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Ann Thorac Surg 2003;76:884-885
© 2003 The Society of Thoracic Surgeons
a Virginia Mason Medical Center, 1100 North Avenue, Seattle, WA 98101, USA
e-mail: donald.low{at}vmmc.org
The classification and treatment of thymic epithelial tumors has been in evolution over the last 40 to 50 years. New systems of histologic classification have been proposed by Levine and Rosai in 1978, Muller-Hermelink in 1985, and Suster and Moran in 1999. The Masaoka system was introduced in the 1970s and 1980s and is based on the presence or absence of capsular invasion, direct extension into surrounding structures, and metastatic disease. This classification system is fairly easily interpreted from the surgical perspective, considering that previous differentiation between invasive and noninvasive thymomas was primarily based not on histological criteria but on surgical interpretation of intraoperative findings.
The W.H.O. classification was introduced in 1999 and represents an attempt to standardize histologic classification of thymic epithelial tumors and to provide guidelines to assess invasiveness on histologic as well as surgical parameters. It provides a more consistent approach to the classification of these tumors, which will not only improve the ability to interpret and compare case series and clinical trials, but will also provide a more accurate prediction of tumor behavior to guide therapy not only following surgical excision but also at the time of biopsy.
The report by Kondo et al is a summation of a very large series of patients with thymic epithelial tumors in Japan. A total of 185 centers were sent a questionnaire that yielded clinical data on 1,320 patients from the 115 institutions that responded. The number of patients is unprecedented. The paper suggests that the Japanese surgical community in general has achieved a remarkable degree of consistency with respect to their overall therapeutic approach.
Simply on the basis of the numbers available, this paper would seem to provide an important opportunity to identify trends and outcomes in patients with thymomas and, perhaps more pertinently, in the rarer situations involving thymic carcinoids and cancer. Unfortunately, the key to any retrospective analysis of outcome begins with accurate and consistent assessment of tumor pathology. Surgeons and pathologists dealing with thymic epithelial tumors routinely deal with the problems associated with differentiation of aggressive thymomas and thymic cancer. The authors do not provide any indication that the pathologic slides of their 1,300 patients were reviewed by a central panel or specialist pathologist to assure appropriate categorization of thymic tumors. It is extremely unlikely that all of the pathologists involved in the assessment of these tumors have equal levels of background or expertise.
In addition, the authors have categorized all of their cases according to the Masaoka clinical staging system. The rest of the world outside of Japan is increasingly utilizing the W.H.O. histologic classification system. The utilization of the Masaoka system makes the interpretation of the findings in this paper much more difficult for surgeons and pathologists outside of Japan. The authors champion the Masaoka staging system suggesting that it remains a good predictor of prognosis for thymoma and thymic cancer. However, the advantages of easily and accurately comparing results with the rest of the medical world should stimulate surgeons and pathologists in Japan to seriously consider either adopting W.H.O. classification or committing themselves to classifying patients in published case series and clinical trials under both classification systems.
The authors infer that the results in their series, especially with respect to recurrence rates in patients with thymomas and thymic cancers of all stages, are lower than in previously cited reports. In the absence of consistent assessment of thymic histology and a readily interpretable international staging system, the accuracy of this statement is more difficult to verify. What the authors have conclusively demonstrated is that Japanese surgeons manage a significant volume of thymic epithelial tumors within a medical system conducive to cooperative clinical trials.
Doctor Kondo appropriately emphasizes that total resection remains the mainstay of management of the majority of thymic epithelial tumors. This would not be considered new or important information. However, the authors also have initial indications, suggesting that adjuvant mediastinal radiation does not decrease the incidence of local recurrence in thymoma and that adjuvant therapy, including radiation, chemotherapy, or chemoradiotherapy, does not seem to impact prognosis in patients with totally resected stage III and IV thymomas and thymic cancer. Many centers would currently recommend adjuvant therapy, most commonly radiotherapy, in patients with totally resected stage II–IV thymomas and thymic cancer. Acknowledging that mediastinal radiation is associated with significant potential side-effects, definitely addressing this issue alone would be a major contribution to the management of these tumors.
The authors themselves indicate that prospective randomized trials will be the most important hallmarks for impacting definitive treatment decision-making in thymic epithelial tumors in the future. Because of Japan's high volume of these tumors and their ability to coordinate care on a national level, they would appear to have a unique opportunity to prospectively assess outcomes in the neoadjuvant and adjuvant treatment of not only thymomas, but the much more rare entities of thymic cancer and carcinoids. The authors should be encouraged to adopt a staging system that will be comparable and interpretable within the international surgical and pathologic communities, and to ensure that all patient's pathology is assessed by a central committee or designated group of pathologists to ensure that initial interpretations of histologic subtypes are standardized.
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