Methylation Profiling of Mediastinal Gray Zone Lymphoma Reveals a Distinctive Signature with Elements Shared by Classical Hodgkin's Lymphoma and Mediastinal Large B-Cell Lymphoma

Mediastinal gray zone lymphoma (MGZL) is a newly recognized entity demonstrating transitional morphologic and immunophenotypic features between classical Hodgkin's lymphoma, nodular sclerosis subtype (CHLNS) and primary mediastinal large B-cell lymphoma (PMLBCL). CHLNS and PMLBCL differ in morphology, immunophenotype, and therapeutic consequences. MGZLs present a challenge both to the pathologist and clinician, as the criteria to distinguish MGZL from CHLNS and PMLBCL are still imprecise, and the optimal treatment approach is as yet undetermined.

Epigenetic changes have been implicated in the loss of the B-cell program in CHL, and might provide a basis for the immunophenotypic alterations seen in MGZL. Thus, we performed a large scale DNA methylation array of MGZL, CHLNS, and PMLBCL as well as diffuse large B-cell lymphoma (DLBCL) to investigate the biological underpinnings of MGZL and how it corresponds to the two related entities CHLNS and PMLBCL and the less related entity DLBCL. Microdissection of tumor cells was performed to identify changes in the tumor cell population, and allow comparison with the background inflammatory and stromal milieu.

Principal component analysis (PCA) demonstrated that MGZLs have a distinct epigenetic profile intermediate between CHLNS and PMLBCL but clearly different from that of DLBCL. Analysis of common hypo- and hypermethylated CpG targets in MGZL, CHLNS, PMLBCL and DLBCL was performed. MGZL showed great overlap with CHLNS (49 common targets) and PMLBCL (50 common targets). In contrast, MGZL shared only two common targets with DLBCL. However, using the epigenetic profiles we were able to establish class prediction models that could distinguish between MGZL, CHLNS and PMLBCL with a final combined prediction of 100%. Pyrosequencing for selected CpG sites from different genes were performed and confirmed the high accuracy of methylation array results.

MGZLs share several clinical and pathological features with CHLNS and PMLBCL. Our findings further underscore the close biological relationship between MGZL, CHLNS and PMLBCL, and ready distinction from DLBCL. However, MGZL has a distinct epigenetic identity that shares elements of both parent disorders. As the first biological study on MGZL, our results provide novel insights into MGZL pathogenesis, and its relationship to CHLNS and PMLBCL.

Emmert-Buck:NIH: Michael Emmert-Buck is an inventor on all NIH patents covering laser capture microdissection technology and receives royalty payments through the NIH technology transfer program., Patents & Royalties.