BCL2 and aneurysmal bone cyst: The C1 subtype is a previously unidentified group of low-risk ABC-DLBCLs; the C2 subtype often exhibits 9p21.13/CDKN2A and 13q14.2/RB1 copy deletions; 95% of C3 subtypes are of GCB origin and exhibit BCL2, KMT2D, CREBBP, and EZH2 mutations, PTEN inactivation and epigenetic enzyme alterations; C4 subtypes are a newly defined group of high-risk GCB-DLBCLs; and the C5 subtype exhibits increased 18q copy number and high BCL2 expression.