A Practical Approach To Differentiate between WHO Types A and B3 Thymomas and Thymic Carcinomas
Anja C Roden, Eunhee S Yi, Jakub Pecl, Stephen D Cassivi, Yolanda I Garces, Marie Christine Aubry. Mayo Clinic, Rochester
Background: Interobserver agreements for the WHO classification of thymic epithelial neoplasms (TEN) is only moderate. Common disagreements occur for type B3 vs thymic carcinoma (TCa), type A vs B3, and A vs TCa. However, the prognosis of TCa is worse with 10-yr survival of 20-67% vs 36-83% for B3 and 76-100% for A. No single marker is available to facilitate the histologic assessment. We studied whether a combination of TdT, Glut-1, and CD205 might be used to facilitate the distinction between type A and B3 thymomas and TCa.
Design: Specimens from 50 pts treated with TEN were included. Three pathologists independently classified all cases according to WHO and agreed upon type A, B3 or TCa. Sections were stained for CD205, TdT, and Glut-1. Membranous (CD205, Glut-1) or nuclear (TdT) staining were considered positive. Staining distribution was assessed for CD205 and Glut-1. Number of + cells was expressed as (100 * number + epithelial cells) / number total epithelial cells (mean of 5 Hpf counted).
Results: Expression of TdT, CD205, and Glut-1 and distribution of CD205+ and Glut-1+ cells are shown in Table 1.
|# + cases¹||# + cases¹||Diffuse||Patchy||# + cases¹||Diffuse||Patchy|
|A (n=16)||11 (68.7)||14 (87.5)||1||13||6 (37.5)||0||6|
|B3 (n=15)||14 (93.3)||15 (100)||8||7||10 (66.7)||0||10|
|TCa (n=19)||0||10 (52.3)||3||7||17 (89.5)||10||7|
|% + cells||CD205||Glut-1|
|Type A||Type B3||TCa||Type A||Type B3||TCa|