This is one of the entries for the THC Ministry's list of info on Cannabinoids. They can explain it better.

29. New research shows that the argument over outlawing cannabis because it "Causes Cancer" is no longer valid. There are Nicotine Receptors in your throat. There are no Cannabinoid Receptors in your throat. Cells have a Bio-chemical Program known as "APOPTOSIS". This Bio-chemical Program is activated when cells too damaged to repair themselves commit suicide. There is a Bio-chemical Pathway that controls that. Nicotine activates a path that protects the cells from dying. Smoking anything puts Carcinogens into your Air Passage-ways and Cardio-Vascular system. Cells that get damaged by smoke die and that's what you want to happen. Cells to die before they become Cancer Cells.

http://www.thc-ministry.net/cannabisinfo.htm