Key Highlights

  • A prespecified HELIOS-B subgroup analysis at ESC (Aug 30) showed a consistent Amvuttra benefit on mortality and CV events regardless of baseline tafamidis use.
  • Q2 Amvuttra sales topped $1 billion, but the TTR Revenue guide was cut to $4.2-$4.5 billion, and shares fell more than 25% on Jul 30.
  • Shares rose 3.4% on Sep 2, tied to continued reaction to the ESC data; upcoming catalysts include Huntington's disease data on Oct 23.
  • Alnylam shares traded around $240 to $245 in mid-to-late September, above the roughly $211 level seen after the July selloff, and the median analyst price target is $350.

Alnylam Pharmaceuticals (NASDAQ:ALNY) has been clawing back ground in September. Market commentary has tied part of the rebound to new HELIOS-B analyses presented at the European Society of Cardiology (ESC) Congress, which suggested that its heart drug Amvuttra (vutrisiran) works consistently whether or not patients also take the older standard therapy, tafamidis. That finding matters because it speaks to Amvuttra's role across the whole transthyretin amyloid cardiomyopathy (ATTR-CM) market, not only in newly diagnosed patients.

The shares rose 3.4% on September 2. The gain appeared tied mainly to continued investor reaction to the August 30 ESC update, and no major new regulatory filing coincided with the move.

The recovery comes from a low base. On July 30, Alnylam cut its full-year sales guidance for its transthyretin (TTR) franchise, and the stock fell more than 25% that day. Market data showed the shares trading around $240 to $245 in mid-to-late September, above the roughly $211 level seen after the July selloff.

What the New HELIOS-B Analyses Showed

According to Alnylam's August 30 release, a late-breaking presentation at ESC examined HELIOS-B patients by whether they were taking tafamidis at baseline. Of 654 randomized and treated patients, 259, or 40%, were on tafamidis. The company said vutrisiran's effect on the primary composite endpoint of all-cause mortality and recurrent cardiovascular events through 33 to 36 months was consistent in both groups. The results were published simultaneously in the Journal of the American College of Cardiology.

Alnylam also flagged limits. HELIOS-B was not powered to prove a benefit specifically in patients already on tafamidis. The quality-of-life improvement measured by the Kansas City Cardiomyopathy Questionnaire was attenuated in that group.

Post hoc analyses added supporting detail. Versus placebo, vutrisiran patients showed 25% less decline in a composite "intrinsic capacity" score and a 52% lower risk of decline. The drug arm also had fewer adverse events overall. A pooled analysis of 1,402 patients across four Phase 3 studies found consistent treatment effects in women and men.

"The data presented at ESC demonstrate the consistency of clinical outcomes achieved by RNAi-powered TTR silencing, reinforcing our conviction in AMVUTTRA as a first-line treatment option for ATTR-CM," Chief Research and Development Officer Pushkal Garg said in the release.

Strong Sales, Softer Guidance

In the second quarter, Alnylam's net product revenue rose 74% to $1,172 million, and total revenue rose 67% to $1,291 million. Amvuttra alone generated $1,011.8 million, up 106%, making it Alnylam's first product to exceed $1 billion in a single quarter. The company swung to GAAP Net Income of $164.5 million, or $1.21 per diluted share, from a loss of $72.2 million a year earlier.

Non-GAAP Earnings were $1.84 per share. US TTR revenue grew $106 million from the first quarter, which the company said reflected a $129 million increase in demand, partly offset by about $20 million of inventory effects. Royalty revenue, driven by Novartis (NYSE:NVS)'s sales of Leqvio, rose 79% to $71.7 million, and Alnylam held $3.3 billion of cash and marketable securities at June 30.

Investors focused instead on guidance. Alnylam lowered its 2026 TTR net product revenue forecast to $4.2 billion to $4.5 billion from $4.4 billion to $4.7 billion. It cut total net product revenue guidance to $4.7 billion to $5.1 billion from $4.9 billion to $5.3 billion. It also raised expected collaboration and royalty revenue to $575 million to $625 million, and kept its non-GAAP Operating Expense range at $2.7 billion to $2.8 billion.

The company said growth in second-line US Demand had "moderated in early 2026" to a normalized level. It explained that the early launch had benefited from pent-up demand among patients progressing on stabilizers. Chief Executive Yvonne Greenstreet said Alnylam remains "confident in the trajectory" of the ATTR-CM launch.

Business and Competitive Context

Amvuttra is a quarterly RNA interference (RNAi) injection that silences TTR production at its source. Stabilizers such as Pfizer (NYSE:PFE)'s tafamidis and BridgeBio (NASDAQ:BBIO)'s acoramidis instead keep the TTR protein from misfolding. The ESC subgroup data are therefore relevant to the second-line segment that disappointed in July: they support adding Amvuttra for patients already on a stabilizer.

Beyond TTR, Alnylam's rare-disease drugs Givlaari and Oxlumo generated $141.9 million, up 11%. The pipeline includes zilebesiran for hypertension, now in the ZENITH Phase 3 outcomes trial with Roche, and nucresiran, a next-generation TTR silencer in Phase 3. It also includes early programs in obesity, Alzheimer's disease and Huntington's disease. In July, Alnylam signed a deal with BeOne Medicines (NASDAQ:ONC) to commercialize Amvuttra in mainland China and Macao, subject to approval there.

Risks to the Rebound

  • Launch trajectory: the July guidance cut shows forecasting second-line uptake has been difficult. Another reset would weigh on the thesis.
  • Subgroup limits: the tafamidis-combination findings come from a trial not powered for that question, and Alnylam says combination strategies Warrant further study.
  • Competition and pricing: stabilizers are entrenched and other silencers are in development. Net price also dipped modestly in the second quarter, according to the company.
  • Costs: R&D spending rose 28% as Phase 3 programs expanded, and Cost of Goods Sold climbed to 25.4% of product revenue because of higher royalty rates.

Analyst views have reset. A median 12-month target of $350 from 29 analysts, with a range of $256 to $536, reflects third-party estimates rather than company forecasts.

Key Dates on the Pipeline Calendar

  • October 23: initial Phase 1 results for ALN-HTT02 in Huntington's disease at the European Huntington's Disease Network congress, followed by an RNAi Roundtable on October 26.
  • November 2026: the FDA target action date for cemdisiran in generalized myasthenia gravis, according to partner Regeneron (NASDAQ:REGN).
  • Second half of 2026: data from ALN-6400 and the obesity candidate ALN-2232.
  • Third-quarter results: US Amvuttra demand trends will show whether second-line growth has stabilized.

Whether the Rebound Turns Into Steadier Growth

The ESC data strengthen Amvuttra's clinical case across patient types. The stock's recovery now depends on whether that evidence turns into steadier prescription growth than the July outlook assumed.