Two recurrent types of IGH ::5' BCL2 breakpoints representing cytogenetic ins(14;18)(q32;q21q21) and t(14;18)(q32;q21), mediated by the VDJ and class switch recombination processes, respectively.

We describe two types of IGH :: BCL2 breakpoints involving the 5' region of BCL2 (5' BCL2 ). One was ins(14;18)(q32;q21q21) observed in 2 follicular lymphoma (FL) cases, in which IGH was cleaved at 3' of IGHD and 5' of IGHJ and BCL2 was cleaved at 5' BCL2 and downstream regions, and a 281- or 201-kilobase pair fragment containing the BCL2 protein-coding sequences was invertedly inserted into IGH . In another type observed in 2 FL and 2 chronic lymphocytic leukemia (CLL) cases, breakage and reunion occurred within the switch region associated with IGHM (Sµ) and 5' BCL2 , creating IGH Sµ::5' BCL2 fusion sequences on der(18)t(14;18)(q32;q21). The former is considered to be mediated by VDJ -recombination, while the latter by the class switch recombination process. There were no particular features in FL or CLL cases with IGH ::5' BCL2 breakpoints compared with those with t(14;18)(q32;q21)/ IGH :: BCL2 involving the 3' breakpoint cluster regions.