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Castleman Disease

Recent research efforts aimed at curing Castleman Disease.

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Castleman Disease

Overview

Castleman disease (CD) is a rare group of disorders in which lymph nodes develop characteristic abnormal immune-cell and supporting-tissue growth. It can be unicentric (UCD), involving one lymph-node region, or multicentric (MCD), involving multiple regions plus body-wide inflammation. MCD includes HHV-8/KSHV-associated disease, POEMS-associated disease, and HHV-8-negative idiopathic MCD (iMCD), in which no established cause has been identified. CD can occur across the age range; UCD is often found incidentally or because a mass presses on nearby structures, while MCD can cause fever, fatigue, weight loss, anemia, fluid retention, enlarged organs, and potentially life-threatening organ dysfunction. UCD consensus guidelines Castleman disease review (pmc.ncbi.nlm.nih.gov)

Prognosis depends strongly on subtype. Complete removal of the affected lymph node(s) is often curative for resectable UCD, whereas MCD generally requires ongoing systemic treatment. For iMCD, the anti-interleukin-6 (IL-6) antibody siltuximab is the principal approved targeted therapy in the United States; HHV-8-associated MCD is generally managed with B-cell-directed therapy such as rituximab, with treatment tailored to HIV status, Kaposi sarcoma, and disease severity. UCD consensus guidelines Siltuximab information Castleman disease review (pmc.ncbi.nlm.nih.gov)

Scope of Recent Research (2020–present)

From 2020 through October 11, 2026, Castleman research has become more mechanistic and more collaborative, but remains limited by the disease’s rarity and biological heterogeneity. The dominant questions are what initiates inflammatory signaling in iMCD, which cell types produce IL-6 and vascular-growth signals, why some patients do not respond to IL-6 blockade, and whether pathway-directed drugs can induce durable, treatment-free remission. UCD is already often curable surgically; for systemic forms, no proven curative therapy has emerged, and the nearest-term goal is durable control through targeted drug repurposing and biologically defined subgroups. Spatial and single-cell mapping iMCD treatment update (pubmed.ncbi.nlm.nih.gov)

Major Breakthroughs and Emerging Therapies

Targeting IL-6 remains the foundation, but is not sufficient for every patient. IL-6 is an inflammatory signaling protein that drives many symptoms and laboratory abnormalities in iMCD. In the pivotal randomized trial, siltuximab produced a durable combined tumor-and-symptom response in 18 of 53 treated participants, compared with none of 26 receiving placebo plus supportive care. This established a targeted standard of care, but the response rate also made clear that many patients need other approaches. Siltuximab randomized trial (pubmed.ncbi.nlm.nih.gov)

mTOR inhibition is the most advanced recent drug-repurposing strategy. mTOR is a cellular signaling hub that helps regulate immune-cell activation, growth, and blood-vessel signaling. Studies of iMCD lymph nodes found increased mTOR-pathway activation, particularly in patients whose disease had not been adequately controlled with IL-6-directed therapy. This supplied a rationale for sirolimus, an oral mTOR inhibitor already used in transplantation and other conditions; early clinical observations suggested that it can reduce inflammatory activity in some refractory iMCD cases. Increased mTOR activation in iMCD PI3K/AKT/mTOR targeting study (pmc.ncbi.nlm.nih.gov)

JAK inhibition has moved from case-level evidence into a prospective trial. JAK-STAT is another signaling pathway through which cytokines transmit inflammatory instructions inside cells. Transcriptomic and spatial studies have implicated JAK-STAT activity in Castleman lymph-node microenvironments, and refractory TAFRO/iMCD-like cases have reported responses to the JAK1/2 inhibitor ruxolitinib. In December 2025, the University of Pennsylvania initiated a phase II study of ruxolitinib for previously treated iMCD, testing whether this pathway can provide a treatment option after intolerance of, relapse on, or lack of response to IL-6-directed therapy. Spatial and single-cell mapping Ruxolitinib trial Ruxolitinib case report (pubmed.ncbi.nlm.nih.gov)

Plasma-cell and proteasome-directed combinations remain an important rescue approach. A prospective multicenter study evaluated bortezomib, cyclophosphamide, and dexamethasone (BCD) in 24 people with relapsed or refractory iMCD. At six months, 15 participants (62.5%) achieved an overall response, with reported improvement in symptoms and several inflammatory and blood markers; the regimen did not produce grade 3 or higher adverse events in that small study. This is promising disease control, not evidence of cure, and the treatment carries the practical burdens and risks of combination anti-cancer therapy. BCD prospective study (pubmed.ncbi.nlm.nih.gov)

Genetic and stromal-cell research is changing the search for a root cause. A 2021 sequencing study identified novel somatic—acquired, non-inherited—alterations in small numbers of UCD and iMCD cases, supporting the possibility that a clonal abnormal cell population contributes to disease in some patients. More recently, spatial proteomics and single-cell transcriptomics identified activated lymph-node stromal cells, including follicular dendritic and reticular-cell populations, as key sources of increased IL-6 and vascular endothelial growth factor (VEGF) signaling. These discoveries may eventually enable therapies aimed at the disease-initiating tissue niche, but they have not yet yielded a validated gene therapy, gene-editing, RNA therapeutic, or cell therapy for CD. Somatic alterations study Spatial and single-cell mapping (pubmed.ncbi.nlm.nih.gov)

Clinical Trials and Experimental Approaches

The leading U.S. repurposing study is the University of Pennsylvania-sponsored phase II, open-label, multicenter trial of sirolimus for previously treated iMCD, NCT03933904. It enrolled a planned seven participants across the University of Pennsylvania, Children’s Hospital of Philadelphia, University of Arkansas for Medical Sciences, and University of California San Diego. The registry listed the study as active but not recruiting in August 2026, with primary completion on June 30, 2024 and estimated final completion in June 2027; registry results have been posted, but a full peer-reviewed outcomes report is still needed to judge durability and safety confidently. Sirolimus phase II trial (ichgcp.net)

The newer University of Pennsylvania phase II ruxolitinib study, NCT07085039, is recruiting adults with previously treated iMCD and plans to assess clinical-benefit response after approximately 12 months of oral treatment. Its anticipated primary completion date is July 31, 2028, so no efficacy results are yet available. In China, the BCD regimen has also been studied prospectively as a phase II strategy for newly diagnosed iMCD, while the completed relapsed/refractory study provides the most informative published BCD outcomes to date. Ruxolitinib trial BCD prospective study (allclinicaltrials.com)

Methodologies and Scientific Approaches

Recent work combines conventional lymph-node pathology with next-generation sequencing, blood-protein profiling, flow cytometry, and single-cell and spatial “omics.” Single-cell methods examine the gene activity of individual cells, while spatial methods preserve their location within a lymph node; together, these approaches have highlighted interactions among stromal cells, B cells, T cells, endothelial cells, and inflammatory signaling networks. Studies of identical twins with iMCD similarly localized IL-6-pathway activity to endothelial and fibroblastic reticular cells and identified an inflammatory monocyte signature in blood. Spatial and single-cell mapping Identical-twin single-cell study (pubmed.ncbi.nlm.nih.gov)

Researchers also rely on international registries and linked biospecimen collections because randomized trials are difficult in an ultra-rare disease. The Castleman Disease Collaborative Network’s ACCELERATE registry collects de-identified medical records, while associated blood and tissue donation programs support biomarker, pathology, and treatment-response studies. This infrastructure enables investigators to compare clinical patterns with tissue biology and to identify patients for small, biologically focused trials. ACCELERATE and sample-donation program (cdcn.org)

Leading Institutions and Funding

The University of Pennsylvania’s Center for Cytokine Storm Treatment & Laboratory and the Castleman Disease Collaborative Network (CDCN) are central to the current U.S. research program, including the sirolimus and ruxolitinib trials, patient registry, and translational tissue studies. Key clinical collaborators include Children’s Hospital of Philadelphia, University of Arkansas for Medical Sciences, University of California San Diego, and international centers contributing pathology, genomics, and clinical cohorts. Chinese investigators at Peking Union Medical College Hospital and Peking University First Hospital have led prospective BCD research. Sirolimus phase II protocol BCD prospective study Spatial and single-cell mapping (cdn.clinicaltrials.gov)

Representative support includes the National Heart, Lung, and Blood Institute grant R01-HL141408, which has supported iMCD mechanism studies and the sirolimus program, alongside CDCN/Castleman’s Awareness & Research Effort support, University of Pennsylvania precision-medicine funding, and NIH intramural funding. Pfizer supplied sirolimus for the phase II study, while the research program itself has drawn on nonprofit, academic, and federal support rather than a large conventional drug-development pipeline. Increased mTOR activation in iMCD Sirolimus phase II protocol (pmc.ncbi.nlm.nih.gov)

Strengths, Limitations, and Challenges

A major strength of the field is that it has shifted from nonspecific chemotherapy toward mechanism-informed treatment: IL-6 blockade for many iMCD cases, mTOR inhibition for a biologically plausible resistant subgroup, and JAK inhibition as a testable next strategy. Advanced profiling is also identifying candidate disease-driving cell populations rather than treating Castleman disease as a single uniform condition. Siltuximab randomized trial Spatial and single-cell mapping (pubmed.ncbi.nlm.nih.gov)

The principal limitation is that “Castleman disease” encompasses conditions with different causes and biology. Somatic changes have been found in some UCD and iMCD samples, but no consistent causal driver has been established for most iMCD; accordingly, currently available systemic therapies suppress downstream inflammation rather than reliably eliminate the initiating cause. Small enrollment, variable diagnostic classification, open-label trial designs, and the difficulty of obtaining repeated lymph-node tissue all make it hard to prove that a response is durable, generalizable, or curative. Somatic alterations study Sirolimus phase II trial (pubmed.ncbi.nlm.nih.gov)

Outlook and Future Directions

As of October 11, 2026, a cure is already realistic for resectable UCD through complete surgery, but a drug-free cure for iMCD or HHV-8-associated MCD is not close enough to claim. The most important near-term milestones are a peer-reviewed report of the sirolimus phase II results, early evidence from the ruxolitinib trial, validation of stromal-cell and cytokine biomarkers that predict which pathway is active in each patient, and discovery of a reproducible initiating lesion that can be directly eliminated. If those milestones converge, Castleman research could progress from controlling cytokine storms to precision treatments capable of sustained remission without indefinite therapy. UCD consensus guidelines Sirolimus phase II trial Ruxolitinib trial (pmc.ncbi.nlm.nih.gov)

References

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