Natural History Study of the KSHV Inflammatory Cytokine Syndrome (KICS)

Background: \- KSHV inflammatory cytokine syndrome (KICS) is a newly recognized disease caused by Kaposi sarcoma-associated herpesvirus (KSHV). This virus can cause cancer. People with KICS can have severe symptoms. They include fever, weight loss, and fluid in the legs or abdomen. People with KICS may also be at risk of getting other cancers associated with KSHV. These cancers include Kaposi sarcoma and lymphoma. Because KICS is a newly identified disease, more information is needed on how the disease works and what can be done to treat it. Objectives: \- To collect genetic and medical information from people with KSHV inflammatory cytokine syndrome. Eligibility: \- Individuals at least 18 years of age who have Kaposi sarcoma herpes virus and symptoms that resemble those caused by KICS. Design: * Participants will have regular study visits. The schedule will be determined by the study researchers. * Participants will provide a complete medical history and have a full physical exam. Blood and urine samples will be collected as well. * People with KICS that requires treatment may get new experimental treatments. These treatments may include antiviral drugs and chemotherapy drugs, depending on the nature of the disease. * Participants will have imaging studies, such as chest x-rays and computed tomography scans, to study the tumors. * Bone marrow and lymph node biopsies may be done to collect tissue samples for study. * Participants who have Kaposi sarcoma will have photographs taken of their lesions.