Except of course for all those that do live long enough, I don't think the centenarians and beyond die of cancer http://biomedgerontology.oxfordjournals.org/content/60/7/862...

From what I can see at FastStats http://seer.cancer.gov/faststats/selections.php?series=age incidence does go up with age, but there's still plenty of cancers that happen at relatively young ages, and if you look at the trend, going back to 1975 which is not that much really, you can see a marked increase towards 1990 and then a stabilization, which to me suggests it's quite likely that environmental and lifestyle factors do come in play, as similar trends occur in other health related issues (metabolic syndrome). Markedly lower Vit-D levels, our increased consumption of n-6 poly-unsaturated fatty acids and processed foods, all likely play a role.

I short, I agree with gp in that there is surely a bigger payoff in prevention, but that doesn't mean that cures wouldn't be welcome too. I can't agree that cancer is inevitable.

Edited to add links, formatting.