Biogen's Salanersen: A Breakthrough in SMA Treatment and a Lifeline for Investors

Biogen (NASDAQ: BIIB) is back in the spotlight with its investigational therapy salanersen, which has just advanced to registrational Phase 3 studies following stunning interim Phase 1 results in spinal muscular atrophy (SMA). For a company grappling with declining sales of its blockbuster drug SPINRAZA, this development couldn't come at a better time. Let's break down why salanersen is a game-changer for SMA patients—and why investors should pay close attention.

The SMA Market: A $2 Billion Opportunity—and Growing

SMA is a rare, devastating neuromuscular disorder with no cure, but the market is booming. Driven by newborn screening programs, rising awareness, and the launch of new therapies, the global SMA treatment market is projected to hit $2 billion by 2025, growing at a 15% CAGR through 2033. Yet existing therapies have clear limitations:

• SPINRAZA (nusinersen): Biogen's $140,000/year ASO therapy is the standard of care but requires quarterly spinal injections, posing adherence challenges. Sales have been declining as patients switch to newer options or insurers push for alternatives.
• ZOLGENSMA (onasemnogene abeparvovec): Roche's one-time gene therapy is a breakthrough for infants but costs $2-4 million, limiting access. Plus, some patients experience suboptimal outcomes over time.

Enter salanersen, which could dominate both markets.

Salanersen: Why It's a Home Run

The Phase 1 data released in June 19, 2025, is unambiguous:

1. Superior Neuroprotection:
2. Patients showed a 70% reduction in neurofilament light chain (NfL), a biomarker of neurodegeneration. This was sustained for a full year—far longer than SPINRAZA's effects.

3. In a subgroup of children who'd already received ZOLGENSMA but were still declining, half achieved new motor milestones like sitting or walking within three months.

4. Breakthrough Dosing Convenience:

5. Administered once yearly, salanersen eliminates the burden of quarterly SPINRAZA injections. This patient-centric design is a major competitive edge.

6. Safety and Tolerability:

7. Mild side effects like fever and respiratory infections were reported, with no severe renal or coagulation issues—a common concern with ASOs.

8. Market Expansion Potential:

9. Phase 3 trials will target both post-gene therapy patients (where ZOLGENSMA falls short) and SPINRAZA-naïve populations, carving out a $1 billion+ revenue stream by 2030.

Why This Matters for Biogen's Bottom Line

Biogen's stock has been dragged down by SPINRAZA's declining sales, which fell to $1.3 billion in 2024, down 8% from 2023. Salanersen isn't just a replacement—it's a superior product with broader applicability:

• Cross-Segment Appeal: It can complement ZOLGENSMA in infants and address the 30% of gene therapy patients who still experience motor decline.
• Pricing Power: A once-yearly ASO could command a premium over SPINRAZA, especially if it outperforms in head-to-head trials.

Analysts project salanersen could generate $1.5–2 billion in annual sales by 2030, offsetting SPINRAZA's decline and propelling Biogen's revenue higher.

The Risks? Don't Worry—They're Manageable

• Phase 3 Hurdles: The trial cohort (n=24) was small, but the 70% NfL reduction is a strong signal. Biogen's partnership with Ionis Pharmaceuticals adds credibility, as they co-developed SPINRAZA.
• Regulatory Scrutiny: Biogen has a proven track record in SMA, with over 14,000 SPINRAZA-treated patients. Regulators are likely to fast-track this critical therapy.

Investment Thesis: Buy Biogen—But Wait for Phase 3 Clarity

Biogen's stock trades at a forward P/E of 11.5x, below its five-year average. While I'd advise buying now to position for salanersen's potential, investors should wait for Phase 3 design finalization (expected Q4 2025) to confirm trial timelines and endpoints.

Target Price: If salanersen hits peak sales of $1.8 billion, a 25% upside from current levels ($187 median analyst target) is achievable.

Final Takeaway

Salanersen isn't just a new drug—it's a paradigm shift in SMA treatment. With its superior efficacy, once-yearly dosing, and address of unmet needs, it has the potential to reignite Biogen's growth. For investors, this is a rare chance to buy a pharmaceutical leader at a discount, with a catalyst (Phase 3 initiation) just months away.

Action to Take: Buy Biogen shares, set a stop-loss at $150, and watch for Phase 3 trial updates. This could be the next big winner in rare disease therapeutics—and a lifeline for a company once overshadowed by its fading star, SPINRAZA.

Disclaimer: This analysis is for informational purposes only. Consult a financial advisor before making investment decisions.