Your previous comment didn't include any evidence, but these are pretty interesting. The second one is more damning, but again the majority of studies were on smokers. I'll update my statement and say there is little evidence that nicotine by itself is carcinogenic. As the second article says "The IARC monograph has not included nicotine as a carcinogen." so it's still not conclusive. The strongest thing I see in the second article is that nicotine can help promote existing tumors, that's concerning.

But the way science works is by having lots of viewpoints and research - there are also plenty of papers on how nicotine is not carcinogenic.

"Smokers commonly misperceive that nicotine is a major carcinogen" - https://thorax.bmj.com/content/66/4/353#ref-2

"The literature to February 2019 suggests that there is no increased cardiovascular risk of nicotine exposure in consumers who have no underlying cardiovascular pathology. There is scientific consensus that nicotine is not a direct or complete carcinogen, however, it remains to be established whether it plays some role in human cancer propagation and metastasis. " - https://f1000research.com/articles/8-1586 (This is what I saw in the second article - looks like there is a chance that nicotine can promote existing cancer)

"The devastating link between tobacco products and human cancers results from a powerful alliance of two factors — nicotine and carcinogens. Without either one of these, tobacco would be just another commodity, instead of being the single greatest cause of death due to preventable cancer. Nicotine is addictive and toxic, but it is not carcinogenic. This addiction, however, causes people to use tobacco products continually, and these products contain many carcinogens." - https://www.nature.com/articles/nrc1190

I am not a vaper, I do use patches and gum. I believe that damning nicotine prevents the development of replacements for smoking which is incredibly dangerous. I don't vape because research on that is in really early stages, and there's a good chance there might be something bad in the long term, though there is no strong evidence that it is worst than other NRT, except that levels of NNAL are higher (see the first paper you posted).

Edit To clarify that you didn't provide evidence in your first post - you linked to https://www.verywellhealth.com/what-is-nicotine-5075412 which has citations, but the comments about nicotine being carcinogenic linked to studies that studied smoking, not NRT or non-smoke based nicotine.