Pardon my naive question, but aren't there more objectives for the clinical trial? Particularly testing for negative side effects? How are those judged if the trial is discontinued?
I generally think of the phases like this (this is just how I think of it):
Phase 1 - is it safe? If you don’t see severe toxicity then you can go to phase 2.
Phase 2 - does it work? You look for good outcomes (cures, better survival, etc). If there is significantly better outcomes relative to placebo, then go to phase 3.
Phase 3 - does it work for a large population? What is the appropriate dose? Dialing in the numbers before public release.
Phase 4 - after you’ve made the drug public, monitor the larger population for side effects or adverse events. You can’t hope to cover all patients in a phase 2/3 trial, so you keep monitoring the first waves of patients that get the drug.