Colon tumour in AIDS. Endoscope view of a Kaposi's sarcoma (a type of cancer) in the sigmoid colon of a patient with AIDS (acquired immune deficiency syndrome). AIDS is caused by HIV (human immuno- deficiency virus) and severely weakens the immune system. This cancer is slow-growing and rare in healthy people, but in those with AIDS it grows and spreads rapidly. In the colon it may cause intestinal bleeding, which can lead to anaemia. Radiotherapy and chemotherapy may kill the tumour in otherwise healthy patients, but in AIDS patients its growth and spread may only be slowed.