ADDITIONAL DETAILED ANALYSES FROM PHASE 2 STUDY 201 OF LECANEMAB PUBLISHED AS
THREE PAPERS IN PEER-REVIEWED JOURNALSTOKYO and CAMBRIDGE, Mass., March 31, 2023 – Eisai Co., Ltd. (Headquarters: Tokyo, CEO: HaruoNaito, "Eisai") and Biogen Inc. (Nasdaq: BIIB, Corporate headquarters: Cambridge, Massachusetts, CEO:Christopher A. Viehbacher, "Biogen") announced today that three additional detailed analyses from thePhase IIb clinical study (Study 201), evaluating the efficacy and safety of lecanemab for mild cognitive
impairment (MCI) due to Alzheimer’s disease (AD) and mild AD (collectively known as early AD), were
published in the peer-reviewed journals.
1. Detailed results on biomarker, cognitive, and clinical effects from Study 201 core to OLE (open-labelextension): Alzheimer's Research and Therapy
2. Consistency of efficacy results across various clinical measures and statistical methods in Study 201:
Alzheimer's Research and Therapy
3. ARIA (amyloid-related imaging abnormality) profile in Study 201: Alzheimer's & Dementia: Translational
Research and Clinical Interventions
Study 201 was a multicenter, double-blind, placebo-controlled, Phase 2b trial conducted in 856 patientswith early AD. Its core study evaluated key efficacy assessments, including clinical change on the AD
Composite Score (ADCOMS) as the primary endpoint at 12 months and as key secondary endpoints,ADCOMS, Clinical Dementia Rating-Sum-of-Boxes (CDR-SB) and AD Assessment Scale-Cognitive
Subscale 14 (ADAS-Cog14) at 18 months. Following analysis of the 18-month core phase, an intervening
off-treatment period (gap period) ranging from 9-59 months (mean 24 months) was taken, which wasfollowed by an OLE with 10 mg/kg IV bi-weekly lecanemab dosing to assess long-term safety and tolerability.
The results of the primary analysis in the core study including clinical efficacy and biomarkers have alreadybeen published, showing a consistent reduction in clinical decline across several clinical and biomarker
endpoints with lecanemab 10 mg/kg bi-weekly dosing.
1. Detailed results on biomarker, cognitive, and clinical effects from Study 201.
“Lecanemab in patients with early Alzheimer’s disease: detailed results on biomarker, cognitive, and clinicaleffects from the randomized and open‑label extension of the phase 2 proof‑of‑concept study”
In the core 201 study, lecanemab was shown to reduce brain Aβ accumulation measured by amyloid PET
in a dose- and time-dependent manner after 12 and 18 months of treatment, and corresponding changes
in plasma biomarkers and reduction in clinical decline. During the gap period, a trend was observed forplasma Aβ42/40 ratio and p-tau181 values to return to the pre-administration levels (re-accumulation) fasterthan amyloid PET.
In the OLE, lecanemab 10 mg/kg biweekly treatment showed a decrease in brain amyloid beta (Aβ)

accumulation measured by amyloid PET, a decrease in the plasma Aβ42/40 ratio, and a decrease in1

plasma p-tau181.
The potential for disease modification with lecanemab is supported by an increasing difference in clinicalmeasures between the lecanemab group and placebo group in line with time during the core period,
differences in clinical progression between subjects who received 10 mg/kg lecanemab and those who
received placebo in the core period, which remained persistent throughout the gap period, and an impact
on biological measures that reflect key pathophysiological changes in AD. Furthermore, the results showed
the potential for monitoring the treatment effects of lecanemab using plasma biomarkers.
2. Consistency of efficacy results across various clinical measures and statistical methods in Study
201.
“Consistency of efficacy results across various clinical measures and statistical methods in the lecanemab
phase 2 trial of early Alzheimer’s disease”
In order to assess the robustness of lecanemab's efficacy in Study 201, sensitivity analyses were performed
using several statistical models for three key clinical endpoints (ADCOMS, CDR-SB, ADAS-Cog14). The
sensitivity analysis showed that 18 months of lecanemab treatment consistently reduced the clinical decline inall statistical models examined. The results of all sensitivity analyses for three key clinical endpoints at the highest
dose (10 mg/kg bi-weekly) at 18 months were consistent, with a 29.1% to 37.4% reduction in clinical deterioration
with lecanemab compared to placebo for ADCOMS, 26.5% to 38.4% for CDR-SB and 37.4% to 55.9% for ADASCog14.
3. ARIA profile in Study 201“ARIA in patients treated with lecanemab (BAN2401) in a phase 2 study in early Alzheimer’s disease”
In the core study 201, amyloid-related imaging abnormalities-edema (ARIA-E) was dose dependent, with anincidence 9.9% at the highest doses (10 mg/kg bi-weekly) for the overall population and 14.3% for ApoE4
positive subjects. Most ARIA-E occurred within 30 days after the initial dose and had mild to moderate severityin radiographic severity. Symptomatic ARIA-E occurred in 3% of participants in the 10mg/kg bi-weekly treatmentgroup. ARIA cerebral microhemorrhages, intracerebral hemorrhage >1cm, and superficial siderosis (ARIA-H)
occurred in 6.2% of subjects who received 10 mg/kg biweekly lecanemab and those events were mostly mild inseverity. There were no symptomatic cases of ARIA-H reported in the core study.
Overall ARIA-E events in the OLE phase were generally consistent with the rate seen in the lecanemab 10 mg/kg
biweekly group in the core study (four subjects treated with placebo in the core study had ARIA-E in the OLE (4of 45: 8.9%). As with the core study, most ARIA-E occurred within 3 months after receiving the initial dose in theOLE and had mostly mild to moderate in radiographic severity. ARIA-H events in the OLE were generally
consistent with the rate seen in the lecanemab 10 mg/kg biweekly group in the core study. ARIA-H events weremostly mild or moderate in severity. One symptomatic case of ARIA-H, intracerebral hemorrhage > 1cm, wasreported in OLE. This subject did not have concurrent ARIA-E, and the adverse event resolved with residual
visual field defect.
PK/PD modeling showed that the incidence of ARIA-E was correlated with Cmax at steady state.
Based on the fact that lecanemab was generally well tolerated at the highest dose in this study, the Phase 3
Clarity AD study was conducted without dose titration. A subcutaneous formulation that may potentially reduce2the Cmax of lecanemab is being developed and evaluated to determine if there is a reduction of the incidenceof ARIA-E compared to intravenous formulation.
Eisai serves as the lead of lecanemab development and regulatory submissions globally with both Eisai
and Biogen co-commercializing and co-promoting the product and Eisai having final decision-making
authority.
To learn more, visit www.LEQEMBI.com.

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

MEDIA CONTACT:
Biogen Inc.
Natacha Gassenbach+ 1-857-777-6573public.affairs@biogen.com

Eisai Inc. (U.S.)
Libby Holman+ 1-201-753-1945
Libby_Holman@eisai.com
Eisai Europe, Ltd.
(UK, Europe, Australia, New Zealand andRussia)
EMEA Communications Department+44 (0) 786 601 1272
EMEA-comms@eisai.net
INVESTOR CONTACT:
Eisai Co., Ltd.
Investor Relations Department
TEL: +81 (0) 3-3817-5122

INVESTOR CONTACT:Biogen Inc.
Mike Hencke+ 1-781-464-2442
IR@biogen.com[Notes to editors]
1. About Lecanemab
Lecanemab (Brand Name in the U.S.: LEQEMBI™) is the result of a strategic research alliance between Eisai andBioArctic. Lecanemab is a humanized immunoglobulin gamma 1 (IgG1) monoclonal antibody directed against
aggregated soluble (protofibril) and insoluble forms of amyloid-beta (Aβ). Lecanemab selectively binds and eliminates
Aβ protofibrils that are thought to contribute to the neurotoxicity in AD. As such, lecanemab may have the potential tohave an effect on disease pathology and to slow down the progression of the disease. LEQEMBI is indicated for thetreatment of Alzheimer’s disease (AD) in the U.S. under an accelerated approval by the U.S. Food and Drug
Administration (FDA). Treatment with LEQEMBI should be initiated in patients with mild cognitive impairment or mild
dementia stage of disease, the population in which treatment was initiated in clinical trials. There are no safety oreffectiveness data on initiating treatment at earlier or later stages of the disease than were studied. This indication isapproved under accelerated approval based on reduction in Aβ plaques observed in patients treated with LEQEMBI.
Continued approval for this indication may be contingent upon verification of clinical benefit in a confirmatory trial. The
Clarity AD study of lecanemab met its primary endpoint and all key secondary endpoints with highly statisticallysignificant results.
Please see full Prescribing Information in the United States.

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Lecanemab-irmb was approved under the accelerated approval pathway in the U.S. and was launched in the U.S. onJanuary 18, 2023. The accelerated approval was based on Phase 2 data that demonstrated that lecanemab reduced
the accumulation of Aβ plaque in the brain, a defining feature of AD, and its continued approval may be contingent
upon verification of lecanemab’s clinical benefit in a confirmatory trial. The FDA determined that the results of the Phase
3 Clarity AD study can serve as the confirmatory study to verify the clinical benefit of lecanemab. In November 2022,
the results of Clarity AD study were presented at the Clinical Trials on Alzheimer's Disease (CTAD) conference andsimultaneously published in the peer-reviewed medical journal, The New England Journal of Medicine.
In the U.S., Eisai submitted a supplemental Biologics License Application (sBLA) to the FDA for approval under thetraditional pathway on January 6, 2023. On March 3, 2023, the FDA accepted Eisai’s sBLA based on the Clarity AD
clinical data, and the lecanemab application has been granted Priority Review, with a Prescription Drug User Fee Act(PDUFA) action date of July 6, 2023. The FDA is currently planning to hold an Advisory Committee to discuss thisapplication but has not yet publicly announced the date of the meeting. Eisai submitted an application for manufacturingand marketing approval to the Pharmaceuticals and Medical Devices Agency (PMDA) on January 16, 2023, in Japan.
The Priority Review was granted by the Ministry of Health, Labour and Welfare (MHLW) on January 26, 2023. Eisai
utilized the prior assessment consultation system of PMDA, with the aim of shortening the review period for lecanemab.
In Europe, Eisai submitted a marketing authorization application (MAA) to the European Medicines Agency (EMA) onJanuary 9, 2023, which was accepted on January 26, 2023. In China, Eisai initiated submission of data for a BLA to
the National Medical Products Administration (NMPA) of China in December 2022, and the Priority Review was grantedon February 27, 2023 .
Eisai has completed a lecanemab subcutaneous bioavailability study, and subcutaneous dosing is currently being
evaluated in the Clarity AD OLE.
Since July 2020 the Phase 3 clinical study (AHEAD 3-45) for individuals with preclinical AD, meaning they are clinicallynormal and have intermediate or elevated levels of amyloid in their brains, has been ongoing. AHEAD 3-45 is conducted
as a public-private partnership between the Alzheimer’s Clinical Trial Consortium that provides the infrastructure foracademic clinical trials in AD and related dementias in the U.S., funded by the National Institute on Aging, part of theNational Institutes of Health, Eisai and Biogen.
Since January 2022, the Tau NexGen clinical study for Dominantly Inherited AD (DIAD), that is conducted by theDominantly Inherited Alzheimer Network Trials Unit (DIAN-TU), led by Washington University School of Medicine in St.
Louis, has been ongoing.
2. About the Collaboration between Eisai and Biogen for AD
Eisai and Biogen have been collaborating on the joint development and commercialization of AD treatments since 2014.
Eisai serves as the lead of lecanemab development and regulatory submissions globally with both companies cocommercializing and co-promoting the product and Eisai having final decision-making authority.
3. About the Collaboration between Eisai and BioArctic for AD
Since 2005, Eisai and BioArctic have had a long-term collaboration regarding the development and commercializationof AD treatments. Eisai obtained the global rights to study, develop, manufacture and market LEQEMBI for thetreatment of AD pursuant to an agreement with BioArctic in December 2007. The development and commercializationagreement on the antibody LEQEMBI back-up was signed in May 2015.
4. About Eisai Co., Ltd.
Eisai's Corporate Concept is "to give first thought to patients and people in the daily living domain, and to increase thebenefits that health care provides." Under this concept (also known as the human health care [hhc] concept), we aim
to effectively achieve social good in the form of relieving anxiety over health and reducing health disparities. With a
global network of R&D facilities, manufacturing sites and marketing subsidiaries, we strive to create and deliver
innovative products to target diseases with high unmet medical needs, with a particular focus in our strategic areas ofneurology and oncology.
In addition, we demonstrate our commitment to the elimination of neglected tropical diseases (NTDs), which is a target(3.3) of the United Nations Sustainable Development Goals (SDGs), by working on various activities together withglobal partners.
For more information about Eisai, please visit www.eisai.com (for global headquarters: Eisai Co., Ltd.), and connect
with us on Twitter @Eisai_SDGs.

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5. About Biogen
Founded in 1978, Biogen is a leading global biotechnology company that has pioneered multiple breakthroughinnovations including a broad portfolio of medicines to treat multiple sclerosis, the first approved treatment for spinal
muscular atrophy, and two co-developed treatments to address a defining pathology of Alzheimer’s disease. Biogen isadvancing a pipeline of potential novel therapies across neurology, neuropsychiatry, specialized immunology and rarediseases and remains acutely focused on its purpose of serving humanity through science while advancing a healthier,more sustainable and equitable world.
The company routinely posts information that may be important to investors on its website at www.biogen.com. Follow
Biogen on social media – Twitter, LinkedIn, Facebook, YouTube.
Biogen Safe Harbor
This news release contains forward-looking statements, including statements made pursuant to the safe harborprovisions of the Private Securities Litigation Reform Act of 1995, about the potential clinical effects of lecanemab; thepotential benefits, safety and efficacy of lecanemab; potential regulatory discussions, submissions and approvals andthe timing thereof; the treatment of Alzheimer's disease; the anticipated benefits and potential of Biogen's collaboration
arrangements with Eisai; the potential of Biogen's commercial business and pipeline programs, including lecanemab;
and risks and uncertainties associated with drug development and commercialization. These statements may be
identified by words such as "aim," "anticipate," "believe," "could," "estimate," "expect," "forecast," "intend," "may,""plan," "possible,"" "potential," "will," "would" and other words and terms of similar meaning. Drug development andcommercialization involve a high degree of risk, and only a small number of research and development programs result
in commercialization of a product. Results in early-stage clinical studies may not be indicative of full results or resultsfrom later stage or larger scale clinical studies and do not ensure regulatory approval. You should not place undue
reliance on these statements or the scientific data presented.
These statements involve risks and uncertainties that could cause actual results to differ materially from those reflectedin such statements, including without limitation unexpected concerns that may arise from additional data, analysis orresults obtained during clinical studies, including the Clarity AD clinical trial and AHEAD 3-45 study; the occurrence ofadverse safety events; risks of unexpected costs or delays; the risk of other unexpected hurdles; regulatory submissions
may take longer or be more difficult to complete than expected; regulatory authorities may require additional informationor further studies, or may fail or refuse to approve or may delay approval of Biogen's drug candidates, including
lecanemab; actual timing and content of submissions to and decisions made by the regulatory authorities regarding
lecanemab; uncertainty of success in the development and potential commercialization of lecanemab; failure to protect
and enforce Biogen's data, intellectual property and other proprietary rights and uncertainties relating to intellectual
property claims and challenges; product liability claims; third party collaboration risks; and the direct and indirect
impacts of the ongoing COVID-19 pandemic on Biogen's business, results of operations and financial condition. The
foregoing sets forth many, but not all, of the factors that could cause actual results to differ from Biogen's expectationsin any forward-looking statement. Investors should consider this cautionary statement as well as the risk factors
identified in Biogen's most recent annual or quarterly report and in other reports Biogen has filed with the U.S. Securities
and Exchange Commission. These statements are based on Biogen's current beliefs and expectations and speak only
as of the date of this news release. Biogen does not undertake any obligation to publicly update any forward-looking
statements, whether as a result of new information, future developments or otherwise.

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