Didier Lardinois, MD, Renate Rechsteiner, MD, R. Hubert Läng, MD, Matthias Gugger, MD, Daniel Betticher, MD, Christian von Briel, MD, Thorsten Krueger, MD, Hans-Beat Ris, MD

Ann Thoracic Surg 2000;69:1550-5

Available online on CTSNet at http://ats.ctsnetjournals.org/cgi/content/full/69/5/1550

Discussion

I cannot claim to be any expert in thymomas. In fact it was my lack of knowledge combined with the pressing need to prepare an educational piece on thymoma which drew my attention to this paper.

This is a surgical series and therefore the uncommon stage 4 is under-represented. In fact it is difficult to work out how stage 4 cases can be included in the analysis of a "completely resected" series. Inherent in the definition of stage 4 is that it is unresectable. Stage 4 will be excluded from this discussion.

The two analyses reported graphically were survival time and disease free survival. The latter has been more discriminatory. A further analysis may have been instructive, that is survival free from disease-related death. The patient group who develop thymomas are aged (age range not quoted in paper) and likely over a ten year period to die from other diseases. Therefore the raw survival data has limited relevance. While this is a large series by thymoma standards (n=71), it is still small to attempt to differentiate between six subsets, particularly when further whittling the numbers to those with complete resection.

It is difficult to make any conclusions on the endocrine tumours as the number is small and all were stage 3. While none were disease-free, there seem to have been no deaths till the tenth year when the remaining case died. They seem to be a separate group of tumours.

Of the Thymic tumour types there seems to be distinct survival differences between three Muller-Hermelink morphological groups:

1. 1.Predominantly medullary including mixed
   

2. 2.Predominantly cortical including organoid
   

3. 3.Well-differentiated thymic carcinoma
   

Not only do pathologists have difficulties differentiating between medullary and mixed, and cortical and organoid, but so do the statistics. Therefore further attempts to divide these groups seems futile.

In the Masaoka classification there is a definite survival difference between stages 1, 2, 3 and 4. However, the numbers in the subsets 2a and 2b are so small, the difference between the curves being a single event, that firm conclusions cannot be made.

As both classifications provide useful prognostic information it would seem wise for pathologists to report both the Muller-Hermelink morphological predominance and the degree of Masaoka invasion as suggested by Engel et al after reviewing 213 Danish cases.

1. 1.Masaoka, Monden Y, Nakahara K, et al, et al: follow-up study of thymomas with special reference to their clinical stages. Cancer 48:2485-2492, 1981
   

2. 2.Didier Lardinois, MD, Renate Rechsteiner, MD, R. Hubert Läng, MD, Matthias Gugger, MD, Daniel Betticher, MD, Christian von Briel, MD, Thorsten Krueger, MD, Hans-Beat Ris, MD: Prognostic relevance of Masaoka and Müller-Hermelink classification in patients with thymic tumors. Ann Thoracic Surg 2000;69:1550-5
   

3. 3.Engel P, Marx A, Muller-Hermelink HK: Thymic tumours in Denmark. A retrospective study of 213 cases from 1970-1993. Pathol Res Pract 1999;195(8):565-70