Key Points
							                    - Childhood soft tissue sarcoma is a disease in which malignant (cancer) cells form in soft tissues of the body.    - Soft tissue sarcoma occurs in children and adults.    - Having certain diseases and inherited disorders can increase the risk of childhood soft tissue sarcoma.     - The most common sign of childhood soft tissue sarcoma is a painless lump or swelling in soft tissues of the body.     - Diagnostic tests are used to detect (find) and diagnose childhood soft tissue sarcoma.    - If tests show there may be a soft tissue sarcoma, a biopsy is done.     - There are many different types of soft tissue sarcomas.          - Fat tissue tumors     - Bone and cartilage tumors     - Fibrous (connective) tissue tumors      - Skeletal muscle tumors     - Smooth muscle tumors     - So-called fibrohistiocytic tumors     - Peripheral nervous system tumors     - Pericytic (Perivascular) Tumors     - Tumors of unknown origin     - Blood vessel tumors        - Certain factors affect prognosis (chance of recovery) and treatment options.
							                
							                
							                    Childhood soft tissue sarcoma is a disease in which malignant (cancer) cells form in soft tissues of the body.
							                    Soft tissues of the body connect, support, and surround other body parts and organs. The soft tissues include the following:         - Fat.    - A mix of bone and cartilage.    -  Fibrous tissue.    - Muscles.    -  Nerves.    -  Tendons (bands of tissue that connect muscles to bones).    -  Synovial tissues (tissues around joints).    -  Blood vessels.    -  Lymph vessels.         Soft tissue sarcoma may be found anywhere in the body. In children, the tumors form most often in the arms, legs, or trunk (chest and abdomen).
							                
							                
							                    Soft tissue sarcoma occurs in children and adults.
							                    Soft tissue sarcoma in children may respond differently to treatment, and may have a better prognosis than soft tissue sarcoma in adults. (See the PDQ summary on Adult Soft Tissue Sarcoma Treatment for information on treatment in adults.)
							                
							                  
							                    There are many different types of soft tissue sarcomas.
							                    The cells of each type of sarcoma look different under a microscope. The soft tissue tumors are grouped based on the type of soft tissue cell where they first formed.    This summary is about the following types of soft tissue sarcoma:     Fat tissue tumors            -   Liposarcoma . This is a rare cancer of the fat cells. Liposarcoma usually forms in the fat layer just under the skin. In children and adolescents, liposarcoma is often low grade (likely to grow and spread slowly).  There are several different types of liposarcoma. Myxoid liposarcoma is usually low grade and responds well to treatment. The cells of myxoid liposarcoma have a certain genetic change called a translocation (part of one chromosome switches places with part of another chromosome). In order to diagnose myxoid liposarcoma, the tumor cells are checked for this genetic change. Pleomorphic liposarcoma is usually high grade (likely to grow and spread quickly) and is less likely to respond well to treatment.              Bone and cartilage tumors    Bone and cartilage tumors are a mix of bone cells and cartilage cells. Bone and cartilage tumors include the following types:            -   Extraskeletal mesenchymal chondrosarcoma . This type of bone and cartilage tumor often affects young adults and occurs in the head and neck.      -   Extraskeletal osteosarcoma . This type of bone and cartilage tumor is very rare in children and adolescents. It is likely to come back after treatment and may spread to the lungs.               Fibrous (connective) tissue tumors     Fibrous (connective) tissue tumors include the following types:             -   Desmoid-type fibromatosis  (also called desmoid tumor or aggressive fibromatosis). This fibrous tissue tumor is low grade (likely to grow slowly). It may come back in nearby tissues but usually does not spread to distant parts of the body. Rarely, the tumor may disappear without treatment. Desmoid tumors sometimes occur in children with changes in the adenomatous polyposis coli (APC) gene. Changes in this gene cause familial adenomatous polyposis (FAP). FAP is an inherited condition in which many polyps (growths on mucous membranes) form on the inside walls of the colon and rectum. Genetic counseling (a discussion with a trained professional about inherited diseases and a possible need for gene testing) may be needed.      -   Dermatofibrosarcoma protuberans . This is a rare tumor of the deep layers of the skin found in children and adults. The cells of this tumor have a certain genetic change called a translocation (part of one chromosome switches places with part of another chromosome). In order to diagnose dermatofibrosarcoma protuberans, the tumor cells are checked for this genetic change.     -   Fibrosarcoma . There are two types of fibrosarcoma in children and adolescents:                  - Infantile fibrosarcoma (also called congenital fibrosarcoma). This type of fibrosarcoma is found in children aged 4 years and younger. It most often occurs in infants and may be seen in a prenatal ultrasound exam. This tumor is often large and fast growing, but rarely spreads to distant parts of the body. The cells of this tumor usually have a certain genetic change called a translocation (part of one chromosome switches places with part of another chromosome). In order to diagnose infantile fibrosarcoma, the tumor cells are checked for this genetic change.       -  Adult-type fibrosarcoma. This is the same type of fibrosarcoma found in adults. The cells of this tumor do not have the genetic change found in infantile fibrosarcoma. See the PDQ summary on Adult Soft Tissue Sarcoma Treatment for more information.                -   Inflammatory myofibroblastic tumor . This is a fibrous tissue tumor that occurs in children and adolescents. It is likely to come back after treatment but rarely spreads to distant parts of the body. A certain genetic change has been found in about half of these tumors.     -   Low-grade fibromyxoid sarcoma . This is a slow-growing tumor that affects young and middle-aged adults. The cells of this tumor usually have a certain genetic change called a translocation (part of one chromosome switches places with part of another chromosome). In order to diagnose low-grade fibromyxoid sarcoma, the tumor cells are checked for this genetic change. The tumor may come back many years after treatment and spread to the lungs and the lining of the wall of the chest cavity. Lifelong follow-up is needed.     -   Myxofibrosarcoma . This is a rare fibrous tissue tumor that is found less often in children than in adults.     -   Sclerosing epithelioid fibrosarcoma . This is a rare fibrous tissue tumor that can come back and spread to other places years after treatment. Long-term follow-up is needed.              Skeletal muscle tumors     Skeletal muscle is attached to bones and helps the body move.             -   Rhabdomyosarcoma . Rhabdomyosarcoma is the most common childhood soft tissue sarcoma in children 14 years and younger. See the PDQ summary on Childhood Rhabdomyosarcoma Treatment for more information.              Smooth muscle tumors    Smooth muscle lines the inside of blood vessels and hollow internal organs such as the stomach, intestines, bladder, and uterus.            -   Leiomyosarcoma . This smooth muscle tumor has been linked with Epstein-Barr virus in children who also have HIV disease or AIDS. Leiomyosarcoma may also form as a second cancer in survivors of inherited retinoblastoma, sometimes many years after the initial treatment for retinoblastoma.              So-called fibrohistiocytic tumors            -   Plexiform fibrohistiocytic tumor . This is a rare tumor that usually affects children and young adults. The tumor usually starts as a painless growth on or just under the skin on the arm, hand, or wrist. It may rarely spread to nearby lymph nodes or to the lungs.              Peripheral nervous system tumors    Peripheral nervous system tumors include the following types:            -   Ectomesenchymoma . This is a rare, fast-growing tumor of the nerve sheath (protective covering of nerves that are not part of the brain or spinal cord) that occurs mainly in children. Ectomesenchymomas may form in the head and neck, abdomen, perineum, scrotum, arms, or legs.      -   Malignant peripheral nerve sheath tumor . This is a tumor that forms in the nerve sheath. Some children who have a malignant peripheral nerve sheath tumor have a rare genetic condition called neurofibromatosis type 1 (NF1). This tumor may be low grade or high grade.     -   Malignant triton tumor . These are very rare, fast-growing tumors that occur most often in children with NF1.              Pericytic (Perivascular) Tumors     Pericytic tumors form in cells that wrap around blood vessels. Pericytic tumors include the following types:            -   Myopericytoma . Infantile hemangiopericytoma is a type of myopericytoma. Children younger than 1 year at the time of diagnosis may have a better prognosis. In patients older than 1 year, infantile hemangiopericytoma is more likely to spread to other parts of the body, including the lymph nodes and lungs.     -   Infantile myofibromatosis . Infantile myofibromatosis is another type of myopericytoma. It is a fibrous tumor that often forms in the first 2 years of life. There may be one nodule under the skin, usually in the head and neck area (myofibroma), or nodules in several skin areas, muscle, and bone (myofibromatosis). These tumors may go away without treatment.              Tumors of unknown origin    Tumors of unknown origin (the place where the tumor first formed is not known) include the following types:            -   Alveolar soft part sarcoma . This is a rare tumor of the soft supporting tissue that connects and surrounds the organs and other tissues. It is most commonly found in the limbs but can occur in the tissues of the mouth, jaws, and face. It may grow slowly and may have spread to other parts of the body at the time of diagnosis. Alveolar soft part sarcoma may have a better prognosis when the tumor is 5 centimeters or smaller or when the tumor is completely removed by surgery. The cells of this tumor usually have a certain genetic change called a translocation (part of one chromosome switches places with part of another chromosome). In order to diagnose alveolar soft part sarcoma, the tumor cells are checked for this genetic change.      -   Clear cell sarcoma of soft tissue . This is a slow-growing soft tissue tumor that begins in a tendon (tough, fibrous, cord-like tissue that connects muscle to bone or to another part of the body). Clear cell sarcoma most commonly occurs in deep tissue of the foot, heel, and ankle. It may spread to nearby lymph nodes. The cells of this tumor usually have a certain genetic change called a translocation (part of one chromosome switches places with part of another chromosome). In order to diagnose clear cell sarcoma of soft tissue, the tumor cells are checked for this genetic change.     -   Desmoplastic small round cell tumor . This tumor most often forms in the abdomen, pelvis or tissues around the testes, but it may form in the kidney. Desmoplastic small round cell tumor may also spread to the lungs and other parts of the body. The cells of this tumor usually have a certain genetic change called a translocation (part of one chromosome switches places with part of another chromosome). In order to diagnose desmoplastic small round cell tumor, the tumor cells are checked for this genetic change.     -   Epithelioid sarcoma . This is a rare sarcoma that usually starts deep in soft tissue as a slow growing, firm lump and may spread to the lymph nodes.      -   Extrarenal (extracranial) rhabdoid tumor . This is a rare, fast-growing tumor of soft tissues such as the liver and peritoneum. It usually occurs in young children, including newborns, but it can occur in older children and adults. Rhabdoid tumors may be linked to a change in a tumor suppressor gene called SMARCB1. This type of gene makes a protein that helps control cell growth. Changes in the SMARCB1 gene may be inherited (passed on from parents to offspring). Genetic counseling (a discussion with a trained professional about inherited diseases and a possible need for gene testing) may be needed.      -   Extraskeletal myxoid chondrosarcoma . This is a rare soft tissue sarcoma that may be found in children and adolescents. Over time, it tends to spread to other parts of the body, including the lymph nodes and lungs. The cells of this tumor usually have a genetic change, often a translocation (part of one chromosome switches places with part of another chromosome). In order to diagnose extraskeletal myxoid chondrosarcoma, the tumor cells are checked for this genetic change. The tumor may come back many years after treatment.     -   Perivascular epithelioid cell tumors (PEComas). Benign (not cancer) PEComas may be found in children with an inherited condition called tuberous sclerosis. They occur in the stomach, intestines, lungs, female reproductive organs, and genitourinary organs.     -   Primitive neuroectodermal tumor (PNET)/extraskeletal Ewing tumor . See the PDQ summary on Ewing Sarcoma Treatment for information.     -   Synovial sarcoma . Synovial sarcoma is a common type of soft tissue sarcoma in children and adolescents. Synovial sarcoma usually forms in the tissues around the joints in the arms or legs, but may also form in the trunk, head, or neck. The cells of this tumor usually have a certain genetic change called a translocation (part of one chromosome switches places with part of another chromosome). Larger tumors have a greater risk of spreading to other parts of the body, including the lungs. Children younger than 10 years and those whose tumor is 5 centimeters or smaller have a better prognosis.     -   Undifferentiated /unclassified sarcoma . These tumors usually occur in the muscles that are attached to bones and that help the body move.                   -  Undifferentiated pleomorphic sarcoma /malignant fibrous histiocytoma (high-grade). This type of soft tissue tumor may form in parts of the body where patients have received radiation therapy in the past, or as a second cancer in children with retinoblastoma. The tumor is usually found on the arms or legs and may spread to other parts of the body. See the PDQ summary on Osteosarcoma and Malignant Fibrous Histiocytoma of Bone Treatment for information about malignant fibrous histiocytoma of bone.                         Blood vessel tumors    Blood vessel tumors include the following types:            -   Angiosarcoma of the soft tissue. Angiosarcoma of the soft tissue is a fast-growing tumor that forms in blood vessels or lymph vessels in any part of the body. Most angiosarcomas are in or just under the skin. Those in deeper soft tissue can form in the liver, spleen, and lung. They are very rare in children, who sometimes have more than one tumor in the skin or liver. Rarely, infantile hemangioma may become angiosarcoma of the soft tissue. (See the PDQ summary on Childhood Vascular Tumors Treatment for more information.)     -  Epithelioid hemangioendothelioma. Epithelioid hemangioendotheliomas can occur in children, but are most common in adults between 30 and 50 years of age. They usually occur in the liver, lung, or bone. They may be either fast growing or slow growing. In about a third of cases, the tumor spreads to other parts of the body very quickly. (See the PDQ summary on Childhood Vascular Tumors Treatment for more information.)            See the following PDQ summaries for information about types of soft tissue sarcoma not included in this summary:         -  Childhood Rhabdomyosarcoma Treatment.    -  Ewing Sarcoma Treatment.    -  Unusual Cancers of Childhood Treatment (gastrointestinal stromal tumors).