Castleman disease is not cancer. It is a lymphoproliferative disorder, meaning it involves abnormal overgrowth of immune cells in the lymph nodes, but the cells themselves are not malignant. Unlike lymphoma, Castleman disease lacks the hallmarks of cancer: the cells are not monoclonal (they don’t arise from a single rogue cell), they don’t show significant abnormal features under the microscope, and they don’t invade and destroy surrounding tissue. That said, the distinction is more nuanced than a simple yes or no, because certain forms of the disease can behave aggressively, cause serious organ damage, and carry an elevated risk of developing into actual cancer over time.
Why It Gets Confused With Cancer
Castleman disease shares a number of features with lymphoma that make the two easy to confuse. Both cause enlarged lymph nodes, both are diagnosed through lymph node biopsy, and both can produce fevers, night sweats, weight loss, and abnormal blood work. The multicentric form of Castleman disease is sometimes treated with chemotherapy, which further blurs the line. Pathologists reviewing tissue samples have noted that the microscopic changes seen in Castleman disease can appear in certain lymphomas, including follicular lymphoma, mantle cell lymphoma, and Hodgkin lymphoma. The key difference is that in lymphoma, these changes involve cancerous cells, while in Castleman disease the overgrowth is reactive, driven by inflammation rather than by a malignant transformation.
The World Health Organization classifies Castleman disease separately from cancers in its most recent edition. It was originally called “giant lymph node hyperplasia” and described as a benign, non-neoplastic growth. It did not even receive its own medical billing code (ICD-10) until October 2016, which contributed to decades of underdiagnosis and confusion about what the disease actually is.
The Three Types of Castleman Disease
There are three recognized forms, and they differ dramatically in severity.
Unicentric Castleman disease (UCD) involves a single enlarged lymph node or a cluster of nodes in one location, most often in the chest. It is benign, usually causes no symptoms, and is cured by surgical removal in nearly all cases. Five-year survival is close to 100%. Most people with UCD are in their 30s or 40s when diagnosed.
Idiopathic multicentric Castleman disease (iMCD) is the form that behaves most like a serious illness. It affects lymph nodes in multiple parts of the body simultaneously and triggers widespread inflammation, organ dysfunction, fluid retention, and blood abnormalities. “Idiopathic” means the cause is unknown. It tends to appear later in life, typically between the 40s and 60s. The five-year survival rate for patients who start with milder, asymptomatic disease is around 94%, but drops to roughly 83% for those whose disease progresses to full-blown iMCD with organ involvement.
HHV-8-associated multicentric Castleman disease is caused by human herpesvirus 8, the same virus responsible for Kaposi sarcoma. This form occurs most often in people living with HIV and can appear even when immune function is relatively preserved. Up to 50% of patients with this subtype also have Kaposi sarcoma. The disease follows a relapsing and remitting course and can progress to multi-organ failure if untreated. Diagnosis requires finding virus-infected cells in a lymph node biopsy, and blood levels of HHV-8 DNA rise during flares.
What Drives the Symptoms
The systemic symptoms of multicentric Castleman disease are largely driven by a single molecule: interleukin-6, or IL-6. IL-6 is an immune signaling protein that normally helps coordinate inflammation and blood cell production. In iMCD, IL-6 is produced in excessive amounts, triggering a cascade of problems. It stimulates the bone marrow to overproduce platelets, causes the liver to churn out inflammatory proteins, drives the expansion of antibody-producing cells, and activates immune cells throughout the body. The result looks and feels a lot like cancer or severe infection: fevers, anemia, low albumin, kidney dysfunction, fluid buildup in the abdomen or chest, and enlarged liver and spleen.
Researchers have confirmed this connection by giving mice a virus engineered to produce IL-6. The animals developed a syndrome that closely resembled iMCD, and it resolved when they received a drug that blocked IL-6. Humans given pharmaceutical doses of IL-6 develop similar symptoms.
The Real Cancer Risk
While Castleman disease itself is not cancer, it does raise the risk of developing one. The multicentric forms carry an increased risk of non-Hodgkin lymphoma and, less commonly, Hodgkin lymphoma. In rare cases, what initially looks like Castleman disease on biopsy turns out to be an early stage of Hodgkin lymphoma that only becomes apparent later. Because of this risk, ongoing monitoring with imaging and lab work is recommended even after successful treatment of unicentric disease.
The HHV-8 subtype carries additional risk of Kaposi sarcoma, which is a true malignancy of blood vessel cells. This overlap between Castleman disease and cancer is part of why the question “is it cancer?” doesn’t have a perfectly clean answer. The disease itself is not malignant, but it exists in a neighborhood where malignancy is more likely to develop.
How It Is Diagnosed
Diagnosing iMCD requires meeting a specific set of criteria established by the Castleman Disease Collaborative Network. Both major criteria must be present: characteristic findings on a lymph node biopsy, and enlarged lymph nodes in more than one region of the body. On top of that, at least two of eleven minor criteria must be met, with at least one being a lab abnormality. These minor criteria include elevated inflammatory markers, anemia, low albumin, kidney problems, abnormal antibody levels, constitutional symptoms like fevers and weight loss, enlarged liver or spleen, fluid accumulation, and certain skin changes.
Crucially, the diagnostic process also requires ruling out diseases that mimic iMCD, including lymphoma, autoimmune conditions, and infections. This exclusion step is essential precisely because Castleman disease overlaps so heavily with cancer in its presentation.
Treatment and Outlook
For unicentric disease, surgery is the standard treatment and is typically curative.
For iMCD, the primary treatment targets IL-6 directly. Siltuximab, a drug that binds and neutralizes IL-6, is the only therapy approved by both the U.S. FDA and the European Medicines Agency for iMCD. A separate IL-6-blocking drug, tocilizumab, is approved in Japan. In a comparison of treatment strategies, siltuximab reduced the risk of disease progression at two years by 64% compared to regimens built around rituximab (a drug that targets immune B-cells). Rituximab-based therapies showed response rates around 55%, but long-term disease control was significantly worse, with five-year progression-free survival of only 43%.
For HHV-8-associated disease, treatment focuses on controlling the virus and the abnormal immune cells it drives, often using rituximab-based approaches alongside management of any coexisting HIV infection.
The practical reality for patients with multicentric Castleman disease is that treatment is ongoing. The disease can flare and remit, lab work needs regular monitoring, and the elevated lymphoma risk means staying vigilant over the long term. But with appropriate treatment, the majority of patients achieve meaningful symptom control and maintain good quality of life for years.