[1435] Utility of PRDM1/BLIMP1 in Differentiating between Marginal Zone and Lymphoplasmacytic Lymphoma

Mohammad O Hussaini, Cecelia Yeung, Anjum Hassan. Washington University, St. Louis, MO

Background: Marginal zone lymphoma (MZL) and lymphoplasmacytic lymphoma (LPL) are low grade B-cell lymphomas postulated to be of post-germinal center origin. While both follow a rather indolent clinical course, LPL carries a worse prognosis. Since plasma cell differentiation is frequently encountered in MZL, distinction from LPL is often difficult in clinical practice.
PRDM1/BLIMP1 has been cited as the “master regulator” of plasma cell differentiation. PRDM1 represses c-myc, as well as beta-interferon gene expression via PRDI promoter binding. Alternative splicing leads to 2 isoforms: alpha, a tumor suppressor, and beta, which lacks the ability to repress transcription. Immunohistochemical (IHC) staining for PRDM1 has been shown to be useful in the discrimination of plasmablastic lymphoma from conventional diffuse large B cell lymphoma. Initial work from our department using RT-PCR has shown the PRDM1 transcript to be more commonly lost in LPL than MZL. We investigated IHC staining for PRDM1 as a practical marker to aid in differentiating between MZL and LPL.
Design: Cases of MZL and LPL from 2007-2010 in patients 18-99 years old were identified. An IHC stain for PRDM1 that recognizes both alpha and beta isoforms was optimized and cases were stained at 1:2 and 1:4 dilutions. Slides were manually graded for percentage staining. Two normal bone marrow core biopsies from patients with prior plasma cell neoplasm and eight benign tonsils were added as controls. The higher of percentage staining between dilutions was adopted. <5% tumor staining was considered negative. Statistical analysis was performed using a two-tailed Fischer's exact test.
Results: 21 lymphoma cases from 12 male and 9 female patients with a median age of 66 years were reviewed. MZL and LPL comprised 67% and 33% of cases, respectively. 40% of MZLs (4/10) but 0% of LPLs (0/7) showed positive staining for PRDM1 (p=0.255).

Both the bone marrow cores showed no staining (0/2). In all 8 tonsils, the mantle zone B-cells were clearly negative while tonsillar plasma cells showed positive staining.
Conclusions: The PRDM1 transcript may be preferentially lost in LPL compared to MZL and immunostaining for PRDM1 may be a helpful adjunct in the sometimes challenging differential of MZL and LPL.
Category: Hematopathology

Monday, March 19, 2012 9:30 AM

Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 214, Monday Morning

 

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