Does nicotine (the chemical itself) cause cancer/problems ociated with cigarettes?

chewing tobacco and cigarettes have both been linked to cancer and other circulatory problems, but is it the tobacco, the additives, or the nicotine itself that causes the problems? if a person chewed nicotine gum, never having smoked a cigar or cigarette, chewed tobacco,or spent a lot of time around smokers, would they still be at risk for cancer and circulatory problems?