Overview
Soft tissue sarcoma is a rare type of cancer that starts as a growth of cells in the body's soft tissues. Soft tissues include muscle, fat, blood vessels, nerves, tendons and the linings of the joints. Soft tissue sarcoma can happen anywhere in the soft tissues of the body. But it happens most often in the arms, legs and belly.
Soft tissue sarcomas can be serious, but some can have a good outlook, also called prognosis. The outlook is generally better for cancer that is less aggressive and hasn't spread.
When talking about cancers in these tissues, you may hear terms such as soft tissue cancer, malignant soft tissue sarcoma, muscle cancer or connective tissue cancer. These terms do not always mean the same thing. A soft tissue sarcoma starts in the body's soft tissues. But cancer also can spread to soft tissues from other parts of the body. When that happens, it is still called the type of cancer where it first started, not soft tissue sarcoma.
There are more than 50 types of soft tissue sarcoma. Some types are more likely to affect children. Others affect mostly adults. These cancers can be hard to diagnose, partly because they may be mistaken for many other types of growths.
Soft tissue sarcoma treatment usually involves surgery. Other treatments might include radiation therapy and medicines. Treatment depends on the size, type and location of the cancer and how quickly it grows.
Soft tissue sarcoma
Soft tissue sarcoma
Soft tissue sarcomas are cancers that start in the soft tissues of the body. This illustration shows a soft tissue sarcoma of the thigh muscle just above the knee.
Types
There are many types of soft tissue sarcoma. Each type can act differently.
- Angiosarcoma. Angiosarcoma is a type of cancer that forms in the lining of the blood vessels and lymph vessels.
- Desmoplastic small round cell tumor. Desmoplastic small round cell tumor (DSRCT) is a rare, aggressive sarcoma that usually starts in the belly or pelvis. It occurs most often in teenagers and young adults.
- Epithelioid sarcoma. Epithelioid sarcoma often starts in the hands, arms, feet or legs of teenagers and young to middle-aged adults. Epithelioid sarcoma tends to grow slowly at first but can become aggressive.
- Kaposi sarcoma. This cancer forms in the lining of blood vessels and lymph vessels and causes growths of cells called lesions on the skin. Kaposi sarcoma is linked to infection with human herpesvirus 8 (HHV-8). It is more likely to happen in people with weakened immune systems, such as people with HIV.
- Leiomyosarcoma. This smooth muscle sarcoma usually starts in the uterus, belly or legs.
- Liposarcoma. Liposarcoma is a cancer that starts in the fat cells. It can happen anywhere in the body but happens most often in the belly, arms or legs.
- Malignant peripheral nerve sheath tumor. These tumors start in the lining that covers nerves that run from the spinal cord into the body. These nerves are called peripheral nerves.
- Myxofibrosarcoma. This soft tissue sarcoma most often starts in the connective tissue of the arms or legs of older adults.
- Rhabdomyosarcoma. This sarcoma most often starts in muscle tissue or organs such as the bladder and uterus. It usually happens in children.
- Synovial sarcoma. This cancer tends to happen near larger joints such as the hip and knee. It usually affects young adults.
- Undifferentiated pleomorphic sarcoma. This cancer gets its name from the way the cancer cells look under a microscope. Undifferentiated means the cancer cells don't look like the healthy cells around them. Pleomorphic (plee-o-MOR-fik) means the cells grow in many shapes and sizes.
- Dermatofibrosarcoma protuberans. Dermatofibrosarcoma protuberans (DFSP) is a type of skin cancer that starts in the connective tissue cells in the middle layer of the skin. It usually grows slowly.
- Gastrointestinal stromal tumor. Gastrointestinal stromal tumor (GIST) is a type of cancer that begins in the digestive system. These tumors happen most often in the stomach and small intestine.
- Solitary fibrous tumor. These tumors start in the connective tissue almost anywhere in the body, including the lining outside of the lungs. They tend to grow slowly.
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Symptoms
At first, a soft tissue sarcoma may not cause symptoms. Some possible general signs and symptoms may include:
- A noticeable lump or swelling. The lump may be painless. It may grow over weeks, months or years. It can grow quickly or slowly.
- Pain, tingling or numbness. These symptoms can happen if a sarcoma presses on nearby nerves or muscles.
Some soft tissue sarcomas can cause signs on the skin. For example, dermatofibrosarcoma protuberans (DFSP) can look like a red, purple or brown bump. Kaposi sarcoma may cause spots that look red, purple or brown. Angiosarcoma may look like a bruise.
Symptoms also can be different depending on the body part where a soft tissue sarcoma grows.
Arm or shoulder
Soft tissue sarcomas in the arm or shoulder can look like:
- A noticeable lump or bulge.
- Swelling.
- One arm or shoulder that appears bigger than the other, maybe even causing clothing to feel tighter in that area.
Other possible symptoms include:
Belly or back
A soft tissue sarcoma in the belly or back of the belly can cause symptoms including:
- A lump that you may feel.
- Feeling full before you usually would when eating.
- Nausea or vomiting.
- Pain or pressure that gets worse in the belly, back or side.
- Weight loss.
Leg
A soft tissue sarcoma in the calf, the thigh or another part of the leg may look or feel like:
- A noticeable lump or bulge.
- Swelling.
- One calf or thigh that appears bigger than the other, maybe even causing a pant leg to feel tighter in that area.
- Leg weakness.
- Leg pain.
Most lumps are not sarcoma. Sometimes, noncancerous lumps, also called benign lumps, develop from fat cells. These are called lipomas.
But a lump that is growing, is larger than about 2 inches (5 centimeters) or is located deep under the skin should be checked by a healthcare professional. You can't tell whether a lump is a sarcoma simply by how it looks or feels.
When to see a doctor
Make an appointment with a doctor or other healthcare professional for symptoms that worry you.
Have a lump checked if it:
- Continues to grow.
- Is larger than about 2 inches (5 centimeters).
- Feels like it is deep beneath the skin.
Do not wait for a lump to become painful before having it checked. A soft tissue sarcoma lump may not hurt.
Causes
It's not clear what causes most soft tissue sarcomas.
Soft tissue sarcoma starts when a connective tissue cell gets changes in its DNA. A cell's DNA holds the instructions that tell a cell what to do. The changes turn the connective tissue cells into cancer cells. The changes tell the cancer cells to grow and make more cells. Unlike healthy cells that die as part of their natural cycles, cancer cells keep growing because they do not have instructions to stop.
The cancer cells form a growth, called a tumor. In some types of soft tissue sarcoma, the cancer cells stay in one location. They continue making more cells and cause the tumor to get bigger. In other types of soft tissue sarcoma, the cancer cells might break away and spread to other parts of the body.
The type of cell with DNA changes is what determines the type of soft tissue sarcoma. For example, angiosarcoma begins in cells in the lining of blood vessels, while liposarcoma starts in fat cells.
Risk factors
Factors that may raise the risk of sarcoma include:
- Inherited syndromes. The risk of soft tissue sarcoma can be passed down in families. Genetic syndromes that increase the risk include hereditary retinoblastoma, Li-Fraumeni syndrome, neurofibromatosis type 1, tuberous sclerosis and Werner syndrome.
- Chemical exposure. Exposure to high doses of some herbicides may raise the risk of soft tissue sarcoma, although the evidence is not certain.
- Radiation exposure. Radiation therapy for other cancers can increase the risk of soft tissue sarcomas.
- Lymphedema. Lymphedema is swelling that happens when something blocks or damages the lymphatic system. Lymphedema raises the risk of a type of sarcoma called angiosarcoma.
- Exposure to viruses. Human herpes virus 8 (HHV-8) causes Kaposi sarcoma. The risk is higher in people with weakened immune systems, including people with HIV.
Sept. 11, 2026