What the ESC Congress Really Reveals About the Failure
Six weeks after the initial shock, Munich delivers the answers — and they're more complicated than the July headlines suggested
When AstraZeneca and Ionis Pharmaceuticals announced in July 2026 that their compound Wainua (eplontersen) had missed the primary endpoint of the CARDIO-TTRansform trial, both companies' stock prices took a massive hit — I reported on this in my first article on the topic. At the time, only the bare result was known, without detailed subgroup analyses. On August 28, 2026, the trial investigators presented the complete dataset at the ESC Congress (European Society of Cardiology) in Munich, in what's known as a Hot Line session — the format reserved for the year's most clinically significant trial results. What emerged there substantially changes how the case should be understood: this isn't a simple efficacy failure, but a methodologically intricate pattern with direct consequences for the entire class of RNA-silencing drugs.
The Complete Numbers: Confirmation, But With a Crucial Addition
The headline finding from Munich initially confirmed the picture already known: among 1,432 patients with wild-type or hereditary ATTR-CM (transthyretin amyloid cardiomyopathy — a heart muscle disease caused by the deposition of misfolded transthyretin protein), the combined rate of cardiovascular mortality and recurrent cardiovascular events through 140 weeks did not differ significantly between eplontersen and placebo (rate ratio 0.89; 95% confidence interval 0.73–1.09; p = 0.277). This occurred despite robust suppression of circulating serum transthyretin by eplontersen — the drug did exactly what it was designed to do, without translating into the hoped-for clinical benefit.
The crucial new finding, however, lies in the subgroup analysis: the overall result was substantially influenced by the use of stabilizer medications at baseline. Among patients already taking a TTR stabilizer such as Pfizer's Vyndaqel/Vyndamax (tafamidis) at baseline, eplontersen showed no additional benefit. Among patients not receiving a stabilizer, however, eplontersen actually produced fewer primary endpoint events than placebo — a difference the study authors described as "nominally significant" (meaning: statistically notable, but without the full evidentiary weight of a primary, pre-specified endpoint, since this was a subgroup analysis). An additional benefit signal emerged among patients with earlier-stage disease.
The Explanation: Why the Combination Didn't Work
Mathew Maurer of Columbia University, the trial's lead investigator, contextualized the results in a statement: ATTR-CM is an under-recognized cause of heart failure, with an estimated 300,000 to 500,000 people affected worldwide — making earlier diagnosis and targeted treatment all the more critical. Fierce Pharma analysts characterized the result as a "post-mortem" that raises doubts about the approach of combining RNA silencers with stabilizers: notably, 57 percent of trial participants were already taking a stabilizer at baseline, with a further 24 percent starting one during the trial — a circumstance that complicated the interpretability of the overall result from the outset, as I had already suspected in my first article.
Dr. Margot Davis of the University of British Columbia explained the clinical significance in an expert interview for the Heart Failure Academy: while the overall trial was neutral, a significant benefit emerged among patients without stabilizer therapy at baseline and among those with earlier-stage disease. According to Davis, open questions remain primarily around treatment sequencing: should treatment begin with a stabilizer or a silencer, and when does switching between the two drug classes make sense?
The Head-to-Head Comparison: Why Alnylam's Vutrisiran Performed Differently
The CARDIO-TTRansform setback gains additional weight through a direct comparison: on August 30, 2026, competitor Alnylam Pharmaceuticals presented new data at the same ESC Congress on its own TTR silencer vutrisiran (brand name Amvuttra), which had already received FDA approval for ATTR-CM in 2025 — unlike Wainua, which so far is only approved for the polyneuropathy indication. A pre-specified subgroup analysis of the pivotal HELIOS-B trial, involving 654 randomized patients (259, or 40 percent, of whom were on background tafamidis therapy), simultaneously published in the prestigious Journal of the American College of Cardiology, showed a consistent treatment effect on the primary endpoint of all-cause mortality and recurrent cardiovascular events — regardless of whether patients were already taking a stabilizer. Functional capacity, measured by the six-minute walk test, was also preserved under vutrisiran in both groups. A post hoc analysis further found a 25 percent smaller decline in so-called intrinsic capacity (a composite measure of physical and cognitive functioning in older patients) as well as a 52 percent risk reduction for its decline versus placebo.
Important context: the HELIOS-B trial was also not statistically powered to demonstrate a specific benefit in the patient group on background tafamidis therapy — so the difference from CARDIO-TTRansform didn't lie in a fundamentally different trial design, but in the fact that vutrisiran showed a consistent benefit signal across both patient groups, whereas Wainua showed a clear divergence between the groups.
Pushkal Garg, Alnylam's chief research officer, told Fierce Pharma that the Wainua trial and the positive HELIOS-B trial together show that not all TTR silencers or trial designs are the same. He expressed continued confidence in both Amvuttra and the company's next-generation compound, nucresiran. Analysts at Stifel, in an August 30 investor note, assessed the prospects for Alnylam's ongoing TRITON-CM trial of nucresiran as still intact — provided the company focuses more on patients with earlier-stage disease. One notable detail from the CARDIO-TTRansform trial itself: Wainua outperformed placebo in stage 1 patients, even though about 60 percent of those patients were also taking Pfizer's stabilizer Vyndamax — suggesting that disease severity may play a larger role than the stabilizer combination question alone.
The Competitive Landscape: A Market With Three Mechanisms of Action
The case illustrates the now-complex competitive situation in the ATTR-CM treatment field, which broadly breaks down into three mechanisms of action. First, TTR stabilizers such as Pfizer's tafamidis, which don't attack already-deposited protein but slow further misfolding. Second, TTR silencers, which themselves split into two subgroups: antisense oligonucleotides like Wainua, administered monthly via GalNAc conjugation (a technology for targeted uptake of the drug into liver cells via the asialoglycoprotein receptor), and siRNA compounds like Alnylam's vutrisiran, which rely on a different molecular silencing mechanism and are administered quarterly. Third, experimental amyloid "depleters" such as ALXN2220 (a collaboration between Neurimmune, AstraZeneca, and AstraZeneca subsidiary Alexion) or coramitug (Prothena/Novo Nordisk), which — unlike stabilizers and silencers — don't prevent new amyloid formation but instead aim to actively clear amyloid already deposited in the heart.
Notably, AstraZeneca is already pursuing a possible follow-up strategy here: an ongoing combination trial is testing eplontersen alongside the amyloid depleter ALXN2220 — the idea being to prevent new amyloid deposition upstream (via the silencer) while simultaneously clearing existing amyloid downstream (via the depleter), a combined approach that no single mechanism can achieve on its own.
What the Case Means for the Industry
The complete CARDIO-TTRansform data illustrate how heavily the interpretation of an apparently failed trial result can depend on subgroup analysis — and how differently two competing compounds, with structurally similar trial designs but different molecular mechanisms, can respond to the same clinical question. For AstraZeneca and Ionis, the result doesn't mean immediate market access to the ATTR-CM indication, but it does provide a signal that could scientifically justify a more targeted future trial strategy — for example, focusing on patients without prior stabilizer treatment or with earlier-stage disease.
For the industry as a whole, the direct comparison between Wainua and vutrisiran at the same congress offers a rare lesson in trial design: two compounds targeting the same molecule (transthyretin) with a similar overarching mechanism (gene silencing) can produce markedly different clinical outcomes depending on molecular mechanism, dosing interval, and — above all — the precise composition of the patient population studied. FirstWord Pharma is currently preparing a physician survey on the implications of the data — an indication that the clinical community has by no means finished evaluating what this means for treatment practice.
Sources
- HCPLive, Aug 28, 2026 – CARDIO-TTRansform: Eplontersen Misses Primary Endpoint in ATTR-CM
- European Society of Cardiology, Press Release, Aug 28, 2026 – Eplontersen trial did not meet its primary endpoint in transthyretin-mediated amyloid cardiomyopathy
- ESC 365 – CARDIO-TTRansform: efficacy and safety of eplontersen in patients with transthyretin amyloid cardiomyopathy
- BioPharm International – AstraZeneca and Ionis' Wainua Misses Primary Endpoint in Phase III ATTR-CM Trial
- AstraZeneca, Press Release – Update on CARDIO-TTRansform Phase III trial for Wainua (eplontersen)
- Fierce Pharma, Aug 30, 2026 – ESC: AZ, Ionis' Wainua post-mortem throws water on silencer-plus-stabilizer approach in ATTR-CM
- Heart Failure Academy – ESC 2026: CARDIO-TTRansform Trial Insights on Eplontersen
- Clinical Trials Arena, Jul 9, 2026 – AstraZeneca and Ionis' stocks drop significantly on Wainua ATTR-CM trial failure
- StreetInsider, Aug 30, 2026 – Alnylam presents vutrisiran and zilebesiran data at ESC 2026
- Barchart / Business Wire – Alnylam Presents New Data at ESC Congress 2026 Reinforcing Strength in RNAi-Powered TTR Silencing Across ATTR-CM Patient Populations and Treatment Settings
- Pharmacally – New Data Reinforce Vutrisiran Benefit Across ATTR-CM Patient Groups
- StockTitan – Alnylam ESC: Vutrisiran Cuts ATTR-CM Decline Risk 52%
- Fierce Biotech, Aug 30, 2026 – ESC: Alnylam's next-gen silencer sees silver linings after fallout of AZ, Ionis trial in ATTR-CM
- Eureka/PatSnap – Eplontersen Competitive Landscape Analysis 2026
- FirstWord Pharma – Physician Views Preview: AstraZeneca's ESC readout puts ATTR-CM combo strategy on trial
Adrian Kempf
Pharma Communications Writer, Graphic & Media Designer Kirchzarten im Dreisamtal, Germany
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