Histologic Classification of Thymic Epithelial Tumors Differs from Classification by Grade and Stage: A Study of 138 Surgically Resected Thymomas and Thymic Carcinomas.
William D Travis, James Huang, Nicolas Girard, David S Klimstra, Gregory J Riely. Memorial Sloan Kettering Cancer Center, New York, NY
Background: Histologic classification of thymic epithelial tumors (TET) has evolved over the past few decades with much controversy and different concepts. The 2004 WHO provides a histologic classification of thymic epithelial tumors that is based primarily upon morphology. These tumors can also be classified according to histologic grade and stage that correspond to different degrees of clinical aggressiveness. These different approaches are frequently confused.
Design: With the purpose of comparing histologic classification of TET with grade and stage, 138 surgical resected TED were classified by the 2004 WHO classification. Tumors were staged according to the Masaoka system and survival analysis was used to consider tumor groups according to grade.
Results: Thymoma were classified as type A (12), AB (19), B1 (8), B2 (48), B3 (26), micronodular (1), and metaplastic (1). There were 23 thymic carcinomas. Tumors were grouped into three grades (GR): GR1 (A, AB, B1, micronodular, metaplastic; n=41; 25F, 16M; age: mean 61 yrs, 23-87 yrs), GR2 (B2 & B3; n=74; 37F, 37F; age: mean 55 yrs, 31-84 yrs) and GR3 (carcinoma; n=23, 8F, 15M; age: mean 58 yrs, 34-83 yrs). A higher percentage of patients with GR3 were Masaoka stage III or IV (17/23; 74%) compared to GR2 (44/74, 60%) and GR1 (5/39, 13%, p<0.001). 5 yr disease free survival (DFS) by Kaplan-Meier analysis with Tarone Ware comparisons was significantly reduced for GR2: 69% and GR3:36% compared to GR1: (77%, p<0.001). DFS was significantly worse for GR2 compared to GR1 (p=0.02) and G3 compared to GR2 (p=0.003). For Stage, in GR1 there were 36/41 Stage I/II (88%) and 5 Stage III/IV; GR2 there were 30/74 Stage I/II (41%) and 44 Stage III/IV (59%); GR3 there were 6/23 Stage I/II and 17 Stage III/IV. For all TET, survival according to stage was significant (p<0.001).
Conclusions: The 2004 WHO TET categories from type A to AB, B1, B2, B3 and thymic carcinoma represent increasing histologic grades with varying degrees of more aggressive behavior as measured by stage and prognosis. While there are tumors that may have similar grade, (i.e. the low grade type A, AB and B1 thymoma which are often low stage), the 2004 WHO categories have morphologic differences that remain the basis for maintaining a histologic classification separate from grading and staging.
Wednesday, March 2, 2011 9:30 AM
Poster Session V # 254, Wednesday Morning