Yeah, I'm a little dubious of these claims. "Cancer" is not one disease caused by one thing. There are many types of cancers caused by a variety of mutations in cells (though a good number involve some of the same ones). I've heard that a lot of things "cure" cancer, but until I see actual studies, I'm not believing any of it.

That being said, marijuana is used to help treat cancer pain, though the US government has appallingly fought that tooth and nail for years. Heaven forbid people who may be dying use a mostly harmless drug to treat their chronic pain.