Kaposi's Sarcoma Health Article

Definition

Kaposi's sarcoma (KS) is a cancer of the skin, mucous membranes, and blood vessels; it is the most common form of cancer in AIDS patients. It was named for Dr. Moritz Kaposi (1837-1902), a Hungarian dermatologist who first described it in 1872. As of 2001, researchers disagree as to whether KS is a true cancer or a disorder of the skin that develops as a reaction to infection by a herpesvirus.

Description

The formal medical term for Kaposi's sarcoma is multiple idiopathic hemorrhagic sarcoma. This term means that KS develops in many different sites on the patient's skin or internal organs; that its cause is unknown; and that it is characterized by bleeding. The lesions (areas of diseased or damaged skin), which are usually round or elliptical in shape and a quarter of an inch to an inch in size, derive their characteristic purple or brownish color from blood leaking out of capillaries (small blood vessels) in the skin. In KS, the capillaries begin to grow too rapidly and irregularly, which causes them to become leaky and eventually break. The lesions themselves may become enlarged and bleed, or cause the mucous membranes of the patient's internal organs to bleed.

There are three types of KS lesions, defined by their appearance:

• Nodular. These are reddish-purple, but are sometimes surrounded by a border of yellowish or brown pigment. Nodular lesions may appear to be dark brown rather than purple in patients with dark skin.
• Infiltrating. Infiltrating lesions may be large or have a raised surface. They typically grow downward under the skin.
• Lymphatic. These lesions are found in the lymph nodes and may be confused with other causes of swollen lymph nodes.

As of 2001, KS is classified into five types:

• Classic KS. This form of KS is sometimes called indolent KS because it is slow to develop. Classical KS is most commonly found in males between 50 and 70 years of age, of Italian or Eastern European Jewish descent.
• African KS. This form of the disease appears in both an indolent and an aggressive form in native populations in equatorial Africa. It accounts for almost 10% of all cancers in central Africa.
• Immunosuppressive treatment-related KS. The third form of KS occurs in kidney transplant patients who have been given drugs to suppress their immune systems-usually prednisone and azathioprine. This form of KS is sometimes called iatrogenic KS, which means that it is caused unintentionally by medical treatment.
• Epidemic KS. Epidemic KS was first reported in 1981 as part of the AIDS epidemic. Most cases of epidemic KS in the United States have been diagnosed in homosexual or bisexual men.
• Non-epidemic gay-related KS. This form of KS occurs in homosexual men who do not develop HIV infection. Non-epidemic gay-related KS is an indolent form of the disease that primarily affects the patient's skin.

Demographics

The demographic distribution of KS varies considerably across its five types:

• Classic KS. Classic KS is considered a rare disease, with a male/female ratio of 10:1 or 15:1. In North America and Europe, most patients are between 50 and 70 years old. Classic KS is more common in men from Mediterranean countries and in Ashkenazic Jews.
• African KS. African KS has the same male/female ratio as classic KS, although most patients with African KS are younger. A form of African KS that attacks the lymphatic system primarily affects children, with a male/female ratio of 3:1.
• Immunosuppresive treatment-related KS. This form of KS occurs mostly in kidney-transplant patients, at a rate of 150 to 200 times as often as in the general population. It represents 3% of all tumors that occur in kidney-transplant patients. The male/female ratio is 2:1.
• Epidemic KS. Epidemic KS is overwhelmingly a disease of adult homosexual or bisexual males. It is 20,000 times more common in people with AIDS than in those without HIV infection. According to the National Institutes of Health (NIH), 95% of all the cases of epidemic KS in the United States have been diagnosed in homosexual or bisexual males. Epidemic KS is far more prevalent among homosexual or bisexual males with AIDS than among hemophiliacs or intravenous drug users with AIDS. Prior to 1995, about 26% of all homosexual males with AIDS had KS as their first symptom or eventually developed KS, as compared with fewer than 3% of heterosexual intravenous drug users with AIDS. This clustering of KS cases among a subpopulation of AIDS patients led to the hypothesis that a blood factor transmitted by sexual contact is a partial cause of KS. The number of new cases of AIDS-related KS has declined in recent years, for reasons that are not yet clear. Some researchers think that the introduction of highly active antiretroviral therapy, or HAART, is related to the decline in the number of cases of epidemic KS. As of 2001, only about 12% of AIDS patients develop KS.
• Non-epidemic gay-related KS. This small group of KS patients is entirely male.