The EPA actually classifies tobacco smoke as a Group A carcinogen. It is one of 15 in the group shared with the likes of asbestos, radon, benzene, etc.
http://www.epa.gov/smokefree/healtheffects.html
Phillip Morris' own (shockingly unpublished) research revealed just how bad it is.
http://tobaccocontrol.bmj.com/cgi/content/abstract/14/6/396