NNK, NNN and polonium 210 are carcinogens specific for -

Nitrosamines such as 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and N'-nitrosonornicotine (NNN), are carcinogenic to humans . NNK and NNN induce carcinogenesis by causing DNA adductions and mutations as well as promoting tumor growth through receptor-mediated effects .Exposure and consumption of tobacco products are causally associated with various types of cancers . Nicotine and nitrosamines form a devastating and fatal alliance. Nicotine activates the brain's reward system, eliciting cravings for continued tobacco consumption, and it often is accompanied by carcinogens inducing tumor initiation and progression Ref Harrison 20th edition pg 567