BCL6-rearrangements Implications in Non-Hodgkin Lymphomas.

Overview

Non-Hodgkin lymphomas (NHLs) constitute a heterogeneous group of malignant neoplasms, with diverse clinical behaviors and distinct pathologic and molecular characteristics. Among these lymphomas, follicular lymphomas (FLs), marginal zone lymphomas (MZLs) and diffuse large B-cell lymphomas (DLBCLs) emerge as the most prevalent entities. While FL and MZL are representative of indolent B-cell lymphomas, characterized by a slow progression of the disease and favorable clinical outcomes, DLBCL stands out as an aggressive lymphoma, often occuring from the transformation of a pre-existing indolent lymphoma. Chromosome translocations are a hallmark of some NHL subtypes, offering insights into their molecular pathogenesis. For instance, the conventional FL is genetically characterized by the t(14;18) chromosomal translocation, found in 85-90% of cases, resulting in sustained elevation of the antiapoptotic protein B-cell lymphoma 2 (BCL2). However, certain FL cases lack BCL2 translocations and exhibit distinct clinical, morphological and phenotypical features with genetic heterogeneity. A subset of BCL2-negative FLs displays rearrangements within chromosomal region 3q27, inducing abnormal modulation of B-cell lymphoma 6 (BCL6) expression. The BCL6 gene plays a critical role in germinal center development and B-cell differentiation. Previous investigations indicate that BCL6 rearrangements (BCL6-R) manifest distinct pathological and genetic features, diverging from classical FL presentations. FLs carrying BCL6-R commonly share a specific CD10- Bcl-2- Bcl-6+ phenotype, often accompanied by a monocytoid component and increased frequency of diffuse architectural patterns. Patients with BCL6-R tend to exhibit advanced clinical stages and complex genetic profiles. MZLs present differential diagnostic challenges due to shared monocytoid components, phenotypes traits, and common genetic features. The similarities observed between BCL6-R FL and MZL suggest a convergence in both morphological and genetic aspects, leading to intricate differentiation. Traditionally, these indolent NHLs with BCL6-R were categorized as FL and incorporated into the FL category in the WHO classification. However, few studies highlight the occurrence of BCL6-R in MZLs. This observation gives rise to the hypothesis that indolent NHLs exhibiting BCL6-R might correspond to a continuum comprising both FL and MZL. Additionally, BCL6-R has been frequently documented in DLBCL cases with residual MZL component. These DLBCL cases might display a mutational profile reminiscent of MZL. This suggests a plausible origin of BCL6-R DLBCL from indolent BCL6-R MZLs or BCL6-R FLs cases.