>Smoking and Cancer.
Single atoms of six side neighbor-covalent bond stabilized Uranium 235 exists everywhere in nature, and plants are perfectly fine to stiffen their stems with those bundles of molecules. When you set it on fire and inhale the fumes, the Uranium 235 atom is free to fly around all by itself and then recover its half-living nature since the fire un-binds it. The alpha-beta decay of the Uranium atom self-splits and drops down to Krypton 59, Plutonium 275, Cesium 137 and a dozen others. The fission event creates a burst of gamma, alpha and beta rays that are powerful enough to shoot a high-energy beam of energy that is just strong enough to BTFO a single tooth out of your DNA, just enough to keep the DNA string intact, but not so much that your body can error-correct it. There is a small chance that the modification from this fission event in your lungs can create a cell that behaves selfishly, and grows to the size of a basketball telling your immune system to get wrecked, and now you have cancer.
https://www.youtube.com/watch?v=Qe5WT22-AO8

And so yes, the exact mechanism for how smoke causes cancer, is completely known now.