Inmunoglobulin light chain enhancer hijacking activates CCND2 and CCND3 in cyclin D1-negative mantle cell lymphoma

Mantle cell lymphoma (MCL) is characterized by the t(11;14)(q13;q32) translocation resulting in overexpression of cyclin D1. However, a small subset of cyclin D1-negative MCL (cyclin D1 MCL) has been recognized, and approximately half of them harbor CCND2 translocations while the primary oncogenic event in cyclin D1/D2 MCL remains elusive. To identify other potential mechanisms driving MCL pathogenesis we investigated 56 cyclin D1/SOX11 MCL by fluorescence in situ hybridization (FISH), whole genome/exome sequencing, gene expression and copy number arrays. FISH with break-apart probes identified CCND2 rearrangements in 39 (70%) cases but not CCND3 rearrangements. We analyzed 3 of these negative cases by whole-genome/exome sequencing and identified IGK (n=2) and IGL (n=1) enhancer hijackings near CCND3 that were associated with cyclin D3 overexpression. By specific FISH probes, including the IGK enhancer region, we detected 10 additional cryptic IGK juxtapositions to CCND3 (6 cases) and CCND2 (4 cases) in MCL that overexpressed, respectively, these cyclins. A minor subset of 4 cyclin D1 MCL cases lacked cyclin D rearrangements and showed upregulation of CCNE1 and CCNE2. These cases had blastoid morphology, high genomic complexity, and CDKN2A and RB1 deletions. Both genomic and gene expression profiles of cyclin D1 MCL cases were indistinguishable from cyclin D1 MCL. In conclusion, virtually all cyclin D1 MCL carry CCND2/CCND3 rearrangements with IG genes, including a novel IGK/L enhancer hijacking mechanism. A subset of cyclin D1/D2/D3 MCL with aggressive features have cyclin E dysregulation. Specific FISH probes may allow the molecular identification and diagnosis of cyclin D1 MCL. IGK/L enhancer hijacking in MCL Martín-Garcia et al