Cassava Sciences' Alzheimer's drug simufilam failed its Phase 3 trial and the stock plummeted ~90%. See why I changed my rating on SAVA to Sell from Strong Sell.

The Cassava Sciences story ended Monday exactly as many knew it would — with the company’s experimental drug for Alzheimer’s disease, simufilam, failing a clinical trial.

Cassava Sciences shares are plunging in premarket trading and are losing most of their value after the biotech firm said its experimental Simufilam drug aimed at treating Alzheimer’s disease failed to show a “significant reduction in cognitive or functional decline” during the Phase 3 trial of the treatment.