Well-differentiated thymic carcinoma: is it thymic carcinoma or not?

We read the article titled “Thymic Carcinoma: Current Staging Does Not Predict Prognosis” by Blumberg and associates of Sloan-Kettering Cancer Center (J Thorac Cardiovasc Surg 1998;115:303-9). Thymic carcinomas in this article consisted of type II malignant thymoma 1 and well-differentiated thymic carcinoma. 2 Our Nagoya City University series of thymic carcinoma consisted of 19 patients treated in 1980 through 1995. Inasmuch as there were 62 thymomas and 3 thymic carcinoids in the same period, the incidence of thymic carcinoma was 22.6% in thymic epithelial tumors. Because thymic carcinoma coincides with type II malignant thymoma according to our criteria, well-differentiated thymic carcinomas are excluded from our series. Histologic subtypes of our thymic carcinomas were as follows: squamous cell carcinoma, 11 cases; undifferentiated carcinoma, 3 cases; small cell carcinoma, 2 cases; lymphoepithelioma-like carcinoma, 1 case; papillary adenocarcinoma, 1 case; and unclassified carcinoma, 1 case. Associated diseases were observed in 2 patients: hypergammaglobulinemia in 1 patient and Cushing syndrome with hypogammaglobulinemia in another. Myasthenia gravis was not present. Applying the classification of thymoma to our thymic carcinomas yields the following stages: stage I, 1 case; stage II, 0 cases; stage III, 9 cases; stage IVa, 4 cases; and IVb, 5 cases. Followup results revealed a 42.7% 5-year survival and a 21.4% 10-year survival. The most important factor influencing survival was histologic subtype. Five-year survival was 65.6% in squamous cell carcinoma and 14.3% in the other types of carcinoma.On comparing our results with those of the Sloan-Kettering series, we observed some differences. First, survivals in our series were inferior to those of Sloan-Kettering. Second, advanced stages of disease (stages III and IV) were prevalent in our series, as in that of Hsu and associates, 3 which consisted exclusively of type II malignant thymoma. Accordingly, it is impossible to compare survivals of the patients with early and advanced stages of disease in our series. Third, none of our patients had associated myasthenia gravis. The explanation for these differences seems to be that our series excludes well-differentiated thymic carcinoma.