Arguably the MYC activity gain is the most constantly observed phenomenon (>70% of cases) in transformed FL/MALT/CLL (Richter's transformation) and co-occurs with specific aberrations such as the loss of p53, CDKN2A/B, or gain of BCL2/BCL6.
This paper describes how we discovered the juxtaposition of the MYC gene to the human immunoglobulin loci and how that finding was extended to characterize molecularly the t(14;18) chromosome translocation of follicular lymphoma and to clone the BCL2 gene.
We showed that DLBCL with MYC/BCL2-DH, and those with BCL2 translocation, harbour the characteristic mutation signatures that are associated with follicular lymphoma and its high-grade transformation.
Our analysis provided a novel look on the transition range between FL and DLBCL, on DLBCL with poor prognosis showing expression patterns resembling that of Burkitt's lymphoma and particularly on 'double-hit' MYC and BCL2 transformed lymphomas.
To clarify the characteristics of double-hit follicular lymphomas, we analyzed 10 cases of double-hit follicular lymphomas and 15 cases of high-grade B-cell lymphomas with MYC and BCL2 and/or BCL6 rearrangements for clinicopathological and genome-wide copy-number alterations and copy-neutral loss-of-heterozygosity profiles.
We focused on one of these miRNAs, namely <i>miR-150</i>, which was uniformly downmodulated in all examined tFLs (∼3.5-fold), and observed that high levels of MYC are responsible for repressing <i>miR-150</i> in tFL by binding in its upstream region.
The most common scenario is transformation of follicular lymphoma to either diffuse large B-cell lymphoma or high-grade B-cell lymphoma with MYC and BCL2 and/or BCL6 translocations; however, other indolent subtypes such as marginal zone lymphoma, lymphoplasmacytic lymphoma, small lymphocytic lymphoma/chronic lymphocytic leukemia, or even nodular lymphocyte predominant Hodgkin lymphoma, can undergo similar histologic transformation.
Fluorescence in situ hybridization (FISH) identified an IGH-BCL2 rearrangement in both the FL and high-grade B-cell components while a MYC rearrangement was detected in the high-grade B-cell component alone.
MYC/BCL2 double hit lymphoma (DHL) has been the subject of many studies; however, no study has systemically compared the clinicopathologic features and prognostic factors between patients with de novo disease versus those with a history of follicular lymphoma (FL).
Our limited experience showed that additional copy of intact MYC may be equivalent to "classic" DHL on the background of DLBCL with additional cytogenetic abnormalities, however isolated t(14;18)(q32;q21) translocation in combination with additional copy of intact MYC may demonstrate histology and clinical outcome more comparable with "classic" low grade follicular lymphoma, albeit with more aggressive morphology.
Mutations in epigenetic modifiers and antiapoptotic genes are introduced early in the common precursor, whereas tFL is specifically associated with alterations deregulating cell-cycle progression and DNA damage responses (CDKN2A/B, MYC, and TP53) as well as aberrant somatic hypermutation.
We detected EZH2 mutations in 12/55 (22%) follicular lymphomas (FL), 5/35 (14%) diffuse large B cell lymphomas with a germinal center immunophenotype (GCB-DLBCL), and 2/11 (18%) high grade B cell lymphomas with concurrent rearrangements of BCL2 and MYC.
Moreover, FISH and molecular genetic study confirmed concomitant MYC translocations and t(14;18) in the high-grade component, thereby suggesting the transformation of atypical Burkitt's lymphoma from an undiagnosed antecedent follicular lymphoma.
Transformation from follicular lymphoma to high-grade B-cell lymphoma/leukemia with additional t(2;8)(p12;q24), with inverse expressions of c-MYC and BCL-2, and light-chain switch.
Occurrence of ASHM in PIM-1, RhoH/TTF, and c-MYC was a constant finding in follicular lymphoma (FL) (all of 11 cases) but not so frequent in diffuse large B-cell lymphoma (DLBCL) (4 (33.3%) of 12 cases) and Marginal zone B-cell lymphoma (MZBCL) (1 (10.0%) of 10 cases).
BCL2(+)/MYC(+) lymphomas were diagnosed as B-cell lymphoma unclassifiable (BCLU; n = 36) with features intermediate between Burkitt lymphoma and diffuse large B-cell lymphoma (DLBCL); DLBCL (n = 17), or follicular lymphoma (n = 1).
This is a small series but one which raises the possibility that the presence of a C-MYC translocations at presentation may identify a particularly aggressive subtype of FL.