Definition:

Diffuse large B-cell lymphoma, not otherwise specified (DLBCL, NOS) is the most common type of DLBCL. DLBCL accounts for 30-40% of all non-Hodgkin lymphomas (NHL), making it the most prevalent form of NHL. DLBCL can occur as primary disease or through histologic transformation from other low-grade B-cell lymphoma, and is a clinically and genetically heterogeneous disease. The cell-of-origin (COO) determination based on gene expression profiling (GEP) subdivides most DLBCL, NOS patients into two main categories, namely germinal center B-cell-like (GCB) and activated B-cell-like (ABC) DLBCL. GCB subtype is characterized by frequent mutations in involved histone methylation or acetylation (EZH2, EP300), B-cell homing (GNA13, GNAI2), PI3K pathway signalling (PTEN), and apoptotic pathway (BCL2). In contrast, ABC subtype is driven by frequent mutations in the B cell receptor and NFKB pathways (CARD11, CD79a/CD79b, TNFAIP3 and MYD88).