Pathological Insights into the Subclassification of Diffuse Large B-Cell Lymphoma (NOS)

Abstract Introduction Diffuse Large B-cell Lymphoma, NOS represents around 25-35% of adult Non- Hodgkin’s lymphoma worldwide. According to the 5th edition of WHO for Hematolymphoid neoplasms, DLBCL, NOS encompasses all biologically heterogeneous cases with no clear criteria for inclusion in a specific diagnostic category. The sixth and seventh decade are reported as the median age for DLBCL, NOS in developed countries and a lower median age in developing countries, with slight male predominance (1.2:1). DLBCL, NOS is further subclassified according to cell of origin (COO) using gene expression profiling (GEP) and various immunohistocehmical (IHC) algorithms into germinal center (GCB) and activated B-cell (ABC) subtypes, which carries a prognostic and therapeutic value. Objectives In our study, we have recorded and compared the demographic and pathological data of the DLBCL, NOS subtypes in Ain Shams University Hospitals over the period of three years. Materials and Methods Our retrospective study was conducted in the Department of Histopathology in Ain Shams University Hospitals from January 2020 till December 2022. We retrieved all available cases with a diagnosis consistent with DLBCL, NOS over the period of these three years. A total of 102 cases with available reports, H&E slides and paraffin blocks with sufficient tissue material were included in this study. We recorded the demographic and pathological data of the cases, re-examined available H& E and IHC slides, and applied immunohistochemical (IHC) staining of CD10, and multiple myeloma oncogene 1(MUM1) to remaining DLBCL cases with available paraffin blocks and sufficient tissue material for further subclassification of into GCB and ABC subtypes according to the Hans and modified Hans immuoalgorithms. Finally, we compared and analyzed the demographic and pathological data of both subtypes. Results DLBCL, NOS represented 35.3 % of all NHL cases and 26.19% of all lymphoma cases overall. Out of 102 cases of DLBCL, NOS, 38.2% were GCB while were 61.8 % ABC subtypes. The median age for DLBCL, NOS was 54.9 with male to female ratio of 1.3:1. The ABC subtype showed a higher median age and female affection predominance as compared to GCB. The most affected site overall was the cervical nodal group while stomach, spleen and liver were reported as the most commonly involved extranodal sites. The ABC subtype showed significant association with extra-abdominal nodal groups as compared to the GCB subtype (P = 0