PRDM1 and aneurysmal bone cyst: This effect appears to underlie the tumorigenic effect of mutations that affect the transcription factor PRDM1 (BLIMP1), which is the master regulator of plasma cell differentiation.50 Translocations that induce constitutive expression of BCL6 may also lead to aberrant repression of PRDM1. 35, 51PRDM1 loss occurs almost exclusively in patients with ABC‐DLBCLs, many of which manifest a plasmablastic transcriptional profile (Figure 1).