Question: If we all start with cancer cells, then why do we have them? Do the cancer cells play an important role in our bodies?

Sue Carney answered on 14 Jun 2011:

As Shane has already said, cells become cancerous when they start to multiply out of control. One of the things that scientists are doing is trying to find out which genes control this process, and some genes have been found which don’t work properly because of a mutation (a change in their DNA sequence.) This means that when cells should be programmed to die, they don’t, and the cells carry on growing instead, forming tumours. The relationship between these genes and the way the process works is very complicated, and there’s more than one way that things can go wrong.

I think the interesting part is investigating some of the things that might cause these mutations in the first place. We already know about some of them such as the harmful chemicals in cigarette smoke or the effect of ultra violet light on our skin from repeated exposure to strong sunlight. We call these things mutagens, because of their ability to damage our DNA. The reason that exposure to mutagens (and there are lots of others, not just cigarettes and sunbathing) doesn’t always cause cancer is that the damage they do to DNA is random. Sometimes it may not have any apparent effect but other times it might damage important bits of DNA leading to cancer. The other difficulty is that it might take a long time before we see the effects of the damaged DNA.

It’s also thought that some people inherit particular genes that might mean they have a higher risk of getting some cancers, than other people who don’t inherit those particular genes. In those instances, the DNA errors ultimately leading to cancer may not have been directly caused by exposure to a mutagen.