Thymoma. A Comparative Study of Clinical Stages, Histologic Features, and Survival in 200 Cases

Two hundred thymomas, surgically treated between 1955 and 1982 at the Marie Lannelongue Surgical Center, were subjected to statistical analysis, comparing clinical stages and histologic types and relating them to survival. Clinical stages were defined as follows. Stage I: no invasiveness, total excision; Stage II: localized invasiveness (no more than two mediastinal structures); Stage III: largely invasive, with or without distant tumorous grafts, lymph node deposits, or metastases. Four histologic types were retained: (1) spindle or oval cell type thymoma, (2) lymphocyte-rich thymoma, (3) differentiated epithelial thymoma, and (4) undifferentiated epithelial thymoma. Invasiveness remained a major prognostic factor, but the degree of invasion did not affect the survival rate or always justify radical surgery. Thus, the survival rate dropped from 85% at 5 years and 80% at 10 years in noninvasive tumors to 50% and 35%, respectively, in invasive tumors, but without significant difference between moderately invasive Stage II and largely invasive Stage III tumors. Histologic typing indicated a good correlation between the degree of differentiation of the tumors and prognosis. The survival rates were 80% at 5 years and 75% at 10 years for spindle cell type 1 and lymphocyte-rich type 2 thymomas, 75% at 5 years and 50% at 10 years for differentiated epithelial type 3, and nil at 5 years for undifferentiated type 4 thymomas. Although invasiveness often paralleled histologic typing, they appeared as two distinct parameters with separate prognostic significance, particularly in differentiated and undifferentiated epithelial tumors. One hundred five patients had myasthenia gravis and 14 had another autoimmune disease. The associated syndromes were no longer an adverse factor in the prognosis of thymoma.