Human herpes virus 8-unrelated primary effusion lymphoma-like lymphoma in the pericardium: A case with latency type III Epstein–Barr virus infection showing good prognosis without chemotherapy

Primary effusion lymphoma (PEL) is a rare subtype of non-Hodgkin lymphoma that proliferates in body cavities without detectable masses. PEL is universally associated with human herpes virus-8 (HHV-8) infection and has an aggressive prognosis. Recently, an HHV-8-unrelated PEL-like lymphoma that usually occurs in elderly individuals and follows a more indolent prognosis has been reported, and it is treated as a disease distinct from PEL. However, its pathogenesis and prognostic factors have not been sufficiently clarified. In PEL-like lymphoma accompanied by Epstein–Barr virus (EBV) infection, latent infection types are not mentioned in the literature. Herein, we report the case of an 85-year-old Japanese man with pericardial PEL-like lymphoma who showed good improvement in condition for 24 months after pericardiocentesis without chemotherapy. Serological test results were positive for EBV capsid antigen and EBV nuclear antigen 2 (EBNA2), but negative for human immunodeficiency virus, hepatitis B virus, and hepatitis C virus. The disease phenotype and EBV infection mechanism were immunohistochemically investigated by the cellblock prepared from pericardial effusion. Atypical cells were positive for CD20, CD30, CD45, BCL2, MUM1, EBNA2, latent membrane protein 1, and EBV-encoded RNA (on in situ hybridization), but negative for CD3, CD5, CD10, CD138, cytokeratin AE1/AE3, and HHV-8. Accordingly, this case was considered to be a B-cell activated phenotype with a type III latent EBV infection. Type III latent EBV infection is unusual in PEL.