... and just to add: no studies anywhere have ever come to the conclusion that nicotine is a carcinogen! There is no evidence whatsoever to back up that statement (despite it being stated several times in the last few days in numerous posts on this board!)
The closest any studies have come to suggesting any link between nicotine and cancer was a study published earlier this year which stated that if someone already had pre-cancerous cells, nicotine may act as a catalyst and make those cells grow faster (and this study itself stated that further study needed to be done to confirm whether or not this was the case).
So just to clarify: according to all medical knowledge curently available, nicotine is NOT a carcinogen.