What is not clear is whether this result is because of cigarettes themselves, or only nicotine. Pure nicotine has many possible health benefits and has been approved by the FDS in patches.
It’s not the nicotine in tobacco that’s carcinogenic but rather the 100s of other chemical compounds. Burned tobacco has a ton of carcinogens but even unburned tobacco (cf. chew) contains “nitrosamines” that cause mouth cancer, etc.
Combustion byproducts and tobacco constituents both. I don’t think nicotine itself plays much of a role except in maintaining the addiction. Could be wrong.