J Thorac Cardiovasc Surg 1999;117:612-613
© 1999 Mosby, Inc.
Commentary
Paul A. Kirschner, MD,
New York, NY
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Introduction
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The article by Okumura and associates should be compared with that of Blumberg and colleagues
1 with regard to the prognostic significance of thymic tumors involving the great vessels. Both articles seem to yield the same results, despite the fact that in the current publication, thymic "carcinomas" were excluded, whereas in the Blumberg article only thymic "carcinomas" were included.
Why this discrepancy? Probably because of a lack of agreement and uniformity in the nomenclature and classification of thymic tumors. Since 1916, no fewer than 21 different histologic classifications of thymic tumors have been proposed. 2
The classification used by the current authors is 37 years old 3 and deals only with the proportions of epithelial cells and lymphocytes, rather than focusing in the true thymic tumor cell, the epithelial cell.
Earlier on, pathologists did not address the significance of microscopy in the determination of benign versus malignant lesions, deferring to the surgeon's observation as to whether or not gross invasion of surrounding structures had occurred. However, in the past 15 years there have been a flood of articles dealing with thymic carcinoma based on microscopy. 4
While the microscopic characterization of thymic carcinoma is being debated, 5-7 the evidence to date tends to support the newer Müller-Hermelink classification.
I agree with Shimosato 8 in deploring the lack of "standard" World Health Organization histologic classification of thymic tumors, as already exists for many other tumors, including lung tumors.
This brings up the validity and applicability of the Masaoka staging system. 9 Originally, it was intended for "thymomas" (bland cytology) only. However, with a more comprehensive view of thymic tumor pathology, the next logical move would be the institution of a TNM staging system to support the Masaoka system. Interestingly enough, such a TNM system has already been proposed by Yamakawa and colleagues, 10 in an article in which Masaoka was a coauthor, and subsequently was also proposed by Tsuchiya and associates 11 in 1994.
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References
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Blumberg D, Burt ME, Bains MS, et al. Thymic carcinoma: current staging does not predict prognosis. J Thorac Cardiovasc Surg 1998;115:303-9. [Abstract/Free Full Text]
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Shimosato Y, Mukai K. Atlas of tumor pathology, third series, fascicle 21. Tumors of the mediastinum. Washington [DC] Armed Forces Institute of Pathology; 1997. p. 34-5.
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Bernatz PE, Harrison EG, Clagett OT. Thymoma; a clinicopathologic study. J Thorac Cardiovasc Surg 1961;42:424-44. [Medline]
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Kirchner T, Müller-Hermelink HK. New approaches to the diagnosis of thymic epithelial tumors. In: Fenoglio-Preiser CM, Wolff M, Rilke F, editors. Progress in surgical pathology, vol 10, New York: Field and Wood Medical Publishers; 1989. p. 167-89.
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Dawson A, Ibrahim NBN, Gibbs AR. Observer variation in the histopathological classification of thymoma. Correlation with prognosis. J Clin Pathol 1994;47:519-23. [Abstract/Free Full Text]
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Quintanilla-Martinez L, Wilkins EW, Choi N, et al. Thymoma: histologic subclassification is an independent prognostic factor. Cancer 1994;74:606-17. [Medline]
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Close PM, Kirchner T, Uys CJ, et al. Reproducibility of a histogenetic classification of thymic epithelial tumors. Histopathology 1995;26:339-43. [Medline]
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Shimosato Y. Controversies surrounding the subclassification of thymoma [editorial]. Cancer 1994;74:542-4. [Medline]
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Masaoka A, Monden Y, Nakahara K, et al. Follow-up study of thymomas with special reference to their clinical stage. Cancer 1981;48:2485-92. [Medline]
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Yamakawa Y, Masaoka A, Hashimoto T, et al. A tentative tumor-node-metastasis classification of thymoma. Cancer 1991;68:1980-7.
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Tsuchiya R, Koga K, Matsano Y, et al. Thymic carcinoma: proposal for pathological TNM and staging. Pathol Int 1994;44:505-12. [Medline]
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Introduction
References