Non-IG::MYC in diffuse large B-cell lymphoma confers variable genomic configurations and MYC transactivation potential

Abstract

MYC translocation occurs in 8-14% of diffuse large B-cell lymphoma (DLBCL), and may concur with BCL2 and/or BCL6 translocation, known as double-hit (DH) or triple-hit (TH). DLBCL-MYC/BCL2-DH/TH are largely germinal centre B-cell like subtype, but show variable clinical outcome, with IG::MYC fusion significantly associated with inferior survival. While DLBCL-MYC/BCL6-DH are variable in their cell-of-origin subtypes and clinical outcome. Intriguingly, only 40-50% of DLBCL with MYC translocation show high MYC protein expression (>70%). We studied 186 DLBCLs with MYC translocation including 32 MYC/BCL2/BCL6-TH, 75 MYC/BCL2-DH and 26 MYC/BCL6-DH. FISH revealed a MYC/BCL6 fusion in 59% of DLBCL-MYC/BCL2/BCL6-TH and 27% of DLBCL-MYC/BCL6-DH. Targeted NGS showed a similar mutation profile and LymphGen genetic subtype between DLBCL-MYC/BCL2/BCL6-TH and DLBCL-MYC/BCL2-DH, but variable LymphGen subtypes among DLBCL-MYC/BCL6-DH. MYC protein expression is uniformly high in DLBCL with IG::MYC, but variable in those with non-IG::MYC including MYC/BCL6-fusion. Translocation breakpoint analyses of 8 cases by TLC-based NGS showed no obvious genomic configuration that enables MYC transactivation in 3 of the 4 cases with non-IG::MYC, while a typical promoter substitution or IGH super enhancer juxtaposition in the remaining cases. The findings potentially explain variable MYC expression in DLBCL with MYC translocation, and also bear practical implications in its routine assessment.

Fig. 1

Summary of DLBCL with MYC translocation and experiments carried out.

Fig. 2. MYC/BCL6 fusion accounts for a high proportion of DLBCL with MYC and BCL6 translocation.

A Example of interphase FISH in a case with a triple hit (TH), in which the MYC and BCL6 translocation detected by their breakapart probes (BAP) are due to MYC/BCL6 fusion. B The frequency of MYC/BCL6 fusion is significantly higher in cases with MYC/BCL6/BCL2-”TH” than those with MYC/BCL6 “double hit” (DH).

Fig. 3

Mutation profile (A) and LymphGen genetic subtype (B) according to translocation status. tr translocation, IHC immunohistochemistry, TH triple hits, DH double hits.

Fig. 4. MYC protein expression and its correlation with MYC translocation partner.

A Examples of MYC immunohistochemistry and grading; (B) high MYC protein expression is invariably seen in DLBCL with IG::MYC, but only in up to 50% cases with non-IG::MYC translocation..

Fig. 5. MYC translocation with BCL6 or other partners lacks genomic configuration that activates MYC transcription.

Genomic breakpoint sequencing analyses was performed by targeted locus capture-based next generation sequencing (TLC-NGS) with sequence annotations based on human genome (hg19). E: exon (fill box: coding exon; non-filled box: non-coding exon). Cen: centromere; Tel: telomere.

Fig. 6. MYC translocation with IGH or novel partner confers genomic configuration that activates MYC transcription.

Genomic breakpoint sequencing analyses was performed by targeted locus capture-based next generation sequencing (TLC-NGS) with sequence annotations based on human genome (hg19). E: exon (fill box: coding exon; non-filled box: non-coding exon). Cen: centromere; Tel: telomere.

Fig. 7. MYC translocation with IGH or novel partner confers genomic configuration that activates MYC transcription.

Genomic breakpoint sequencing analyses was performed by targeted locus capture-based next generation sequencing (TLC-NGS) with sequence annotations based on human genome (hg19). E: exon (fill box: coding exon; non-filled box: non-coding exon). Cen: centromere; Tel: telomere.