Biogen's Leqembi Outshines Lilly's Kisunla: Safety and Diagnostics Drive Alzheimer's Dominance

The race to dominate the Alzheimer's therapeutics market is intensifying, with Biogen's Leqembi (lecanemab) and Lilly's Kisunla (donanemab) vying for supremacy. While both drugs target amyloid plaques, Leqembi's superior safety profile and alignment with FDA-approved diagnostic advancements position it to secure a larger market share and stronger long-term growth. This analysis argues that Biogen's strategic advantages make its stock a more compelling investment than Lilly's amid regulatory and competitive headwinds.

The Safety Divide: Leqembi's Lower ARIA Risk

Amyloid-Related Imaging Abnormalities (ARIA), particularly the edema (ARIA-E) and hemorrhage (ARIA-H) subtypes, are critical safety concerns for monoclonal antibody therapies. Clinical trial data reveals a stark contrast:

• Leqembi: Phase 3 trials reported an 12.6% incidence of ARIA-E and 17.3% ARIA-H, with most cases mild-to-moderate and self-resolving.
• Kisunla (Donanemab): Phase 3 data showed a 24% ARIA-E and 31.4% ARIA-H, nearly double Leqembi's rates.

The higher ARIA risk with Kisunla poses significant hurdles. Insurers may push back on coverage due to increased monitoring costs, and patients may avoid therapies with higher complication risks. Biogen's lower ARIA profile reduces these barriers, making Leqembi more attractive to both providers and payers.

Diagnostic Synergy: Lumipulse and Leqembi's Access Advantage

The FDA's recent clearance of the Lumipulse G pTau217/β-Amyloid 1-42 Plasma Ratio test (developed by Fujirebio) is a game-changer. This blood-based diagnostic simplifies Alzheimer's diagnosis by identifying amyloid plaques without invasive lumbar punctures or costly PET scans. Key implications:

1. Cost Efficiency: The test costs ~$200–$300, far cheaper than PET scans ($3,000–$5,000) or CSF tests. Medicare reimbursement for the Lumipulse is already established.
2. Accessibility: A simple blood draw eliminates geographic and logistical barriers, enabling broader patient access to Leqembi.
3. Clinical Workflow Integration: The test's 91.7% sensitivity and 97.3% specificity streamline patient selection for Leqembi, reducing the need for confirmatory tests.

Lilly's Kisunla lacks such a diagnostic partner. While donanemab demonstrates slightly greater efficacy in slowing cognitive decline (35% vs. Leqembi's 27%), its higher ARIA risk and reliance on costlier diagnostics could limit uptake.

Sales Projections and Market Dynamics

Analysts at RBC Capital Markets project Leqembi to capture ~60% of the U.S. market share by 2030, versus Kisunla's ~25%, citing Leqembi's safety and diagnostic synergies. Key drivers include:
- Reimbursement Certainty: Leqembi's lower ARIA risk reduces payer pushback, ensuring smoother coverage.
- Early Pipeline Adoption: Leqembi's FDA approval in 2023 gave Biogen a 12-month head start over Kisunla, which awaits final FDA approval pending long-term safety data.
- Patient Pipeline Growth: The Lumipulse test could diagnose ~500,000+ U.S. patients annually, directly funneling candidates to Leqembi.

Investment Implications: Biogen's Stronger Growth Profile

Biogen's stock (NASDAQ: BIIB) trades at a 16.5x forward P/E, while Lilly (NYSE: LLY) is at 22.3x. Biogen's lower valuation reflects its broader portfolio risks but also sets it up for upside if Leqembi meets sales targets. Key risks for Lilly include:
- Regulatory Hurdles: Kisunla's delayed approval and need for long-term safety data could extend its time to market.
- Safety Concerns: Higher ARIA rates may force costly post-marketing studies or restricted labeling.

In contrast, Biogen's $26,500 annual price tag for Leqembi is already accepted by Medicare and commercial insurers, ensuring steady cash flow. The Lumipulse test's cost-effectiveness further reduces payer objections.

Conclusion: Biogen's Leqembi is the Safer, Smarter Play

Leqembi's lower ARIA risk, FDA-backed diagnostics, and first-mover advantage create a moat against Kisunla. With RBC's bullish sales outlook and a valuation tailwind, Biogen is poised to dominate the Alzheimer's space. Investors seeking exposure to this $20B+ market should prioritize BIIB over LLY, as Biogen's strategic moves reduce execution risks and amplify long-term returns.