I am a MMJ medical patient and smoking anything can cause lung cancer. Have you seen what your bong or pipe looks like after smoking? That same resin does stick to your lungs as well, and there is no way that is healthy. That is why many people have switched to the vaporizer sticks. You can get the medical benefits of MMJ without the smoke.
Marijuana can cause lung cancer because anything that is inhaled into the lungs that would be considered an odd substance could cause a cell to take on a different form. It is all about how that persons body reacts to it. Look there are people that smoke for years and do not get it. But some who smoke very little and do. It is all about that individual.
Any form of smoking where smoke is inhaled into the lungs, there is an increased chance of developing lung cancer. This applies to tobacco, marijuana, or anything else. Since marijuana smokers tend to deeply inhale the smoke and hold it in for longer periods of time, it can be especially damaging to the lungs.
There are many studies by reputable scientists that show the compounds in Marijuana may actually kill Cancer cells. If you read U.S. government studies, you will find the scientists found Marijuana to be safe, but the U.S. government skewed the results to keep marijuana illegal. Plus, you don't have to smoke Marijuana to get the benefits, so the smoking argument is a moot point at best.
Up to this point, there is no definitive evidence to demonstrate that marijuana causes lung cancer unlike tobacco. However, the reason is that no sound studied have been conducted to show the potential of marijuana to cause cancer. Therefore, caution is needed to establish any policy related to marijuana in terms of its risk to cause cancer.