Kaposi's sarcoma is a type of cancer that forms in the lining of blood vessels and lymphatic vessels. It often appears as purple, red, or brown spots on the skin or mucous membranes. This cancer is most commonly associated with HIV/AIDS and can occur in people with weakened immune systems. There are different forms of Kaposi's sarcoma, including classic Kaposi's sarcoma, which typically affects older men of Mediterranean descent, and epidemic Kaposi's sarcoma, which is linked to HIV. Treatment options may include chemotherapy, radiation therapy, or medications to boost the immune system.