"it helps cancer patients" is vastly different than "it cures cancer" which is what OP claimed he heard. And yes, it does help cancer patients as well as anyone else in pain. And the smoke is far less harmful than cigarette smoke, it has no additives at all (when grown in a controlled environment without pesticides). And you don't even need to smoke it, it can be ingested in an edible/pill, making most of the arguments against ingesting marijuana completely bogus.