In general, there are going to be a lot more people reproducing successfully now than compared to a thousand years ago, let alone ten thousand years ago, and so

In general, there are going to be a lot more people reproducing successfully now than compared to a thousand years ago, let alone ten thousand years ago, and some of those people may have genes that would be disadvantageous in a more cut-throat environment that kills a lot of people before they hit breeding age. I can't really say that scans as a plausible major causal contribution to various digestive tract cancers going from 5 per 100,000 to 6 per 100,000 before age 50 from 1990 to 2019. The proposition that any meaningful environmental pressure selected against genes that might cause you to die at 45 instead of 55 doesn't make a whole lot of sense. That is well beyond peak breeding age. These people's ancestors were always susceptible to cancer, but they either didn't live long enough to get it or environmental contaminants that actually trigger the susceptibility were not present. Now they are.