MYC-ID3 Pathway in a Cohort of Diffuse Large B Cell Lymphomas: Immunoistochemical Analysis and Prognostic Implications
Authors: Doni Elisa , Pagni Fabio , Rossini Fausto , Belotti Angelo , Bolis Silvia , Casaroli Ivana , Cattoretti Giorgio , Pioltelli Pietro Enrico , Gambacorti-Passerini Carlo 
Published: October 2019

Abstract
Background: Centroblasts and centrocytes are distributed to opposite poles of the GC structure: a centrocyte-rich light zone (LZ) and a centroblast-rich dark zone (DZ). Some studies support the hypothesis of a cyclic reentry model in which LZ and DZ cells regularly move between the LZ and DZ compartments. Recent profiling of DZ and LZ cells showed that Burkitt lymphomas () most closely resembles DZ cells, whereas the GC-derived GCB subtype of DLBCL is more similar to LZ cells. Recently the role of a regolatory loop involving MYC and ID3 has been investigated in BL. In this setting ID3 is highly expressed because it is a direct target of MYC. Nobody has investigated this mechanism in DLBCL; only a few data about the prognostic role of ID3 expression in DLBCL are available. Aims: We used immunohistochemical analysis to investigate the role of the regolatory loop involving MYC and ID3 and the prognostic impact of ID3 expression in terms of 2 years-overall survival (OS) and event free survival (EFS) in a cohort of DLBCL patients (pts) treated with immunochemotherapy at our institution from 2009 to 2013. Material and methods: We selected 140 DLBCL pts on the basis of diagnosis formalin-fixed-paraffin embedded (FFPE) tissues availability; tissue microarrays (TMAs) that contained two representative cores from each tumor were prepared according to standard methods. Immunohistochemical stainings were performed using the following antibodies: MYC Y69 Epitomics, Burlingame, CA, ID3 clone 17-3, rabbit monoclonal anti-mouse, Biotech. We considered positive a nuclear staining in more than 75% cells. BCL-2 cytoplasmatic expression and MIB-1 were determined at diagnosis. Among this cohort we selected 100 pts treated with RCHOP and with follow up data available. OS and EFS were defined according to standard criteria. Survival analyses were performed using Kaplan-Meier curves and compared using the Log-rank test. Chi square test was applied to assess differences between biomarkers and clinical and laboratory parameters. Results: Median age was 68 years. Median follow up was 30 months. Among 140 DLBCL MYC positivity and ID3 positivity were found in 41 and 29 pts, respectively (29.3% and 20.7%). We found a significant correlation between MYC and ID3 expression (p=0.006). A significant correlation between ID3 expression and a MIB-1>75% was documented (p=0.044). Regarding outcome data on 100 pts, 2 year-OS was significantly lower in ID3 positive than in ID3 negative groups (45% vs 85%, p=0.001). By 6 months from diagnosis, 6 of 18 ID3 positive pts died. No differences were found in terms of 2 year-EFS. Conclusion: Our data support the hypothesis of a regolatory mechanisms involving MYC and ID3 also in DLBCL. Considering the absence of ID3 mutations in DLBCL as shown in previous studies, cases positive for MYC and negative for ID3 need further investigation.

Disclosures
Gambacorti-Passerini: Pfizer: Consultancy, Research Funding; Bristol-Myers Squibb: Consultancy.