Follicular lymphoma with Epstein-Barr virus-associated transformation: A case report and review of the literature.

Follicular lymphoma (FL) is a common type of B-cell lymphoma, accounting for about 20% of all lymphomas. Although FL is primarily characterized by an indolent clinical course, histological transformation (HT) remains one of the significant challenges in managing patients with FL. Here, we present a case of FL with partial large-cell transformation due to Epstein-Barr Virus (EBV) arising in a 50-year-old Japanese woman with no known immunodeficiency. Immunohistochemical studies revealed that medium-sized FL cells expressed CD20, CD10, BCL2, and BCL6, whereas large cells were positive for CD20, and MUM1. In situ hybridization (ISH) revealed large cells to be positive for EBV-encoded small RNA (EBER) and further immunohistochemical investigation demonstrated EBER+ cells to express latent membrane protein 1 (LMP1). The Ki-67 index was about 30% in FL cells, and over 70% in large cells. Fluorescence in situ hybridization for BCL2 combined with EBER-ISH identified BCL2 rearrangement in both EBV-infected large cells and EBV-uninfected FL cells, suggesting these two components were clonally related. These findings indicate that EBV contributes to the transformation of FL. As far as the authors could find, only four previous cases of FL development to EBV-positive aggressive lymphoma have been reported. Further studies are needed to clarify the role of EBV in the HT of FL.