It will take 2 of those 5 years just to ascertain at what levels it is safe, and then another two years to determine whether it is better than the current standard-of-care.
While we're all desperate (some more than others) for a break-through in cancer treatment, it seems perfectly reasonable to demonstrate that something is both safe and better than the current standard-of-care before physicians start rolling this out to everyone affected by the brain tumours this therapy would help.
I sympathize with the sentiment that delaying rolling out a therapy like this seems inhumane, it would be no less (and arguably more) inhumane to roll out a therapy where we didn't establish safe doses and effectiveness to the best of our ability. Both potentially result in deaths.
Maybe there are some efficiencies to be found, but we are talking about experimental treatments where the efficacy takes weeks to years to measure. You can't run an overnight benchmarking test.
But in saying that, if a trial is showing very positive results then it can be fast tracked, as it is unethical to withhold that kind of treatment. Conversely, plenty of trials that look good in phase I/II fail in phase III and are terminated early.
To your point, as soon as enough evidence is obtained in Phase III that the drug is better than standard of care, the trial ends early and patients in the trial get switched to it. At least, that was the case in the case studies we looked at in my lectures.
