June 8, 2023

EISAI FILES MARKETING AUTHORIZATION APPLICATION FOR LECANEMAB AS
TREATMENT FOR EARLY ALZHEIMER’S DISEASE IN SOUTH KOREATOKYO and CAMBRIDGE, Mass., June 8, 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 Eisai has submitted a marketing
authorization application for lecanemab (brand name in the U.S.: LEQEMBI®), an investigational antiamyloid beta (Aβ) protofibril* antibody, for the treatment of early Alzheimer’s disease (mild cognitive
impairment due to Alzheimer’s disease (AD) and mild AD dementia) with confirmed amyloid pathology
in the brain, to the Ministry of Food and Drug Safety (MFDS) in South Korea. This application is the first
application for lecanemab in Asia outside of Japan and China. Eisai plans to submit additional
applications in other Asian countries.
The application is based on the results of the confirmatory Phase III Clarity AD study and Phase IIb clinicalstudy (Study 201), which demonstrated that lecanemab treatment showed a reduction of clinical decline inearly AD. Lecanemab selectively binds to and eliminates soluble, toxic Aβ aggregates (protofibrils) thatare thought to contribute to the neurotoxicity in AD. As such, lecanemab may have the potential to havean effect on disease pathology and to slow down the progression of the disease. The Clarity AD studyof lecanemab met its primary endpoint and all key secondary endpoints with highly statisticallysignificant results.
Eisai serves as the lead of lecanemab development and regulatory submissions globally with both Eisaiand Biogen co-commercializing and co-promoting the product and Eisai having final decision-making
authority.
* Protofibrils are large Aβ aggregated soluble species of 75-5000 Kd.1
1 Söderberg, L., Johannesson, M.,

Nygren, P. et al. Lecanemab, Aducanumab, and Gantenerumab - Binding
Profiles to Different Forms of Amyloid-Beta Might Explain Efficacy and Side Effects in Clinical Trials for Alzheimer’sDisease. Neurotherapeutics (2022). https://doi.org/10.1007/s13311-022-01308-6. Accessed February 9, 2023

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

MEDIA CONTACT:
Biogen Inc.
Jack Cox+1-781-464-3260
public.affairs@biogen.com

Eisai Inc. (U.S.)
Libby Holman
TEL: + 1-201-753-1945
Libby Holman@eisai.com

INVESTOR CONTACT:
Biogen Inc.
Chuck Triano+1-781-464-2442
IR@biogen.com

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

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[Notes to editors]
1. About Lecanemab
Lecanemab (Brand Name in the U.S.: LEQEMBI®) is the result of a strategic research alliance between
Eisai and BioArctic. Lecanemab is a humanized immunoglobulin gamma 1 (IgG1) monoclonal antibody
directed against aggregated soluble (protofibril) and insoluble forms of amyloid-beta (Aβ).
In the U.S., LEQEMBI was launched after being granted accelerated approval by the U.S. Food andDrug Administration (FDA) in January, 2023. LEQEMBI is indicated for the treatment of Alzheimer’s
disease (AD). 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. Thereare no safety or effectiveness data on initiating treatment at earlier or later stages of the disease thanwere studied. The accelerated approval is based on Phase II data which demonstrated that LEQEMBI
reduced the accumulation of Aβ plaque in the brain, a defining feature of AD, and its continued approval
may be contingent upon verification of clinical benefit in a confirmatory trial. The FDA determined thatthe results of Clarity AD can serve as the confirmatory study to verify the clinical benefit of LEQEMBI.
Eisai submitted a supplemental Biologics License Application (sBLA) to the FDA for approval under thetraditional pathway in January, 2023. The FDA accepted Eisai’s sBLA granted Priority Review, with aPrescription Drug User Fee Act (PDUFA) action date of July 6, 2023. The FDA is planning to hold an
Advisory Committee to discuss this application on June 9, 2023.
Please see full Prescribing Information in the United States.
Eisai has also submitted applications for approval in Japan, Europe, China, Canada, and Great Britain.
In Japan and China, the applications have been designated for priority review, and in Great Britain,
lecanemab has been designated for the Innovative Licensing and Access Pathway (ILAP), which aims
to reduce the time to market for innovative medicines.
Eisai has completed the lecanemab subcutaneous bioavailability study, and subcutaneous dosing iscurrently 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 clinically normal and have intermediate or elevated levels of amyloid in their brains, is ongoing.
AHEAD 3-45 is conducted as a public-private partnership between the Alzheimer’s Clinical Trial
Consortium (ACTC) that provides the infrastructure for academic clinical trials in AD and relateddementias in the U.S, funded by the National Institute on Aging, part of the National Institutes of Health,Eisai and Biogen. The Tau NexGen clinical study for Dominantly Inherited AD (DIAD), that is conductedby Dominantly Inherited Alzheimer Network Trials Unit (DIAN-TU), led by Washington University Schoolof Medicine in St. Louis, has been ongoing since January 2022.
2. About the Collaboration between Eisai and Biogen for ADEisai 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 co-commercializing and co-promoting the product and Eisai having final
decision-making authority.

23. About the Collaboration between Eisai and BioArctic for AD
Since 2005, Eisai and BioArctic have had a long-term collaboration regarding the development andcommercialization of AD treatments. Eisai obtained the global rights to study, develop, manufacture
and market lecanemab for the treatment of AD pursuant to an agreement with BioArctic in December
2007. The development and commercialization agreement on the antibody lecanemab back-up wassigned 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, andto increase the benefits that health care provides.” Under this Concept (also known as human healthcare (hhc) Concept), we aim to effectively achieve social good in the form of relieving anxiety overhealth and reducing health disparities. With a global network of R&D facilities, manufacturing sites andmarketing subsidiaries, we strive to create and deliver innovative products to target diseases with highunmet medical needs, with a particular focus in our strategic areas of Neurology and Oncology.
In addition, our continued commitment to the elimination of neglected tropical diseases (NTDs), which
is a target (3.3) of the United Nations Sustainable Development Goals (SDGs), is demonstrated by ourwork on various activities together with global partners.
For more information about Eisai, please visit www.eisai.com (for global headquarters: Eisai Co., Ltd.),and connect with us on Twitter, LinkedIn and Facebook.
5. About Biogen
Founded in 1978, Biogen is a leading global biotechnology company that has pioneered multiple
breakthrough innovations 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 is advancing a pipeline of potential novel therapies acrossneurology, neuropsychiatry, specialized immunology and rare diseases and remains acutely focusedon its purpose of serving humanity through science while advancing a healthier, more sustainable andequitable 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 thesafe harbor provisions of the Private Securities Litigation Reform Act of 1995, about the potential clinicaleffects of lecanemab; the potential benefits, safety and efficacy of lecanemab; potential regulatory
discussions, submissions and approvals and the timing thereof; the treatment of Alzheimer’s disease;
the anticipated benefits and potential of Biogen’s collaboration arrangements with Eisai; the potentialof Biogen’s commercial business and pipeline programs, including lecanemab; and risks anduncertainties 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. Drugdevelopment and commercialization involve a high degree of risk, and only a small number of research

3and development programs result in commercialization of a product. Results in early-stage clinicalstudies may not be indicative of full results or results from later stage or larger scale clinical studies anddo not ensure regulatory approval. You should not place undue reliance on these statements or thescientific data presented.
These statements involve risks and uncertainties that could cause actual results to differ materially fromthose reflected in such statements, including without limitation unexpected concerns that may arise
from additional data, analysis or results obtained during clinical studies, including the Clarity AD clinical
trial and AHEAD 3-45 study; the occurrence of adverse safety events; risks of unexpected costs ordelays; the risk of other unexpected hurdles; regulatory submissions may take longer or be more difficult
to complete than expected; regulatory authorities may require additional information or 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 potentialcommercialization of lecanemab; failure to protect and enforce Biogen’s data, intellectual property andother proprietary rights and uncertainties relating to intellectual property claims and challenges; productliability claims; third party collaboration risks; and the direct and indirect impacts of the ongoing COVID19 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 therisk 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 speak only as of the dateof this press release. We do not undertake any obligation to publicly update any forward-looking
statements.
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