Lowering lipoprotein(a) with pelacarsen did not cut cardiovascular events

Lipoprotein(a), usually written Lp(a), is a cholesterol-carrying particle whose level is set largely by genes and barely moves with diet, exercise or statins. For years, genetic studies have tied a high Lp(a) to a greater risk of heart attacks and narrowed aortic valves, making it one of the most tantalising targets in cardiology: an inherited risk factor that nothing in the standard toolkit could touch. The obvious question was whether a drug that drove Lp(a) down would prevent cardiovascular events. On 7 November, the first large trial built to answer it reported — and the answer was no [s1][s2].

The drug and the question

Pelacarsen is an antisense oligonucleotide, a short strand of genetic material designed to switch off production of the protein backbone of Lp(a), cutting blood levels sharply [s1]. The Lp(a)HORIZON trial, registered as NCT04023552, was a randomised, placebo-controlled study in patients with established cardiovascular disease and a high Lp(a), testing whether adding pelacarsen reduced major cardiovascular events [s1][s3].

This is what the field calls a test of the "Lp(a) hypothesis": the idea that because high Lp(a) causes cardiovascular disease, lowering it pharmacologically should reduce events. Genetics can show association and even strongly imply causation, but only a randomised trial can show that the drug actually helps patients.

What the trial found

The primary result, reported in the main New England Journal of Medicine paper, was that pelacarsen did not reduce the risk of major adverse cardiovascular events compared with placebo [s1][s2]. A companion set of extended analyses, published simultaneously in NEJM Evidence, probed that null result from several angles to see whether a benefit was hiding in it — and did not find one [s1].

When the analysis was restricted to patients while they were actually on treatment, the primary composite endpoint — cardiovascular death, non-fatal heart attack, non-fatal stroke or urgent coronary revascularisation — occurred in 380 participants (9.1%) assigned to pelacarsen and 434 (10.4%) assigned to placebo, a hazard ratio of 0.98 (95% CI 0.85 to 1.12) [s1]. The confidence interval runs well across 1.0, so this does not represent a benefit. Among participants with uninterrupted treatment the point estimate actually sat on the other side: a hazard ratio of 1.09 (95% CI 0.89 to 1.34) [s1]. Counting all events, first and recurrent, there were 644 in the pelacarsen group and 646 on placebo, a rate ratio of 1.00 (95% CI 0.87 to 1.14) [s1].

The most pointed test was a landmark analysis of the patients in whom the drug worked best biochemically. Even among those whose Lp(a) fell by at least the median reduction of 170 nmol/L, there was no benefit (hazard ratio 1.09, 95% CI 0.92 to 1.29), and the same held for those who reached a low achieved Lp(a) of 69.5 nmol/L or less (hazard ratio 1.10, 95% CI 0.93 to 1.29) [s1]. Nor did any benefit emerge in subgroups defined by baseline Lp(a), LDL cholesterol, inflammation measured by C-reactive protein, or time since the qualifying cardiovascular event [s1].

What is, and is not, established

Lp(a)HORIZON establishes something consequential: in this trial, sharply lowering Lp(a) with pelacarsen did not translate into fewer cardiovascular events, and the extended analyses show the null result was robust to how the data were sliced — on-treatment, by total events, and even among the patients who achieved the largest reductions [s1]. For a hypothesis that rested heavily on genetic inference, that is a sobering real-world check.

The limits cut in more than one direction, and they are where the ongoing debate sits. A single trial of a single drug does not close the Lp(a) question for good; other agents that lower Lp(a), including small-interfering-RNA drugs, are in their own outcomes trials, and their results are still to come [s1]. Trial-level factors — how much Lp(a) was lowered, how long patients were followed, who was enrolled, how well other risk factors were already controlled — all shape whether an effect could be detected, and these analyses examined several of them without rescuing a benefit [s1]. What the trial cannot tell us is whether a different drug, a different population, or a longer horizon might yet show something; it can only report what this one found.

For now, the practical takeaway is narrow. These results do not support using pelacarsen to prevent cardiovascular events, and they temper the expectation that lowering Lp(a) will straightforwardly reduce risk. This article describes research and is not medical advice.