World Castleman Disease Day 2026: A rare disease, its subtypes, and the research moving forward

Castleman disease is a rare disorder that affects the lymph nodes, the small immune system structures found throughout the body. Because the disease is uncommon and its symptoms overlap with more familiar conditions, many patients wait a long time before receiving a correct diagnosis. World Castleman Disease Day, observed each year on July 23, exists to change that. It brings patients, families, physicians, and researchers together to raise awareness, share information, and support the studies that are gradually improving how the disease is understood and managed.

What World Castleman Disease Day marks each July 23

World Castleman Disease Day is a global awareness day dedicated to a small but growing patient community. The date, July 23, was chosen by the international Castleman disease community as a fixed annual moment to focus public attention on the disease. Activities center on three goals: education about a disorder that many people, including some clinicians, have never encountered; recognition of patients currently living with the disease and those who have died from it; and support for the research needed to find better answers.

Awareness days matter more for rare conditions than for common ones. When a disease affects only a small number of people, public understanding tends to be limited. That gap can slow diagnosis, delay access to specialists, and reduce the number of patients who enroll in clinical studies. A dedicated day gives patients, families, and advocacy groups a shared platform to explain what the disease is and why continued research is important. It also connects people who otherwise rarely encounter anyone else living with the same condition, which is meaningful in a disease community this small. For a broader look at this dynamic, see Hope in Research: How Clinical Trials Are Transforming Rare Disease Treatment.

What Castleman disease is, in plain terms

Castleman disease is what physicians call a lymphoproliferative disorder. That term means the cells inside the lymph nodes grow more than they should. Lymph nodes are small, bean-shaped structures spread throughout the body that filter fluid and help the immune system respond to infection. In Castleman disease, one or more of these nodes become enlarged and take on a distinctive appearance under a microscope.

The disease was first described in 1954 by Dr. Benjamin Castleman, a pathologist who identified an unusual pattern of lymph node overgrowth in his patients. It is not cancer in the traditional sense, though some forms behave aggressively and require careful medical attention. It is also not contagious, and it is not passed down through families.

Many cases involve an immune signaling protein called interleukin-6, often abbreviated IL-6. When the body produces too much IL-6, the resulting inflammation can cause fevers, fatigue, and other whole-body symptoms. In severe forms, this immune overactivity can affect major organs. Readers new to clinical research terminology may find Clinical Trials Explained: Simple Guide for Beginners a helpful companion piece.

The two main forms: unicentric and multicentric

Castleman disease is divided into two main categories based on how many lymph node regions are involved.

Unicentric Castleman disease affects a single lymph node or a single group of nearby nodes in one area of the body. It is the more common form. Many people with unicentric disease have few or no symptoms and only discover the enlarged node during an unrelated scan or physical examination. Outcomes in this form are generally excellent, especially when the affected node can be surgically removed.

Multicentric Castleman disease affects lymph nodes in multiple regions and usually comes with systemic symptoms, meaning symptoms that affect the whole body. These can include fevers, night sweats, unexplained weight loss, fatigue, low red blood cell counts, and, in serious cases, problems with organs such as the liver, kidneys, or spleen. This form is less common and more challenging to manage.

The subtypes within multicentric Castleman disease

Multicentric Castleman disease is not a single condition. Researchers now recognize several distinct subtypes, each with its own underlying cause and management pathway.

One subtype is linked to human herpesvirus-8, sometimes written as HHV-8. This virus is more common in people whose immune systems are weakened, including those living with HIV. When HHV-8 is present, it drives the disease process in a specific way that can be addressed with therapies aimed at the virus and the immune response it triggers.

A second subtype is called idiopathic multicentric Castleman disease. The word idiopathic simply means that no specific cause has been identified. In this form, the immune system produces excessive IL-6 and related signals without a clear trigger. Idiopathic disease is further divided into additional subgroups based on symptom patterns, including one known by the acronym TAFRO, which stands for a specific combination of low platelet counts, fluid buildup, fever, kidney involvement, and organ enlargement.

A third subtype occurs alongside a separate rare condition called POEMS syndrome, which affects nerves, hormones, blood cells, and the skin.

Distinguishing between these subtypes is important because each responds differently to different approaches, and each has its own outlook. Community organizations play an important role in helping patients understand these distinctions, as covered in Patient Advocacy Groups: Finding Support and Trial Information.

How doctors identify Castleman disease

Castleman disease cannot be diagnosed from symptoms alone. Because its symptoms overlap with those of lymphoma, autoimmune disorders, and various infections, a careful workup is needed to confirm what is actually going on.

The most important step is a biopsy, in which a small sample of an affected lymph node is removed and examined under a microscope by a pathologist. Castleman disease has a characteristic appearance in tissue samples that a trained pathologist can recognize. Imaging tests such as CT scans, MRI, or PET-CT scans help doctors see how many lymph node regions are involved and whether any organs are affected. Blood tests measure inflammation markers, red blood cell counts, kidney and liver function, and, in some cases, levels of IL-6.

An international group of physicians and researchers has developed consensus criteria to standardize the diagnosis of idiopathic multicentric disease. These criteria require specific tissue findings, involvement of multiple lymph node regions, a defined number of clinical or laboratory abnormalities, and the exclusion of other conditions that might mimic Castleman disease. Standardized criteria have made diagnosis more consistent across hospitals and countries. Understanding these workup steps also helps patients prepare for study screening, a subject covered in Pre-Study Requirements: What You Need Before Enrolling.

How Castleman disease is currently managed

Medical management depends on the form of the disease.

For unicentric disease, surgical removal of the affected lymph node is often curative. Patients with unresectable unicentric disease may need additional approaches such as immune-directed therapy or corticosteroids.

For idiopathic multicentric disease, the first-line approach targets IL-6 directly. An anti-IL-6 antibody is the only medication approved by the U.S. Food and Drug Administration specifically for this form. Related IL-6-blocking therapies are also used. Many patients respond well to this approach. A meaningful share do not, and those patients need alternative options. This is one of the main reasons research into new mechanisms continues.

For HHV-8-associated disease, therapy addresses both the immune activity and the underlying viral driver. Antiviral medications and immune-directed therapies are commonly combined.

For all forms, care is best coordinated at centers with experience in Castleman disease, because the disorder is rare enough that most general practices see very few cases.

Why clinical research matters for a rare condition like this

Rare diseases face a specific research challenge. When only a small number of people are affected, it is harder to run large studies, harder to detect small differences between approaches, and harder for patients to find the research programs that might benefit them.

Castleman disease illustrates this pattern. Only one medication is approved specifically for the idiopathic multicentric form. Everything else used to manage severe or refractory cases is either borrowed from other conditions or being evaluated through active studies. A small but growing set of clinical studies is currently investigating new mechanisms, including drugs that block specific immune signaling enzymes, medications that dampen overactive immune pathways, and therapies originally developed for related blood disorders.

A separate long-term study, sometimes called a natural history study, invites patients living with Castleman disease to share de-identified information about their symptoms, care, and outcomes over time. Studies of this kind help researchers understand how the disease behaves in real people over long periods and generate the evidence needed for future study design.

For a patient, taking part in a well-run study is one of the few ways to access investigational options and contribute to knowledge that will help future patients living with the same condition.

How patients and families can take part through DecenTrialz

Finding a suitable study for a rare disease can be difficult. Patients are often spread across many states, active studies are limited in number, and eligibility criteria are specific. This is exactly the recruitment challenge that DecenTrialz was built to address.

DecenTrialz is a clinical trial participant recruitment platform that uses AI-assisted matching to connect people with studies that fit their situation, followed by pre-screening led by registered nurses. The nurse pre-screens only. Final eligibility, informed consent, the full study walk-through, and enrollment are always handled by the research site team running the study. That separation keeps clinical decisions with the qualified investigators while making the earlier steps faster and less burdensome for the patient.

For someone exploring participation in a Castleman disease study or any other rare disease study, the process on DecenTrialz begins with a short intake that captures the information needed to match against active studies. If a possible match is identified, a registered nurse reaches out to gather additional details and confirm whether the initial fit holds. When pre-screening indicates a strong match, the research site team takes over from there. Anyone interested in exploring participation can begin at decentrialz.com.

Frequently asked questions

Is Castleman disease a form of cancer?

Castleman disease is not classified as a traditional cancer, but some of its features overlap with cancers of the immune system, and some forms behave aggressively. It is best thought of as a disorder of the immune system that causes lymph node overgrowth and, in multicentric forms, whole-body symptoms.

Is Castleman disease inherited?

No. Castleman disease is not passed from parent to child.

Can Castleman disease be cured?

Unicentric Castleman disease can often be effectively resolved through surgical removal of the affected node. Multicentric forms are managed rather than cured in most cases, with the goal of controlling symptoms, reducing disease activity, and improving long-term outlook. Ongoing research is aimed at improving these outcomes.

How long does diagnosis usually take?

Because symptoms overlap with many other conditions, diagnostic delays measured in months or years are common. Awareness among primary care physicians and specialists is one of the reasons World Castleman Disease Day exists.

How can someone find out about active Castleman disease studies?

A short intake through DecenTrialz can begin the matching process. Visit decentrialz.com to get started.