Kaposis sarcoma. Light micrograph of a malignant (cancerous) tumour (light purple) in the liver of a patient with Kaposis sarcoma. Kaposis sarcoma is characterised by the abnormal growth of blood vessels. This patient also has AIDS (acquired immune deficiency syndrome), a disease caused by the human immunodeficiency virus (HIV) that weakens the immune system. Kaposis sarcoma is a type of skin cancer that in AIDS patients often spreads to the lungs and liver and can be rapidly fatal.