Hypothetical model of the role of PRDM1 in DLBCL pathogenesis. Germinal center (GC) B cells, upon activation through antigen binding to high-affinity receptor, undergo terminal differentiation to plasma cells as a result of PRDM1 induction. Genetic defects in PRDM1 prevent accumulation of functional PRDM1 and inhibit terminal differentiation. As a result, the GC B cells are forced to remain in an activated state and continue to proliferate, possibly driven by BCL6 deregulated expression (as described in “Discussion”). They may then acquire additional genetic alterations that lead to development of full-blown DLBCLs.