Often context matters. Something can be good for one cancer and bad for another. Or be good for cancer but bad for heart disease. Or bad for cancer but good for heart disease. Something may cause cancer if you force feed far more than a human could reasonably consume, but harmless at normal quantities.

which is why so many of us just say "moderation and eat a varied diet". Once in a while science settles on something that is true for everyone, but real science is hard.