Kaposi's sarcoma is a type of cancer that forms in the lining of blood and lymph vessels. The tumors (lesions) of Kaposi's sarcoma typically appear as painless purplish spots on the legs, feet or face. Lesions can also appear in the genital area, mouth or lymph nodes. In severe Kaposi's sarcoma, lesions may develop in the digestive tract and lungs.
The underlying cause of Kaposi's sarcoma is infection with a virus called human herpesvirus 8 (HHV-8). In healthy people, HHV-8 infection usually causes no symptoms because the immune system keeps it under control. In people with weakened immune systems, however, HHV-8 has the potential to trigger Kaposi's sarcoma.
People infected with human immunodeficiency virus (HIV) — the virus that causes AIDS — have the highest risk of Kaposi's sarcoma. The immune system damage caused by HIV allows cells harboring HHV-8 to multiply. Through unknown mechanisms, the characteristic lesions form.
Recipients of organ transplants who take immune system-suppressing drugs to prevent transplant rejection also are at risk of Kaposi's sarcoma. In this population, though, the disease tends to be milder and easier to control than it is in people with AIDS.
Another type of Kaposi's sarcoma occurs in older men of Eastern European, Mediterranean and Middle Eastern descent. Known as classic Kaposi's sarcoma, this cancer progresses slowly and typically causes few serious problems.
A fourth type of Kaposi's sarcoma that affects people of all ages occurs in equatorial Africa.
To determine if a suspicious-looking skin lesion is Kaposi's sarcoma, your doctor will need to perform a biopsy, which involves removing a small piece of tissue for examination in a laboratory.
Tests to diagnose internal Kaposi's sarcoma include:
- Fecal occult blood test. This test detects hidden blood in stool, which can be a sign of Kaposi's sarcoma in the digestive tract.
- Chest X-ray. A chest X-ray may reveal abnormalities suggesting Kaposi's sarcoma in the lung.
- Bronchoscopy. In this test, a thin tube (bronchoscope) is passed through your nose or mouth into your lungs to view their lining and take samples of abnormal areas.
- Upper endoscopy. This test uses a thin tube (endoscope) passed through your mouth to examine the esophagus, stomach and first part of your small intestine. If your doctor suspects Kaposi's sarcoma inside any of these organs, a biopsy of the affected tissue is taken to confirm the disease.
- Colonoscopy. In this test, a thin tube (colonoscope) is passed through your rectum and advanced into your colon to examine the walls of these organs. Abnormalities suggesting Kaposi's sarcoma in the rectum or colon can also be biopsied during colonoscopy.
Bronchoscopy is unnecessary for diagnosis of Kaposi's sarcoma unless you have unexplained breathing problems or an abnormal chest X-ray. Similarly, unless a fecal occult blood test finds blood in your stool, you may be able to avoid upper endoscopy or colonoscopy.
The treatment for Kaposi's sarcoma varies, depending on these factors:
- Type of disease. Historically, AIDS-related Kaposi's sarcoma has been more serious than classic or transplant-related disease. Thanks to increasingly effective antiviral drug combinations and improved prevention of other AIDS-related infections, Kaposi's sarcoma has become less common and less severe in people with AIDS.
- Number and location of lesions. Widespread skin lesions and internal lesions require different treatment from isolated lesions.
- Effects of the lesions. Lesions in the mouth and throat make eating difficult, while lesions in the lung can cause shortness of breath. Large lesions, particularly on the upper legs, can lead to painful swelling and difficulty moving around.
- General health. The immune system impairment that makes you vulnerable to Kaposi's sarcoma also makes certain treatments, such as powerful chemotherapy drugs, too risky to try. The same is true if you also have another type of cancer, poorly controlled diabetes or any serious, chronic disease.
For AIDS-related Kaposi's sarcoma, the first step in treatment is to start or switch to an antiviral drug combination that will reduce the amount of the virus that causes HIV/AIDS and increase the number of certain immune cells in your body. Sometimes, this is the only treatment needed.
When possible, people with transplant-related Kaposi's sarcoma may be able to stop taking immune system-suppressing medication. This allows the immune system to eliminate the cancer in some cases. Switching to a different immunosuppressive medication can also bring improvement.
Treatments for small skin lesions include:
- Minor surgery (excision)
- Burning (electrodessication) or freezing (cryotherapy)
- Low-dose radiation, which is also helpful for lesions in the mouth
- Injection of the chemotherapy drug vinblastine directly into lesions
- Application of a vitamin A-like drug (retinoid)
Lesions treated in any of these ways are likely to return within a couple of years. When this happens, treatment can often be repeated.
Radiation is the usual treatment for those with multiple skin lesions. The type of radiation used and the locations of lesions being treated vary from person to person. When more than 25 lesions are present, chemotherapy with standard anti-cancer drugs may be helpful. Chemotherapy is also used to treat Kaposi's sarcoma in the lymph nodes and digestive tract.