RecruitingNatural History Study of Kaposi SarcomaBackground: Kaposi sarcoma (KS) is a type of tumor caused by the Kaposi sarcoma herpesvirus. KS usually affects the skin, but lesions can also appear in the lymph nodes, lungs and digestive tract. KS is most common in people with compromised immunity, but it also appears in otherwise healthy people. Researchers want to understand more about how KS develops, why it may recur, and how it affects the immune system and organs. Objective: To learn more about the natural history of KS. Eligibility: People aged 18 years and older with KS. Design: Participants will be screened. They will have a physical exam with blood tests. They will have an imaging scan. They may need a new biopsy: Tissue samples may be cut from their tumor. Their ability to perform normal activities will be assessed. Participants will visit the clinic to have their KS evaluated. In addition to the imaging scans and other tests performed during screening, procedures may include: Eye exam. Ultrasound exam of the heart (electrocardiogram). Collection of saliva and urine samples. Biopsies of the skin or lymph nodes. Swabs of the anus and cervix. Photographs of skin lesions. Removal of fluid samples from the space around the lungs, intestine, or heart. The evaluation visit will be repeated 5 more times over 18 months and then yearly for up to 10 years. Participants will follow their standard treatment for KS during the study.