This makes me weirdly sad. Can you imagine entering the trial for a long sought drug against a deadly disease that turn out to be working, and end up in the control group? I know that there's more to it (it's necessary, they knew, it could have not worked, plainly be nocive, etc.) but it's like being unlucky twice in a row and die out of that while having received the real thing would have saved you
It is difficult to overstate just how much thought and argument has gone into clinical trial design in the last half century. It may seem detached and unfeeling, but basically every step is carefully considered compassion, ethics, and a desire for unambiguous causal truth of drug effectiveness.
It would be unethical if this placebo was given in place of a known working alternative treatment.
From what little I know of cancer treatment, that isn't how studies are generally run. When you're part of a trial, you're either given the experimental treatment, or the "standard of care", not a placebo.
So for cancer at least, you're either getting a novel treatment, or standard chemo.