A gene-silencing drug missed its endpoint in transthyretin heart amyloidosis

Transthyretin amyloid cardiomyopathy is caused by a protein that misfolds and deposits in the heart muscle, and the obvious therapeutic idea is to make less of the protein [s1]. Eplontersen is an antisense oligonucleotide that does exactly that, reducing hepatic production of transthyretin [s1]. CARDIO-TTRansform, published in the New England Journal of Medicine on 28 August and presented at the ESC Congress in Munich, tested whether that translates into fewer deaths and cardiovascular events. It did not reach statistical significance [s1].

What the trial did

CARDIO-TTRansform was a phase 3, international, double-blind trial [s1]. Patients with ATTR-CM were randomly assigned in a 1:1 ratio to subcutaneous eplontersen 45 mg or placebo every four weeks for 140 weeks, on top of standard treatment [s1].

The primary end point was a cumulative composite of death from cardiovascular causes and recurrent cardiovascular clinical events up to week 140 — a design that counts repeat hospitalisations rather than only a patient's first event [s1]. Because deaths from other causes can distort that kind of recurrent-event analysis, the trial prespecified a second composite of death from any cause and cardiovascular events over the same window to check the effect [s1].

A total of 1,432 patients were randomised and received at least one dose: 715 on eplontersen and 717 on placebo [s1]. The mean age was 76.4 years and 90.6% of participants were men [s1] — a demographic skew consistent with who is diagnosed with this condition, and a limit on how far the result travels.

What happened

There were 381 primary end-point events in 210 patients (29.4%) receiving eplontersen, against 392 events in 231 patients (32.2%) receiving placebo, giving a rate ratio of 0.89 (95% CI 0.73 to 1.09, P = 0.28) [s1].

That interval is the whole story. Its lower bound of 0.73 is a meaningful reduction in event rate; its upper bound of 1.09 is on the other side of no effect [s1]. The data are compatible with a worthwhile benefit and with no benefit at all, and the trial does not establish either.

Broken into components, death from cardiovascular causes occurred in 74 patients on eplontersen and 70 on placebo, while there were 307 cardiovascular clinical events on eplontersen and 322 on placebo [s1]. The prespecified check using death from any cause returned a rate ratio of 0.86 (95% CI 0.71 to 1.04) — slightly more favourable, still crossing one [s1].

Serious adverse events occurred in 413 patients (57.8%) on eplontersen and 426 (59.4%) on placebo [s1]. On the evidence reported, the drug did not appear to make patients sicker over nearly three years.

Why the mechanism is not the answer

Before the congress, the ESC's own preview described CARDIO-TTRansform as the trial that would show whether an antisense therapy lowering the amyloid-forming protein could improve outcomes in a condition it called a once-rare but increasingly recognised cause of heart failure [s2]. The framing is worth holding onto, because the trial answers a narrower question than the mechanism suggests.

Knocking down transthyretin production is a plausible way to slow amyloid deposition. But the primary end point here was not protein concentration or imaging; it was death and hospitalisation over 140 weeks in patients whose mean age was 76.4 years and whose hearts already carried established amyloid burden [s1]. A treatment can reliably do the biochemical thing it was designed to do and still fail to change that composite within that window, in that population.

The reverse caution applies too. A rate ratio of 0.89 with an upper bound of 1.09 is not a demonstration that the drug is inert. It is a trial that did not have the precision, or the effect size, to separate the two.

What this does not settle

CARDIO-TTRansform tested one agent, at one dose, on top of whatever standard treatment patients were already receiving [s1]. The ATTR-CM field now contains several approaches — stabilisers, silencers and depleters — and this result speaks to none of them directly.

It also cannot tell you about patients unlike the ones enrolled. With 90.6% men and a mean age of 76.4 years, the trial is thin evidence about women with ATTR-CM and about younger patients with hereditary forms of the disease [s1].

The trial was funded by Ionis Pharmaceuticals and AstraZeneca and registered as NCT04136171 [s1].

What to watch

Two things. First, whether the full publication's secondary and imaging analyses show the biological effect the mechanism predicts, which would sharpen the question of why it did not convert into the clinical composite. Second, how guideline committees treat a recurrent-event primary end point that missed while its all-cause-death companion analysis pointed the same direction — 0.86 against 0.89 — without either crossing the significance threshold [s1].

For now the honest summary is the authors' own: among patients with ATTR-CM, eplontersen therapy did not lead to a lower risk of the composite of cardiovascular death and recurrent cardiovascular events than placebo up to 140 weeks [s1].

This article describes trial results. It is not advice about any medicine, and nothing here should be used to start, stop or change treatment.

Sources

• Eplontersen for Transthyretin Amyloid Cardiomyopathy, New England Journal of Medicine, 28 August 2026
• Hot Lines revealed - the trials that will make the headlines at ESC Congress 2026, European Society of Cardiology, 23 July 2026