Staging System of Thymoma

Introduction: Thirty years have gone by since the Masaoka staging system of thymoma was proposed in 1981. Although the Masaoka staging system has been accepted by many surgeons and pathologists, some proposals of revision and improvements have been suggested. At this time, I reinvestigated the Masaoka staging system based on the recent follow-up study of the thymomas resected at Nagoya City University. Methods: Using the follow-up results of 211 thymomas in Nagoya, I analyzed the following aspects: (1) evaluation of the Masaoka staging system as a prognostic factor in the Nagoya series and (2) critical assessment of the proposals of revision to the Masaoka staging system. Results: (1) Univariate analysis showed that Masaoka stages were significantly prognostic for overall survival (p < 0.0001). (2) The difference of survivals between stage I and II was not significant, but progression-free survival of stage I was 100% for up to 20 years, whereas one tumor death case in stage II was found. (3) Differences of survival between the cases with and without great vessel invasion in stage III were not significant. (4) Prognosis of N+ tumors was yet better defined. Conclusion: (1) The Masaoka staging system remains a valuable prognostic factor. (2) Combination of stage I with II and separation of stage III into subgroups are not recommended. (3) At the moment, it is better to include N+ tumors in stage IVb.