Schematic diagram of the possible IGH locus rearrangements present in the (COO) and the genomic breakpoints of the shared t(14;19) and t(12;14). (A) Scenario of the possible IGH locus rearrangements present in the (COO). Scenario 1 has the COO at the stage prior to IGH VDJ rearrangement. Some of these cancer cells may undergo full IGH VDJ rearrangements and subsequent secondary rearrangements, however these would not be shared between the twins. Scenario 2 has the COO at the stage with a partial IGH DJ rearrangement that is shared between the twins. Some of these cancer cells can undergo further IG V- DJ and/or secondary rearrangements (where a primary immunoglobulin DJ rearrangement can be replaced by an upstream D to downstream J) that may be present only in 1 twin. Scenario 3 has the COO with a full IgH VDJ rearrangement. Some of these cancer cells may undergo further secondary immunoglobulin V rearrangements. Only Scenario 2 is supported by the data. (B) Schematic representation of the genomic breakpoints determined by whole-genome sequencing at the base pair level for t(14;19) and t(12;14).