WBGhiro: if every cellsplitting had a chance to produce cancer, even at astronomically low odds, any person would probably develop it multiple times a day.
0Grapher: Sorry, ^ this doesn't make any sense. :)
I think most people don't think about this. You probably have a few cancerous cells, I probably have a few. Under normal circumstances it isn't an issue because they don't divide quickly enough to overwhelm the body. Normally they divide a few times then the body recognizes there's a problem and kills the cancerous cells.
And, I can't blame people for not wanting to think about it. There are things you can do that mitigate some of the risk, but even just free radicals from the oxygen we breathe can damage DNA and result in cancer forming. Only about 80% of lung cancer can be attributed to smoking, so there's the other 20% that's largely unaccounted for.
And even when it does develop into cancer and keeps dividing, it doesn't mean that the tumor is going to be malignant. There's a dog in my neighborhood that has a tumor that's literally the size of it's head. But, for whatever reason, the tumor hasn't spread, so the dog is otherwise healthy, if a bit funny looking with a huge tumor.
hedwards: to about 50-60 years for neurons.
0Grapher: That's also the reason why brain cancer is not caused by mutated neurons, I think.
I'd have to look into that. It wouldn't surprise me if that's correct though. Neurons are hardly the only cells in the brain. I have to admit that you've piqued my curiosity there.