Molecular Profiling of Large B-Cell Lymphomas

Abstract

Background: Large B-cell non-Hodgkin's lymphoma (NHL) comprises of a heterogeneous group of lymphomas with a high-grade morphology and aggressive nature. The diagnosis has gradually evolved from morphological characterization to classification of this group based on ancillary techniques such as immunohistochemistry (IHC), fluorescence in situ hybridization (FISH), and molecular studies. Diffuse large B-cell lymphomas (DLBCL), not otherwise specified (NOS) is the most common B-cell NHL reported and a new diagnostic entity termed high-grade B-cell lymphoma harboring an MYC rearrangement with a BCL2 and/or BCL6 have been introduced by the WHO in 2017. MYC and BCL2/BCL6 proteins expression on IHC due to mutations leading to nuclear factor kappa B pathway activation is considered as double-expressor lymphoma (DEL). Materials and Methods: Sixty-two patients diagnosed with DLBCL, NOS on histopathology were subjected to IHC markers such as (CD20, CD79a, PAX5, CD10, Bcl6, Bcl2, MUM1, TDT, and Myc) and classified into activated B-cell and germinal center B-cell based on Hans' Algorithm. The samples were consequently subjected to tissue FISH for the detection of MYC, BCL2, and BCL6 gene translocations and classified as double-hit lymphoma (DHL)/triple-hit lymphoma (THL). The FISH results were subsequently compared for IHC expression of c-myc, Bcl2, and Bcl6. The staging, international prognostic index (IPI) scoring and lactate dehydrogenase levels were compared with progression-free survival (PFS) of 15 months among DHL/THL and DEL/TEL. Results: The median age of presentation among DLBCL-NOS patients is 58 years, while males (66.7%) were affected more commonly than females (33.3%). The majority of the patients presented with nodal involvement (71%) while extranodal involvement was seen in 29% cases. Hans' algorithm showed a significant P value with the IHC expression of BCL2, BCL6 and C-MYC. IHC and FISH correlation for BCL2 and BCL6 showed 100% sensitivity and 100% negative predictive value. IHC and FISH for c-MYC showed concordant results with a significant P < 0.03. The clinicopathological results of S/D/THL showed association with higher stage disease, higher IPI scoring, and high Ki-67 index with inferior PFS. Conclusions: IHC MYC is a sensitive screening modality for MYC translocation and can be used for the identification of rearrangement in lower socioeconomic areas. Based on clinicopathological studies, all patients with DLBCL must undergo MYC FISH testing as these patients behave as high-grade lymphomas. Hence, a new entity DLBCL with MYC rearrangement without BCL-2/6 rearrangements maybe considered as a novel entity and to be studied in future cohorts.