Science Questions

How does a depleted immune system bring on cancer?

I understand that AIDS is a disease of the immune system. After watching a TV documentary recently I was surprised to learn that many AIDS sufferers actually die of cancers as well. I couldn’t work out how the two are connected. How does a depleted immune system bring on cancer?

This is a really interesting one. It’s something that’s only started to become clear relatively recently – the role of the immune system in preventing cancer. For example, in patients with HIV they have a very depleted immune system. This leaves them vulnerable to infections like viruses that can cause cancer. Also, it’s thought now that the immune system is actively patrolling your body, spotting early dodgy looking cells and getting rid of them. Obviously sometimes that goes wrong and cancer can develop. It’s really becoming an interesting field is how the immune system may be able to recognise some cancer cells. Whether we can turn it into overdrive and use immunotherapy to really kick start the immune system into killing cancer cells in patients: that’s a very active area of research. Another thing that’s quite interesting is that the whole role of the immune system first started to become clear, partly through studying people with HIV, also through studying patients who’ve had transplants. They take immuno-suppressing drugs and are also more likely to get certain types of cancers. That started to make a link, also with patients with melanoma. It was noticed that some people with melanoma just spontaneously get better. That’s thought to be that their immune system has woken up and recognised their cancer. It’s a really active field of research studying how the immune system is involved in this. We’ll probably, in the future, see a lot more coming out about it.

December 2007