Figure 1. Diagrammatic depiction of a chromosomal translocation between two hypothetical chromosomes, A and B, in which an enhancer, associated with a gene on chromosome A, is juxtaposed to a gene containing three exons, 1, 2 and 3, on chromosome B. This results in increased expression of the gene on the derivative B chromosome.

Figure 2. Diagrammatic depiction of a chromosomal translocation between two hypothetical chromosomes, A and B, in which two three-exon genes are fused to form a four-exon gene consisting of the first two exons of the gene on chromosome A and the last two exons of the gene on chromosome B.

Figure 3. Diagrammatic depiction of five different chromosomal translocations in which the promoters of various genes (P1–P5) – heavy- and light-chain immunoglobulin (IgH and IgL), heat shock protein 69 (HSP069), RhoH and L-Plastin – are juxtaposed to the BCL-6 gene. In each case, the Bcl-6 gene is overexpressed. The fact that many different translocations (those shown here represent just some of the translocations found, each in a different tumour) can cause overexpression of BCL-6 has led to the term ‘promiscuous’ in the context of the use of multiple promoters.

Figure 4. B-cell lymphomas and some associated translocations. From left to right, in the lower part of the figure, the most common B-cell lymphomas are depicted in the context of the components of secondary (germinal) follicles in lymphoid tissue – morphology and immunophenotype of these lymphomas closely resemble those of normal cells of the secondary follicle. The lymphomas are small lymphocytic lymphoma, nodal marginal cell lymphoma, mantle cell lymphoma, BL, diffuse large B-cell lymphoma and, again, lymphocytic lymphoma (which includes both ‘prefollicular’ and ‘postfollicular’ subtypes). The components of the secondary follicle are labelled MaZ (marginal zone), MZ (mantle zone) and GC (germinal centre). In the upper part of the figure,a stem cell differentiating into precursor B cells is depicted. Four different translocations are shown as though occurring in precursor B cells (see text for discussion). The arrows pointing to the lymphoma cells indicate which translocation is associated with each of the lymphomas, except for small lymphocytic lymphoma and nodal marginal zone lymphoma, in which, to date, nonrandom chromosomal translocations have not been observed. Whereas essentially all mantle zone lymphomas and BLs, and the majority of follicular lymphomas, bear the indicated translocations, only a small fraction of diffuse large B-cell lymphomas have 3;14 translocations.