Colorectal cancers would increase because detection has increased. It became fairly popular to get a probe done at a certain age. I seriously can't give these sorts of numbers credit, just like having a percieved increase in autism after including more folks in it and having better screening and awareness.
Why do some people insist on rationalizing these trends away?
However, I stand by my general stance. Many cancers simply wouldn't show up in a population with a much shorter life expectancy. I'm not about to say it isn't partially environment or lifestyle (other things do cause cancer), just that we notice because of our life span and ability to detect these. I get this from articles like the one listed at the end, which states: The main reason cancer risk overall is rising is because of our increasing lifespan. And the researchers behind these new statistics reckon that about two-thirds of the increase is due to longevity. Colon cancer seems to be an outlier, and there are a couple of these. Cervical cancer is caused by a very common virus and often affects younger women, just to give another example.
http://scienceblog.cancerresearchuk.org/2015/02/04/why-are-c...
Colorectal cancers in young people have increased 40% in just 16 years. Melanoma rates in young people have increased 250% in four decades.