Molecular structure of double reciprocal translocations: significance in B-cell lymphomagenesis

The molecular structure of reciprocal translocations associated with low grade and high grade non-Hodgkin's lymphomas occurring together was analysed in two tumors. Sequential biopsies documented histological transformation of a large cell lymphoma to an immunoblastic lymphoma bearing t(14;18)(q32;q21) and t(8;22)(q24;q11). A second tumor, a small non-cleaved cell lymphoma, demonstrated a t(8;14)(q24;q11) as well as t(18;22)(q21;q11). DNA analysis from these tumors showed rearrangements at the Ig heavy chain, kappa and lambda light chains, BCL2 and c-MYC loci. Utilizing multiple enzyme digests and different probes spanning the BCL2, c-MYC and Ig genes, mapping of DNA break-points was performed. In both these tumors primary translocation events dysregulating the BCL2 or c-MYC were identified to have occurred in a pre-B-cell. Based on these results and those published previously, a sequence of B-cell development during which somatic recombination errors lead to the genesis of specific translocations is proposed. From these studies it is inferred that secondary dysregulation of a c-MYC in a lymphoma tumor carrying dysregulated BCL2 gene leads to rapid progression to high grade disease.