Nicotine has no association with cancer. There is no supportable evidence to link nicotine with cancer, and a vast amount of evidence (and irrefutable facts) that there is no such link. The UK national clinical guidance authority, NICE, have made this very clear in their official guidance to doctors.
This is a point-by-point analysis of the facts, evidence and opinion that prove beyond any doubt that nicotine has no association with cancer in humans. Any link reported in animal or cell models is clearly shown to be irrelevant, since the facts are clear.
NICE PH45  makes it very clear that nicotine has no association with cancer. This is the official medical advice for all UK medical practitioners: if they ignore the guidance of their clinical guidance authority, they risk sanctions or civil suits.
In other words, if a doctor tells you that nicotine has some form of association with cancer, they are directly contradicting the official medical instructions they work to, and if they offered treatment based on that position, you would be within your rights to sue and you would have a strong case. So, if a UK doctor, having been officially told that nicotine has no association with cancer, then prescribed you Champix (varenicline) for smoking cessation because he believed the risks of Chantix and NRT are comparable, and you subsequently murdered someone or committed suicide as a result of a severe psychotic event, then that doctor has no grounds for defence in a civil suit for negligence (iatrogenesis). They have been told officially that nicotine has no association with cancer.
We might also consider the fact that the UK medical establishment may be the most conservative grouping of any kind in the world, and if they reject what might otherwise be considered 'establishment propaganda', then, regardless of the evidence, this alone presents a strong case that no such link exists.
What if we had a vast mountain of data collected over more than three decades, concerning an isolated population who consumed nicotine without smoke, in high volumes, for extended periods spanning multiple decades, and where hundreds of thousands of subjects were followed for multiple decades, and the epidemiology was indisputable, and the national health statistics unique as a result? What if those facts (as they are facts, with such a volume / time combination) revealed that extensive consumption of nicotine without smoke has no readily-discernible effect?
We do have those facts, and that vast mountain of data, and it is the Swedish Snus data. This data mountain quite clearly reveals that consumption of high quality, carefully manufactured tobacco, without smoke, has no significant implications for health. Hundreds of clinical studies, some with nearly 100,000 subjects followed for several decades, reveal that Snus has no statistically-identifiable association with any form of cancer. The health outcomes for smokers who switch to Snus or who totally quit are the same.
Then we have the facts: Sweden has an incidence of tobacco-related cancer only comparable to the number of smokers - Snus consumers are invisible.
The Snus data was used by Benowitz and others in applications for long-term NRT licenses, since no elevation of risk can be identified.
Data from nicotine replacement therapy studies shows the same result: no identifiable association with cancer can be found. The NRT data is microscopic in size, in comparison with the Snus data, and only began in 1984, with useful data from much later; but it does have the advantage of targeting only the compound concerned: nicotine.
NRT therapies have now been licensed for long-term use as no harm of any kind can be identified: no association with cancer, no association with CVD, no liability for abuse (no potential for dependence), and no evidence for harm of any kind with the exception of those with pre-existing medical conditions.
No senior medical personnel in this field will state that nicotine has any statistically-significant association with cancer in humans as demonstrated either by clinical studies or national health stats. No evidence for it can be found, and there is a vast amount of evidence to utilise here.
Animal models and in vitro models of nicotine's effects clearly do not transfer to the human organism. In other words, fraudulent research can be constructed with models ad nauseam to try and associate nicotine with cancer, but the vast mountain of data and facts makes this entirely pointless, apart from the headline value of course (as the media will publish anything that sells papers, subscriptions and advertising inventory, and that pleases large-scale advertisers).
The anti-nicotine propaganda has a commercial value and is probably successful because it aligns well with the type of puritanical ideology that zealots are vulnerable to. It appears to be self-perpetuating to a degree, and has to be regarded as one of the most successful commercially-initiated campaigns since it comes close to being a perpetual motion machine as very little encouragement appears to be needed from those who benefit. Its success also illustrates the tremendous power of propaganda: it can even cause experts to believe the opposite of the truth.
The effect on doctors
We normally think of doctors as medical experts, at least in general terms - they are the people we choose to advise us on health issues in general. A recent survey of British and Swedish doctors , however, revealed that 44% of British doctors reported they believe nicotine is associated with cancer, and an even larger number (incredibly) reported they believe nicotine is one of the more harmful components of cigarette smoke; but their official national clinical guidance authority issues guidance to them that nicotine has no association with cancer and is not one of the harmful components in cigarette smoke (NICE PH45).
So it appears that about half of British GPs don't know anything about the issues and will be guilty of medical negligence if they give advice on anything related to smoking cessation - this despite the fact that the average UK GP practice is paid around £10,000 a year for smoking cessation services. For example, if a patient asks whether NRTs (nicotine therapies) or varenicline (a psychotropic therapy) is the best option, they might take into account a false opinion that NRTs may have some kind of risk for cancer or other negative health effect, and prescribe varenicline (Chantix/Champix). If the patient then experiences heart problems or severe psychosis (side effects associated with varenicline), the doctor is clearly guilty of malpractice. It is impossible, given the scale of ignorance, that this has not happened.
The effect on surgeons
There are also going to be effects on general surgery due to the prevalence of specific propaganda attacks on nicotine. Two opposing positions are promoted, at the same time, both incorrect, either of which may affect the choices and actions of surgeons and other medical personnel:
"Nicotine promotes or even causes cancer because it promotes blood vessel growth and increased vascularity in tissue, and in damaged tissue, and in tissue regrowth. Thus it assists the growth of tumours or may help cause them."
- and also:
"Nicotine should not be consumed prior to surgery in any form, such as by smoking or smokeless tobacco or vaping, since it prevents repair of damaged tissue by preventing repair of blood vessels and restricting vascularity. Thus it prevents healing post-surgery."
Now both of these popular propaganda statements cannot be true at the same time. The people who promote these fantasies ought to pick one to run with, because using both of them reveals the utter stupidity of anti-nicotine attacks. In fact neither are true, as perhaps might be obvious from their self-cancelling nature.
Smoking is associated with cancer and may slow post-surgery healing; this has nothing whatsoever to do with nicotine, otherwise we might be obliged to stop eating vegetables (nicotine is an active component present in the normal diet; everyone consumes it; everyone tests positive for it).
Since we have decades of experience with nicotine outside of smoking, and as a result there is a data mountain on real-world experience, and no association between nicotine and cancer can be found, and we can also look at what happens at population level in isolated populations where the majority take their nicotine without smoke, and as a result the cancer incidence can be minutely analysed and is found to represent only the smokers (e.g. in Sweden), it is safe to say (as NICE has) that nicotine does not cause cancer, it does not facilitate cancer, it does not promote cancer, it does not worsen cancer and it has no association with cancer in humans in the real world.
It may well have an association with lots of things, in the lab, but you can get any result you pay for in a CT or RCT. The buyer specifies the result they want, which is something of a tradition with anything vaguely tobacco-related where it impacts pharmaceutical industry revenues. Keep in mind that animal and in vitro models for nicotine effects do not transfer to humans and we have a vast mountain of real-world data on humans over multiple decades that strongly demonstrate this; and that facts that prove it, namely the national health statistics.
Finally, if you want a fundamental guide to the relative safety of nicotine and tobacco without combustion, then look up the giant-scale meta-analyses by PN Lee, and Lee and Hamling . Snus has no reliably-identifiable association with any cancer, which by extension can be taken to mean that nicotine has none .
There are not many experts on these subjects, and perhaps even less who are unconflicted and can be relied on to give straightforward and honest answers about the nicotine and disease issue. It seems unlikely, though, that Profs Lee, Rodu, Phillips, Houezec, Foulds or Benowitz would claim nicotine has any association with cancer and they are in a better position than most to evaluate the evidence. Foulds for example reported in 2003, after an exhaustive examination of the evidence, that no reliable connection between Snus and cancer could be found . Note that Snus products often supply more nicotine than any other source, including cigarettes.
No evidence that stands up to scrutiny exists to link nicotine with cancer. There is a vast amount of evidence that there is no such link. More importantly, the facts are perfectly clear: no elevation of incidence of cancer is found in Western populations who consume large amounts of nicotine without smoke.
 NICE PH45: http://www.ecigarette-politics.com/references-health-public-health.html
>> Public Health
 Lee; Lee and Hamling: http://www.ecigarette-politics.com/references-thr-snus.html
>> Snus & ST
 Foulds et al 2003: http://www.ecigarette-politics.com/references-thr-snus.html
>> Snus & ST
 See: References - Nicotine
 From a personal point of view, I don't believe anything I read even if it appears to agree with my own perspective. It is always necessary to take a step back and ask: can this really be true?
There is a very good example in this case, and it is the practical experience of the use of carotenes vs the natural form in vegetables, and there is a possibility that it may be paralleled by the use of nicotine outside of tobacco (or vegetables).
To explain: carrots contain around 20 beta-carotenes, one of which is the precursor for vitamin A. It was noted that people who ate a diet rich in natural carotenes, such as carrots and tomatoes (simply put: red vegetables) got less cancer than those whose diets lacked such vegetables. The natural next step was to try to identfy any active agent, isolate it, and supply that as a simple anti-cancer prophylactic. It looked as if it might be vitamin A, so they gave subjects plenty of vitamin A. Those people got more cancer, not less. There are multiple questions here, such as whether or not the vitamin A supplied was the synthetic form with the opposite isomer, and so on - but it does indicate there could be a problem with assumptions of this type. Because there is a known example of this effect, it is a valid argument to question assumptions in this area. Perhaps it is not an isolated example.
Therefore it may be a fallacy to state that because high-volume long-term Snus consumption has no measurable association with cancer, then consumption of one compound from the mix of thousands will have the same result: no association with cancer. Thus, isolating nicotine from tobacco (or its normal position in vegetables in the diet, of course), and consuming it in isolation, does not necessarily have the same implications for lack of any link with cancer. There may conceivably be an ameliorating factor contained within tobacco (or the vegetables it is normally found in); this is the subject of debate as it is clearly logically correct though perhaps impractical, according to individual opinion.
It is true that the NRT data do not show any such association; but the drawback is that the NRT data resource is microscopic and severely limited in comparison with the Snus data and always will be. This is because hundreds of thousands of Snus consumers have been followed for multiple decades and will be continued to be followed (just one study for example had nearly 100,000 subjects followed for multiple decades); but NRT is a medical intervention, prescribed mainly in the short term, has very few long-term users in comparison and is not designed to be pleasant to use, and therefore has a self-limiting function (as all licensed medicines are normally required to have).
If we knew what the timelapse to the reported increase of cancer was in the vitamin A studies, then perhaps if we applied that timelapse to pure nicotine consumers such as NRT and ecig users, the answer might be apparent. Indeed, it may have already passed.
This example is included because it is important to present a true and balanced view, and to clearly illustrate that all the evidence was examined and not just some of it.