MYC Protein Expression Correlates with C-MYC Transcriptional Activity in Absence of Gene Rearrangement in Diffuse Large B-Cell Lymphoma

Introduction. MYC increases proliferative capacity of malignant B-cells, independently from mechanisms led to increased protein expression. Tumors with solely MYC expression are highly effective curable with doses intensification. Ability of cells to escape apoptosis by several mechanisms like BCL2 or P53 соехpression promotes malignant B-cells growth and survival and represents a big therapeutic problem.

Aim. To investigate mechanism of MYC hyperexpression in absence of c-MYC -rearrangement in DLBCL (diffuse large B-cell lymphoma). To analyze efficacy of intensive chemotherapy in pts with DLBCL who underwent modified NHL-BFM-90 (m-NHL-BFM-90) plus rituximab (R) in correspondence with MYC and BCL2 protein expression.

Patients and methods. Data of 62 DLBCL pts (35 males and 27 females) who underwent m-NHL-BFM-90+R in National Research Center for Hematology (Moscow) between 2004 and 2013 years were analyzed. Tumor samples were stained with antibody to BCL2 (clone 124, Dako) and MYC (clone Y69, Epitomics). We used a previously reported cut off for MYC expression ≥40% and BCL2 ≥50% (N. Johnson et al., 2012). G-banding data were available in 19 pts. In one case was revealed c-MYC rearrangement into heavy chain locus t(8;14)(q24;q32). In all other cases FISH didn't reveal c-MYC orBCL2 rearrangements with DNA probes Vysis LSI MYC Dual color, Break Apart Rearrangement Probe, Vysis LSI BCL2 Dual color, Break Apart Rearrangement Probe. RQ-PCR was performed in 17 cases to estimate mRNA level of c-MYC expression relatively to ABL. To assess relation between mRNA of c-MYC and MYC protein expression was used correlation analysis (R²). To estimate treatment results were performed Kaplan-Meyer and Cox regression analyses (SAS 9.3).

Results: Majority of pts - 48/62 (78%) attended to a high-risk group according IPI (3-5). 9/62 (14,5%) patients had MYC+/BCL2- tumors, 15 (24%) - "double-expressor" (DE) MYC+/BCL2+, 21 (34%) - MYC-/BCL2+, 17 (27,5%) - MYC-/BCL2-. Median age of DE pts was statistically higher than others (61 (25-73) vs 47 (15-73) years old, P<0,05). In case with t(8;14)(q24;q32) MYC protein expression was ≥40%. In 18/50 (36 %) cases in absence of c-MYC -rearrangement MYC protein expression was ≥40%. In 27/43 (63 %) cases in absence of BCL2 rearrangement BCL2 expression was ≥50%. Median level c-MYC mRNA-expression was 1748 % (492 % - 5408 %). There was a tendency to increase MYC expression level with rising quantity of c-MYC mRNA (R² = 0,13, P = 0,08). In case with t(8;14)(q24;q32) c-MYC mRNA level was higher than median (3940 %). 45 (78%) of pts achieved a complete remission, 4 from them had second remission. Relapses and progression of DLBCL developed in 9 (15%) and 7 (11%) pts. 5 (8%) pts died because of other reasons. DE DLBCL pts had the highest risk of relapse or progression within 4 years: MYC+/BCL2- - 14%, MYC-/BCL2 - 14%, MYC+/BCL2+ - 65%, MYC-/BCL2+ - 24% (P=0,02). In multivariate analysis MYC/BCL2 double expression had an independent prognostic power (HR 4,717, P=0, 0024) from IPI.

Conclusion. We illustrated that MYC protein expression level correlates with c-MYC transcriptional activity in absence of c-MYC rearrangement. MYC hyperexpression alone didn't influence on prognosis, only coexpression of MYC and BCL2 had a crucial role increasing probability of relapse or progression in DLBCL patients.