# Primary effusion lymphoma

Source: https://onco.cc/cancers/primary-effusion-lymphoma/  
OnCo record `primary-effusion-lymphoma` (Cancer). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

A rare lymphoma that grows as fluid rather than as a lump: it fills the space around the lungs, the heart or the bowel without forming a mass. It is caused by Kaposi sarcoma herpesvirus and arises mostly in people with advanced HIV infection, and it is diagnosed by sending the fluid itself for testing.

## Summary

What it is. A large B-cell lymphoma driven by Kaposi sarcoma herpesvirus, also called human herpesvirus 8, the same virus that causes Kaposi sarcoma. The lymphoma cells float free in a body cavity and produce fluid: a pleural effusion around the lung, a pericardial effusion around the heart, or ascites in the abdomen. Classically there is no tumour mass at all, which is why the diagnosis is made on the fluid.

How it differs from the lymphomas around it. WHO-HAEM5 groups it in a family of conditions caused by the same virus: multicentric Castleman disease, germinotropic lymphoproliferative disorder, primary effusion lymphoma, its extracavitary form, and KSHV/HHV8-positive diffuse large B-cell lymphoma. The classification acknowledges that the boundaries between them are not clean, that individual patients overlap, and that difficult cases should be settled in a multidisciplinary meeting rather than by rule. In particular, telling a lymph node-based extracavitary primary effusion lymphoma from a KSHV/HHV8-positive diffuse large B-cell lymphoma can be arbitrary; the International Consensus Classification prefers the latter diagnosis where Epstein-Barr virus is negative and the tumour expresses IgM lambda.

The lymphoma it is most often confused with, and the 2022 change that separates them. There is a second disease that also presents as lymphoma confined to a body cavity, in older people without immune deficiency who have heart failure, kidney failure or cirrhosis causing fluid to accumulate. It is not caused by Kaposi sarcoma herpesvirus, its cells look like ordinary mature B cells rather than plasmablasts, and it behaves considerably better. WHO-HAEM5 made it a separate entity in 2022, calling it fluid overload-associated large B-cell lymphoma; the International Consensus Classification calls it primary effusion-based lymphoma that is negative for both viruses, and lists it as provisional. Distinguishing the two matters because the outlook is different.

Who gets it. Most often a person with advanced, often undiagnosed, HIV infection; it also occurs after organ transplant and in older people from regions where Kaposi sarcoma herpesvirus is common, including parts of the Mediterranean and sub-Saharan Africa. In people with HIV the tumour usually carries Epstein-Barr virus as well; in older HIV-negative people it usually does not.

How it is diagnosed and treated. The fluid is drained and sent for cell counts, cytology, flow cytometry and immunohistochemistry or in situ hybridisation for the virus. The cells are large and plasmablastic, usually lacking the B-cell markers (CD20 is typically negative) and carrying plasma cell markers instead, which is why anti-CD20 antibodies have no role. Treatment is combination chemotherapy together with full antiretroviral therapy where there is HIV; the regimens, which have never been compared in a randomised trial, sit in the treatment layer of this family and on the HIV-associated lymphoma page.

## Fields

- Kind: Cancer
- Last checked: 2026-09-29
- Also known as: PEL; Body cavity-based lymphoma; Extracavitary primary effusion lymphoma; KSHV/HHV8-associated lymphoma; HHV8-positive primary effusion lymphoma
- Tags: heme; lymphoma; subtype-page
- Group: haematologic
- Burden: In the United States, 236 adults were recorded in the SEER registries between 2001 and 2021, with a median age of 51 years and 88 per cent of them men. The age-adjusted incidence rose from 1.0 to 1.6 cases per ten million person-years between the first and second halves of that period. Five-year relative survival improved from 21 to 37 per cent across the same two periods, and median overall survival from 4 to 12 months, which the authors attribute to advances in both lymphoma treatment and HIV care.
- Subtypes: Classic primary effusion lymphoma, confined to a body cavity, which is an extranodal site with no mass; Extracavitary primary effusion lymphoma, which forms a mass with the same biology
- Biomarkers: Kaposi sarcoma herpesvirus (human herpesvirus 8) in the tumour nuclei, by immunohistochemistry for the latency-associated nuclear antigen; this is the diagnosis; Epstein-Barr virus, usually positive in people with HIV and usually negative in older people without; A plasmablastic phenotype: CD45 positive, CD20 and CD79a usually negative, CD138 and MUM1 positive; HIV status, which changes the whole of the management; Absence of the virus, which moves the diagnosis to fluid overload-associated large B-cell lymphoma and changes the outlook

## Sections of this record

The page is a hub with ten sections in reading order; large sections have their own page. The same plan as JSON: https://onco.cc/api/v1/cancers/primary-effusion-lymphoma/sections.json

- Overview (on the hub): The TL;DR, the family this cancer belongs to, the organ, who gets it and what the state of the art is. https://onco.cc/cancers/primary-effusion-lymphoma/#overview
- Types and stages (on the hub): Anatomy, the subtypes and how they differ, how it is staged, and where advanced disease spreads. https://onco.cc/cancers/primary-effusion-lymphoma/#what-it-is [2 subtypes]
- Symptoms and diagnosis (on the hub): How this cancer shows itself, how the diagnosis is confirmed, and the biomarkers clinicians test for. https://onco.cc/cancers/primary-effusion-lymphoma/#finding-it [5 biomarkers]
- Treatment (on the hub): The standard of care by setting, the medicines, surgery and radiotherapy named in it, and the regimens behind them. https://onco.cc/cancers/primary-effusion-lymphoma/#treating-it [2 settings, 1 decision with options]
- Trials and papers (on the hub): Trials recruiting now, the landmark trials, the trials held by this cancer's subtypes, the key papers and what they mean, the latest literature, and the milestones year by year. https://onco.cc/cancers/primary-effusion-lymphoma/#evidence [3 milestones]
- Biology and targets (on the hub): The molecular landscape: the targets and how often each appears, the pathways, the mechanics stages and the preclinical models. https://onco.cc/cancers/primary-effusion-lymphoma/#science [1 target, 1 pathway]
- Countries and centres (own page): Cases by country, the UK and NHS pathway and other country lenses, the expert centres with trials on record, and the centres named on this cancer's subtypes. https://onco.cc/cancers/primary-effusion-lymphoma/where-you-are/
- Decisions and support (on the hub): The decisions you may face, the aids that walk through them, the warnings on record, the first sixty days and the questions to ask. https://onco.cc/cancers/primary-effusion-lymphoma/#living-with-it [11 questions, 6 red cards]
- Pipeline and open problems (own page): Everything in development, the medicines held by this cancer's subtypes, the open problems and what is being done about them, the roadmaps, and what changed on this record. https://onco.cc/cancers/primary-effusion-lymphoma/coming/ [3 medicines, 3 open problems]
- Data (own page): Every connected record, the notes, the JSON, Markdown and RDF twins, and where the record came from and when it was checked. https://onco.cc/cancers/primary-effusion-lymphoma/data/ [18 connected records]

## Standard of care

- Making the diagnosis on the fluid: The effusion is drained and sent, fresh, for cytology, flow cytometry and immunohistochemistry. The diagnosis requires the Kaposi sarcoma herpesvirus latency-associated nuclear antigen in the tumour nuclei. A cavity lymphoma without the virus is a different disease, recognised separately in 2022, that arises in fluid overload from heart failure, kidney failure or cirrhosis and behaves better. HIV testing is part of the work-up in every case. ([HHV-8 (KSHV) status and LANA-1 immunohistochemistry](https://onco.cc/terms/hhv8-kshv/), [Epstein-Barr virus (EBV) in cancer](https://onco.cc/terms/ebv-term/), [Histopathology & immunohistochemistry](https://onco.cc/technologies/histopathology-ihc/), [The two lymphoma classifications of 2022 (WHO-HAEM5 and ICC)](https://onco.cc/terms/lymphoma-classification-2022/))
- Treatment: Combination chemotherapy, with antiretroviral therapy started or optimised at the same time where there is HIV, because controlling the HIV is part of controlling the lymphoma. Anti-CD20 antibodies have no role: the cells do not carry CD20. There has never been a randomised trial in this entity and the regimens come from series and from the HIV-associated lymphoma literature; they sit in the treatment layer of this family and on the HIV-associated lymphoma page. Entry into a trial is a reasonable first choice rather than a last resort. ([HIV-associated (AIDS-related) lymphomas](https://onco.cc/cancers/hiv-associated-lymphoma/), [Cyclophosphamide](https://onco.cc/drugs/cyclophosphamide/), [Doxorubicin](https://onco.cc/drugs/doxorubicin/), [Etoposide](https://onco.cc/drugs/etoposide/), [The lymphoma regimen alphabet: R-CHOP, pola-R-CHP, DA-EPOCH-R, ABVD, BEACOPP and the rest](https://onco.cc/terms/lymphoma-tx-regimen-alphabet/))

## Open problems

- There has never been a randomised trial in primary effusion lymphoma, and median overall survival in the most recent population series was 12 months.
- The boundaries between the conditions caused by Kaposi sarcoma herpesvirus are acknowledged by the classification itself to be unclear, and individual patients overlap between them.
- The commonest route to this diagnosis is advanced, undiagnosed HIV infection, which is a failure of testing rather than of oncology.

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Primary_effusion_lymphoma
- WHO Classification of Haematolymphoid Tumours, 5th edition: lymphoid neoplasms (Alaggio, Leukemia 2022): https://doi.org/10.1038/s41375-022-01620-2
- International Consensus Classification of Mature Lymphoid Neoplasms (Campo, Blood 2022): https://doi.org/10.1182/blood.2022015851
- Trends in incidence and survival of patients with primary effusion lymphoma in the United States, a population-based cohort study of 236 patients (Hematological Oncology 2026): https://doi.org/10.1002/hon.70168
- NCI PDQ: adult non-Hodgkin lymphoma treatment (health professional version): https://www.cancer.gov/types/lymphoma/hp/adult-nhl-treatment-pdq

## Connected records

- cancers: [Diffuse large B-cell lymphoma](https://onco.cc/cancers/dlbcl/), [HIV-associated (AIDS-related) lymphomas](https://onco.cc/cancers/hiv-associated-lymphoma/), [Kaposi sarcoma](https://onco.cc/cancers/kaposi-sarcoma/), [Non-Hodgkin lymphoma (all types)](https://onco.cc/cancers/non-hodgkin-lymphoma/), [Plasmablastic lymphoma](https://onco.cc/cancers/plasmablastic-lymphoma/)
- technologies: [Histopathology & immunohistochemistry](https://onco.cc/technologies/histopathology-ihc/)
- terms: [Epstein-Barr virus (EBV) in cancer](https://onco.cc/terms/ebv-term/), [HHV-8 (KSHV) status and LANA-1 immunohistochemistry](https://onco.cc/terms/hhv8-kshv/), [Nodal and extranodal lymphoma](https://onco.cc/terms/lymphoma-nodal-versus-extranodal/), [The lymphoma regimen alphabet: R-CHOP, pola-R-CHP, DA-EPOCH-R, ABVD, BEACOPP and the rest](https://onco.cc/terms/lymphoma-tx-regimen-alphabet/), [The two lymphoma classifications of 2022 (WHO-HAEM5 and ICC)](https://onco.cc/terms/lymphoma-classification-2022/)
- pathways: [Oncogenic viruses](https://onco.cc/pathways/oncogenic-viruses/)
- drugs: [Cyclophosphamide](https://onco.cc/drugs/cyclophosphamide/), [Doxorubicin](https://onco.cc/drugs/doxorubicin/), [Etoposide](https://onco.cc/drugs/etoposide/)

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JSON: https://onco.cc/api/v1/entities/primary-effusion-lymphoma.json