Both GCB and ABC DLBCL present genetic alterations on genes encoding chromatin modifiers [KMT2D/MLL2 or KMT2C/MLL3 (mutations); CREEBBP (mutations or 16p13 deletions) or EP300 (mutations or 22q13 deletions)], the germinal center master regulator BCL6 (BCL6 chromosomal translocations, MEF2B mutations), proteins involved in DNA damage response ([TP53 (mutations or 17p13 deletions)], or proteins contributing to immune surveillance [B2M (mutations or 15q21 deletions); CD58 (mutations or 15q21 deletions)]. The gene discussed is B2M; the disease is aneurysmal bone cyst.