Do not confuse tradition with precedent.
Trials have been approved on P2 data, single P3 data and multiple P3 trial data.
Regulators have some flexibility in the approval process. They will consider the unmet need, the current SOC, the strength of the trial data, what percent of the target population the drug demonstrates efficacy for, and then make a decision.
It is true that AD has typically required 2 P3 trials or a confirmatory P4 post approval. Part of that is the lack of biomarkers in the past and the variability in the progression rate of patients, issues with accurate diagnosis, and the short term variability of many AD function tests. Patients have good days and bad days.
There are now more biomarkers available and better diagnostic tests available than before, which change the landscape for drug testing. As we have seen at the FDA , the UK MHRA, and the EU, there is change in the way trials are viewed and what should be considered as appropriate demonstration of efficacy.
So, change is afoot and that muddies the waters in terms of predictability.
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