Results from the landmark Phase 3 Lp(a)HORIZON cardiovascular outcomes trial, led by the Cleveland Clinic, were presented on November 7, 2026, during a late-breaking science session at the American Heart Association Scientific Sessions 2026 in Chicago and simultaneously published in The New England Journal of Medicine. The international, multicenter trial demonstrated that pelacarsen, an investigational antisense oligonucleotide funded by Novartis, significantly reduced lipoprotein(a) levels by an average of 78% but failed to reduce major adverse cardiovascular events in patients with established cardiovascular disease after a median follow-up of 4.7 years. Neutral Cardiovascular Outcomes After 4.7 Years of Follow-Up The double-blind, randomized, placebo-controlled Lp(a)HORIZON trial was conducted across 797 sites in 42 countries between December 2019 and 2026. Investigators screened 14,249 adults and enrolled 8,322 patients in the primary efficacy cohort who had established cardiovascular disease and elevated baseline lipoprotein(a) levels of at least 70 mg/dL. The study population had a mean age of 59.7 years, with 27.0% women, 26% diagnosed with diabetes, 76.6% with a prior myocardial infarction, 10% with prior ischemic stroke, and 14% with symptomatic peripheral artery disease. At baseline, background guideline-directed therapies were well established, with 77.6% of participants taking high-intensity statin therapy. Participants were randomly assigned to receive self-administered monthly subcutaneous injections of pelacarsen 80 mg or a matching placebo.
The primary composite endpoint was defined as the time to the first occurrence of cardiovascular death, nonfatal myocardial infarction, nonfatal ischemic stroke, or urgent coronary revascularization requiring hospitalization. Over a median follow-up period of 57 months (4.7 years), the primary endpoint occurred in 12.3% (511 of 4,157) of patients in the pelacarsen group and 12.1% (503 of 4,165) in the placebo group. The between-group difference was statistically neutral, yielding a hazard ratio of 1.02 (95% CI, 0.90–1.15; P = .76). Among the pre-specified subgroup with baseline lipoprotein(a) levels at or above 90 mg/dL, outcomes remained identical between arms, with a hazard ratio of 1.00 (95% CI, 0.87–1.15; P = .99). Secondary endpoints affirmed the neutral finding: a three-component MACE excluding urgent revascularization occurred in 10.2% versus 10.1% (HR, 1.01; 95% CI, 0.88–1.16), the coronary composite occurred in 9.4% versus 9.7% (HR, 0.97; 95% CI, 0.85–1.12), and all-cause mortality occurred in 5.7% versus 5.9% (HR, 0.98; 95% CI, 0.82–1.17). Robust Lipoprotein(a) Lowering Accompanied by Adverse Reactions Pelacarsen demonstrated potent biochemical efficacy in suppressing circulating lipoprotein(a). At 12 months, lipoprotein(a) levels fell by 78.4% from baseline in the pelacarsen cohort compared with 3.2% in the placebo group, representing an estimated treatment difference of 77.7 percentage points (95% CI, 77.0–78.4). Median lipoprotein(a) concentrations dropped from 235.8 nmol/L at baseline to 64.4 nmol/L at one year in treated patients. Furthermore, LDL cholesterol fell to 62.3 mg/dL with pelacarsen but rose to 71.2 mg/dL with placebo, producing a 13.3 percentage point reduction relative to placebo.
Despite profound biomarker modulation, clinical tolerability presented noticeable challenges. While overall rates of serious adverse events were balanced between arms—occurring in 37.3% (1,553 of 4,166) of pelacarsen recipients versus 41.1% (1,709 of 4,154) on placebo—specific drug-related toxicities were substantially higher. Influenza-like symptoms affected 31.9% of pelacarsen-treated patients compared with 5.8% on placebo, and injection-site reactions occurred in 25.6% versus 2.9%, respectively. Adjudicated anaphylaxis was documented in 19 patients receiving pelacarsen compared with none receiving placebo, including eight hypersensitivity events that required hospital admission without associated fatalities. Due to adverse reactions, 20.6% of pelacarsen patients permanently discontinued the study medication, compared to 7.5% of placebo participants. Expert Interpretation and Implications for Future Lipoprotein(a) Research Dr. Steven E. Nissen, senior author of the trial and Chief Academic Officer of the Heart, Vascular & Thoracic Institute at the Cleveland Clinic, addressed the scientific implications of the findings at the presentation. “I cannot avoid the disappointing conclusion – it didn't work. Pelacarsen improved Lp(a) measures significantly – 78% lower; however, cardiovascular outcomes were unchanged. The neutral finding was unexpected and surprising to the medical community,” Dr. Nissen stated.
Dr. Nissen stressed that while the outcome was disappointing, the trial provides critical scientific insights. “Although the results are disappointing, neutral trials also provide scientific insights that help inform future research efforts,” said Dr. Nissen. “A single trial does not provide definitive evidence of a lack of benefit of lowering lipoprotein(a) as a strategy to reduce cardiovascular risk.” Emphasizing that “The HORIZON trial is not the end of the story,” Dr. Nissen noted that ongoing cardiovascular outcome trials evaluating alternative modalities—including small interfering RNA candidates olpasiran and lepodisiran, as well as the oral inhibitor muvalaplin—will help clarify whether differing mechanisms, greater potency, or earlier primary prevention intervention can successfully translate lipoprotein(a) reduction into clinical benefit.
