A review of human carcinogens—Part E: tobacco, areca nut, alcohol, coal smoke, and salted fish: The Lancet Oncology, Volume 10, Issue 11, Pages 1033 - 1034, November 2009
New evidence continues to add to the extensive list of tobacco-related cancers (table); there is now sufficient evidence that tobacco smoking causes cancer of the colon3 and of the ovary.4 More than 150 epidemiological studies of tobacco smoking and breast cancer were reviewed. Large cohort studies5, 6 published since 20022 consistently show a small positive association (relative risks 1·1—1·3). Many chemicals in tobacco smoke cause mammary-gland tumours in animals, and these carcinogens are stored in breast adipose tissue in women; therefore, the Working Group concluded that there is limited evidence that tobacco smoking causes breast cancer.
A causal link between parental smoking and childhood cancers has been established. Four recent studies showed that children born of parents who smoke (father, mother, or both, including the preconception period and pregnancy) are at significantly higher risk of hepatoblastoma, a rare embryonic cancer. The UK Childhood Cancer Study7 reported a relative risk of 1·86 for paternal smoking only and 2·02 for maternal smoking only, increasing to 4·74 (95% CI 1·68—13·35) when both parents smoke. For childhood leukaemia, a meta-analysis reported an association with paternal smoking before pregnancy (summary relative risk 1·12, 1·04—1·21).8
Second-hand smoke causes lung cancer.2 There is now limited evidence for an association with cancers of the larynx and the pharynx,9 whereas evidence for female breast cancer remains inconclusive. Since second-hand smoke contains most of the constituents of mainstream smoke, it might also be associated with other cancer sites.
Many types of smokeless tobacco are marketed and all contain nicotine and nitrosamines. Hundreds of millions of people use smokeless tobacco, mainly in India and southeast Asia, but also in Sweden and the USA. Earlier findings showed a causal association between use of smokeless tobacco and cancers of the oral cavity and pancreas, and there is now sufficient evidence for cancer of the oesophagus.10
All of the forms of tobacco discussed above induce malignant tumours in laboratory animals.
