Good News

New data presented at the 2025 CTAD conference bring good news for families facing early Alzheimer’s. Eisai and Biogen released long-term findings showing that continued LEQEMBI (lecanemab) treatment meaningfully slows disease progression, especially when started early.

8.3 Year Delay

Researchers analyzed outcomes from the Clarity AD extension study along with 16 clinical datasets. The results point to a powerful trend:

• Patients who begin treatment with lower amyloid levels experience the strongest benefit.
• In these early-stage patients, LEQEMBI may delay the shift from mild impairment to moderate Alzheimer’s by as much as 8.3 years.
• Sustained treatment creates significant “time savings,” slowing cognitive decline compared to those who remain untreated.

Easier Dosing

The update also highlighted promising progress on subcutaneous (SC) dosing, including the newly approved U.S. option that may make ongoing treatment more convenient than IV infusions.

Official Results

Estimating the 10-Year Time-Savings Benefits of Lecanemab Treatment (Presentation: December 3, 2:40 PM PT)

This analysis used data from the Clarity AD open-label extension (OLE) and 16 clinical studies of monoclonal antibodies for AD to estimate long-term AD progression over 10 years and the slowing effect of continued lecanemab treatment. The analysis evaluated estimated “time savings” (slowing of disease progression) compared to natural decline based on ADNI** (Alzheimer’s Disease Neuroimaging Initiative) data (untreated group), using Clinical Dementia Rating – Sum of Boxes (CDR-SB). These results suggest that early initiation and long-term lecanemab treatment may continue to slow AD progression and help maintain cognitive function over a longer period.

Findings from each group:

• Time Savings from Mild Cognitive Impairment (MCI) Due to AD to Mild AD
  • The time to progression from MCI due to AD to mild AD was 7.2 years in the untreated group, whereas with continued LEQEMBI treatment to the onset of moderate AD, progression to mild AD took 9.7 years, indicating a time savings of 2.5 years.
  • In the low-amyloid group (patients who started treatment at an early stage: amyloid PET <60 centiloids), the time to progression from MCI to mild AD was 13.2 years with continued LEQEMBI treatment to the onset of moderate AD, suggesting a time savings of 6.0 years.
• Time Savings from MCI due to AD to Moderate AD
  • The time to progression from MCI due to AD to moderate AD was 10.1 years in the untreated group, whereas with continued LEQEMBI treatment to the onset of moderate AD, progression to moderate AD took 13.6 years, indicating a time savings of 3.5 years.
  • In the low-amyloid group, the time to progression with continued LEQEMBI treatment to the onset of moderate AD was 18.4 years, suggesting a time savings of 8.3 years.

These findings indicate that earlier initiation of LEQEMBI treatment may provide a greater delay in disease progression. Furthermore, each additional year on LEQEMBI could further delay disease progression compared to stopping treatment, even long after plaque is expected to have been cleared.

Lecanemab Subcutaneous Formulation

For Treatment Initiation in Early Alzheimer’s Disease: Optimizing Patient Care with a Potential New Option (Symposium Presentation: December 3, 3:10 PM PT)

In this symposium, the latest data from the lecanemab subcutaneous clinical development program were presented focusing on treatment initiation, including results from the subcutaneous (SC) formulation subcohort (n=273) in the Clarity AD trial OLE. It was shown that weekly administration of lecanemab SC-AI at 500 mg (two 250 mg injections) demonstrated bioequivalence in drug exposure compared to intravenous (IV) dosing of 10 mg/kg every two weeks (exposure ratio: 104%, 90% CI: 99.1%–109%).

Amyloid Removal

Based on clinical data and modeling analysis, the effect on amyloid removal in the brain and safety (ARIA-E incidence) was shown to be independent of the route of administration and explained by exposure, suggesting that weekly 500 mg SC dosing provides similar efficacy and safety to biweekly 10 mg/kg IV dosing. Additionally, ARIA-E incidence was also predicted to be comparable between SC and IV administration (12.4% overall, 30.9% in ApoE4 homozygotes).

In this sub-cohort which had prior exposure to lecanemab, safety evaluation showed systemic infusion reactions occurred in 0% of patients receiving 500 mg SC, all of whom had previously received IV lecanemab, and 1.4% of patients who initiated on 720 mg SC by vial, which is favorable compared to systemic infusion reactions in the IV group (26.4%). Immunogenicity assessment indicated a low incidence of anti-drug antibodies (ADA) at 1.4%.

These results indicate that the subcutaneous formulations of lecanemab, designed with consideration for the convenience of patients and their care partners, maintains efficacy with a low incidence of systemic infusion reactions, and is otherwise equivalent to conventional IV administration.