In the Alzheimer’s affected brain, abnormal levels of the beta-amyloid protein clump together to form plaques, seen in brown.

Biogen is declaring success with a once-failed treatment for Alzheimer’s disease, pointing to positive secondary results from a mid-stage study in hopes of saving a drug many in the field had written off entirely.

The treatment, BAN2401, failed its primary goal of beating out placebo over the course of 12 months. But looking at 18 months worth of data from the Phase 2 trial, Biogen and its partner, Japanese drug maker Eisai, said late Thursday that one dose of the treatment — the highest of five tested — had a significant effect on both cognition and the accumulation of toxic plaques in the brain.