Soft Tissue Sarcoma
What Is It?
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 human immunodeficiency virus (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 1 of 3 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 the 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.
In most cases, someone with soft tissue sarcoma will have a lump in some part of the body, usually an arm, a leg or the trunk. The lump may be painful. In physically active people, the lump can be mistaken for a sports-related injury.
Rhabdomyosarcoma that does not affect the arms and legs can cause a painless lump in the head or neck. Or it can cause other symptoms that reflect the tumor's location. For example, rhabdomyosarcoma:
- In the eye or eyelid can cause a bulging eye, a swollen eyelid or paralysis of the eye muscles
- In the sinuses can cause a stuffy or blocked nose; any nasal discharge can contain pus or blood
- In the skull can erode the bones that protect the brain, triggering headache and nausea
- In the urinary tract and reproductive organs can cause difficulty urinating and blood in the urine. Other symptoms include constipation; a lump inside the vagina; vaginal discharge that contains blood and mucus; and a painless enlargement of one side of the scrotum, affecting the testicle.
After reviewing your symptoms, your doctor will examine you. He or she will pay special attention to the lump and the area around it. After that, you may need a series of X-rays. A computed tomography (CT) scan or magnetic resonance imaging (MRI) scan can provide a detailed view of the tumor. Your doctor may order basic blood and urine tests as part of your exam.
To confirm the diagnosis and determine the type of sarcoma, you will need to have a biopsy. A biopsy sample can be obtained by withdrawing bits of tissue from the lump with a needle. In some cases, the tissue sample may be obtained during surgery. The tissue sample is examined under the microscope by a pathologist. In addition to making the diagnosis, this specialist can determine how active the sarcoma is by estimating the number of dividing cells (mitoses) in the specimen. Cancers with a large number of mitoses have a worse prognosis and may need aggressive treatment.
Because sarcomas are relatively rare, and because there are so many types, the diagnosis should be confirmed by a pathologist who specializes in sarcomas. The pathologist's report should also include the sarcoma's grade and mitotic rate. (The grade is an assessment of how abnormal the cells look and how aggressive the cancer might be.) Some pathologists also do detailed analyses of the cancer's genes. That can aid in the diagnosis of undifferentiated varieties of sarcoma.
If you are diagnosed with cancer, more tests will be done to see if it has spread. These tests may include:
- Chest X-ray
- CT scan
- MRI scan
- Radionuclide bone scan
- Bone marrow biopsy
In some cases, a positron emission tomography (PET) scan may be done to identify a spreading tumor. Evidence suggests that a PET scan combined with a CT scan may provide a more accurate picture of where cancer is located. Because PET looks at the entire body, it can be useful when your doctor thinks the cancer may have spread but isn't sure where it might be.
The next step is to determine the cancer's stage -- a measure of how much it has spread. The stage is based on:
- The tumor's size
- The tumor's grade
- Whether or not cancer cells are in nearby lymph nodes
- Whether or not the cancer has spread beyond its original site to other parts of the body
All of this information -- the cancer's grade, stage and mitotic rate -- factors into treatment decisions.
If you are diagnosed with a sarcoma, your doctor will refer you to a medical center that has the facilities, personnel and experience to treat it.
A sarcoma will continue to grow until it is treated. Without proper treatment, some soft tissue sarcomas will spread to the lungs, lymph nodes or other parts of the body.
Even if a sarcoma is surgically removed, it can come back. To reduce the risk of recurrence, your surgeon should remove plenty of healthy tissue from around the tumor.
There is no known way to prevent sarcomas. However, because HIV infection seems to increase the risk of some sarcomas, you should avoid behaviors that can lead to HIV. Practice safer sex by using a condom. Do not inject illegal drugs. If you do inject drugs, do not share needles.
If your occupation exposes you to substances that can cause soft tissue sarcomas, use proper protective equipment to reduce your exposure. For more information about specific protective measures and equipment, contact the National Institute for Occupational Safety and Health (NIOSH).
Surgery is the most common treatment for soft tissue sarcomas. The entire tumor is removed, along with a good amount of normal tissue surrounding the tumor. This is called a wide excision. It helps ensure that all cancer cells are removed and that the cancer doesn't come back.
In the past, amputation was an accepted treatment for osteosarcomas (bone cancer) and some soft tissue sarcomas. Removing the limb helped ensure that the cancer would not return. Today, thanks to improved surgical techniques, along with the use of radiation therapy and chemotherapy, limbs are spared if at all possible.
After surgery, further treatment usually depends on the:
- Type of sarcoma
- Tumor's stage, grade and location
- The person's age and overall health
The tumor grade is especially important. It predicts how far the tumor has spread and its future behavior. For example, high-grade soft tissue sarcomas (those containing very abnormal cells and tissue destruction or having a large number of mitoses) tend to spread to distant areas of the body. Low-grade soft tissue sarcomas (those with cells that closely resemble normal cells) are less likely to spread. However, they may come back again if they are not completely treated.
If rhabdomyosarcoma is in an arm or leg, and all of the tumor can be removed, chemotherapy usually follows surgery. However, if surgery fails to remove the entire tumor, further treatment with both radiation and chemotherapy usually follows.
Doctors also use chemotherapy and radiation to treat rhabdomyosarcomas that have spread to other parts of the body. In the eye, rhabdomyosarcoma is usually treated with radiation and chemotherapy, without removing the eye. For rhabdomyosarcomas in the bladder or female reproductive tract, chemotherapy and radiation can shrink the tumor before surgery. That helps the surgeon preserve as much of the affected organ as possible.
Other soft tissue sarcomas
Again, surgery is usually the treatment of choice. For fibrosarcoma, doctors often give chemotherapy to shrink the tumor before surgery. For synovial sarcoma, radiation therapy may be done after surgery to destroy any remaining cancer cells. For angiosarcoma, which is particularly difficult to treat, some doctors combine chemotherapy and radiation.
Certain proteins in the blood may help to predict the aggressiveness of a soft tissue sarcoma. These proteins, called growth factors, can also be targets for drug treatment. Targeted therapies can search out cancer cells that make these proteins and block them. Without the protein, the cancer cells cannot divide and grow. For example, a targeted therapy called imatinib (Gleevec) has proven effective at treating GIST. Researchers are developing and testing other targeted therapies against various cancers.
When To Call a Professional
Call your doctor promptly if you develop swelling or a lump that doesn't go away. Also, call your doctor if you have unexplained symptoms that might be caused by a growing lump, such as a bulging eye or swollen eyelid.
In general, people with localized soft tissue sarcomas have a very good prognosis with a high rate of cure. The main feature of an excellent prognosis is a tumor that is completely removed by surgery and hasn't spread beyond the margins of the tumor. Children tend to have a better prognosis than adults for both localized tumors and those that have spread.
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