Sarcoma is a type of cancer that develops in bone or soft tissue. Soft tissue includes blood vessels, nerves, tendons, muscles, fat, fibrous tissue, lower layers of the skin (in other words, not the outside layer), and the lining of joints.
Several types of abnormal growths can occur in soft tissue, but if a growth is labeled a sarcoma, that means it’s a malignant tumor or cancer. "Malignant" means that parts of the tumor can break off and spread into surrounding tissues. These escaped cells move throughout the body, lodging in the liver, lungs, brain, or other important organs.
Sarcomas of soft tissue are relatively uncommon, especially when compared with carcinomas, another type of malignant tumor. Sarcomas can be life threatening, especially if they are diagnosed when a tumor is already large or has spread to other tissues.
There are many kinds of soft tissue sarcomas, categorized by the tissue in which it has grown:
Malignant tumors in fat are liposarcomas. In smooth muscle (around internal organs), cancerous sarcomas are called leiomyosarcomas. Rhabdomyosarcomas are malignant tumors in skeletal muscle (in arms, legs, muscle that allows movement). Although they also occur in adults, rhabdomyosarcomas are the most common soft tissue sarcomas in children.
Other (very rare) soft tissue sarcomas include
- malignant schwannomas
- neurogenic sarcomas
- gastrointestinal stromal tumors
- synovial sarcomas
- Kaposi’s sarcomas
- malignant mesenchymomas
- alveolar soft-part sarcomas
- epithelioid sarcomas
- clear cell sarcomas
- pleomorphic undifferentiated sarcomas
- spindle cell tumors
Usually, there is no known cause of a soft tissue sarcoma. The exception is Kaposi’s sarcoma. Kaposi’s sarcoma is a cancer of the lining of blood or lymph vessels. This cancer forms purple or brown lesions on the skin. It may be caused by infection with the human herpesvirus 8 (HHV-8). It occurs frequently in people with reduced immune function, such as those infected with untreated human immunodeficiency virus (HIV) but can also arise without HIV infection.
Genetic Risk Factors
Some hereditary genetic defects can make you more prone to developing a soft tissue sarcoma:
- Basal cell nevus syndrome increases your risk of basal cell skin cancer, rhabdomyosarcoma, and fibrosarcoma.
- Inherited retinoblastoma causes a kind of childhood eye cancer, but can also increase the risk of other soft tissue sarcomas.
- Li-Fraumeni syndrome increases the risk of many kinds of cancer, often from radiation exposure.
- Gardner’s syndrome leads to cancers in the stomach or bowel.
- Neurofibromatosis can cause nerve sheath tumors in one out of 20 people with the gene.
- Tuberous sclerosis can result in rhabdomyosarcoma.
- Werner’s syndrome can cause many health problems, including an increased risk of all soft tissue sarcomas.
Exposure to certain toxins, such as dioxin, vinyl chloride, and herbicides that contain phenoxyacetic acid, may increase your risk of developing soft tissue sarcomas.
Radiation exposure, especially the intense radiation of radiation therapy, can be a risk factor. Radiation therapy is often used to treat more common cancers such as breast cancer, prostate cancer, or lymphomas. Unfortunately, this effective therapy can increase your risk of developing certain other forms of cancer—such as a soft tissue sarcoma. Patients who have received radiation therapy in the past should be checked for the development of new soft tissue sarcomas.
A painless lump under the skin of your arm or leg may be the first sign of a soft tissue sarcoma. If a soft tissue sarcoma develops in the stomach, it may not be discovered until it is very large and pressing on other structures. You may have pain or breathing difficulties from a tumor pushing on your lungs. Another possible symptom is an intestinal blockage. This can occur if a soft tissue tumor is growing in your stomach. The tumor pushes too hard against your intestines and prevents food from moving through easily.
The most common types of soft tissue sarcomas are gastrointestinal stomal tumors (GIST) and tumors that affect the limbs. About 60 percent of soft tissue sarcomas occur in the arms, legs, hands, feet, or buttocks. These will show up as a lump under the skin. 20 percent of soft tissue sarcomas affect the stomach or chest and will press against the intestines or the lungs. Ten percent of these tumors are found in the head and neck.
If you feel a lump under your skin that doesn’t go away, grows in size, or is painful to the touch, see your doctor.
Soft tissue sarcoma is usually only diagnosed when the tumor has grown to become fairly large, because there are very few early symptoms. By the time the cancer is causing recognizable signs, it may already have spread to other tissues and organs in the body.
If your doctor suspects a soft tissue sarcoma, he or she will interview you to get a complete family history to see if other members of your family may have had any rare forms of cancer. You will also likely have a physical exam to check your general health. This may help determine what treatments would be best for you.
The tumor and its exact location will be studied using imaging scans such as simple X-rays or a computed tomography (CT) scan. The CT scan may also involve using an injected dye to make the tumor easier to see. Magnetic resonance imaging (MRI) may also be done.
Ultimately, the diagnosis must be confirmed with a biopsy. A biopsy usually involves a needle being inserted into the tumor and a small sample being removed. Sometimes, a scalpel is used to cut away part of the tumor so that it can be examined. Other times, especially if the tumor is pressing on an important organ such as the intestines or the lungs, the entire tumor and surrounding lymph nodes are removed even before a biopsy is done.
The tissue from the tumor is examined under a microscope to determine whether the tumor is benign (meaning it doesn’t invade other tissue) or malignant (when the tumor cells can invade other tissue).
Some other tests that are done to a tumor sample from a biopsy include
- immunohistochemistry—looks for antigens or sites on tumor cells that certain antibodies can attach to
- cytogenic analysis—looks for changes in the chromosomes of the tumor cells
- fluorescence in situ hybridization (FISH)—a test to look for certain genes or short pieces of DNA
- flow cytometry—a test that looks at the number of cells, their health, and the presence of tumor markers on the surface of cells
Staging the Cancer
After a biopsy confirms cancer, the tumor is then graded and staged by looking at the cells under the microscope and comparing them to normal cells of that kind of tissue. Stage I is a small tumor with cells that appear almost normal, whereas in Stage IV, the cells appear very abnormal and the tumor cells have invaded other parts of the body.
Soft tissue sarcomas are rare, and it is best to seek treatment at a facility that is familiar with your type of cancer.
Treatment depends on the location of the tumor and the exact cell type that the tumor originated from (e.g., muscle, nerve, fat, etc.). If the tumor has metastasized (spread to other tissues), this also affects treatment.
Surgical treatment is the most common initial therapy. The tumor and some of the surrounding healthy tissue is removed and tested to see if some tumor cells may still be left in the body. If the tumor has spread to other sites and those locations are known, the secondary tumors can also be removed. Surrounding lymph nodes, which are small organs of the immune system, may also be removed. Lymph nodes are often the first places where tumor cells spread.
In the past, tumors in the arms and legs may have required a limb to be amputated. Now, the use of advanced surgical techniques, radiation, and chemotherapy can often allow a limb to be saved. However, large tumors that affect major blood vessels and nerves may still require a limb to be removed.
Risks of surgery include:
- reactions to anesthetic
Chemotherapy is also used to treat some soft tissue sarcomas. Chemotherapy is the use of toxic drugs to kill cells which divide and multiple rapidly, such as tumor cells. Other cells that divide rapidly—such as bone marrow cells, the lining of your intestine, or hair follicles—are also damaged by chemotherapy. This damage leads to many side effects. However, if cancer cells have spread beyond the original tumor, chemotherapy may effectively kill them off before they begin to form new tumors and harm vital organs.
Not all soft tissue sarcomas are killed off by chemotherapy. But one of the most common sarcomas, rhabdomyosarcoma, has been effectively treated with chemotherapy regimens. Drugs such as doxorubicin and dactinomycin have been used with soft tissue sarcomas. There are many other drugs that are specific to the tissue type that the tumor started in.
In radiation therapy, high-energy beams of particles such as X-rays or gamma rays are used to damage the DNA of cells. Rapidly dividing cells such as tumor cells are much more likely to die from this exposure than normal cells, though some normal cells will die as well. Sometimes, chemotherapy and radiation therapy are combined to make each more effective and kill more tumor cells.
Side effects of chemotherapy and radiation include:
- nausea or vomiting
- weight loss
- hair loss
- nerve pain
- other side effects that are specific to each type of drug regimen
Long-term survival from a soft tissue sarcoma depends on the specific type of sarcoma. Outlook also depends on how advanced the cancer is when it is first diagnosed. A Stage I cancer will likely be much easier to treat than a Stage IV cancer. A tumor that is small, has not spread into surrounding tissues, and is located in an easily accessible location, such as the forearm, will be easier to treat and remove completely with surgery. A tumor that is large, is surrounded by many blood vessels (making surgery difficult), and has metastasized cells into the liver or lung is much harder to treat and may result in eventual death.
Chance of recovery depends on the location of the tumor, the cell type, and the grade and stage of the tumor. Additionally, recovery depends on whether or not the tumor can be removed by surgery, your age and health, and whether the tumor has reoccurred or is new.
After initial diagnosis and treatment, if the tumor is in remission (not detectable or not growing), you still need to see your doctor often for checkups. X-rays, CT scans, and MRIs may be done to check if any tumor is still present at its original growth site or at other locations in the body.
Complications from the tumor itself depend upon the location and size of the tumor. The tumor may press on important structures such as the lungs, intestines, nerves, or blood vessels. The tumor may actually invade and damage nearby tissues as well. If the tumor metastasizes, meaning cells break off and end up in other locations such as bone, brain, liver, or lung, new tumors can grow in these organs. There they can cause extensive, life-threatening damage.