Clinicopathologic and molecular features of primary effusion lymphoma and fluid overload-associated large B-cell lymphoma: A retrospective study.

Primary effusion lymphoma (PEL) and fluid overload-associated large B-cell lymphoma (FO-LBCL) are rare B-cell neoplasms presenting as serous effusions without solid masses, distinguished primarily by human herpesvirus-8 status. We analyzed three PEL and seven FO-LBCL cases using immunohistochemistry, Epstein-Barr virus-encoded RNA in situ hybridization, immunoglobulin heavy chain (IGH), T-cell receptor beta (TRB) and T-cell receptor gamma (TRG) gene rearrangement analyses, and targeted next-generation sequencing. The median age was 72 years for PEL and 83 years for FO-LBCL. All PEL cases lacked CD20, whereas FO-LBCL tumors retained pan-B-cell markers. Aberrant T-cell antigen expression was observed in two PEL cases, both showing clonal T-cell receptor rearrangements in addition to IGH clonality. FO-LBCL harbored recurrent alterations involving CD79B, PIM1, and MYD88, suggesting partial molecular overlap with the molecular features characteristic of the MCD subtype of diffuse large B-cell lymphoma (DLBCL). Clinically, all patients with PEL died of disease, whereas FO-LBCL appeared to have a more favorable clinical course, with four patients remaining alive at the last follow-up. Despite morphologic overlap, PEL and FO-LBCL showed distinct immunophenotypic, genetic, and clinical features. These preliminary findings support further investigation of B-cell receptor/NF-κB-related signaling pathways in FO-LBCL and may contribute to improved molecular classification and future therapeutic stratification.