Childhood soft tissue sarcomas develop in soft tissues such as muscles, tendons, fat, blood vessels, nerves, and synovial tissues (tissues around joints). Just over 50 percent of all childhood soft tissue sarcomas have a histology (how the cells look under a microscope) that is different from rhabdomyosarcoma. As a group, non-rhabdomyosarcoma soft tissue sarcomas comprise about 4 percent of all malignant tumors in children. They include:

•  Alveolar soft part sarcoma. This rare and slow-growing sarcoma is found most often in older children. It arises in skeletal muscle of the extremities, head, and neck.

•  Extraosseous Ewing sarcoma. Ewing sarcoma is usually a bone sarcoma, but it can also occur in soft tissues. It is most often diagnosed in older adolescents and young adults; the median age at diagnosis is 20. The most common tumor sites are the trunk, arms, legs, head, and neck. For more information on the treatment of Ewing sarcoma, see Chapter 2, Bone Sarcomas.

•  Fibrosarcoma. This soft tissue sarcoma is the most frequently occurring non-rhabdomyosarcoma soft tissue sarcoma in children younger than age 1. These tumors occur most often in the arms and legs, and the majority of children diagnosed have tumors that have not spread to other parts of the body (metastasized). Children younger than 4 diagnosed with this disease have an excellent prognosis after treatment with only surgery.

•  Hemangiopericytoma. This tumor of the blood and lymph vessels occurs most often in infants.

•  Leiomyosarcoma. This sarcoma develops in smooth muscle and most often occurs in the gastrointestinal tract, especially the stomach.

•  Liposarcoma. This sarcoma arises in fatty tissue and is found most frequently in young teenagers. The most common sites of origin are the legs or trunk.

•  Malignant fibrous histiocytoma. This form of soft tissue sarcoma most frequently occurs in the lower extremities and the trunk area. Other sites include the arms, scalp, and kidney.

•  Malignant peripheral nerve sheath tumor (also known as neurofibrosarcoma or malignant schwannoma). This aggressive cancer often occurs in association with neurofibromatosis. The most common site of origin is an arm, hand, foot, or leg.

•  Synovial sarcoma. This sarcoma is diagnosed most often in children ages 10 and older. The disease occurs frequently in the legs, especially in the area of the thigh or knee. It is also found in the arms, head, neck, and trunk.

Genetic factors

Many soft tissue sarcomas are distinguished by particular chromosome abnormalities that are identified after the tumor is biopsied. These are usually not inherited chromosomal abnormalities, but are mutations in the tumor cells. Because many soft tissue sarcomas look very similar under the microscope, identification of these unique genetic changes helps the treatment team diagnose your child’s particular type of tumor. This allows them to understand how aggressive the cancer is and tailor the treatment plan and follow-up care.

Staging

There is no standard staging or grading system that applies to all non-rhabdomyosarcoma soft tissue sarcomas. To determine the most promising treatment, oncologists will consider the grade of the tumor (how aggressive it looks under the microscope), the size of the tumor, the extent of tumor spread, and how much of the tumor has been surgically removed.

Treatment

At diagnosis, many parents do not know how to find experienced doctors and the best treatments for their child. State-of-the-art care is available from physicians who participate in the Children’s Oncology Group (COG). This study group includes pediatric surgeons and oncologists, radiation oncologists, researchers, and nurses. COG conducts studies to discover better therapies and supportive care for children with cancer. You can learn more about COG and find a list of its member treatment centers at www.childrensoncologygroup.org.

Non-rhabdomyosarcoma soft tissue sarcomas are rare in children, so the treatments are based on experience with adults. Generally, the size and location of the tumor, as well as tumor histology (how the cells look under a microscope), are used to choose the best treatment. Treatments should be individually tailored to the child’s tumor and designed to give the best chance of survival with the fewest long-term effects.

Surgery is the cornerstone of treatment for soft tissue sarcomas (see Chapter 14, Surgery). Many of the non-rhabdomyosarcoma soft tissue sarcomas can be treated successfully with just surgery, and they do not respond as well to chemotherapy or radiation therapy as rhabdomyosarcomas do. An experienced pediatric surgeon who has extensive experience with the treatment of pediatric sarcomas should perform biopsies and surgeries.

Ideally, the pediatric surgeon will attempt to remove the mass completely with wide margins (portions of the surrounding tissue) to ensure that no microscopic disease remains. The most important prognostic factor is whether the surgeon is able to completely remove the primary tumor.

Radiation is generally recommended for:

•  All large (more than 5 cm), high-grade soft tissue sarcomas, even if the tumor is completely removed and no tumor cells are found in the margins.

•  High-grade sarcomas of any size when tumors cells are present in the margins.

•  Large tumors that cannot be completely removed surgically.

The dose and field of radiation therapy are based on the age of the child and the size and location of the tumor. Children who receive radiation therapy for nonrhabdomyosarcoma soft tissue sarcomas generally have better outcomes than those who do not. However, radiation therapy without complete surgical removal of the tumor is rarely successful at permanently controlling the tumor.

Chemotherapy is often recommended:

•  After the removal of large (more than 5 cm), high-grade sarcomas, because they are associated with a greater risk of spread to other parts of the body.

•  For tumors that cannot be removed surgically or have already spread to other parts of the body.

Some types of non-rhabdomyosarcoma soft tissue sarcomas do not respond to chemotherapy, so it may not be recommended even in the above situations.

Although medical science has made advances in treating non-rhabdomyosarcoma soft tissue sarcomas while reducing the side effects and long-term impact to the child, amputation is sometimes necessary. For older children and teens, limb-sparing procedures are sometimes used instead of amputation. For information about amputation and limb-sparing procedures, see Chapter 2, Bone Sarcomas.