[1841] 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.

Results of Cell-kinetic Parameters by WHO Type
KI67 LIMABcl-2
A13.0 (2.4,5.3)1.6 (0.8,4.4)1.0 (1.0,3.0)
B317.5 (5.7,13.7)3.3 (1.2,5.6)1.0 (1.0,1.0)
TCa123.2 (17.9, 39.9)21.0 (6.4,23.4)2.0 (1.0,3.0)
A vs B32<0.00010.170.019
B3 vs TCa20.00660.00030.97
A vs TCa2<0.00010.00010.11
1median (Q1,Q3); 2p-values, only p≤0.017 are considered significant

Significant Bcl-2 expression (>90% EC) was observed in types A (n=12/29), B3 (n=2/16) and TCa (n=5/11). However, there was no significant difference in Bcl-2 expression between types A, B3 and TCa. Ki67 LI significantly differed between WHO A and B3 thymomas and TCa. MA was not significant in distinguishing WHO A vs B3 thymomas.
Conclusions: Ki67 and MA differ significantly between WHO types A, B3 and TCa and might represent a useful tool to distinguish between these subtypes. Although Bcl-2 might be important in the pathogenesis of thymic neoplasms, its expression by EC was not of diagnostic significance.
Category: Pulmonary

Tuesday, March 23, 2010 1:00 PM

Poster Session IV # 262, Tuesday Afternoon


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