Abstract
Context
MYC is a critical driver gene for many human cancers, and its deregulation by translocations resulting in Myc soverexpression has been implicated in lymphomagenesis and tumor progression. The MYC mutation status and its relevance in human cancers, especially in diffuse large B-cell lymphoma (DLBCL), are unknown.
Objective
To determine the spectrum of MYC mutations in a large group of DLBCL patients treated with R-CHOP immunochemotherapy, and to evaluate the clinical significance of MYC mutations in this study group.
Patients and Methods
The MYC gene was assessed by Sanger sequencing methods in 708 de novo DLBCL patients, diagnosed between 1998 and 2010, and treated with R-CHOP therapy. Patients were excluded from analysis if they had been treated with CHOP regimen or had transformed DLBCL, primary mediastinal, cutaneous or central nervous system large B-cell lymphomas, or HIV infection. The results of MYC sequencing were compared with the MYC reference sequence in the Genebank database. The variants were subdivided as either single nucleotide polymorphisms (SNP) or novel single nucleotide variations (SNV). We correlated the MYC genetic status with clinical outcome, including treatment response, overall survival (OS) and progression-free survival (PFS).
Results
351 (49.6%) patients harbored variations in MYC gene sequence that potentially affect Myc biological function and expression, either non-synonymous variations in the coding sequence (CDS) or variations in the regulatory regions including the 5’- and 3’-untranslated regions (UTR). Most variations occurred in the CDS and 5’UTR (predominantly single nucleotide substitutions), whereas infrequently (9.4%) in the 3’UTR. Only two patients carried variations in the splicing sites. Significantly elevated transition versus transversion rate of the variations, the presence of WRCY/RGYW motifs in the CDS and 5’UTR, association with MYC translocation, and the presence of up to 37% synonymous CDS variations (silent mutations), suggest that most of these mutational events arise via somatic hypermutations mediated by activation-induced (cytidine) deaminase.
Variations in the CDS, 5’UTR and 3’UTR had different prognostic implications. Variations in the CDS region were associated with better survival (P=0.0005 for OS and P=0.0002 for PFS), whereas variations in the 3’UTR and 5’UTR variations had no prognostic significance. Variations in the CDS regions also were heterogeneous in regard to the prognostic impact: (1), One germline SNP, N11S which occurred in 46 patients, conferred a significant better survival than patients with wild type MYC CDS (P=0.011 for OS, and P=0.06 for PFS); (2), Four codons (57P, 58T, 79P and 138F) had frequent variations in patients (n=4-5), which were located in the domain Myc box II essential for Myc functional. In addition, patients with SNVs at these codons had significantly poorer survival than patients with other SNVs or wild type CDS indicating they are somatic gain-of-function mutants; (3), The group with the remaining SNPs or SNVs, which occurred infrequently, were associated with a better survival than patients who had a wild type CDS (P=0.0016 for OS, and P=0.039 for PFS) indicating loss-of-function of Myc. For the 5’UTR, patients with SNP appeared to have better survival than patients with wild type 5’UTR, but the difference is not significant. More interestingly, patients carrying 3’UTR variations that are disrupting microRNA target sites had poorer survival compared with other 3’UTR variants and wild type 3’UTR. This unique observation, in addition to the lower frequency of 3’UTR variants as compared to variants of CDS and 5’UTR of MYC, suggest that deregulation of MYC expression by microRNAs is important in the pathogenesis and progression of DLBCLs.
Conclusions
The MYC gene is commonly mutated in DLBCL patients. These variationsdistinguished from wild type can be subdivded into variants involving the 5’UTR, CDS and 3’UTR regions which have different prognostic significance, as well as clinical and therapeutic importance.
Disclosures:
Winter: Millenium: Research Funding; Novartis : Research Funding; Pfizer (Wyeth): Research Funding; Seattle Genetics: Research Funding; Spectrum: Research Funding; Janssen (Pharmacyclics): Research Funding; Spectrum (Allos): Consultancy; Sanofi Aventis: Consultancy; Tgen: Consultancy; AMBIT Biosciences (Spouse): Research Funding; Celgene (Spouse): DSMB, DSMB Other, Research Funding; Ariad Pharmaceuticals (Spouse): Research Funding; Novartis (Spouse): Consultancy, Research Funding; Amgen (Spouse): Consultancy, Research Funding; Astellas (Spouse): Research Funding; Caremark/CVS: Consultancy; Pfizer (Spouse): Consultancy; Sanofi Aventis (Spouse): DSMB, DSMB Other; Bristol Myers Squibb (Spouse): DSMB, DSMB Other; UptoDate, Inc.(Spouse): Patents & Royalties.
Multiplex Droplet Digital PCR Quantification of Recurrent Somatic Mutations in Diffuse Large B-Cell and Follicular Lymphoma
