Smoking pot will not cause cancer. Smoking tobacco will. This is because certain compounds that are found in cannabis smoke actually protect you against the carcinogenic compounds found in both tobacco and marijuana smoke. Its a simple as that. The bulk of recent research supports this.

The reason why people with cancer do not see tumour shrinkage from smoking pot is because the amounts of cannibanoids needed to have an effect are too small when pot is just smoked. If you want to use cannabis to fight cancer you can either wait for pharmaceutical companies to start producing these types of medicine (you'll be waiting a very, very long time) or you can make your own. This is what a growing number of people are doing and they are having extremely positive results (e.g Rick Simpson www.phoenix tears.ca).

I agree with people who say that to vapourise/make edibles,etc is better than smoking. Burning plant material will always produce harmful substances. Although pot smoke has anti-carcinogenic properties, its still better to avoid these carcinogens in the first place!