In the ABC subtype, the pathway is chronically active due to auto-antigenic stimulation of the BCR, auto-activating BCR clustering or enrichment for BCR/NF-κB activating mutations, e.g., at the level of the BCR complex-associated CD79a/b proteins, CARD11 or the tumor necrosis factor-α (TNFα)-induced protein 3 (TNFAIP3)/A20, collectively driving high-level NF-κB activity [69,70,71]. This evidence concerns the gene TNFAIP3 and aneurysmal bone cyst.