Warning: mini rant ahead....not directed at you @ringling, just at the issue.
This is one of those things that kinda gets me. From my brief time in school when I was studying biotech and working with cancer cells (which I know does not qualify me to really say anything at all, but I'm going to anyway) I can tell you that LOTS of things will kill cancer cells in a petri dish. Like, not feeding them, acid, peroxide, etc. That doesn't necessarily mean it will be an effective therapy for using in a person. Killing the cells isn't enough. You have to be able to kill the cells without killing all the other cells, and that's when things get tricky. I killed several plates of cancer cells with apple cider vinegar, but the amount it would take to do it in vivo would mean a person would have to drink a ton of ACV and by that time, all their other cells would be dying also. Part of the reason chemo works (when it works) and produces the side effects that it does is because it targets all rapidly dividing cells—one of the distinguishing characteristics of a cancer cell. But, the cells that make up your skin, hair follicles, the lining in your gut, the lining in your mouth, bone marrow, etc. are also all rapidly dividing cells so they die, too.
Cancer cells also mutate rapidly. Their whole foundation is that the DNA is mutated beyond repair and the cell cycle has gone haywire. So there won't be a single cure for 'cancer' there will have to be many different cures for different types of cancer. This is where an ounce of prevention (when possible) is worth a pound of cure. Avoiding things that mutate DNA (again, when possible) will help lower the risks of getting cancer. Don't tan, wear sunscreen, don't smoke, eat healthy food, etc. Also, don't drink caffeine or water, because those are mutagenic, too. LoL.
Cancer is really complicated. It just isn't as simple as throwing a chemical in a plate, injecting it into an animal, and then putting it out to market as a treatment. The average research and development life for a drug (not necessarily cancer) is 15 years. A tiny fraction of things that begin testing actually make it all the way through to marketable product, despite what it may seem. I'm not trying to defend the exorbitant cost of medication or big pharma policies at all, the whole thing is skewed toward the big guys making the big bucks, but the scientist in me remembers the fact that it took a week+ to do a single assay on a simple compound using known elements and procedures.
All that to say that cannabis may be a legit possible treatment or at the least effective for the side effects of cancer, chemo, radiation, etc. But, saying "it kills cancer cells" isn't enough of a reason for it to be considered a cure any more than saying something is mutagenic is enough of a reason to call it a deadly poison.