Success of Lecanemab in Alzheimer's Disease: 27% Slowing of Cognitive Decline
In Phase III clinical trials, lecanemab (Leqembi) became the first confirmed disease-modifying therapy to remove amyloid plaques and receive full FDA approval.
Introduction
In July 2023, a long-awaited milestone for Alzheimer's researchers finally arrived. The U.S. Food and Drug Administration (FDA) granted full approval to lecanemab (Leqembi) for the treatment of early-stage Alzheimer's disease. This is the first drug in history to receive not accelerated but full regulatory approval based on confirmed clinical benefit—a 27% slowing of cognitive decline.
Lecanemab, developed by Eisai and Biogen, became the first disease-modifying therapy that does not merely alleviate symptoms but targets the presumed cause of the disease by removing amyloid plaques from patients' brains. For the more than 1.8 million people with dementia in Germany alone (and millions worldwide), this news means that Alzheimer's disease is no longer a hopeless diagnosis. However, as is often the case with breakthrough technologies, behind the promising numbers lie complex questions of efficacy, safety, and accessibility.
Event Details and Timeline
Historical Context: The path to this moment was rocky. In 2021, the FDA granted accelerated approval to aducanumab (Aduhelm)—the first anti-amyloid antibody—but the decision was marred by controversy due to ambiguous clinical trial data. Lecanemab was meant to be different.
Key Milestones:
- September 2022: Eisai announces positive results from the Phase II study (Study 201), which formed the basis for accelerated approval.
- November 2022: Publication of results from the Phase III Clarity AD study in the New England Journal of Medicine. The study involved 1,795 patients with early-stage Alzheimer's disease. The results stunned the scientific community: the drug met its primary endpoint—a 27% reduction in clinical decline on the CDR-SB scale compared to placebo[p. 9].
- January 2023: The FDA grants lecanemab accelerated approval based on Phase II data.
- July 6, 2023: A historic moment—the FDA converts accelerated approval to traditional (full) approval based on compelling data from the Clarity AD study. This changed the game: physicians and patients now have a tool with proven efficacy.
- 2024–2026: Following FDA approval, other regulators followed suit. The drug was approved in Japan, China, South Korea, Israel, and the United Kingdom. However, challenges arose in the European Union and Australia—local regulators (EMA and TGA) initially denied approval due to safety concerns, though the EMA later reversed its decision.
- March 2026: The German S3 guideline on dementias recommends antibody therapies (lecanemab and donanemab) for the first time for treating early-stage Alzheimer's disease.
Impact and Significance (for the World / Industry / Society)
For the World and Science: Lecanemab confirmed the amyloid hypothesis—the theory that beta-amyloid accumulation is a key driver of Alzheimer's disease. The Clarity AD study showed that patients receiving the drug had a 59.1 centiloid greater reduction in brain amyloid burden than the placebo group. Moreover, a meta-analysis confirmed a direct link between the degree of amyloid removal and slowing of cognitive decline.
For the Industry: The success of lecanemab opened the floodgates for the entire class of anti-amyloid antibodies. It was followed by donanemab (from Eli Lilly), which showed a 28.9–36% slowing. Investment in neurodegenerative diseases surged. As Christopher van Dyck from Yale University, lead author of the Clarity AD study, put it: "This is truly the first time in history that we have a therapy demonstrating an unambiguous slowing of decline in Alzheimer's disease." However, it is important to understand the context: a 27% slowing is not a halt. It means a patient may retain the ability to drive or pay bills for an additional 4–5 months.
For Society: Lecanemab has sparked both hope and fierce debate. The Lancet and the journal Neurology published articles urging to "temper hype and hope." Critics point to three key issues:
- Modest clinical effect: According to neurologists, a difference of 0.5 points on the CDR-SB scale over 18 months may be imperceptible to most patients and their families.
- Serious risks: Amyloid-related imaging abnormalities (ARIA)—brain edema or microhemorrhages—occur in a significant proportion of patients. Clinically significant edema (symptomatic ARIA-E) is observed in 3–6%. Concomitant use of anticoagulants is particularly dangerous—deaths from stroke and intracerebral hemorrhage were reported in the open-label extension phase.
- Exorbitant cost: The price is $26,500 per patient per year. If all eligible patients in the US received the therapy, drug costs would exceed $120 billion annually—more than is currently spent on all drugs under Medicare Part D.
Reactions of Key Players
Regulators: The response was paradoxical. The FDA (US) and MHRA (UK) approved the drug. However, the European Medicines Agency (EMA) and Australia's TGA initially refused, citing that risks outweigh potential benefits. The TGA specifically noted that the benefit is not clinically obvious for patients with more pronounced symptoms.
Scientific Community: Divided. On one hand, the German S3 guideline (March 2026) recommends the therapy for early stages, calling it "the first opportunity to treat the causes of Alzheimer's disease." On the other hand, the journal Neurology and a group of experts from 37 organizations express serious concern, comparing lecanemab to donepezil (standard symptomatic therapy), which is 100 times cheaper and safer.
Insurers and Healthcare System: The situation in Germany is telling. Despite the national guideline recommendation, the Gemeinsamer Bundesausschuss (G-BA) in February 2026 did not recognize additional benefit for lecanemab. Thus, physicians may prescribe the drug, but public insurers are not obligated to cover it. As Prof. Richard Dodel, guideline coordinator, notes, the IQWiG methodology (which assessed the drug) was too narrow—only a subgroup of 44% of patients was analyzed, making it statistically difficult to prove an effect.
Manufacturers (Eisai/Biogen): Unsurprisingly, they celebrate victory. Full FDA approval is a vote of confidence in their approach. They are already working on a subcutaneous formulation (instead of intravenous infusions every two weeks) and exploring use in patients with two copies of the APOE-ε4 gene (the highest risk group for ARIA).
Forecast and Conclusions
Where We Stand in 2026:
Lecanemab is the first swallow of a new era in Alzheimer's treatment. It does not cure but buys time—precious months of relatively independent living. Its efficacy (~27% slowing) has been confirmed in the largest high-quality study. However, the breakthrough has presented healthcare systems with a dilemma: how to pay for a very expensive therapy with moderate efficacy and non-trivial risks for a broad population?
Key Challenges Ahead:
- Patient targeting. The main task now is to accurately identify who will derive maximum benefit with minimal risk. Genetic testing for APOE-ε4 (carriers of two copies are excluded from therapy in many protocols) and screening using plasma p-tau217 are becoming standard.
- Price and access. The emergence of donanemab (possibly more effective but with a somewhat worse safety profile for ARIA-E) will create competition, which may affect pricing.
- Beyond amyloid. As review authors themselves acknowledge, we need to "continue exploring the complex pathology of Alzheimer's disease beyond amyloid clearance." Drugs targeting tau protein or inflammation are the future.
Conclusion: Lecanemab is a historic milestone and a reminder of the complexity of neurodegenerative diseases. It has opened the era of disease-modifying therapy for dementia, but we are only at the beginning. Patients and physicians can now choose treatment rather than just observation. However, for this choice to become a reality for the majority, we must solve challenges no less daunting than those faced by the drug developers—challenges of funding, logistics, and personalized therapy selection.
— Editorial Team
