The primary effusion lymphoma subtype is also known as 'body cavity-based' lymphoma and is considered one of three types of AIDS-related lymphoma.
Primary effusion lymphoma (PEL) is a very rare sub-subtype of extranodal diffuse large B-cell lymphoma. It is more frequently found to be affecting young and middle-aged men, much more often than women, and only occasionally is it found in elderly patients.
Medically, the term 'effusion' means that some body fluid—typically blood but any body fluid will do—has escaped into a body cavity or surrounding tissue (thus the alias of body cavity-based lymphoma). 'Effusion' can also refer to that escaped fluid.
Thus, in PEL, lymphoma develops within the effusion. It does not typically cause a mass or tumor.
Patients diagnosed with Primary effusion lymphoma are almost always found to be positive for the HIV virus. Other viruses often found in patients with PEL, specifically within the cancerous lymphocytes, include both Epstein-Barr virus (EBV) and human herpes virus 8, better known as Kaposi-sarcoma associated herpes virus. That said, there is a distinction between EBV-positive and EBV-negative PEL, although it is unclear whether this factors into progression, prognosis or treatment considerations.
Patients with primary effusion lymphoma have a poor prognosis, in large part because by the time of diagnosis not only is the lymphoma in advanced stage, the patients themselves are typically already highly immunocompromised. Death among these patients is generally caused by one of three diseases: the PEL, another cancer known as Kaposi's sarcoma, or an opportunistic infection characteristic of mortality in HIV/AIDS.
Researchers have noted that prognosis tends to be slightly better in (HIV positive) primary effusion lymphoma patients who are on antiretroviral therapy.