You can have HIV (= the virus) without ever getting AIDS (= the disease) though. If you're lucky the virus never gets activated in your body. You're still contagious though. Cancer is pretty much straightforward, you either have it or you don't.
The newest thing in cancer research is using a virus to fight cancer. Sounds strange but it's very promising. Nowadays you can pretty much build a virus from scratch and design it so it only attacks cancer cells. They already tested it in humans and it stopped cancer growth in almost 80% of the patients. Of course there were under 10 test subjects and in the other 20% the virus actually reproduced in healthy cells so we're not quite there yet.
All I know is it scares the shit out of me!....And virus that targets specific things???? Thats the beginning of Fox Die!!