LEQEMBI(R) Real-World LEADER Study Presented at AAIC(R) 2026 Finds Over 75% of Early Alzheimer's Patients Enrolled in the Study Remained Stable and Nearly 7% Improved Over an Average of 17 Months of Treatment

TOKYO and CAMBRIDGE, Mass., July 15, 2026 - (JCN Newswire) - Eisai Co., Ltd. and Biogen Inc. (Nasdaq: BIIB) announced today that results from the real-world Lecanemab in Early Alzheimer's Disease (LEADER) Study show that nearly 83% of early Alzheimer’s disease (AD) patients enrolled in the study remained stable (75.9%) or improved (6.6%) while receiving LEQEMBI® therapy over an average of 17 months. The results were consistent across sex, race, ethnicity and APOE genotype. The data was presented during the “Developing Topics Session #3-33-DEV-A: Lecanemab Three Years Post-Approval: A Comprehensive Multicenter, Real-World, Retrospective Study (LEADER) in Diverse US Clinical Settings” at the Alzheimer’s Association International Conference® (AAIC®) 2026 in London and online.

AD is a chronic, progressive disease that requires ongoing treatment. LEQEMBI targets the underlying pathology of the disease and works in two ways throughout treatment - by removing insoluble (plaque) and soluble amyloid beta (protofibrils), helping to slow cognitive decline and loss of daily functioning. Data show continued treatment with LEQEMBI may be able to help keep patients in early AD for longer. Early AD includes mild cognitive impairment (MCI) due to AD and mild AD dementia.

LEADER Study Design

The three-year LEADER Study is a multicenter, retrospective real-world study designed to examine LEQEMBI utilization, treatment persistence, transition to maintenance therapy, safety, cognitive and functional assessments, and healthcare professional (HCP) implementation learnings in diverse U.S. clinical settings for patients with early Alzheimer's disease (AD). The study integrated deidentified chart and electronic medical record (EMR) data from 13 U.S. sites, HCP surveys and HCP interviews. This interim analysis included 432 patients with early AD who received at least seven LEQEMBI infusions as of May 2026.

Patient Characteristics at Baseline
* Mean age: 74 years
* Female Patients: 55.8%

Disease Stage at Baseline
* Mild cognitive impairment (MCI) due to AD: 63.9%
* Mild AD dementia: 36.1%.

Treatment
* The mean duration of LEQEMBI treatment was 520 days.• The mean number of LEQEMBI doses was 26.
* Change in disease stage was defined as:
- Stable - Patient remaining in the same disease stage (MCI due to AD or mild AD dementia)from baseline throughout the course of LEQEMBI treatment.
- Improvement - Patient transitioning from mild AD dementia at baseline to MCI due to AD overthe course of LEQEMBI treatment.
- Progression - Patient advancing from MCI at baseline to mild/moderate AD dementia or from mild AD dementia at baseline to moderate AD dementia throughout the course of LEQEMBI treatment.

LEADER Study Key Findings

Real-World Evidence Shows Long-Term Benefit with Continuous LEQEMBI Treatment Across Sex,Race, Ethnicity and APOE Genotype

Overall Study Population Findings
* Of the 432 participants enrolled in the LEADER study, disease stage could be evaluated in 427. Among these patients with early Alzheimer's disease, 82.5% remained stable or improved while receiving LEQEMBI, with consistent results across sex, race, ethnicity, and APOE genotypegroups.
* 75.9% remained stable compared with baseline, meaning they remained in the same disease stagethroughout treatment.
* 6.6% improved from baseline, moving from mild AD dementia to MCI due to AD.
* Nearly 87% of patients chose to remain on LEQEMBI treatment.
* In analyses by APOE ε4 status, clinician-evaluated stable or improved disease stage was observed in:
- 81.7% of APOE ε4 heterozygotes (stable: 73.8.%; improved: 7.9%)
- 81.0% of APOE ε4 homozygotes (stable: 75.9%; improved: 5.2%).

Maintenance Dosing Population Findings
• Of the 432 participants in the LEADER study, 155 transitioned to once-every-four-weeks intravenous(IV) maintenance treatment, and 14 transitioned to once-weekly subcutaneous (SC) maintenance treatment.
• Among the 155 participants who transitioned to IV maintenance therapy, nearly 81% remained stable(72.3%) or improved (8.4%).
• Of the 14 patients who transitioned to SC maintenance treatment, 12 (85.7%) maintained their disease stage.

Real-World Safety Consistent with U.S. FDA-Approved Label

Overall safety observations in this real-world study were consistent with the U.S. FDA-approved label.
• ARIA (amyloid-related imaging abnormalities)* was observed in 12.3% of patients overall; ARIA-E was observed in 6.3% and ARIA-H in 7.9% and isolated ARIA-H in 6.0%. Most ARIA cases were asymptomatic and mild in radiographic severity.
• No new ARIA-E events, macrohemorrhages or intracerebral hemorrhages greater than 1 cm were reported during once-every-four-weeks IV maintenance therapy.

APOE ε4 status safety observations were consistent with the overall cohort and the U.S. FDA-approved label.
• ARIA-E was observed in 5.3% of APOE ε4 noncarriers, 6.1% of APOE ε4 heterozygotes and 10.3%of APOE ε4 homozygotes.
• ARIA-H was observed in 12.1%, 4.8% and 12.1%, respectively.
• In APOE ε4 homozygotes, no severe ARIA was reported, and all graded ARIA cases were mild to moderate in radiographic severity.

Antithrombotic therapy, including anticoagulants or antiplatelet medications, was used by 106 patients, representing 24.5% of the study population.
• Of these, 11 patients were receiving an anticoagulant, either alone or with an antiplatelet medication, and 95 patients were receiving antiplatelet therapy only.
• Among patients receiving antithrombotic therapy, the incidence of ARIA was not meaningfully different from that observed in patients not receiving antithrombotic therapy.

* ARIA refers to amyloid-related imaging abnormalities that can be observed with anti-amyloid beta antibody treatment and includes ARIA-E, which involves edema/effusion, and ARIA-H, which involves hemosiderin deposition, including cerebral microhemorrhage, cerebral macrohemorrhage and superficial siderosis, as observed on brain magnetic resonance imaging (MRI).

Eisai serves as the lead for lecanemab’s development and regulatory submissions globally with Eisai and Biogen co-commercializing and co-promoting the product and Eisai having final decision-making authority.

MEDIA CONTACTS
Eisai Co., Ltd.
Public Relations Department
TEL: +81 (0)3-3817-5120

Eisai Europe, Ltd.
EMEA Communications Department
+44 (0)7760 619251
Emea-comms@eisai.net

Eisai Inc. (U.S.)
Julie Edelman
+1-862-213-5915
Julie_Edelman@eisai.com

Biogen Inc.
Madeleine Shin
+1-781-464-3260
public.affairs@biogen.com

INVESTOR CONTACTS

Eisai Co., Ltd.
Investor Relations Department
TEL: +81 (0) 3-3817-5122

Biogen Inc.
Tim Power
+ 1-781-464-2442
IR@biogen.com

For more information: https://www.eisai.com/news/2026/pdf/enews202641pdf.pdf