Most of the carcinogens found in mass-produced cigarretes come from the additives, chemicals used in the cigarrette making process that enhance flavor, protect from rot, enhance color, cover up bad smells or tastes, etc.
http://en.wikipedia.org/wiki/List_of..._in_cigarettes
Here is a german study showing the effects of just certain select additives.
http://www.dkfz.de/de/tabakkontrolle...cts_Report.pdf