Synovial Sarcoma: Symptoms, Causes, Diagnosis, and Treatment Explained
Updated: 3 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 2026
TL;DR: Synovial sarcoma is a rare soft tissue sarcoma — a cancer of the body's connective tissues — that tends to occur near large joints, mainly the knees, and usually affects young adults. [1] The first symptom is usually a painless lump or bump under the skin that slowly gets bigger, though the lump may or may not hurt; joint stiffness, pain, and swelling also occur, and tumors in the head or neck can affect breathing, swallowing, and the voice. [1] The cause is not clear, and there is no way to prevent it; younger age (older children and young adults) is a risk factor. [1] Because it grows slowly, diagnosis can take years, and it is sometimes mistaken for arthritis or bursitis. [2] Diagnosis uses imaging (MRI, X-rays, CT) and a biopsy. Surgery is the main treatment, with radiation, chemotherapy, targeted therapy, and cell therapy (afamitresgene autoleucel/Tecelra) used alongside or for advanced cases; amputation is now far less likely than in the past. [2]
Quick Answer: What is synovial sarcoma?
Synovial sarcoma is a rare cancer of connective tissue that usually forms near large joints, especially the knees, most often in young adults. [1] It typically starts as a slowly growing, painless lump and can take years to diagnose. [2] It is diagnosed with imaging and biopsy. Surgery is the main treatment, often combined with radiation or chemotherapy. [2]
What the research says
Cell therapy can work in heavily pre-treated advanced disease. In the SPEARHEAD-1 phase 2 trial, 52 patients (44 with synovial sarcoma) with HLA-A*02 and MAGE-A4-expressing tumors, all previously treated with chemotherapy, received a single infusion of afamitresgene autoleucel. The overall response rate was 39% in the synovial sarcoma group (17 of 44; 95% CI 24–55%). Cytokine release syndrome occurred in 71% of patients, and most had low blood counts (D'Angelo et al., Lancet, 2024) [3].
Older second-line drugs have modest results. A meta-analysis of 16 studies of pazopanib or trabectedin in previously treated metastatic synovial sarcoma found a pooled median overall survival of 10.4 months and a pooled overall response rate of 14.7%, which the authors said highlights the need for better treatments (Carroll et al., Future Oncol, 2022) [4].
What Is Synovial Sarcoma?
Synovial sarcoma is a rare type of cancer that tends to occur near large joints, mainly the knees. It usually affects young adults. [1]
Synovial sarcoma begins as a growth of cells that can multiply quickly and destroy healthy tissue. The first symptom is usually swelling or a lump under the skin. The lump may or may not hurt. [1]
This cancer can occur almost anywhere in the body. The most common places are in the legs and arms. [1]
Synovial sarcoma is a type of cancer called a soft tissue sarcoma. Soft tissue sarcoma happens in the body's connective tissues. There are many types of soft tissue sarcoma.
What Are the Symptoms of Synovial Sarcoma?
Signs and symptoms of synovial sarcoma depend on where the cancer starts. Most people notice a painless lump or bump that slowly gets bigger. The lump usually starts near the knee or ankle, but it can appear on any part of the body. [1]
Synovial sarcoma symptoms may include a lump or bump under the skin that slowly gets bigger, joint stiffness, pain, and swelling. [1]
When synovial sarcoma happens in the head or neck, it can cause other symptoms. These may include problems breathing, difficulty swallowing, and changes in the way the voice sounds. [1]
Symptom | What it involves |
|---|---|
Growing lump or bump | A lump under the skin that slowly gets bigger; usually near the knee or ankle, but can appear anywhere on the body |
Joint stiffness | Stiffness in the nearby joint |
Pain | The lump may or may not hurt |
Swelling | Swelling around the affected area |
Head and neck symptoms
Symptom (head or neck location) | What it involves |
|---|---|
Problems breathing | Airway can be affected by the tumor |
Difficulty swallowing | The tumor can make swallowing difficult |
Voice changes | Changes in the way the voice sounds |
Why does synovial sarcoma take so long to diagnose?
Synovial sarcoma is usually slow growing, so it can be years before a diagnosis is made. [2] Sometimes, synovial sarcoma is diagnosed in error as a joint problem, such as arthritis or bursitis. [2]
When should you see a doctor?
Make an appointment with a doctor or other healthcare professional if you have any symptoms that don't go away and that worry you.
What Causes Synovial Sarcoma?
The cause of synovial sarcoma isn't clear, but the cancer forms when cells develop DNA changes that make them multiply quickly and form a tumor. [1]
What is understood is how it begins at the cellular level. This kind of cancer forms when cells develop changes in their DNA. A cell's DNA holds the instructions that tell the cell what to do. In healthy cells, the DNA gives instructions to grow and multiply at a set rate. The instructions tell the cells to die at a set time.
In cancer cells, the DNA changes give different instructions. The changes tell the cancer cells to make many more cells quickly. Cancer cells can keep living when healthy cells would die. This causes too many cells.
The cancer cells might form a mass called a tumor. The tumor can grow to invade and destroy healthy body tissue. In time, cancer cells can break away and spread to other parts of the body. When cancer spreads, it's called metastatic cancer. [1]
Who Is at Risk? Can It Be Prevented?
Younger age is a risk factor for synovial sarcoma. This cancer happens most often in older children and young adults. [1]
Risk factor | Details |
|---|---|
Younger age | Synovial sarcoma happens most often in older children and young adults |
No known prevention | There is no way to prevent synovial sarcoma [1] |
How Is Synovial Sarcoma Diagnosed?
Tests and procedures used to diagnose synovial sarcoma include imaging tests and a biopsy. [2]
Diagnostic step | How it works |
|---|---|
Imaging tests | Take pictures of the body. They can show where a synovial sarcoma is, how large it is, and if it has spread to other areas of the body. Tests might include MRI scans, X-rays, and CT scans [2] |
Biopsy | A procedure to remove a sample of tissue for testing in a lab. The tissue might be removed using a needle put through the skin and into the cancer, or sometimes surgery is needed to get the tissue sample. The sample is tested in a lab to see if it is cancer. Other special tests give more details about the cancer cells. Your healthcare team uses this information to make a treatment plan |
How Is Synovial Sarcoma Treated?
Treatment options for synovial sarcoma include surgery, radiation therapy, chemotherapy, targeted therapy, cell therapy, and clinical trials. [2]
Treatment | How it works | When it's used |
|---|---|---|
Surgery | Removes the cancer and some of the healthy tissue around it; can sometimes mean removal of an entire muscle or muscle group | The main treatment for synovial sarcoma [2] |
Radiation therapy | Powerful energy beams directed to precise points on the body while you lie on a table and a machine moves around you | Before surgery, to shrink the cancer and make successful surgery more likely; after surgery, to kill cancer cells that might still be there |
Chemotherapy | Strong medicines that treat cancer | Before or after surgery; also when cancer has spread to other parts of the body |
Targeted therapy | Medicines that attack specific chemicals in the cancer cells, causing cells to die or stop growing | Being studied for advanced synovial sarcoma |
Cell therapy | Immune system cells are taken from your body, made better at recognizing the cancer cells, and put back in your body; can take months to set up | One option is afamitresgene autoleucel (Tecelra), which might treat advanced synovial sarcoma that hasn't been helped by chemotherapy [2] |
Clinical trials | Studies of new treatments that give a chance to try the latest options; side effects may not be known | Ask your healthcare team if a trial is available |
How has surgery changed?
In the past, surgery might have included removing an arm or leg, known as amputation. But medical advances have made amputation less likely. [2]
To lower the chances of the cancer returning, radiation therapy or chemotherapy might be used as well. [2]
How Should You Prepare for Your Appointment?
Make an appointment with your usual doctor or other healthcare professional if you have any symptoms that worry you. If your health professional thinks you might have synovial sarcoma, you will likely be referred to a specialist.
Specialists who care for people with synovial sarcoma include medical oncologists (doctors who specialize in cancer), orthopedic oncologists (surgeons who specialize in operating on people with cancers that affect the soft tissue and bones), and radiation oncologists (doctors who treat cancer with radiation therapy). [2]
What you can do
Write down any symptoms you have, including when you first noticed a lump.
Write down any key medical information, including any medical conditions or surgeries that you have had.
Make a list of all medicines, vitamins, or supplements you're taking — how much, when, and why.
Consider bringing a family member or friend, who can help you remember key information.
Write down questions you would like to ask, in order of most important to least important.
Potential questions include:
Do I have cancer?
Do I need more tests?
What are my treatment options?
What are the potential risks of these treatment options?
Do any of the treatments cure my cancer?
Will I get a copy of my pathology report?
How much time can I take to consider my treatment options?
Are there brochures or other printed materials that I can take with me? What websites do you recommend?
What happens if I choose not to have treatment?
What to expect from your doctor
Your healthcare professional will likely ask what symptoms worry you, when you first noticed your symptoms, whether anything makes your symptoms worse or better, and how bad your symptoms are.
Conclusion
Synovial sarcoma is a rare, slow-growing soft tissue sarcoma that hides in plain sight near the joints where young adults — and sometimes older children — first feel stiffness or pain. Its most common presentation is a painless lump near the knee or ankle that grows gradually, and that very slowness is what makes it tricky: it can take years to diagnose, and it is sometimes mistaken for arthritis or bursitis. That is why a lump or symptom that doesn't go away deserves a professional look rather than months of waiting.
The outlook for treatment has evolved considerably. Surgery remains the main treatment, but advances mean amputation is now far less likely than it once was. Radiation and chemotherapy help lower the chances of the cancer returning, while targeted therapy and newer cell therapies such as afamitresgene autoleucel (Tecelra) offer options for advanced cases. Knowing which specialists to see, what questions to ask, and what information to bring to your appointment gives you real agency in a process that often begins with nothing more than a lump that wouldn't go away.
What are the next steps after a synovial sarcoma diagnosis?
If you've noticed a lump or bump under the skin that slowly gets bigger — especially near your knee or ankle — or unexplained joint stiffness, pain, or swelling that doesn't go away, make an appointment with a doctor or healthcare professional. If synovial sarcoma is suspected, expect referrals to medical oncologists, orthopedic oncologists, and radiation oncologists. Before your appointment, write down your symptoms and when they started, gather your medical history and medication list, bring a family member or friend, and prepare your questions in order of importance. Ask about clinical trials and advanced options like cell therapy if your case is advanced.
Related reading on Rinnit: Soft Tissue Sarcoma: Complete Guide to Symptoms, Types, Diagnosis, and Treatment · Sarcoma Guide: Symptoms, Causes, Diagnosis, and Treatment · Radiation Therapy: A Comprehensive Guide to Treatment and Recovery · Liposarcoma: Symptoms, Causes, Diagnosis & Treatment — What to Know · Fibrosarcoma: Types, Symptoms, Causes, Diagnosis, Treatment and Outlook — What You Need to Know
Frequently Asked Questions
What is synovial sarcoma?
Synovial sarcoma is a rare type of cancer that tends to occur near large joints, mainly the knees, and usually affects young adults. It is a type of soft tissue sarcoma, meaning it happens in the body's connective tissues.
Is synovial sarcoma a soft tissue sarcoma?
Yes. Soft tissue sarcoma happens in the body's connective tissues, and there are many types of soft tissue sarcoma. Synovial sarcoma is one of them.
Where does synovial sarcoma usually occur?
It tends to occur near large joints, mainly the knees. It can occur almost anywhere in the body, but the most common places are in the legs and arms.
Who gets synovial sarcoma?
It usually affects young adults. Younger age is a risk factor — the cancer happens most often in older children and young adults.
What is the first symptom of synovial sarcoma?
The first symptom is usually swelling or a lump under the skin. The lump may or may not hurt.
What does the lump feel like?
Most people notice a painless lump or bump that slowly gets bigger. The lump usually starts near the knee or ankle, but it can appear on any part of the body.
What are the symptoms of synovial sarcoma?
Symptoms may include a lump or bump under the skin that slowly gets bigger, joint stiffness, pain, and swelling. Signs depend on where the cancer starts.
Can synovial sarcoma occur in the head or neck?
Yes. Synovial sarcoma that happens in the head or neck can cause problems breathing, difficulty swallowing, and changes in the way the voice sounds.
What causes synovial sarcoma?
It's not clear what causes synovial sarcoma. It forms when cells develop changes in their DNA that give the cells different instructions — to make many more cells quickly and to keep living when healthy cells would die.
Can synovial sarcoma spread to other parts of the body?
Yes. In time, cancer cells can break away and spread to other parts of the body. When cancer spreads, it's called metastatic cancer.
Is there a way to prevent synovial sarcoma?
No. There is no way to prevent synovial sarcoma.
Why does synovial sarcoma take years to diagnose?
Synovial sarcoma is usually slow growing, so it can be years before a diagnosis is made. Sometimes it is diagnosed in error as a joint problem, such as arthritis or bursitis.
Is synovial sarcoma the same as arthritis?
No. Synovial sarcoma is a cancer of connective tissue that can be mistaken for a joint problem like arthritis or bursitis. This misdiagnosis happens partly because the cancer is slow growing.
How is synovial sarcoma diagnosed?
Through imaging tests — which show where the cancer is, how large it is, and whether it has spread — including MRI scans, X-rays, and CT scans, plus a biopsy. In a biopsy, a tissue sample is removed, sometimes with a needle through the skin into the cancer and sometimes with surgery, and tested in a lab to see if it is cancer. Special tests give more details about the cancer cells, and the team uses this information to make a treatment plan.
What is the main treatment for synovial sarcoma?
Surgery is the main treatment. The goal is to remove the cancer and some of the healthy tissue around it. This can sometimes mean the removal of an entire muscle or muscle group.
Does synovial sarcoma surgery involve amputation?
In the past, surgery might have included removing an arm or leg (amputation). But medical advances have made amputation less likely.
How is the chance of the cancer returning lowered?
To lower the chances of the cancer returning, radiation therapy or chemotherapy might be used as well as surgery.
How does radiation therapy work for synovial sarcoma?
Radiation therapy treats cancer with powerful energy beams. During treatment, you lie on a table while a machine moves around you, directing radiation to precise points on the body. Before surgery, radiation can shrink the cancer and make successful surgery more likely. After surgery, it can kill cancer cells that might still be there.
When is chemotherapy used?
For synovial sarcoma, chemotherapy might be used before or after surgery. It also may be used when cancer has spread to other parts of the body.
What is targeted therapy for synovial sarcoma?
Targeted therapy uses medicines that attack specific chemicals in the cancer cells. This can cause cancer cells to die or stop growing. Targeted therapy medicines are being studied for advanced synovial sarcoma.
What is cell therapy for synovial sarcoma?
Cell therapy helps the immune system find and stop the cancer cells. It involves taking some of your immune system cells, making them better at recognizing the cancer cells, and putting them back in your body. This treatment can take months to set up.
What is afamitresgene autoleucel (Tecelra)?
One cell therapy used for synovial sarcoma is afamitresgene autoleucel (Tecelra). It might be an option for treating advanced synovial sarcoma that hasn't been helped by chemotherapy.
Should I consider a clinical trial?
Clinical trials are studies of new treatments that provide a chance to try the latest treatment options. The side effects may not be known. Ask your healthcare team if there is a clinical trial available to take part in.
Which specialists treat synovial sarcoma?
Medical oncologists (doctors who specialize in cancer), orthopedic oncologists (surgeons who specialize in operating on cancers that affect the soft tissue and bones), and radiation oncologists (doctors who treat cancer with radiation therapy).
What should I bring to my appointment?
Write down any symptoms you have, including when you first noticed a lump; key medical information such as past medical conditions or surgeries; a list of all medicines, vitamins, or supplements (how much, when, and why); and your questions in order of most to least important. Consider bringing a family member or friend who can help remember key information.
What questions should I ask my doctor?
Do I have cancer? Do I need more tests? What are my treatment options? What are the potential risks? Do any of the treatments cure my cancer? Will I get a copy of my pathology report? How much time can I take to consider my options? Are there brochures or printed materials or recommended websites? What happens if I choose not to have treatment?
What questions will my doctor ask me?
What symptoms worry you? When did you first notice your symptoms? Does anything make your symptoms worse or better? How bad are your symptoms?
When should I see a doctor about a lump?
Make an appointment with a doctor or other healthcare professional if you have any symptoms that don't go away and that worry you.
References
Mayo Clinic Staff. Synovial sarcoma - Symptoms and causes. Mayo Clinic. January 3, 2025. https://www.mayoclinic.org/diseases-conditions/synovial-sarcoma/symptoms-causes/syc-20577380
Mayo Clinic Staff. Synovial sarcoma - Diagnosis and treatment. Mayo Clinic. January 3, 2025. https://www.mayoclinic.org/diseases-conditions/synovial-sarcoma/diagnosis-treatment/drc-20577401
D'Angelo SP, Araujo DM, Abdul Razak AR, et al. Afamitresgene autoleucel for advanced synovial sarcoma and myxoid round cell liposarcoma (SPEARHEAD-1): an international, open-label, phase 2 trial. Lancet. 2024;403(10435):1460-1471. PMID 38554725. https://doi.org/10.1016/S0140-6736(24)00319-2
Carroll C, Patel N, Gunsoy NB, et al. Meta-analysis of pazopanib and trabectedin effectiveness in previously treated metastatic synovial sarcoma (second-line setting and beyond). Future Oncol. 2022;18(32):3651-3665. PMID 36399116. https://doi.org/10.2217/fon-2022-0348
Medical Disclaimer
This article is for informational purposes only and does not constitute medical advice. Persistent symptoms should be evaluated by a qualified healthcare professional.
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