LEQEMBI® (Lecanemab) Approved for the Treatment of Alzheimer’s Disease in Australia

Rhea-AI Summary

Biogen (NASDAQ:BIIB) and Eisai announced that Australia's Therapeutic Goods Administration (TGA) has approved LEQEMBI® (lecanemab) for the treatment of early Alzheimer's disease. The approval specifically targets adults with mild cognitive impairment or mild dementia who are either ApoEε4 non-carriers or heterozygous carriers.

The approval follows a review process initiated in March 2025 after an initial rejection in February 2025. LEQEMBI uniquely targets both toxic protofibrils and amyloid plaque, potentially impacting tau downstream. This approval is particularly significant as Australia faces growing dementia cases, with numbers expected to rise from 425,000 in 2024 to approximately 1,100,000 by 2065.

Positive

• None.

Negative

• Limited approval to specific genetic populations (ApoEε4 non-carriers or heterozygous carriers)
• Known side effect of ARIA (brain swelling and potential bleeding)
• Initial regulatory rejection required additional review process

Insights

Biotech & Healthcare Analyst

Australia's approval of LEQEMBI for early Alzheimer's expands Biogen/Eisai's market reach in a region with growing dementia prevalence.

The TGA's approval of LEQEMBI (lecanemab) in Australia represents a significant regulatory milestone for Eisai and Biogen after an initial rejection in February 2025. This approval specifically targets adults with mild cognitive impairment or mild dementia due to Alzheimer's disease who are either ApoEε4 non-carriers or heterozygous carriers – a precisely defined patient population reflecting safety considerations around ARIA (amyloid-related imaging abnormalities).

The approval unlocks a substantial market opportunity in Australia, where approximately 425,000 people were living with dementia in 2024, projected to increase to nearly 1.1 million by 2065. With Alzheimer's typically accounting for 60-70% of dementia cases, this represents a significant potential patient population.

What makes LEQEMBI particularly notable is its dual mechanism of action – targeting both toxic protofibrils (considered the most harmful form of amyloid beta) and amyloid plaque, potentially affecting downstream tau pathology. This mechanistic approach addresses multiple aspects of Alzheimer's pathophysiology, differentiating it from earlier treatments.

The approval follows an Administrative Review Tribunal process initiated after the TGA's initial rejection, demonstrating Eisai's persistence in securing market access. While financial terms and pricing weren't disclosed, this approval enables Eisai and Biogen to tap into the Australian healthcare market under their established collaboration, where Eisai leads development and has final decision-making authority, with both companies sharing commercialization responsibilities.

TOKYO and CAMBRIDGE, Mass., Sept. 24, 2025 (GLOBE NEWSWIRE) -- Eisai Co., Ltd. (Headquarters: Tokyo, CEO: Haruo Naito, “Eisai”) and Biogen Inc. (Nasdaq: BIIB, Corporate headquarters: Cambridge, Massachusetts, CEO: Christopher A. Viehbacher, “Biogen”) announced today that the Therapeutic Goods Administration (TGA) of Australia has approved the humanized anti-soluble aggregated amyloid-beta (Aβ) monoclonal antibody “LEQEMBI^®” (brand name, generic name: lecanemab) for mild cognitive impairment (MCI) or mild dementia due to Alzheimer's disease (AD) (collectively referred to as early AD) in adults who are either ApoEε4* non-carriers or heterozygous carriers.

In response to February 2025 TGA decision not to approve lecanemab as a treatment for people with early AD, in March 2025, Eisai requested a review by the Administrative Review Tribunal. As a result of discussions during this process, the TGA and Eisai reached an agreement that led to the approval of LEQEMBI.

In Australia, the number of people living with dementia was estimated to be approximately 425,000 in 2024, and is reported to increase to nearly 1,100,000 by 2065.¹ AD is considered the most common cause of dementia, typically accounting for 60-70% of cases.² AD is a progressive, relentless disease with amyloid beta (Aβ) and tau as hallmarks that is caused by a continuous underlying neurotoxic process that begins before amyloid plaque removal and continues afterward.^3,4,5 Only LEQEMBI fights AD in two ways – targeting both the toxic protofibrils** and amyloid plaque ², which can impact tau downstream.

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.

* Apolipoprotein E is a protein involved in the metabolism of fats in humans. It is implicated in AD. People with only one (heterozygous) or no copy (non-carriers) of the ApoE ε4 gene are less likely to experience ARIA than people with two ApoE ε4 copies (homozygous).² ARIA is a recognized important side effect with lecanemab that involves swelling and potential bleeding in the brain.^6,7

** Protofibrils are believed to contribute to the brain injury that occurs with AD and are considered to be the most toxic form of Aβ, having a primary role in the cognitive decline associated with this progressive, debilitating condition.³ Protofibrils cause injury to neurons in the brain, which in turn, can negatively impact cognitive function via multiple mechanisms, not only increasing the development of insoluble Aβ plaques but also increasing direct damage to brain cell membranes and the connections that transmit signals between nerve cells or nerve cells and other cells. It is believed the reduction of protofibrils may prevent the progression of AD by reducing damage to neurons in the brain and cognitive dysfunction.⁴

MEDIA CONTACTS
Eisai Co., Ltd. Public Relations Department +81 (0)3-3817-5120	Biogen Inc. Madeleine Shin + 1-781-464-3260 public.affairs@biogen.com
Eisai Europe, Ltd. (UK, Europe, Australia, New Zealand and Russia) EMEA Communications Department +44 (0) 7739 600678 EMEA-comms@eisai.net
Eisai Inc. (U.S.) Libby Holman + 1-201-753-1945 Libby_Holman@eisai.com
INVESTOR CONTACTS
Eisai Co., Ltd. Investor Relations Department +81 (0) 3-3817-5122	Biogen Inc. Tim Power + 1-781-464-2442 IR@biogen.com

Notes to Editors

1. About lecanemab (LEQEMBI^®)
   Lecanemab is the result of a strategic research alliance between Eisai and BioArctic. It is a humanized immunoglobulin gamma (IgG1) monoclonal antibody directed against aggregated soluble (protofibril) and insoluble forms of amyloid-beta (Aβ). Protofibrils are believed to contribute to the brain injury that occurs with AD and are considered to be the most toxic form of Aβ, having a primary role in the cognitive decline associated with this progressive, debilitating condition. Protofibrils cause injury to neurons in the brain, which in turn, can negatively impact cognitive function via multiple mechanisms, not only increasing the development of insoluble Aβ plaques but also increasing direct damage to brain cell membranes and the connections that transmit signals between nerve cells or nerve cells and other cells. It is believed the reduction of protofibrils may prevent the progression of AD by reducing damage to neurons in the brain and cognitive dysfunction.^3,4,5
   
   Lecanemab has been approved in 50 countries and is under regulatory review in 8 countries. In January 2025, the supplemental Biologics License Application (sBLA) for intravenous (IV) maintenance dosing of the treatment was approved in the U.S., and application have been filed in 9 countries and regions. LEQEMBI's approvals in these countries was based on Phase 3 data from Eisai's, global Clarity AD clinical trial, in which it met its primary endpoint and all key secondary endpoints with statistically significant results. The primary endpoint was the global cognitive and functional scale, Clinical Dementia Rating Sum of Boxes (CDR-SB).^7,8 The U.S. FDA approved Eisai’s Biologics License Application (BLA) for subcutaneous maintenance dosing with LEQEMBI IQLIK in August 2025. In September 2025, the rolling sBLA application to the U.S. FDA for the subcutaneous initiation dosing with LEQEMBI IQLIK was also initiated.
   
   The TGA approval was primarily based on Phase 3 data from Eisai’s global Clarity AD clinical trial, in which it met its primary endpoint and all key secondary endpoints with statistically significant results.^7,8 Clarity AD was a Phase 3 global, placebo-controlled, double-blind, parallel-group, randomized study in 1,795 patients with early AD (MCI or mild dementia due to AD, with confirmed presence of amyloid pathology). Of the total number of patients randomized, 1,521 were in the Australia indicated population (ApoE ε4 non-carriers or heterozygotes).⁶ The treatment group was administered lecanemab 10 mg/kg bi-weekly, with participants allocated in a 1:1 ratio to receive either placebo or lecanemab for 18 months.⁶
   
   The primary endpoint was the global cognitive and functional scale, CDR-SB (n=764). In the Clarity AD clinical trial, treatment with lecanemab (n=757), in the Australia indicated population (ApoE ε4 non-carriers or heterozygotes), reduced clinical decline on CDR-SB by 33% at 18 months compared to placebo.⁶ CDR-SB is a global cognitive and functional scale that measures six domains of functioning, including memory, orientation, judgement and problem solving, community affairs, home and hobbies, and personal care.
   
   In the core Clarity AD study for early AD, the most frequently reported adverse reactions were infusion-related reaction (26%), ARIA-H (14%), ARIA-E (13%), and headache (11%). The most important serious adverse reactions were serious ARIA-E (0.8%), serious ARIA-H (0.2%) and serious hypersensitivity including infusion-related reactions (1.3%).
   
   In the Australia indicated population (ApoE ε4 non-carriers or heterozygotes) (n=757), ARIA (ARIA-E or ARIA-H) was observed in 17% of patients treated with LEQEMBI, compared to 7% of patients on placebo. Symptomatic ARIA occurred in 2% of patients on LEQEMBI. Serious ARIA events were reported for 0.5% of patients treated with LEQEMBI. ARIA-E was observed in 9% of patients treated with LEQEMBI compared with 1% of patients on placebo. ARIA-H can occur spontaneously in patients with AD independent of treatment. ARIA-H was observed in 13% of patients treated with LEQEMBI compared with 7% of patients on placebo.⁶
   
   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 that provides the infrastructure for academic clinical trials in AD and related dementias in the U.S, funded by the National Institute on Aging, part of the National Institutes of Health, Eisai and Biogen. Since January 2022, the Tau NexGen clinical study for Dominantly Inherited AD (DIAD), that is conducted by Dominantly Inherited Alzheimer Network Trials Unit (DIAN-TU), led by Washington University School of Medicine in St. Louis, is ongoing and includes lecanemab as the backbone anti-amyloid therapy.
   
   
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 Eisai and Biogen co-commercializing 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 commercialization 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 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 the benefits that health care provides." Under this Concept (also known as 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 of Neurology 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 with global partners.
   
   For more information about Eisai, please visit www.eisai.com (for global headquarters: Eisai. Co., Ltd.), us.eisai.com (for U.S. headquarters: Eisai, Inc.) or www.eisai.eu (for Europe, Middle East, Africa, Russia, Australia and New Zealand headquarters: Eisai Europe Ltd.), and connect with us on X (global and U.S), LinkedIn (for global, U.S. and EMEA) and Facebook (global).
   
   
5. About Biogen
   Founded in 1978, Biogen is a leading biotechnology company that pioneers innovative science to deliver new medicines to transform patients’ lives and to create value for shareholders and our communities. We apply deep understanding of human biology and leverage different modalities to advance first-in-class treatments or therapies that deliver superior outcomes. Our approach is to take bold risks, balanced with return on investment to deliver long-term growth.
   
   The company routinely posts information that may be important to investors on its website at www.biogen.com. Follow Biogen on social media – Facebook, LinkedIn, X, YouTube.
   
   Biogen Safe Harbor
   This news release contains forward-looking statements, including about the potential clinical effects of lecanemab; the potential benefits, safety and efficacy of lecanemab (marketed as LEQEMBI); 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 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 and commercialization 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 results from later stage or larger scale clinical studies and do not ensure regulatory approval. You should not place undue reliance on these statements. Given their forward-looking nature, these statements involve substantial risks and uncertainties that may be based on inaccurate assumptions and could cause actual results to differ materially from those reflected in such statements.
   
   These forward-looking statements are based on management’s current beliefs and assumptions and on information currently available to management. Given their nature, we cannot assure that any outcome expressed in these forward-looking statements will be realized in whole or in part. We caution that these statements are subject to risks and uncertainties, many of which are outside of our control and could cause future events or results to differ materially from those stated or implied in this document, including, among others, uncertainty of our long-term success in developing, licensing, or acquiring other product candidates or additional indications for existing products; expectations, plans, prospects and timing of actions relating to product approvals, approvals of additional indications for our existing products, sales, pricing, growth, reimbursement and launch of our marketed and pipeline products; the potential impact of increased product competition in the biopharmaceutical and healthcare industry, as well as any other markets in which we compete, including increased competition from new originator therapies, generics, prodrugs and biosimilars of existing products and products approved under abbreviated regulatory pathways; our ability to effectively implement our corporate strategy; difficulties in obtaining and maintaining adequate coverage, pricing, and reimbursement for our products; the drivers for growing our business, including our dependence on collaborators and other third parties for the development, regulatory approval, and commercialization of products and other aspects of our business, which are outside of our full control; risks related to commercialization of biosimilars, which is subject to such risks related to our reliance on third-parties, intellectual property, competitive and market challenges and regulatory compliance; the risk that positive results in a clinical trial may not be replicated in subsequent or confirmatory trials or success in early stage clinical trials may not be predictive of results in later stage or large scale clinical trials or trials in other potential indications; risks associated with clinical trials, including our ability to adequately manage clinical activities, unexpected concerns that may arise from additional data or analysis obtained during clinical trials, regulatory authorities may require additional information or further studies, or may fail to approve or may delay approval of our drug candidates; and the occurrence of adverse safety events, restrictions on use with our products, or product liability claims; and any other risks and uncertainties that are described in reports we have filed with the U.S. Securities and Exchange Commission, which are available on the SEC’s website at www.sec.gov.
   
   These statements speak only as of the date of this press release and are based on information and estimates available to us at this time. Should known or unknown risks or uncertainties materialize or should underlying assumptions prove inaccurate, actual results could vary materially from past results and those anticipated, estimated or projected. Investors are cautioned not to put undue reliance on forward-looking statements. A further list and description of risks, uncertainties and other matters can be found in our Annual Report on Form 10-K for the fiscal year ended December 31, 2024 and in our subsequent reports on Form 10-Q. Except as required by law, we do not undertake any obligation to publicly update any forward-looking statements whether as a result of any new information, future events, changed circumstances or otherwise.

References

1. Dementia in Australia https://www.aihw.gov.au/reports/dementia/dementia-in-aus/contents/population-health-impacts-of-dementia/prevalence-of-dementia
2. World Health Organization. Dementia Fact Sheet. March 2023. Available at: https://www.who.int/news-room/fact-sheets/detail/dementia
3. Amin L, Harris DA. Aβ receptors specifically recognize molecular features displayed by fibril ends and neurotoxic oligomers. Nat Commun. 2021;12:3451. doi:10.1038/s41467-021-23507-z
4. Ono K, Tsuji M. Protofibrils of Amyloid-β are Important Targets of a Disease-Modifying Approach for Alzheimer's Disease. Int J Mol Sci. 2020;21(3):952. doi: 10.3390/ijms21030952. PMID: 32023927; PMCID: PMC7037706.
5. Hampel H, Hardy J, Blennow K, et al. The amyloid pathway in Alzheimer's disease. Mol Psychiatry. 2021;26(10):5481-5503.
6. LEQEMBI Australia Product Information
7. van Dyck. C, et al. Lecanemab in Early Alzheimer’s Disease. The New England Journal of Medicine. DOI: 10.1056/NEJMoa2212948. https://www.nejm.org/doi/full/10.1056/NEJMoa2212948
8. Eisai presents full results of lecanemab Phase 3 confirmatory Clarity AD study for early Alzheimer's disease at Clinical Trials on Alzheimer's Disease (CTAD) conference. Available at: https://www.eisai.co.jp/news/2022/news202285.html

FAQ

What is LEQEMBI's new approval status in Australia for Alzheimer's treatment?

LEQEMBI has been approved by Australia's TGA for treating mild cognitive impairment or mild dementia due to Alzheimer's disease in adults who are ApoEε4 non-carriers or heterozygous carriers.

How does LEQEMBI (lecanemab) work differently from other Alzheimer's treatments?

LEQEMBI uniquely fights Alzheimer's disease in two ways by targeting both toxic protofibrils and amyloid plaque, which can impact tau downstream.

What are the main side effects of LEQEMBI (lecanemab)?

The main recognized important side effect is ARIA (Amyloid-Related Imaging Abnormalities), which involves swelling and potential bleeding in the brain.

How many people in Australia could benefit from LEQEMBI?

With approximately 425,000 people living with dementia in Australia as of 2024, and Alzheimer's accounting for 60-70% of cases, a significant portion could potentially benefit, depending on their genetic profile.

What is the significance of ApoEε4 carrier status for LEQEMBI treatment?

ApoEε4 carrier status is important because people with one copy (heterozygous) or no copies (non-carriers) of the gene are less likely to experience ARIA side effects compared to those with two copies (homozygous).