Sarcoma

In oncology, a sarcoma is a neoplasm formed from connective tissue, or the precursor to connective tissue, mesenchymal cells. There are two broad types, the most common being soft tissue sarcomas, and the other in bone and cartilage.

Soft tissue sarcomas
Examples of soft tissue sarcomas and the type of tissue in which they begin include the following:
 * 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's 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, for which the precursor tissue type is not known, include alveolar soft part sarcoma, epithelioid sarcoma, desmoplastic small cell tumor, and clear cell sarcoma.

Incidence
Soft tissue sarcomas are rare. About 9,500 new cases were diagnosed in the United States in 2006, 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. Rhabdomyosarcoma is the most common soft tissue sarcoma in children.

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). 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.

Risk factors
External radiation therapy is the most well-established risk factor for soft tissue sarcomas, with the risk being proportional to the radiation dose. 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. Environmental chemical exposures have been reported as a risk factor, including vinyl chloride, arsenic, herbicides such as phenoxyacetic acids, and wood preservatives that contain chlorophenols. Chronic lymphedema 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.

Bone and cartilage
These include osteosarcoma and Ewing's tumor.