types (types A, AB, B2, B3 and C), showing no specific pattern of chromosomal imbalances. In 19 thymomas, no chromosomal imbalances could be detected (3 type B2 and 5 type A thymomas of our study as well as 11 type A thymomas investigated by Zettl et al., Am J Pathol 2000;157:257-66). Chromosomal imbalances were more frequent in type C thymomas than in other subtypes. The distribution of tumour stages according to Masaoka (p = 0.003) and the World Health Organisation (WHO) classification (p < 0.0001) was significantly different in the clusters and subgroups obtained. The groups reflect the staging system and the WHO classification and show that type B3 and type C carcinomas have a strong relationship concerning their chromosomal imbalances. Furthermore, chromosomal imbalances detected in some type A thymomas might be responsible for the aggressive behaviour described in a few cases of this thymoma subtype.