Tumours of the thymus and their nomenclature

Unusual presentation of mycosis fungoides as pigmented purpura with malignant thymoma

Thymoma is known to be associated with many lymphoreticular and nonlymphoreticular tumors. A woman who presented with patch stage mycosis fungoides with skin lesions resembling a pigmented purpura was found to have an anterior mediastinal mass on routine staging evaluation. A core needle biopsy of the mass revealed a lymphocyte predominant malignant thymoma. Review of the literature reveals many diseases with dermatologic manifestations associated with thymoma; however, malignant thymoma coexisting with mycosis fungoides has not previously been reported.

Thymic epithelial cells as a diagnostic pitfall in the fine-needle aspiration diagnosis of primary mediastinal lymphoma

The cytologic diagnosis of primary mediastinal lesions is challenging due to the large number of lesions which may arise (i.e., lymphoma, thymoma, germ cell tumor), often with overlapping cytomorphologic features. We present an instructive case of primary mediastinal non-Hodgkin's large-cell lymphoma with sclerosis, entrapping thymic epithelium. Preoperative fine-needle aspiration yielded predominantly epithelial fragments and few lymphoid cells leading to the cytologic misdiagnosis of thymoma. The entity of primary mediastinal large-cell lymphoma (LCL) is discussed and correlated with the cytologic features seen. In addition, histologic sections from 15 additional cases of primary mediastinal LCL were evaluated to determine the frequency with which significant numbers of epithelial fragments may be observed.

Oncogene proteins and proliferation antigens in thymomas: increased expression of epidermal growth factor receptor and Ki67 antigen

AIMS

To examine thymomas for proteins encoded by oncogenes and to determine whether their presence correlates with tumour growth and associated myasthenia gravis.

METHODS

Sections of 24 thymomas were incubated with anti-EGF receptor (EGF-R), anti-Ki67 antigen, anti-p53, and anti-bcl-2 antibodies, and then stained using the alkaline phosphatase/anti-alkaline phosphatase (APAAP) technique. Cell suspensions and epithelial cell cultures from some of the tumours were also studied.

RESULTS

Whereas EGF-R expression was not detected in any of the controls (but only in a 20 week old fetus), it was detected in neoplastic epithelial cells of all thymomas, and was most strongly expressed in metastases and in samples from donors with severe myasthenia gravis. Ki67 labelling was also increased, especially in the larger thymomas. Epithelial expression of both of these markers was confirmed in fresh cell suspensions and monolayer cultures from the five available cases. In contrast, p53 and bcl-2 were not detected in the neoplastic cells, but bcl-2 was present in the intermingling thymocytes.

CONCLUSIONS

Neoplastic thymoma cells express EGF-R and Ki67, but there is no concomitant increase in the expression of p53 and bcl-2 proteins. Increased EGF-R expression may result in increased proliferation of neoplastic cells and also in myasthenia gravis. Measurement of EGF-R concentrations may be of prognostic value. The bcl-2 staining pattern in T lymphocytes illustrates the broad spectrum of maturational stages in thymoma lymphocytes.

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.