It is believed by many that Nicotine causes cancer, and passively vaping may also cause cancer due to the nicotine content.
My research into the idea whilst looking at questions such as Does 'vaping' affect your lungs? has uncovered that Nicotine is also found in various fruit and vegetables (Davis, et al. 1991; Castro & Monji, 1986; Sheen, 1988 & Domino, et al. 1993). It is also mentioned in How much nicotine is in tea and vegetables.
Further to the answers given so far by @Narusan and @wolf-revo-cats along with further research I have conducted
I feel there is more that can be gleaned regarding cancer risks of Nicotine.
[E]-cigarettes don’t contain cancer causing tobacco. They do contain nicotine, which is addictive, but isn’t what causes the damage from smoking.
Nicotine showed cocarcinogenic effect with DMBA (7,12-dimethylbenz[a]anthracene) in the hamster cheek pouches model (Chen & Squier, 1990), but...
To our knowledge, there are no relevant study in humans on carcinogenic effects from pure nicotine including products, such as NRT and e-cigarettes (Sanner & Grimsrud, 2015).
When looking at passive smoking and cancer, Domino et al. (1993) points out that 10g of eggplant contains the equivalent nicotine of passively smoking for 3 hours in a room with a "minimum amount" of tobacco smoke. 10g is not a lot of eggplant and passive smoking causes cancer (e.g. Hori, et al. 2016). If Nicotine causes cancer, and as eggplant, potato and tomatoes contain nicotine as well according to the studies above, would these plants cause cancer as well?
Don’t get me wrong, as an ex-smoker myself, I know how stopping boosts health. My question is whether Nicotine does cause cancer, or is it Nicotine-derived N-Nitrosamines (Hoffmann & Hecht, 1985), or is it actually Tobacco-specific nitrosamines (TSNAs) formed from tobacco alkaloids during the curing and processing of tobacco (Hecht, 1999)?
Castro, A., & Monji, N. (1986). Dietary nicotine and its significance in studies on tobacco smoking. Biochemical Archives, 2(2), 91-97.
Chen, Y. P., & Squier, C. A. (1990). Effect of nicotine on 7, 12-dimethylbenz [a] anthracene carcinogenesis in hamster cheek pouch. JNCI: Journal of the National Cancer Institute, 82(10), 861-864. doi: 10.1093/jnci/82.10.861 pubmed: 2110268
Davis, R. A., Stiles, M. F., & Reynolds, J. H. (1991). Dietary nicotine: a source of urinary cotinine. Food and Chemical Toxicology, 29(12), 821-827. doi: 10.1016/0278-6915(91)90109-K pubmed: 1765327
Domino, E. F., Hornbach, E., & Demana, T. (1993). The nicotine content of common vegetables. New England Journal of Medicine, 329(6), 437-437. doi: 10.1056/NEJM199308053290619
Hecht, S. S. (1999). Metabolism of Carcinogenic Tobacco Specific Nitrosamines. NIH Grant Application R01-CA081301-05 Retrieved from http://grantome.com/grant/NIH/R01-CA081301-05
Hoffmann, D., & Hecht, S. S. (1985). Nicotine-derived N-nitrosamines and tobacco-related cancer: current status and future directions. Cancer research, 45(3), 935-944. Retrieved from http://cancerres.aacrjournals.org/content/canres/45/3/935.full.pdf
Hori, M., Tanaka, H., Wakai, K., Sasazuki, S., & Katanoda, K. (2016). Secondhand smoke exposure and risk of lung cancer in Japan: a systematic review and meta-analysis of epidemiologic studies. Japanese journal of clinical oncology, 46(10), 942-951. doi: 10.1093/jjco/hyw091
Sanner, T., & Grimsrud, T. K. (2015). Nicotine: carcinogenicity and effects on response to cancer treatment–a review. Frontiers in oncology, 5, 196. doi: 10.3389/fonc.2015.00196
Sheen, S. J. (1988). Detection of nicotine in foods and plant materials. Journal of Food Science, 53(5), 1572-1573. doi: 10.1111/j.1365-2621.1988.tb09328.x