PF303 THE IMPACT OF EZH2 MUTATIONS (Y641N/Y641F/Y641H/Y641S) ON DISEASE‐FREE SURVIVAL OF PATIENTS WITH DIFFUSE LARGE B‐CELL LYMPHOMA: A STROBE‐COMPLIANT COHORT STUDY
Authors: Candelaria M. , Ponce M. , Gutierrez‐Hernández O. , Taja‐Chayeb L. , Aviles A. , Lome C. , Oñate‐Ocaña L. , Dueñas‐Gonzalez A. 
Published: June 2019

Background:

Diffuse Large B Cell Lymphoma (DLBCL) is the most frequent type of non‐Hodgkin lymphoma. Although two subtypes with different prognosis have been defined, the addition of target therapies, such as ibrutinib, to the standard RCHOP regimen did not improve the long‐term results of patients with non‐GC DLBCL. Therefore, new molecular markers are required in order to optimize their treatment

Aims:

To define impact of the EZH2 mutations on survival of patients with DLBCL.

Methods:

Patients: A cohort study of untreated patients with recent diagnosis of DLBCL, attended at a single national reference centre. Cohorts were defined according to the presence of EZH2 (Y641N/Y641F/Y641H/Y641S) mutations. Clinical variables were age, comorbidities, IPI score, bulky disease, clinical stage, serum albumin, LDH and B2‐mycroglobuline levels, and ECOG. Histopathologic variables were GC versus no‐GC by Hans nomogram, BCL2, BLC6, & MYC expression, as well as double hit. All patients were treated with six cycles of standard RCHOP. Clinical response was evaluated by PET‐CT, using the Deauville's criteria. Patients who were treated with other schemas, or did not receive chemotherapy were excluded. Methods: DNA was extracted from paraffin‐embedded tissue of the primary neoplasm. Thereafter, PCR reactions were carried out in a 2700 Thermalcycler (Applied Biosystems) to search for the presence of mutations in Exon 16 of EZH2; the PCR products were sequenced in at least two independent amplification reactions. Sequencing reactions were electrophoresed in an ABI3100 genetic analyser. Electropherograms were analysed by eye, and the sequences obtained were compared with the EZH2 reference sequence (GenBank NG_032043.1). The protocol was approved by IRB (register number CEI/966/15). Statistics: After descriptive analysis, the Kaplan‐Meier method was used to construct Disease‐free survival (DFS) curves and the Logrank test was used for comparisons. The Cox regression model was employed to define variables associated with DFS.

Results:

230 patients (120 male), were included. Median age was 58.3 (SD 14.25; range: 21–91). Of them, 169 (73.4%) had an advanced disease and 224 (97.3%) had ECOG <2. Absence of B symptoms or bulky disease was documented in 154 (67%) and 136 cases (59.1%), respectively. GC‐type was documented in 65%. Although sixty cases (26%) were considered double expressors (MYC +BLC2 overexpression) DLBCL, only 15% were double‐hit DLBCL. Mutations at codon 641, exon 16 of EZH2 were documented in 15% of cases, as follows: Tyr 641 Asn (Y641N) [6 %],Tyr 641 Phe(Y641F) [6%], Tyr 641 His (Y641H) [3%] and Tyr 641Ser (Y641S) [1%]. Response was classified as complete in 75% of cases, partial in 3.5%, and progressive disease in 11%. The association of these mutation on DFS is shown in the table 1.

Summary/Conclusion:

Conclusions. These are preliminary results but are highly suggestive that the presence of EZH2 (Y641F) mutation has an impact of DFS of patients with DLBCL. Our results require to be confirmed with a larger sample, and a longer follow‐up.

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