Ann Thorac Surg 2005;80:2000-2001
© 2005 The Society of Thoracic Surgeons
Original article: General thoracic
Invited commentary
Kazuya Kondo, MD, PhD
Department of Oncological and Regenerative Surgery, University of Tokushima Graduate School, Kuramoto-cho, Tokushima, 770-8503 Japan
(Email: kondo{at}clin.med.tokushima-u.ac.jp).
The idea of clinical staging of thymoma was introduced by Bergh and colleagues [1], which was later modified by Wilkins and Castleman [2], and was advanced by Masaoka and associates [3] in 1981. Masaoka's system has been widely adopted and is an excellent system for predicting prognosis for thymomas. Several articles including the article by Bedini and associates [4] have pointed out problems and have suggested that an update of the system is desirable.
The authors identified seven major criticisms of the Masaoka system. I think that some criticisms are important (1 through 4), and I would like to add two additional staging issues (5 and 6):
- 1 The classification system does not provide appreciable prognostic separation between stages I and II.
- 2 Some definitions are not clinically applicable because surgical or pathological assessment is required. In particular, the definition of stage II is unclear. Some pathologists propose that microscopic invasion into the capsule in stage II should be replaced by microscopic transcapsular invasion. The most recent World Health Organization classification of thymic epithelial tumors in 2004 defined T2 thymoma as "tumor invades pericapsular connective tissue" [5].
- 3 The system is not well suited for staging thymic carcinomas.
- 4 Presence residual tumor is classified by use of the "R" category. Many reports demonstrate completeness of thymoma resection is the most important predictor of survival, although some reports show a value of so-called debulking procedures.
- 5 As stage III thymoma is highly heterogenous in terms of involved organs, classification should divide the subgroups according to prognosis. Okumura and associates [6] report that involvement of the great vessels is an independent prognostic factor in patients with stage III thymoma.
- 6 The TNM system classification of thymic epithelial tumors has not been established. Yamakawa and Masaoka [7] presented a tentative TNM system classification of thymoma in 1991, which some reports subsequently supported. In Masaoka's system, the presence of local invasion (T factor) is strongly emphasized in comparison with lymphogenous and hematogenous metastasis (N and M factors) because of the rarity of lymphogenous and hematogenous metastasis in thymoma. However, it is necessary to determine how N or M factors influence prognosis to establish a TNM system classification of thymic epithelial tumors including thymic cancer and carcinoid. The World Health Organization's histologic classification of 1999, which can distinguish thymic carcinoma and carcinoid from thymoma, has been widely adopted, and large-scale clinicopathologic studies of thymic carcinoma and carcinoid may provide sufficient prognostic information to include N or M factors in a TNM system of thymic epithelial tumor.
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- Bergh NP, Gatzinsky P, Larsson S, Lundin P, Ridell B. Tumors of the thymus and thymic region: I. Clinicopathological studies on thymomas Ann Thorac Surg 1978;25:91-98.[Abstract]
- Wilkins Jr EW, Castleman B. Thymomaa continuing survey at the Massachusetts General Hospital. Ann Thorac Surg 1979;28:252-256.[Abstract]
- Masaoka A, Monden Y, Nakahara K, Tanioka T. Follow-up study of thymomas with special reference to their clinical stages Cancer 1981;48:2485-2492.[Medline]
- Bedini AV, Andreani SM, Tavecchio L, et al. Proposal of a novel system for the staging of thymic epithelial tumors Ann Thorac Surg 2005;80:1994-2001.[Abstract/Free Full Text]
- Müller-Hermelink HK, Ströbel P, Zettl A, et al. Combined thymic epithelial tumoursIn: Travis WD, Brambilla E, Müller-Hermelink HK, Harris CC, editors. Pathology and genetics of tumours of the lung, pleura, thymus and heart (WHO classification of tumours series). Lyon, France: IARC Press; 2004. pp. 196-198.
- Okumura M, Miyoshi S, Takeuchi Y, et al. Results of surgical treatment of thymomas with special reference to the involved organs J Thorac Cardiovasc Surg 1999;117:605-613.[Abstract/Free Full Text]
- Yamakawa Y, Masaoka A, Hashimoto T, et al. A tentative tumor-node-metastasis classification of thymoma Cancer 1991;68:1984-1987.[Medline]
This article has been cited by other articles:
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T. Utsumi and M. Okumura
A Staging System for Thymic Epithelial Tumors: More Discussion is Required.
Ann. Thorac. Surg.,
September 1, 2006;
82(3):
1170 - 1170.
[Full Text]
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