EZH2 Upregulation Is Associated with Unfavorable Prognosis in Diffuse Large B-Cell Lymphoma through Potential RUNX3 Downregulation

Introduction: The runt-related transcription factor 3 (RUNX3) is a downstream effector of the transforming growth factor-β (TGF-β) signaling pathway, and has critical roles in apoptosis, angiogenesis, cell migration and invasion. Putative tumor suppressor activity of RUNX3 has been presented extensively in the literature, particularly in solid epithelial tumors and recently in lymphoma with loss of expression favoring tumorigenesis and/or prognosis, but its role in diffuse large B-cell lymphoma (DLBCL) has not been studied. Enhancer of zeste homolog-2 (EZH2), a histone methyltransferase, has been shown to mediate silencing of RUNX3. RUNX3 downregulation due to EZH2 upregulation has been shown in various solid tumors. In the present study, we investigated the EZH2 and RUNX3 RNA expression status in DLBCL and its impact on clinical outcome.

Methods: A retrospective chart review was performed and 169 cases of DLBCL treated with chemoimmunotherapy between 2003 and 2013 were included. Immunodeficiency- or EBV-associated and MYC+ LBCL were excluded. Archived formalin-fixed-paraffin-embedded tissue samples were retrieved and RNA was extracted using commercially available kits. We correlated the RNA expression levels for EZH2 and RUNX3 in various sites using quantitative real-time PCR (Taqman assay) and custom designed primers for each gene. Control samples included three benign lymph nodes free of a neoplastic process.

Results: We identified 66 cases of DLBCL, including25 nodal DLBCL and 41 extranodal DLBCL, with sufficient RNA extracted. Extranodal locations included testis (n=12), orbit (n=6), primary central nervous system (n=5), bone (n=3), breast (n=2) and viscera (n=13). The median age was 64 years (range 29- 81 years) with a female to male ratio of 0.4 (F=20 and M=46). Median overall survival (OS) was 28 months (1-156 months). Immunophenotypic subtype based on cell-of-origin using Hans algorithm was available in 63 cases; 34 cases were germinal center B-cell (GCB) type while 29 were non-GCB type. Treatment data was available in 63 cases and all patients received R-CHOP as initial therapy except three patients who died shortly after diagnosis. Forty-four cases showed higher expression of EZH2 and RUNX3 when compared to normal lymph nodes (p < 0.05). Nineteen out of 44 cases showed increased EZH2 and decreased RUNX3 expression (Group 1) while EZH2 expression was lower than RUNX3 in the remaining cases (Group 2). The remaining 22 DLBCL cases did not show significant correlation for expression (Group 3). Overall survival was significantly low in Group 1 compared to Group 2 and Group 3 (p =0.030 and p=0.026, respectively). There was no difference for OS between Groups 2 and 3 (p>0.05) (Figure 1).

Conclusions: Our results showed that decreased RUNX3 RNA expression is associated with EZH2 overexpression and poses an adverse prognostic factor in DLBCL. Larger studies are needed to establish the prognostic and therapeutic utility of EZH2 and/or RUNX3.

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