Pelacarsen Heart Trial: What Does the Lp(a) Setback

What did the pelacarsen heart trial find?

The Lp(a)HORIZON study enrolled people with elevated lipoprotein(a), or Lp(a), and established cardiovascular disease. Participants received pelacarsen or placebo alongside recommended cardiovascular treatment. The primary outcome combined cardiovascular death, nonfatal heart attack, nonfatal stroke and urgent procedures to restore coronary blood flow requiring hospitalization. Novartis reported that the trial missed this endpoint despite lowering Lp(a). [Novartis announcement](https://www.novartis.com/news/media-releases/novartis-announces-lpahorizon-phase-iii-topline-results-pelacarsen-patients-elevated-lpa-and-established-cardiovascular-disease-cvd)

The National Lipid Association's September 14 response emphasized that full trial results were not yet available. That limits interpretation: the announcement alone cannot show the size and precision of the treatment effect or explain differences between individual outcomes. Missing the primary endpoint does not establish that every possible benefit has been excluded. Equally, a favorable laboratory result cannot substitute for demonstrated protection against clinical events. [National Lipid Association assessment](https://www.lipid.org/resource/top-line-results-from-the-phase-3-lpahorizon-trial/)

Why had doctors expected pelacarsen to prevent heart attacks?

Pelacarsen is an antisense oligonucleotide, a medicine designed to act on RNA instructions involved in producing apolipoprotein(a), a component of Lp(a). A randomized phase 2 trial published in the New England Journal of Medicine in 2020 enrolled 286 patients with cardiovascular disease. Treatment produced dose-dependent reductions in Lp(a), with an average decrease of 80% in the group receiving 20 mg weekly, compared with 6% with placebo. Injection-site reactions were the most common adverse events. [Phase 2 clinical trial](https://www.nejm.org/doi/full/10.1056/NEJMoa1905239)

That earlier study primarily assessed changes in a blood marker; it did not establish that treatment prevented heart attacks or strokes. The distinction explains why a larger outcomes trial was necessary. A plausible biological target and a substantial laboratory response provide reasons to investigate a medicine, but its clinical value depends on patient outcomes and safety.

The setback also leaves questions for other approaches. The National Lipid Association identifies ongoing outcomes trials of the injectable RNA treatments olpasiran and lepodisiran, as well as oral muvalaplin, which disrupts Lp(a) particle assembly. These studies must establish their own benefits and risks. The interpretation is that HORIZON raises uncertainty for the field without determining the results of every other drug or prevention strategy. [Other Lp(a) outcomes trials](https://www.lipid.org/resource/top-line-results-from-the-phase-3-lpahorizon-trial/)

What should people with high lipoprotein(a) do now?

Lp(a) levels are largely inherited, and an elevated result can help identify cardiovascular risk that a routine cholesterol assessment may miss. Guidance summarized by the National Lipid Association on September 25 supports measuring Lp(a) at least once in adulthood. Testing close relatives can also be useful, especially when a family has premature cardiovascular disease. Healthy habits remain valuable for overall cardiovascular protection even when they do not substantially change the inherited Lp(a) level. [NLA guidance on testing and management](https://www.lipid.org/resource/lipoproteina-management-simplified-the-national-lipid-association-lipid-simplified-series/)

Treatment decisions should address the person's full risk profile, including LDL cholesterol and other modifiable factors. The NLA's 2024 scientific statement specifically advises against stopping or discouraging statins because they may raise Lp(a). For selected high-risk patients who need additional LDL reduction despite maximally tolerated statin treatment, a PCSK9 inhibitor may be considered. These decisions depend on established indications and individual risk, rather than an assumption that lowering Lp(a) itself has already proved beneficial. [NLA scientific statement](https://www.lipid.org/sites/default/files/files/PIIS1933287424000333.pdf)