P1292: MOLECULAR CHARACTERIZATION OF DIFFUSE LARGE B-CELL LYMPHOMA ASSOCIATED TO HEPATITIS C VIRUS INFECTION

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Background: HCV positive DLBCL has distinct clinical and pathological characteristics compared to its negative counterpart; however, in the era of DLBCL genomic profiling, its molecular landscape has been scarcely outlined. Aims: To investigate the clinico-pathological and molecular features of a well characterized bicentric series of 54 patients (pts) with HCV positive DLBCL. Methods: With Illumina HiSeq 2500, we applied targeted next generation sequencing (NGS) of 184 genes on DNA extracted from archived formaline fixed paraffin embedded tissue; the core panel probes was designed using IDT tool and libraries were prepared using Illumina DNA-prep-with enrichment. We applied fluorescence in-situ hybridisation (FISH) for MYC, BCL2 and BCL6 rearrangements detection and NanoString technology (Lymph2Cx assay) for cell-of-origin (COO) determination. We performed cluster analysis with LymphGen genetic classifier. Results: Median age was 71 (33-84). Stage was III/IV in 34 pts (63%). Extranodal sites and spleen were involved in 22 pts (41%) each. R-IPI was intermediate in 22 pts (40%) and poor in 30 (56%). HCV-RNA was detectable in 52 pts (96%). Overall, 19 out of 37 pts with available data (51%) received an antiviral therapy course, including 7 (19%) with interferon-based regimens and 12 (32%) with direct-acting antivirals. Twenty-seven pts (50%) received rituximab-based regimens, 23 (43%) chemotherapy alone and 1 (2%) surgery alone. With a median follow up of 7.7 years (yrs) (IQR: 4.6-10.6), 5-yrs overall survival (OS) was 49.3% (95%CI 34.1-62.8%) and 5-yrs progression free survival (PFS) 39.5% (95%CI 25.5-53.3%). FISH analysis showed rearrangements involving BCL2 in 2/54 pts (4%), BCL6 in 27/53 pts (51%), MYC in 6/53 pts (11%). Hans algorithm classified 25 pts as Germinal Center B Cell (GCB) and 27 as non-GCB. Lymph2Cx-based assay was successful in 38 cases and classified 16 cases each (42%) as Activated B Cell (ABC) or GCB subtypes, while 6 cases resulted unclassified. NGS showed mutations in 158 out of the 184 analyzed genes. All pts harbored at least one oncogenic variant with a median mutation load (MML) of 13 mutated genes per case (2-26; IQR: 9-16). Most frequently mutated genes were the epigenetic regulators KMT2D (n=23; 42.6%) and SETD1B (n=17; 31.5%), followed by FAS, PIM1 and RERE (n=15; 27.8%), TBL1XR1 (n=14; 26%), BCL11A (n=13; 24%) and SGK1 (n=12; 22%). Mutated pathways involved the epigenetic regulation (94% of pts; MML: 3; range 1-7; IQR: 1.25-4), apoptosis (90% of pts; MML: 2; 1-7; IQR: 1-3), BCR/NFkB signaling (77% of pts; MML: 2; 1-7; IQR: 1-3), immune regulation (56% of pts; MML: 1.7; 1-5; IQR: 1-2) and the NOTCH pathway (25% of pts; MML: 1.2; range 1-2). The LymphGen tool classified 29 out of 54 pts (54%) in defined clusters, including 14 in BN2 (48%), 7 in ST2 (24%), 4 in MCD (14%) and 4 in EZB subtype (14%). Notably, all assessable MCD cases (3/3) displayed an ABC signature, while all EZB tumors (3/3) showed a GCB COO. Conversely, ST2 and BN2 subtypes comprised mixed COO subgroups. No significant differences in terms of OS or PFS were detected according to either genetic clusters or COO. Image:Summary/Conclusion: Our study elucidates molecular landscape of HCV-positive DLBCL, showing scarcity of BCL2 translocations, an equal distribution of COO subgroups according to NanoString and high prevalence of mutated genes within the epigenetic and immune regulation pathways. BN2 cluster prevalence and enrichment of mutations of NOTCH pathway genes seem to indicate a preferential marginal-zone origin for a consistent subgroup of HCV-positive DLBCL cases.

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