The largest studies to date have found no ties to lung cancer or COPD, however there's still other damage present which can take the form of reduced lung capacity, chronic bronchitis, etc. As for refuting the "THC cures cancer" thing, there's certain forms of testicular cancer which do show slightly increased risk of statistical significance. The lack of worse lung problems is somewhat surprising but I've seen speculation from doctors about other possible causes than a miracle cancer cure.

I'm not much of a pot head, but my country is legalizing in a few weeks so I did some research - Dry leaf vaporizer is absolutely the way to go if you can afford it, full inhalation dose control and speed, no extra shit from flavorings or solvents, far less risk of those lung issues.