Primary effusion lymphoma with biphenotypic and bigenotypic features of T-cell receptor and IGH genes in an HIV-negative patient with kidney transplant

Primary effusion lymphoma typically lacks B-cell markers but involves immunoglobulin gene rearrangements, indicating a B-cell origin. This case highlights the unusual co-expression of T-cell antigens and clonal gene rearrangements for both T- and B-cell lineages in PEL. The findings underscore the complex lineage infidelity in PEL, making diagnosis challenging. Primary effusion lymphoma (PEL) is a rare and aggressive non-Hodgkin lymphoma that primarily involves body cavities and is characterized by human herpes virus-8 (HHV-8) positivity and the presence of immunoblastic, plasmablastic or anaplastic cells. PEL typically lacks B-cell antigens, but involves immunoglobulin gene rearrangements, suggesting a B-cell origin. Here, we present a highly unusual case of PEL in which tumor cells expressed T-cell antigens but were also monoclonal for both T-cell receptor (TCR) and immunoglobulin heavy locus (IGH) gene rearrangements. An 81-year-old man with bilateral pleural effusions presented with atypical lymphoid cells. Immunohistochemistry revealed positivity for CD3, CD4, MUM-1, OCT2, BOB1, and HHV-8, but negativity for other T- and B-cell antigens. In situ hybridization identified Epstein-Barr virus and lambda light chain restriction. Gene rearrangement studies demonstrated monoclonal TRB (T-cell receptor beta locus) and TRG (T-cell receptor gamma locus) as well as IGH rearrangement. This unusual case of PEL with T-cell antigen expression and clonal rearrangement of both the TCR and IGH genes highlights the lineage complexity of this tumor.