As AIDS progresses, the immune system gets weaker. As it becomes weaker the risk of developing certain cancers increases. These include Kaposi's sarcoma, certain types of non-Hodgkin lymphoma, and cancer of the cervix (the neck of the womb). These cancers are known as 'AIDS-defining cancers'.

This does not mean that everyone who gets one of these cancers is HIV positive, or has AIDS. Most lymphomas and cervical cancers occur in people who have never been HIV positive and who do not have AIDS.

There is also evidence that some other types of cancer occur more often in people with HIV infection than the rest of the population. These include anal cancer, Hodgkin lymphoma, angiosarcoma and multiple myeloma.