I've actually read up a bit on cancer stats a while ago.
Firstly you've got to develop cancer before you die from it, so for men the odds of that are 1 in 2 for men, 1 in 3 for women. when you extrapolate that out its more like 1 in 8 men will die from cancer, and 1 in 15 women.
Those odds are averaged out over your lifetime, its only when you reach 70-80 years of age that the chance of developing cancer reaches 1 in 2 people or greater, which brings the average down.
In western society you are just as likely to die from a car accident, heart disease or diabetes as you are from cancer. For all we know about cancer there seems little we can do about it anyway. Some of the healthiest people I know have been struck down by it while some people with terrible habits seems to charge along without problems.
The fact is you gotta die of something no matter how healthy you are so there's no point staying up at night worrying about it.
As far as dying from an asteroid impact goes, I think the odds of getting cancer are greater than that

Most asteroids are small enough to burn up in the atmosphere, that's where you get shooting stars from. The ones that make it to the surface do cause some devastation but not usually enough to wipe out life on the planet. Here's a really old one
http://news.nationalgeographic.com/news/2005/03/0310_050310_meteorcrater.html this 1.2km crater was theorized to be caused by something 50m in diamater. Odds are that it was significantly larger before it entered the atmosphere.
So the odds of dying from an asteroid impact are pretty low. The cool thing about this however it is really makes you think about earth's place in the universe. We think we're all high and mighty but in reality we are but one small planet in one small system, there's millions more out there. The people who say that there is no such thing as extraterrestrial life don't understand what they are talking about, with the sheer number of planets in the universe its almost inconceivable that there
wouldn't be life on some of them.