There's actually been a lot of research on nicotine, and the conclusion is that it's _slightly_ carcinogenic. But more to the point, there was little reason to

There's actually been a lot of research on nicotine, and the conclusion is that it's _slightly_ carcinogenic. But more to the point, there was little reason to believe it would cause cancer in the first place, compared to any other random compound. Its association with tobacco is a wash, because other compounds, like aldehydes, are completely sufficient to explain the carcinogenicity of smoking tobacco.