My 2 cents, its not opinion anymore there are more than enough studies done if you'll google thc/cancer together. I can't post links, but i used the library of congress to search for medical studies and journal references. The info does exist and its legitimate science. They're not saying smoking up kills cancer, as the carcinogens that exist in tar and such are still there with smoke same as analog cigarettes, and there are the obvious immuno effects but given immunosteroids(generally given in conjuction with chemo) it can be easily countered. These studies generally aren't done in the USA b/c currently GW pharmaceuticals has the patent on Sativex which is a 99% pure thc oral spray but has solution form as well. The fda demands research but wont grant permits for research. But the most recent studies have been not just on the slowing effect of THC on tumors, but on intratumorally injecting thc. Even our synthetic endocannabinoids altered good cells whereas the natural thc was shown to actually destroy tumor cell's abilities to survive and leave the good cells intact. Interesting science, but application and execution are key. Cancer's a horrible disease, but adding another tool to the arsenal of treatments with such demonstrable results seems obvious. btw those intratumor injections had no noticeable psychoactive effects, so no worries about making people "high"
