Soft tissue sarcoma is a rare type of cancer that develops in the body’s connective tissues, including muscle, fat, blood vessels, nerves, tendons, and joint linings. An estimated 13,520 new cases will be diagnosed in the United States in 2025, with roughly 5,410 deaths expected. While it can appear almost anywhere in the body, it most commonly shows up in the arms, legs, and abdomen.
Where Soft Tissue Sarcomas Start
Your soft tissues are the structures that connect, support, and surround everything else in your body. Unlike cancers that begin in organs or bones, sarcomas arise from these in-between tissues. A sarcoma growing in fat is called a liposarcoma. One that starts in smooth muscle (the kind that lines hollow organs like the uterus, bladder, or stomach) is a leiomyosarcoma. Others can develop in blood vessels, peripheral nerves, fibrous connective tissue, or in tissues whose exact origin is hard to classify under a microscope.
There are more than 50 recognized subtypes, which is part of what makes these cancers tricky to diagnose and treat. Some of the more common ones include undifferentiated pleomorphic sarcoma (which can appear anywhere), synovial sarcoma, and malignant peripheral nerve sheath tumors. Each subtype behaves differently, grows at different speeds, and responds to different treatments.
What It Feels Like
Soft tissue sarcomas often grow for weeks or months before anyone notices them. The most common first sign is a painless lump or swelling, typically in an arm, leg, or the trunk of the body. Because many benign lumps (like lipomas) are far more common, sarcomas are easy to dismiss early on.
Pain is not always present. When it does occur, it usually means the tumor has grown large enough to press on nearby nerves or organs. A sarcoma deep in the abdomen may cause vague fullness, bloating, or discomfort before a noticeable mass is ever felt. In the limbs, a lump that is growing steadily, is deep within the muscle rather than just under the skin, or is larger than about 5 centimeters (roughly the size of a golf ball) warrants prompt evaluation.
Known Risk Factors
Most soft tissue sarcomas have no clear cause. They can occur at any age, though certain subtypes are more common in children and others in older adults. A small number of cases are linked to identifiable risk factors:
- Inherited genetic conditions: Several rare syndromes raise sarcoma risk significantly, including Li-Fraumeni syndrome, neurofibromatosis, retinoblastoma, tuberous sclerosis, Gardner syndrome, Werner syndrome, and Gorlin syndrome. These conditions involve mutations in genes that normally suppress tumor growth.
- Previous radiation therapy: People who received radiation for earlier cancers, such as breast cancer or lymphoma, have a higher chance of developing a sarcoma in the treated area, sometimes years or decades later.
- Chemical exposure: Long-term contact with certain industrial chemicals, including vinyl chloride, arsenic, and thorium dioxide, has been associated with increased risk.
- Chronic lymphedema: Prolonged swelling in the arms or legs, often from damaged or removed lymph nodes, can occasionally give rise to a type of sarcoma called angiosarcoma.
How It Is Diagnosed
Diagnosing soft tissue sarcoma typically starts with imaging. MRI is the preferred tool for tumors in the arms and legs because it provides detailed views of soft tissue layers. CT scans are more useful for sarcomas in the abdomen or chest. PET scans and X-rays may also play a role, depending on the location and whether doctors need to check for spread to other parts of the body.
A biopsy is essential to confirm the diagnosis. Doctors usually perform a core needle biopsy, inserting a needle into the mass to collect tissue samples from several areas. This step requires careful planning. The biopsy needs to be done in a way that won’t interfere with future surgery, which is one reason sarcoma specialists recommend being seen at a medical center experienced with these cancers. The wrong biopsy approach can complicate later treatment.
Once tissue is collected, a pathologist examines it under a microscope and assigns a grade based on how abnormal the cells look, how quickly they are dividing, and how much of the tumor tissue has died (necrosis). This grading, developed by the French Federation of Cancer Centers, is one of the strongest predictors of how aggressively the cancer will behave. Low-grade sarcomas tend to grow slowly and are less likely to spread, while high-grade tumors are more aggressive and carry a greater risk of metastasis.
Treatment Approaches
Surgery is the primary treatment for most soft tissue sarcomas. The goal is to remove the entire tumor along with a margin of healthy tissue around it. When sarcomas occur in the arms or legs, limb-sparing surgery is the standard approach, meaning surgeons aim to remove the cancer while preserving as much function as possible. Amputation is reserved for rare situations where the tumor is so large or so entangled with critical structures that removing it would leave the limb nonfunctional.
Clean surgical margins matter a great deal. If cancer cells are found at the edge of the removed tissue, the risk of the tumor returning in the same spot increases significantly. In some cases, a second surgery is performed to widen the margins.
Radiation therapy is frequently used alongside surgery, either before the operation to shrink the tumor or afterward to destroy any remaining cancer cells. For tumors that are too large or too difficult to operate on initially, radiation can sometimes make surgery possible.
Chemotherapy plays a more selective role. It is used more often for certain subtypes, for high-grade tumors, or when the cancer has spread to distant sites like the lungs. Over the past decade, the FDA has approved several targeted drugs and immunotherapies for specific sarcoma subtypes. These include drugs that block the blood vessel growth tumors need to survive, therapies that target specific molecular pathways driving certain subtypes, and a newer cell-based immunotherapy. The right option depends heavily on the subtype, the genetic profile of the tumor, and how far the disease has progressed.
Prognosis and What Affects It
Outcomes for soft tissue sarcoma vary widely depending on the subtype, grade, size, and whether the cancer has spread at the time of diagnosis. A small, low-grade sarcoma caught early and removed completely carries a very different outlook than a large, high-grade tumor that has metastasized. Tumor grade is one of the most important factors. Location matters too: sarcomas in the limbs are generally easier to treat surgically than those deep in the abdomen, where complete removal can be more difficult.
Because there are so many subtypes and each behaves differently, broad survival statistics can be misleading. What matters most is the specific characteristics of the individual tumor. Sarcomas also have a tendency to recur, sometimes years after initial treatment, which is why long-term follow-up with imaging is a standard part of care.