Ann Thorac Surg 2004;78:997-998
© 2004 The Society of Thoracic Surgeons
Invited commentary
Juan Rosai, MD
Department of Pathology, Istituto Nazionale Tumori, Via Venezian, 1, Milan 20133, Italy
juan.rosai{at}istitutotumori.mi.it
The current WHO classification of thymic epithelial tumors has incorporated the most salient elements of the two main preexisting classifications (colloquially known as the American and German, respectively) and has arranged the various tumor types into categories identified by a combined alphabetical and numerical code (A, AB, B1, B2, B3, C). Several articles that have appeared following this publication, including the one by Park and associates in this issue of The Annals of Thoracic Surgery, have reported that the scheme is easy to follow and that it correlates closely with tumor stage and outcome. The point still being argued is whether its influence on prognosis is entirely dependent upon its correlation with stage or whether it is independent from it. There is no question that the correlation between WHO histologic type and prognosis that is strikingly apparent when all stages are included loses much of its discriminatory power if evaluated within a given stage. Several authors, including Park and colleagues, have concluded on the basis of multivariate analysis that the WHO histologic subtypes are significant independent prognostic factors with respect to survival. However, they also demonstrate that the importance of the histologic subtypes becomes only marginal if only surgically resected patients are evaluated. It would thus appear that the main clinical significance of thymoma histologic subtyping, especially in a biopsy specimen, is in providing a reasonably predictive assessment of the tumor stage and hence of the prognosis, not a small contribution to the handling of thymomas.
Another important aspect of the work by Park and coworkers is a further demonstration that, despite some early concerns, the WHO scheme has proved readily acceptable to pathologists, easy to apply, and easy to remember. Alas, it has also proved short-lined, not because of any intrinsic deficiencies but because of a decision by the WHO to produce a whole new series of booklets in a short time span (perhaps unduly short) on the histologic classification of human tumors. As a result, the scheme being touted as "new" in the title of the article by Park and colleagues will soon lose its status. Not to worry, though. The scheme being proposed in the forthcoming WHO publication on thymic tumors is essentially the same as the current one, except for one minor semantic change. In the current classification scheme, thymomas are subdivided into types A, AB, B (B1, B2, B3), and C, the last being a synonym for thymic carcinoma. In the forthcoming scheme, thymomas are subdivided into exactly the same types, except that the term type C thymoma will not longer be used as a synonym for thymic carcinoma. The basic facts remain: the WHO histologic clasification is easy to use, it correlates well with clinical stage, and it is an indirect (and perhaps independent) indicator of prognosis.
Related Article
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Prognosis of thymic epithelial tumors according to the new World Health Organization histologic classification
- Moo Suk Park, Kyung Young Chung, Kil Dong Kim, Woo Ick Yang, Jae Ho Chung, Young Sam Kim, Joon Chang, Joo Hang Kim, Sung Kyu Kim, and Se Kyu Kim
Ann. Thorac. Surg. 2004 78: 992-997.
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