In short, the medication does appear to reduce the beta-amyloid plaque buildup in the brains of patients with Alzheimer's. However, in the phase 3 study that plaque reduction did not appear to result in any clinical improvement in patients. The Phase 3 trial was "stopped for futility."
That's why the advisory panel could recommend rejection -- the drug did not appear to help patients. But equivalently, it did do the thing it set out to do, so that justified (ish?) the final approval.
In short, the medication does appear to reduce the beta-amyloid plaque buildup in the brains of patients with Alzheimer's. However, in the phase 3 study that plaque reduction did not appear to result in any clinical improvement in patients. The Phase 3 trial was "stopped for futility."
That's why the advisory panel could recommend rejection -- the drug did not appear to help patients. But equivalently, it did do the thing it set out to do, so that justified (ish?) the final approval.