Cassava's Simufilam Fails Both Pivotal Phase 3 Alzheimer's Trials on Every Endpoint, Peer-Reviewed Data Confirm

Simufilam, an oral drug developed by Cassava Sciences, did not meet its co-primary, secondary or exploratory biomarker endpoints in either of two Phase 3 randomized controlled trials, according to a peer-reviewed report published online January 6, 2026 in the Journal of Prevention of Alzheimer's Disease. The paper, authored by Cassava-affiliated and independent investigators including the company's chief scientific officer Lindsay Burns, gives the full results of RETHINK-ALZ, which randomized 804 people with mild-to-moderate Alzheimer's disease to simufilam or placebo for 52 weeks, and REFOCUS-ALZ, which randomized about 1,125 people to two doses of simufilam or placebo for a planned 76 weeks. Co-primary endpoints in both trials were change from baseline on the ADAS-Cog12 cognitive scale and the ADCS-ADL function scale.

RETHINK-ALZ's topline miss was first disclosed by Cassava on November 25, 2024. REFOCUS-ALZ was stopped early, with 22 percent of participants still active, after its own topline results missed the same endpoints; Cassava announced on March 25, 2025 that it would discontinue the Alzheimer's program. The newly published paper adds the peer-reviewed detail: in a predefined subgroup of patients with milder disease in REFOCUS, simufilam appeared to slow cognitive decline versus placebo through week 64, but that signal vanished by week 76, a point at which 45 percent of the trial's data were missing because of the early termination, and it did not repeat in RETHINK. A separate exploratory analysis tied to higher plasma p-tau181 levels showed a favorable signal in RETHINK but not in REFOCUS. The authors reported no significant safety concerns.

The results close a program that had already drawn outside scrutiny. In 2023, a City University of New York investigative committee found evidence that a Cassava collaborator, Hoau-Yan Wang, had manipulated images in earlier laboratory papers supporting simufilam's proposed mechanism; Wang was later indicted on federal fraud charges tied to NIH grant funding, a case still working through the courts. The Phase 3 trials themselves, run under a Food and Drug Administration-approved Special Protocol Assessment, were designed and executed independently of that laboratory research, and the new paper's authors describe simufilam as safe and well tolerated even as it failed to show benefit.