What are soft tissue sarcomas?

Sarcomas are malignant (cancerous) tumors that develop in tissues which connect, support, or surround other structures and organs of the body. Muscles, tendons (bands of fiber that connect muscles to bones), fibrous tissues, fat, blood vessels, nerves, and synovial tissues are types of soft tissue. Soft tissue sarcomas are grouped together because they share certain microscopic characteristics, have similar symptoms, and are generally treated in similar ways (1). They are usually named for the type of tissue in which they begin.

Examples of soft tissue sarcomas and the type of tissue in which they begin include the following (2):

• Fibrous tissue (tissue that holds bones, muscles, and organs in place)—fibrosarcoma, malignant fibrous histiocytoma
• Fatty tissue—liposarcoma
• Smooth muscle (e.g., uterus)—leiomyosarcoma
• Skeletal muscle—rhabdomyosarcoma
• Blood and lymph vessels—epithelioid hemangioendothelioma, angiosarcoma, lymphangiosarcoma, Kaposi sarcoma
• Perivascular tissue (near or around blood vessels)—glomangiosarcoma, malignant hemangiopericytoma
• Synovial tissue (tissue that lines joints, tendon sheaths, and fluid-filled sacs between tendons and bones)—synovial sarcoma
• Peripheral nerves—malignant granular cell tumor, malignant peripheral nerve sheath tumor (also called malignant schwannoma or neurofibrosarcoma)
• Mesenchymal cells (cells that develop into connective tissue, blood vessels, and lymphatic tissue)—gastrointestinal stromal tumor (GIST), malignant mesenchymoma

Other types of soft tissue sarcomas include alveolar soft part sarcoma, epithelioid sarcoma, desmoplastic small cell tumor, and clear cell sarcoma. At this time, scientists do not know the types of tissue in which these sarcomas begin (2). Many sarcomas have specific chromosomal alterations, which are used to help classify the tumors (2).

Sarcomas that develop in the bone and cartilage (osteosarcoma, Ewing sarcoma, and chondrosarcoma) are not classified as soft tissue sarcomas and are not described in this resource. (More information about these types of cancer is available in the National Cancer Institute (NCI) fact sheet Bone Cancer: Questions and Answers at http://www.cancer.gov/cancertopics/factsheet/Sites-Types/bone on the Internet.)

Where in the body are soft tissue sarcomas more likely to develop?

Soft tissue sarcomas can arise almost anywhere in the body. About 43 percent occur in the extremities (e.g., arms, legs); 34 percent occur in and around the internal organs (e.g., uterus, heart); 10 percent occur in the trunk (e.g., chest, back); and 13 percent occur in other locations (2). In very rare cases, these tumors develop in the gastrointestinal tract. A small percentage of these are GISTs. Malignant GISTs occur most commonly in the stomach and small intestine.

What are the possible causes of soft tissue sarcomas?

Although most soft tissue sarcomas do not have a clearly defined cause, researchers have identified several factors that increase the likelihood of developing these tumors (2). External radiation therapy is the most well-established risk factor for soft tissue sarcomas. Patients treated with radiation therapy for cancers of the retina, breast, cervix, ovary, testes, or lymphatic system have a much higher chance of developing soft tissue sarcomas than the general population (1). The risk appears to be related to the dose of radiation. To limit this risk, radiation treatment for cancer is planned to ensure that the greatest amount of radiation is delivered to diseased tissue while surrounding healthy tissue is protected as much as possible.

Another risk factor for soft tissue sarcomas is exposure to certain chemicals in the workplace, including vinyl chloride, arsenic, herbicides such as phenoxyacetic acids, and wood preservatives that contain chlorophenols (2). Chronic lymphedema (a condition in which excess fluid collects in the tissue and causes swelling) following radiation to, or surgical removal of, lymph nodes is also a risk factor.

Certain inherited diseases are associated with an increased risk of developing soft tissue sarcomas. Studies have focused on genetic changes that may lead to the development of soft tissue sarcomas. For example, people with Li-Fraumeni syndrome (associated with alterations in the p53 tumor suppressor gene), von Recklinghausen disease (also called neurofibromatosis type 1 and associated with alterations in the NF1 gene), hereditary leiomyomatosis and renal cell cancer syndrome (with alterations in the FH gene), and hereditary retinoblastoma (with alterations in the RB1 gene) are at increased risk of developing soft tissue sarcomas.

Kaposi sarcoma is a soft tissue sarcoma that sometimes develops in people with human immunodeficiency virus (HIV) infection. The primary cause of Kaposi sarcoma is infection with Kaposi sarcoma-associated herpesvirus (KSHV), or human herpesvirus 8. However, people infected with KSHV, but not HIV, rarely develop Kaposi sarcoma (3).

How often do soft tissue sarcomas occur?

Soft tissue sarcomas are rare. About 9,500 new cases were diagnosed in the United States in 2006 (4), which is less than 1 percent of all new cancer cases. However, sarcomas occur more often in children and young adults. For example, soft tissue sarcomas account for about 7 percent of all childhood cancers. The most common soft tissue sarcomas are leiomyosarcoma, malignant fibrous histiocytoma, and liposarcoma. By site of origin, leiomyosarcoma is the most common sarcoma of the organs, while liposarcoma and malignant fibrous histiocytoma are the most common sarcomas of the extremities (5). Rhabdomyosarcoma is the most common soft tissue sarcoma in children.

What are the symptoms of soft tissue sarcomas?

Soft tissue sarcomas usually appear as a lump or mass, but they rarely cause pain, swelling, or other symptoms (1). A lump or mass might not be a sarcoma; it could be benign (noncancerous), a different type of cancer, or another problem. It is important to see a doctor about any physical change, such as a lump or mass, because only a doctor can make a diagnosis.