How do we know something causes cancer? Aren’t there essentially infinite variables it would be impossible to control for?
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There generally isn’t a single study you can do to establish if something causes cancer. What you have to do is put together a variety of evidence.
Theoretical understanding, do we have an idea of why a substance might cause cancer? Do we have a mechanism in mind?
Mechanistic evidence, so can we do studies showing that that substance causes cancer in cells in “test tubes”?
Animal experiments. Can we give a rat the substance and see if it causes cancer. Here we can control for everything else, so it’s just that one thing that is different.
Longitudinal studies. Do people who consume more of that substance have higher levels of cancer.
So if we know a substance would cause cancer, and we have done RCT in animals showing it causes cancer while controlling for everything else, and we have correlational studies in humans linking it to cancer then it’s reasonable to assume that substance causes cancer.
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