2023: Lecanemab: First Clearly Effective Amyloid Drug (2023)
Lecanemab (Leqembi, Eisai and Biogen) received traditional FDA approval in July 2023—the first
anti-amyloid Alzheimer's therapy to receive traditional rather than accelerated approval—based on
demonstration of both amyloid reduction and statistically significant slowing of clinical decline
in the CLARITY AD Phase III trial. The result came two years after the controversial accelerated
approval of aducanumab and represented a pivotal, if partial, vindication of the amyloid cascade
hypothesis that had guided Alzheimer's drug development for over three decades.
Lecanemab is a humanised IgG1 monoclonal antibody with preferential binding to soluble amyloid-
beta protofibrils—high-molecular-weight oligomeric species thought to be particularly neurotoxic—
developed from a murine antibody (mAb158) generated by Lars Lannfelt's group at Uppsala University.
In CLARITY AD, 1,795 patients with early symptomatic Alzheimer's disease and confirmed amyloid
pathology were randomised to lecanemab 10 mg/kg intravenously biweekly or placebo. After 18 months,
the treatment group showed 27 % slowing on the CDR-SB (Clinical Dementia Rating-Sum of Boxes)
compared with placebo—a statistically significant and pre-specified primary endpoint.
The drug substantially cleared amyloid plaques on PET imaging and also reduced tau and
neurodegeneration biomarkers in cerebrospinal fluid, suggesting downstream effects on the
pathological cascade. However, 21 % of treated patients experienced amyloid-related imaging
abnormalities-oedema (ARIA-E) and 9 % experienced ARIA-H (haemorrhage), requiring intensive
MRI monitoring and raising safety concerns for patients on anticoagulants. Two deaths possibly
related to intracerebral haemorrhage in ARIA-H-positive patients on anticoagulants attracted
particular scrutiny.
The modest but statistically significant efficacy—representing a change of approximately 0.45
points on an 18-point scale—prompted debate about clinical meaningfulness and cost-effectiveness
at the $26,500 annual list price.
Pourquoi c'était important
Lecanemab became the first Alzheimer's therapy to demonstrate both amyloid clearance and
statistically significant slowing of clinical decline in a prospectively designed Phase III trial
under traditional approval standards, providing the strongest evidence to date for the amyloid
cascade hypothesis and establishing anti-amyloid immunotherapy as a disease-modifying class.
It also set the regulatory and monitoring template for subsequent agents—donanemab, remternetug—
advancing in the same mechanistic category.