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Frequently Asked Questions
Castleman disease (CD) is a rare condition in which cells of the lymph nodes and related tissues grow rapidly but are not cancerous. If left undiagnosed and untreated, CD can lead to organ failure or other harmful conditions—even if it isn’t cancerous.
Unicentric Castleman disease (UCD): Affects only a single lymph node
Multicentric Castleman disease (MCD): Affects multiple lymph nodes
Idiopathic multicentric Castleman disease (iMCD), a subtype of Castleman disease, is a rare disorder in which multiple groups of lymph nodes are swollen and are accompanied by other symptoms like fluid accumulation, enlarged organs, and flu-like symptoms such as night sweats, fever, and fatigue.
Common symptoms of iMCD include swollen lymph nodes, fatigue, anemia, night sweats, fever, unintended weight change, flu-like symptoms, rash, fluid accumulation, and abnormal enlargement of organs, such as the liver and spleen.
There are no known causes or risk factors for iMCD. Some people with iMCD have interleukin 6 (in-ter-LOO-kin-six), or IL-6, levels that are elevated, which may explain some of the symptoms they experience, such as swollen lymph nodes, fever, and night sweats.
iMCD is not cancer, but it can mimic the symptoms of many other diseases, including some cancers, and can be challenging to diagnose.
SYLVANT® (siltuximab) is the only therapy approved by the US Food and Drug Administration (FDA) for the treatment of people with multicentric Castleman disease (MCD) who have tested negative for human immunodeficiency virus (HIV) and human herpesvirus-8 (HHV-8).
Siltuximab is recommended by the National Comprehensive Cancer Network® (NCCN®) as a first-line treatment option for iMCD.* NCCN makes no warranties of any kind whatsoever regarding their content, use or application and disclaims any responsibility for their application or use in any way.
NCCN makes no warranties of any kind whatsoever regarding their content, use or application and disclaims any responsibility for their application or use in any way.
*Referenced with permission from the NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines®) for Castleman Disease V.2.2025. © National Comprehensive Cancer Network, Inc. 2025. All rights reserved. Accessed November 3, 2025. To view the most recent and complete version of the guideline, go online to NCCN.org.
SYLVANT is the only therapy approved by the US Food and Drug Administration (FDA) for the treatment of people with multicentric Castleman disease (MCD) who have tested negative for human immunodeficiency virus (HIV) and human herpesvirus-8 (HHV-8). It is not known if SYLVANT is safe and effective in children. It is given as a 1-hour intravenous (IV) infusion under the supervision of a healthcare professional at an infusion center.
SYLVANT works by targeting interleukin-6 (IL-6), a molecule that some people with iMCD produce too much of. Over time, SYLVANT has been shown to resolve common symptoms of iMCD and to reduce lymph node size in some people.
Below are some of the most common side effects observed in people taking SYLVANT. These are not all the possible side effects of SYLVANT. Call your HCP for medical advice about side effects. You are encouraged to report side effects of prescription drugs to the FDA. Call 1-800-FDA-1088 or visit www.fda.gov/medwatch:
- Rash
- Upper respiratory tract infections
- Swelling or fluid accumulation
- Elevated uric acid in the blood, which is passed through urine
- Weight gain
Most medications are associated with side effects, which vary from person to person.
To see if you qualify for help with co-payments or other financial assistance, contact the Patient Solutions Program, Monday-Friday, 8 AM to 8 PM ET: Phone: 1-855-299-8844, Fax: 1-888-223-1746.
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IL-6, interleukin-6.
What is SYLVANT?
SYLVANT® (siltuximab) is a prescription medicine used to treat people with multicentric Castleman’s disease (MCD) who do not have human immunodeficiency virus (HIV) and human herpesvirus-8 (HHV-8) infection.
It is not known if SYLVANT is safe and effective in children.
IMPORTANT SAFETY INFORMATION
Who should not receive SYLVANT?
Do not receive SYLVANT if you have had a severe allergic reaction to siltuximab or any of the ingredients in SYLVANT. See the Patient Information leaflet for SYLVANT for a complete list of ingredients.
Before starting SYLVANT, tell your healthcare provider (HCP) about all of your medical conditions, including if you:
- have an infection. You should not receive SYLVANT if you have a severe infection.
- have had a recent vaccination or are scheduled to receive any vaccinations. You should not receive a live vaccine during your treatment with SYLVANT.
- have or have had any stomach or bowel (intestine) problems, such as diverticulitis or ulcers. Tell your healthcare provider if you have pain in your stomach area.
- are pregnant or plan to become pregnant. It is not known if SYLVANT will harm your unborn baby. You should not become pregnant while receiving treatment with SYLVANT. Females who are able to become pregnant should use effective birth control during treatment with SYLVANT and for 3 months after stopping treatment.
- are breastfeeding or plan to breastfeed. It is not known if SYLVANT passes into your breast milk. You and your healthcare provider should decide if you will take SYLVANT or breastfeed. You should not do both.
Tell your healthcare provider about all the medicines you take, including any prescription and over-the-counter medicines, vitamins, and herbal supplements.
What are the possible side effects of SYLVANT?
SYLVANT may cause serious side effects, including:
- Infections. SYLVANT may lower your ability to fight infections. Tell your healthcare provider right away if you have any signs or symptoms of an infection during treatment with SYLVANT.
- Infusion and allergic reactions. If you have an infusion or allergic reaction while receiving SYLVANT, your healthcare provider will stop your infusion and treat your reaction. If you have a severe infusion or allergic reaction, your healthcare provider may stop your treatment completely. Tell your healthcare provider or get medical help right away if you have any of these symptoms during or after your infusion of SYLVANT: back pain, chest pain or tightness, nausea and vomiting, flushing, redness, irregular heart beat (palpitations), trouble breathing, wheezing, dizziness or light-headedness, swelling of the lips, skin rash, headache, or itching.
- The most common side effects of SYLVANT include rash, itching, upper respiratory tract infection, swelling, weight gain, and increased blood level of uric acid.
These are not all the possible side effects of SYLVANT. Call your HCP for medical advice about side effects. You are encouraged to report side effects of prescription drugs to the FDA. Call 1-800-FDA-1088 or visit www.fda.gov/medwatch.
SYLVANT® (siltuximab) for injection, for intravenous use, is available as 100 mg or 400 mg of lyophilized powder in a single-dose vial.
Please see full Prescribing Information, including Patient Information.
