Kaposi's sarcoma (KS) is the most common tumor found in patients with HIV infection and occurs with an incidence more than 7,000 times higher than that in the non-HIV-infected population. A sarcoma is a cancer that develops in connective tissues such as cartilage, bone, fat, muscle, blood vessels, or fibrous tissues (related to tendons or ligaments). Kaposi's sarcoma was named for Dr. Moritz Kaposi who first described it in 1872. KS causes tumors to develop in the tissues below the skin surface, or in the mucous membranes of the mouth, nose or anus. These lesions appear as raised blotches or nodules and may be purple, brown, or red in color. Sometimes the disease causes painful swelling, especially in the legs, groin and around the eyes.