Kaposi's sarcoma (KS) consists of characteristic skin lesions: flat to raised purple plaques. They are tumors that have a rich network of small blood vessels. Red blood cells moving slowly through these channels lose their oxygen, changing in color from red to blue. The mixture of red and blue cells gives the KS lesion its characteristic purple color.
There are several types of KS based on cause rather than appearance. The "classic" Kaposi's sarcoma is found predominantly in Mediterranean males and often also in males of Ashkenazic origin (mid-European Jews). This type of KS, described years ago, is rare.
In the 1950s a large number of KS cases were found in Africa, with the total number of cases increasing dramatically since then.
KS was later found to be a common result of altered body immunity. There are two circumstances under which this takes place. The first is in cases when direct depression of the immune system—the body's constant guard against outside threats—is part of a specific treatment, for example in kidney or other organ transplants. Powerful drugs are given to shut down the immune system so that the foreign organ will not be rejected. KS may arise after such drugs are used and will sometimes disappear when the drugs are stopped. The second circumstance is associated with AIDS (Acquired Immune Deficiency Syndrome).
