Cancer is when cells in the body change and grow out of control. Your body is made up of tiny building blocks called cells. Normal cells grow when your body needs them and die when your body does not need them any longer.

Cancer is made up of abnormal cells that grow even though your body doesn't need them. In most cancers, the abnormal cells grow to form a lump or mass called a tumor. If cancer cells are in the body long enough, they can grow into (invade) nearby areas. They can even spread to other parts of the body (metastasis).

Sarcoma is a type of cancer that starts in the body's connective tissues. These are tissues like bones and muscles that support or protect other parts of the body. Soft tissue sarcomas can start in muscles, tendons, blood vessels, fat, nerves, and deep skin tissues. These cancers can start in almost any part of the body.

Although body parts such as the lungs, kidneys, and liver are soft, they are organs and not called soft tissues. Most cancers that start in these organs are not soft tissue sarcomas.

There are dozens of different types of soft tissue sarcomas. But many of these are rare. Here are some of the more common types of soft tissue sarcomas:

• Angiosarcomas. These cancers start in blood or lymph vessels.
• Fibrosarcomas. These cancers start in fibrous tissues, usually in the arms, legs, chest, or back.
• Gastrointestinal stromal tumors (GISTs). These cancers can occur anywhere along the digestive tract. They are treated differently from most other types of sarcomas. This is because they often respond to treatment with targeted therapy medicines.
• Leiomyosarcomas. The cells in these cancers are related to smooth muscle cells. These cancers are often found in the abdomen or uterus. But they can also start in other parts of the body. These include the leg or arm muscles.
• Liposarcomas. These cancers start in fat cells. Although they can be found anywhere in the body, they often start in the abdomen or thighs.
• Malignant peripheral nerve sheath tumors. These cancers include neurofibrosarcomas and malignant schwannomas. They are cancers of the cells that wrap around nerves. These tumors are rare. They may be seen in people with some inherited syndromes, such as neurofibromatosis.
• Synovial sarcomas. These are cancers of the synovial tissues that surround joints. These cancers most often occur in the hip, knee, ankle, or shoulder. They are more common in young adults and children. But older adults can also get this type of sarcoma.
• Undifferentiated pleomorphic sarcomas. These cancers used to be called malignant fibrous histiocytomas. They are most common in the arms or legs. But they can also start in other parts of your body.
• Rhabdomyosarcoma. This cancer is the most common sarcoma in children. It starts in skeletal muscles but can also be found in other parts of the body.

Soft tissue sarcomas can start nearly anywhere in the body. At first, they grow as a single tumor. This may show up as a lump if it's close to the surface of your body, such as on an arm or leg. You may not notice sarcomas that start deeper in your body until they cause other symptoms, by which time they might have grown larger. Over time, cancer cells can break away from the original tumor and might spread (metastasize) to other parts of your body, such as the lungs.

If you have questions about soft tissue sarcoma, talk with your doctor. They can help you understand more about this cancer.