Primary effusion lymphoma: a liquid phase lymphoma of fluid-filled body cavities.

Primary effusion lymphoma (PEL) is a B-cell neoplasm characterized by infection of the tumor clone by human herpesvirus type-8/Kaposi's sarcoma-associated herpesvirus (HHV-8/KSHV) and by liquid growth in fluid-filled body spaces. During its entire clinical course, the lymphoma tends to remain localized to the serous body cavities with no formation of solid tumor masses. The epidemiology of PEL points to a close link with underlying immunodeficiency of the host, as most cases develop in individuals severely immunocompromised because of preexisting acquired immunodeficiency syndrome. The histogenesis and pathogenesis of PEL have been clarified to a sizeable extent by intensive investigations performed since the disease recognition in 1995. PEL is composed of postgerminal center B cells, which bridge immunoblastic and anaplastic features and typically display a non-B, non-T phenotype consistent with late stages of B-cell differentiation. HHV-8/KSHV is thought to play a major role in PEL pathogenesis via expression of several viral latent genes, which have the potential to affect B-cell growth. Other factors involved in PEL pathogenesis include deregulation of cytokine and growth factor autocrine loops, molecular alterations of the tumor DNA, cell cycle abnormalities, stimulation and selection by antigen, and infection by Epstein-Barr virus, which occurs in 70% of PEL cases. In the years since the disease discovery, the distinctiveness of the biological and clinicopathological features of PEL has prompted its recognition as an independent lymphoma category by the World Health Organization classification system of hematologic neoplasms.