Page 149 - Haematologica Vol. 107 - September 2022

ARTICLE - FL3B and simultaneous DLBCL K. Koch et al.
Figure 2. Mutational pattern of the different growth patterns of follicular lymphoma grade 3B + diffuse large B-cell lymphoma.
Within each lymphoma the patterns were analyzed separately. Individual cases are indicated by the case identifie (ID) and growth pattern as D: diffuse large B-cell lymphoma (DLBCL) component; F: follicular component; C: confluent component. The immunophenotype was scored in a five-tiered way 0%; 1-25%; 26-50%; 51-75%; >75% positive tumor cells and is displayed as a color code as shown in the scale bar. Fluorescence in situ hybridization (FISH) was done using break apart probes (BA). Potential protein-changing variants identified in the different components were colored according to the variant effect prediction (red: high; dark orange: moderate, deleterious; yellow: moderate, deleterious and tolerated effect based on different algorithms used, black: region was not covered in the DLBCL sample, gray: variant was identified with low variant allele frequency (<10%) in the confluent component. If more than one variant with different effects targeting one gene was identified in one component both variant effects are shown separately. E: exon; CDS: coding region; #: region was not covered in the DLBCL component of that sample. $: variant was identified with low (<10%) variant allele frequency in the confluent component. IHC: immunohistochemistry.
FL3B+DLBCL (FL3B: BCL2 in 2/19 [11%], BCL6 in 8/19 [42%], MYC in 1/19 [5%]; FL3B+DLBCL: BCL2 in 6/21 [29%], BCL6 in 7/21 [33%], MYC in 3/21 [14%], P=0.2409 for BCL2, P>0.9999 for BCL6, P=0.6094 for MYC, Fisher exact test). FISH results for at least two growth patterns of the same lymphoma were available for 21 cases. In most cases the chromosomal aberrations were shared between the different growth pat- terns (20/21 cases, 95%). However, in 1/21 (5%) cases a di- vergent result was observed concerning BCL6. This case harbored a BCL6 break in the confluent area but not in the follicular areas of a FL3B (data not shown).
The microenvironmental composition of follicular lymphoma grade 3B and diffuse large B-cell lymphoma differs
In order to understand whether the growth patterns rep-
resent molecular progression/evolution of the disease, gene expression was analyzed in FL3B+DLBCL cases. As- suming that the follicular pattern and DLBCL represent the two ends of a spectrum of growth patterns in each indi- vidual lymphoma, these areas were analyzed separately in cases with both components available (n=6). Since DLBCL are known to be a heterogeneous disease with their mol- ecular features differing from patient to patient, we ana- lyzed differential expression within each patient comparing the follicular FL3B with the DLBCL component in cases with both components available. Using the crite- ria described in the Methods section we identified a low number of genes (n=45) differentially expressed in multiple patients (Online Supplementary Figure S1). Of these, 33/45 (73%) genes were more highly expressed in the follicular FL3B area and reflected the expression pat-
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