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Table 4 Carcinogenicity classifications of chemical exposures found in cigarette smoke

From: State of the evidence 2017: an update on the connection between breast cancer and the environment

Chemical IARC NTP
Tobacco smoking: Active and passive   K
Polycyclic aromatic hydrocarbons (PAHs)   RA
Benzene 1 K
Vinyl chloride 1 K
1,3-butadiene 1 K
Nitrosamine ketone (NNK)   
  1. International Agency for Research on Cancer (IARC) classifications: 1 = Carcinogenic to humans, 2A = Probably carcinogenic to humans, 2B = Possibly carcinogenic to humans, 3 = Not classifiable as to its carcinogenicity to humans; U.S. National Toxicology Program (NTP) classifications: K = Known to be a human carcinogen, RA = Reasonably anticipated to be a human carcinogen. Source of exposure list contains most common exposure sources