Diagnostic Significance of Cell-Kinetic Parameters in WHO Type A and B3 Thymoma and Thymic Carcinoma
AC Roden, ES Yi, SM Jenkins, JL Donovan, SD Cassivi, YI Garces, RS Marks, MC Aubry. Mayo Clinic, Rochester, MN
Background: Recent studies have shown only moderate interobserver agreements for the WHO classification of thymoma and the distinction between thymoma and thymic carcinoma (TCa). Our data showed common disagreements for WHO B3 thymoma vs TCa, followed by WHO A vs B3, and A vs TCa, disagreements of 26%, 7.4% and 6.7%, respectively. However, the prognosis of TCa is much worse than thymomas with reported 5-yr survival of 28%. Furthermore, several studies suggest that WHO B3 thymoma have worse prognosis than other thymoma with reported 5-yr survival as low as 51%, in contrast to WHO A thymoma with usual 5-yr survival of 100%. Therefore, adjunctive studies are sought to facilitate the distinction between these histological subtypes.
Design: Medical records from 64 patients with thymic neoplasm (1946-2008) were reviewed. Two pathologists independently classified all cases according to WHO and agreed upon type A (n=31), B3 (n=22) or TCa (n=11). Ki-67 LI (n=56) was expressed as %pos/100 epithelial cell (EC) nuclei (mean of 1000 EC counted over 3 areas) and mitotic activity (MA) (n=64) as mitoses/10Hpf (mean of 50Hpf counted). Bcl-2 (n=56) expression was graded as 0 (neg) through 3 (>90% EC+). Statistical analyses were performed. Data are presented as median (Q1,Q3) for each group, and were compared with Kryskal-Wallis tests.
Results: 40 men & 24 women had a median age of 59.4 yrs.
|A1||3.0 (2.4,5.3)||1.6 (0.8,4.4)||1.0 (1.0,3.0)|
|B31||7.5 (5.7,13.7)||3.3 (1.2,5.6)||1.0 (1.0,1.0)|
|TCa1||23.2 (17.9, 39.9)||21.0 (6.4,23.4)||2.0 (1.0,3.0)|
|A vs B32||<0.0001||0.17||0.019|
|B3 vs TCa2||0.0066||0.0003||0.97|
|A vs TCa2||<0.0001||0.0001||0.11|