Most cancers preventable? Lung cancers maybe (and only maybe), but on the whole (and as far as we know) cancer isn't affected all that strongly by lifestyle factors.
cancers are not only preventable, but also reversible -- see ch3 turning off cancer, especially starting from the indian report on rat studies given aflatoxin in 'the china study' by collin campbels, hosted on google books for reference: http://books.google.com/books?id=FIRLLcLjyC8C&lpg=PA74&#...
solution? whole-plant-based diet, no, not vegetarian nor vegan diet. basically non-processed food (marketing does play trick saying, correctly, sugar/hfcs is natural plant-based because it's made from cane/corn -- but we know it's harmful)
why whole-plant and not vegan? because one can eat fried potatoe, chewing candies, drinking sodas, sipping alcohol, smoking cigarretes ... and still claim (validly) to be vegan, but s/he probably isn't healthy
Well, there's your problem. They didn't find a lot of things back in 1913, and the ability to detect cancer back then was about as advanced as their ability to detect neutrinos. All of the studies cited are more than 40 years old, with questionable methods or tools used.
I'd love to see newer studies on the few surviving traditionally-living populations. Here's one: http://www.medsci.org/v04p0053.htm
While I'm a layman and would like to be enlightened (how should they have done these studies? What evidence would make you think there's something to look into?), I don't think you're fair to the linked sources. Like, "One of these physicians was captain George B. Leavitt. He actively searched for cancer among the traditionally-living Inuit from 1885 to 1907. Along with his staff, he performed 50,000 examinations a year for the first 15 years, and 25,000 a year thereafter. He did not find a single case of cancer. At the same time, he was regularly diagnosing cancers among the crews of whaling ships and other Westernized populations. It's important to note two relevant facts about Inuit culture: first, their habit of going shirtless indoors. This would make visual inspection for external cancers very easy. Second, the Inuit generally had great faith in Western doctors and would consult them even for minor problems. Therefore, doctors in the arctic had ample opportunity to inspect them for cancer."