I'd speculate that a lot of this is down to the kind of diagnostic tests run on the typical patient coming in for treatment. I know from personal experience that in Europe it's a lot less and tends to be a "take an advil, go home and rest" while on my last trip to hospital for broken toe I got every blood test possible done too.
As a doctor friend of mine says, if you apply enough analysis you'll find something wrong somewhere. I think this might be the case in the US and Canada.
I don’t think that’s the main culprit. US has higher incomes than most Euro countries but generally 5 years less of life expectancy. I think there’s at least one major environmental culprit that Americans will eventually be incensed at, like the Sackler situation but much worse.
I wouldn’t bet on construction materials, unless it’s something PFAS-like that accumulates indefinitely and causes problems. But I like the suggestion because we need more out of the box theorizing instead of the obesity trope which clearly isn’t unique to the US.
I'd get this if we were talking about say influenza incidence rates, or cancer survival rates, but not cancer incidence rates.
Given the progressive and terminal nature of cancer, there comes a point where any relatively modern healthcare system will be forced to diagnose it.
That said, non-malignant tumors and other "could be cancer if you squint a bit" like states are relatively common in perfectly healthy people. If you go looking for them on a shoot first and ask questions later, you might very well inflate incidence rates quite significantly. The economic incentives at least in the US healthcare system seems to strongly favor discovering new diagnoses, whether or not they are actually there.
As a doctor friend of mine says, if you apply enough analysis you'll find something wrong somewhere. I think this might be the case in the US and Canada.