A sarcoma is a cancer that develops from particular tissues, such as muscle or bone. There are two types of sarcoma: osteosarcoma, which develops from bone, and soft tissue sarcoma. Soft tissue sarcoma can arise from muscle, fat, nerves, cartilage, or blood vessels. Cancerous tumors can develop when abnormal cells in these tissues multiply and grow out of control. Scientists do not yet fully understand why these cells become abnormal. However, most cancers are thought to develop due to genetic changes (mutations).
The tumor is named based on the type of tissue it resembles. For example, a soft tissue sarcoma that looks like fat is called a liposarcoma; a tumor that looks like fibrous tissue is called a fibrosarcoma. If a soft tissue sarcoma resembles more than one type of tissue, its name will reflect its complex appearance. For example, a neurofibrosarcoma develops in the fibrous tissue surrounding a nerve. A soft tissue sarcoma that doesn't look like any normal tissue is undifferentiated or unclassified.
More than half of soft tissue sarcomas develop in the arms and legs. About one-third develop in the trunk. Few develop in the head and neck. Most soft tissue sarcomas occur in adults over age 55. But about one-fifth of these tumors occur in children. In children, soft tissue sarcomas are twice as common in whites as in African Americans.
Soft tissue sarcomas have been associated with a variety of factors:
Radiation therapy. Patients treated with radiation therapy for certain types of cancer have a higher risk of developing a soft tissue sarcoma than the general population. These include lymphoma and retinal, breast, cervical, ovarian, and testicular cancers.
Exposure to chemicals. People who have been exposed to certain cancer-causing agents (carcinogens), particularly vinyl chloride, have a higher risk of developing a sarcoma. Exposure to polycyclic hydrocarbons, asbestos, and dioxin can also up the risk.
Diseases or conditions. People who have a weakened immune system have an increased risk of sarcoma. This includes people with HIV, those born with an immune deficiency, and those taking medications to suppress the immune system following an organ transplant. A particular type of sarcoma called Kaposi's sarcoma often develops in people with HIV, but people who don't have HIV can develop it, too.
Genetic abnormalities. Several varieties of soft tissue sarcomas run in families. Often, these sarcomas are associated with other types of tumors, especially those in the gastrointestinal tract and brain. Sarcomas are also more common in people with certain genetic (inherited) syndromes, particularly Li-Fraumeni syndrome and neurofibromatosis type I. People with these diseases can develop multiple cancers or sarcomas.
Doctors have identified about 20 different types of soft tissue sarcomas based on how their cells look under a microscope. Of these, rhabdomyosarcoma accounts for more cases of soft tissue sarcoma than all other types combined. (Rhabdomyosarcoma is a cancer of skeletal muscle.) Because this cancer mainly affects children, some doctors separate childhood soft tissue sarcomas into two distinct groups: rhabdomyosarcomas and all other types. These groupings are not used for soft tissue sarcomas affecting adults.
Rhabdomyosarcoma is the most common form of soft tissue cancer in children. It typically appears in one of three locations: the arms and legs, the head and neck area, or the urinary tract and reproductive organs. In most cases, rhabdomyosarcoma affects children under age 10. Less often, it affects teenagers. The disease is rare in adults. Under the microscope, rhabdomyosarcoma tumor cells look like primitive muscle, similar to the immature muscle cells of a developing fetus.
There are two main types of rhabdomyosarcoma: embryonal and alveolar. In general, embryonal rhabdomyosarcoma tends to be localized; it rarely spreads (metastasizes) away from where it started. It usually responds well to treatment. Alveolar rhabdomyosarcoma tends to be more aggressive and harder to treat. Although some types of sarcoma are less likely to spread than others, they all have the ability to metastasize. If a sarcoma spreads, it usually travels to the lungs.
Other soft tissue sarcomas (children and adults)
Other types of sarcoma can occur in fatty tissues, fibrous tissues, blood vessels, nerves, smooth muscles, and tissues in joints. Some of the most frequently diagnosed types are
Malignant fibrous histiocytoma — This sarcoma starts in primitive immune cells called histiocytes or in cells that make fibrous (connecting) tissue. It usually appears as an area of bone destruction on x-rays. It occurs primarily in adults, and affects men more often than women. It typically begins in the long bones of the arms and legs, especially around the knee. It tends to spread rapidly. Although most cases develop for unknown reasons, some cases may be triggered by a bone condition called Paget's disease or by radiation used to treat another cancer.
Liposarcoma — This sarcoma has cells that resemble fat. Liposarcoma tends to develop in the arms, legs, or at the back of the abdomen near the kidneys. It rarely spreads. However, this sarcoma can return in the same spot after the initial tumor is removed. This is called a local recurrence; it can happen when surgery leaves some cancer cells behind.
Kaposi's sarcoma — This tumor begins in the skin, mouth or digestive tract, or airways. The tumor contains blood vessels, so it looks like one or more pink, purple, or blue lumps. It affects men who have HIV but aren't taking highly active retroviral therapy. It can also affect people who take drugs to suppress the immune system after an organ transplant. It occurs 15 times more often in men than in women.
Fibrosarcoma — Cells of this tumor most closely resemble those of fibrous tissue. (Fibrous tissue holds bones, muscles, and organs in place.) Fibrosarcomas tend to occur in the legs, arms, or trunk. It generally occurs between ages 20 and 60, but it can develop in infants and children.
Synovial sarcoma — Cells of this tumor resemble those of the synovium, the tissue that surrounds joints. These cancer cells have a specific genetic mutation. Synovial sarcoma tends to occur in either the knee or ankle in people under age 30. It can behave aggressively.
Neurofibrosarcoma — Cells of this tumor resemble the protective cells that normally cover nerves. Neurofibrosarcoma most commonly affects people with a disease called neurofibromatosis type I. It usually appears in the trunk or extremities. Neurofibrosarcoma is also known as a malignant peripheral nerve-sheath tumor.
Angiosarcoma — Cells of this tumor resemble those of blood vessels. An angiosarcoma may start almost anywhere on the body. However the most common sites are muscles, the skin, the liver, a breast, or bone. It usually occurs in adults, especially those exposed to vinyl chloride. It has also been linked to radiation exposure.
Leiomyosarcoma — Cells of this tumor most closely resemble those of smooth muscle. Smooth muscle cells line hollow organs, such as the stomach. These cells cause the organ to contract. (Your intestines, for example, squeeze to move food through the body.) Leiomyosarcoma most often develops in the gastrointestinal tract and abdominal organs.
Gastrointestinal stromal tumor (GIST) — These sarcomas develop in the digestive tract. They arise from cells that control muscles lining the stomach and intestines. GIST has been associated with a specific genetic abnormality.