Diffuse large cell lymphoma (DLCL)

this biologically heterogeneous group of lymphomas in the REAL proposal accounts for as many as 40% of NHL in western countries and includes the entities of centroblastic lymphoma, immunoblastic lymphoma and B-cell anaplastic lymphoma recognized by the Kiel classification

the cell of origin is probably a large transformed B-cell, frequently deriving from the follicle centre, harbouring somatic hypermutation of the Ig genes and ongoing mutations (antigen driven stimulation). The phenotype is usually CD19+, CD22+, CD10-/+, SIg+

10-20% of DLCL carry 3q27 translocations detectable at banding analysis, appoximately 50% of which may be expected to be associated with BCL6 rearrangement; molecular genetic methods proved very efficient in demonstrating this genetic lesion and studies using southern blotting detecting BCL6 breaks in the 4.0 kb major breakpoint region showed 20-30% of unselected DLCL to be rearranged

there is no distinctive histological features in DLCL with 3q27/BCL6 rearrangement as compared with other DLCL; the proliferation consists of a diffuse infiltrate of large cells with vescicular nuclei and prominent nucleoli with basophilic cytoplasm; criteria for distinguishing those cases with a predominance of immunoblasts or of anaplastic B-cells were put forward but were felt not to be enough reproducible as to allow for proper categorization of distinct pathological entities; 3q27 abnormalities were seen in similar frequency in the immunoblastic variant and in the centroblastic variant of DLCL in a study

a predominance of extra-nodal forms and a relatively favourable outcome was observed in BCL6-rearranged DLCL but BCL6 failed as a prognostic indicator when compared to other molecular genetic lesions; thus, the assessment of the prognostic significance of 3q27 or BCL6 breaks in DLCL needs further investigation in prospective studies

Follicle centre cell lymphoma (FCCL)

FCCL accounts for approximately 30-40% of all NHL in western countries

the neoplasia derives from centrocytes / centroblasts unable to progress through the germinal centre, carrying somatic hypermutation of the IgV genes and a pan-B+, CD10+/-, CD5-, sIg+ phenotype

3q27 translocations involving the chromosome regions where Ig genes are located (2p11: IgK, 14q32: IgH, 22q11: IgL) were detected in 6.5% of FCCL; a 16% incidence for any 3q27 break was reported; the association of 3q27/BCL6 involvement with the classical t(14;18) was described; molecular genetic studies found a 6-14% incidence for BCL6 rearrangement in FCCL

no specific correlation was established between 3q27 breaks and specific clinicopathological features of FCCL

Marginal zone B-cell lymphoma (MZBCL)

7-8% of NHL show the clinicopathological features of MZBCL

the transformed cells derive form marginal zone lymphocytes harbouring hypermutated IgV genes with the following phenotype: pan-B+, CD5-/+, CD10-, CD23-, CD11c+/-, cyIg +(40% of the cells), sIgM+ bright, sIgD-

a minority of MZBCL may carry a 3q27/BCL6 translocation, mostly t(3;14)(q27;q32)

there is no distinctive clinicopathological feature in this cytogenetic subset of MZBCL, but a predominance of extra-nodal forms over splenic and nodal types and an excess of large blast-like cells were noted

below are listed translocations involving -or likely to involve- BCL6 in 3q27, and a partner gene in the other breakpoint

3q27 anomalies are often associated with well known primary anomalies such as t(8;14)(q24;q32), t(11;14)(q13;q32), t(14,18)(q32;q21)

the translocation partners of BCL6 are not confined to the immunoglobulin superfamily, contrarily to the situation found with c-MYC, BCL1, or BCL2

breakpoint in the first non-coding exon (containing the 2 promoters) or the first intron of BCL6; the partner gene therefore fuses with the second exon of BCL6, resulting in a 5 partner - 3 BCL6 fusion transcript; it is supposed that substitution of the promoter of BCL6 may be responsible for BCL6 regulation, or that a break in the breakpoint cluster region of BCL6 may inhibit a sequence involved in BCL6 regulation; partners other than immunoglobulin lack homology with switch regions, VDJ sequences, or Chi sequencesno fusion protein; the 5 regulatory region of BCL6 is replaced by the 5 regulatory region of the partner gene.