No evidence to suggest that nicotine is carcinogenic, although it is an alkaloid, and can be lethal in high enough doses. It also appears to have teratogejnic effects;In one large study, women who used nicotine patches and gum during the first trimester of pregnancy had a larger incidence of birth defects.
There are some studies though which suggest that some of the metabolites of nicotine could be carcinogenic, so although nicotine itself is probably not carcinogenic, it could be considered a kind of pre-carcinogen...