[1246] CD23 and TRAF1 Expression and Lack of BCL2/IGH Fusion Help Discriminate Primary Mediastinal Large B-Cell Lymphoma from Mediastinal Involvement by Systemic DLBCL.

Linda N Dao, Mark E Law, Grzegorz S Nowakowski, William R Macon. Mayo Clinic, Rochester, MN

Background: Primary mediastinal large B-cell lymphoma (PMLBCL) is a distinct large B-cell lymphoma of thymic B-cell origin. It often forms a bulky anterior mediastinal mass and can invade adjacent structures. Clinical staging is required to rule out secondary mediastinal involvement by systemic diffuse large B-cell lymphoma (DLBCL) and the distinction can be clinically difficult in the case of secondary dissemination of PMLBCL. The purpose of this study was to try to determine pathologic diagnostic discriminants between PMLBCL and systemic DLBCL by immunohistochemistry and fluorescence in-situ hybridization (FISH).
Design: We evaluated the expression of CD10, CD20, CD23, BCL6, LMO2, MUM1, p63, REL and TRAF1 by immunohistochemistry and BCL2/IgH, BCL6, IgH, JAK2/PAX5 and MYC by FISH on 52 cases of PMLBCL and 16 cases of systemic DLBCL that occurred in the mediastinum.
Results: The immunohistochemistry and FISH results are summarized in the table. CD23 and TRAF1 tended to be expressed by the tumor cells in PMLBCL but not by the neoplastic cells of systemic DLBCL in the mediastinum. Other antigens were expressed to a variable non-discriminatory extent in the two lymphoma types. BCL2/IgH translocations were identified in none of the PMLBCL and in 36% of the DLBCL. JAK2 amplification was detected in 13/46 (28%) PMLBCL and 7/15 (47%) DLBCL. MYC was translocated in a single case of DLBCL but in none of the PMLBCL.

Immunohistochemistry and FISH findings
 PMLBCL n=52 (%)DLBCL n=16 (%)
CD10+13 (25)9 (56)
CD23+20 (38)2 (12)
BCL6+21 (40)9 (56)
LMO2+37 (71)9 (56)
MUM1+12 (23)1 (6)
p63+17 (33)3 (19)
REL+9/14 (64)15/15 (100)
TRAF1+11/14 (79)3/15 (20)
BCL2/IgH fusion0/26 (0)5/14 (36)
BCL2 amplification3/26 (21)1/14 (7)
BCL6 translocation4/48 (8)2/15 (13)
IgH translocation8/45 (18)8/14 (57)
JAK2 amplification13/46 (28)7/15 (47)
MYC translocation0/14 (0)1/16 (6)

Conclusions: These findings suggest that the presence of CD23 and TRAF1 expression and lack of BCL2/IGH fusion may provide diagnostic utility in distinguishing PMLBCL from mediastinal involvement by systemic DLBCL. JAK2 amplifications do not discriminate PMLBCL from DLBCL as they may be seen with relative frequency in both lymphoma types.
Category: Hematopathology

Wednesday, March 2, 2011 1:00 PM

Poster Session VI # 207, Wednesday Afternoon


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