The Lp(a) HORIZON trial, a 7-year, phase III, multicenter international study, has delivered a sobering result: despite reducing lipoprotein(a) levels by an average of 78%, the novel medication pelacarsen did not reduce the time to major adverse cardiovascular events (MACE) in more than 8,300 adults with established cardiovascular disease across 42 countries. The findings, presented at the American Heart Association’s Scientific Sessions 2026 and simultaneously published in The New England Journal of Medicine and NEJM Evidence, challenge assumptions about the direct causal role of Lp(a) in cardiovascular outcomes and highlight the complexity of translating biomarker reductions into clinical benefit.
Lp(a) is a genetically determined form of cholesterol that, when elevated, is associated with a significantly increased long-term risk of heart attack and stroke. Approximately 1 in 5 people globally—about 1.4 billion individuals—are thought to have elevated Lp(a) levels. The 2026 multi-society guideline on the management of dyslipidemia recommends that Lp(a) be measured at least once in adulthood, and the American Heart Association provides detailed information on Lp(a) and its risks. However, no FDA-approved therapy currently exists to lower Lp(a), and lifestyle changes or statins have little effect on its levels.
The trial enrolled adults with Lp(a) levels of 70 mg/dL or higher and established cardiovascular disease. Participants received monthly injections of pelacarsen or placebo. Despite the substantial reduction in Lp(a), the primary composite outcome—nonfatal heart attack, stroke, urgent revascularization, or cardiovascular death—was unchanged. Extended analyses of secondary endpoints, including death from any cause, were similarly neutral. “I cannot avoid the disappointing conclusion – it didn’t work,” said Steven E. Nissen, M.D., FAHA, senior author and chief academic officer of the Miller Family Heart, Vascular & Thoracic Institute at the Cleveland Clinic. “The neutral finding was unexpected and surprising to the medical community.”
The results carry important implications. They suggest that lowering Lp(a) alone, even dramatically, may not be sufficient to reduce cardiovascular events in patients already well-treated with statins and antiplatelet therapies. Yet experts caution against interpreting the findings as evidence that Lp(a) is irrelevant. “This does not mean Lp(a) is irrelevant. It means we need more in-depth research to help us fully understand the underlying mechanisms of Lp(a), its interactions with other CVD risk factors and how it does or does not impact cardiovascular outcomes,” Nissen said. He urged participants in ongoing Lp(a) trials not to drop out, noting that three other cardiovascular outcome trials are underway with investigational compounds targeting Lp(a) through different mechanisms. Those results, expected in the next few years, will help clarify the relationship between Lp(a) lowering and clinical outcomes.
For now, the trial reinforces the importance of measuring Lp(a) at least once in adulthood. “Measuring Lp(a) is still absolutely worthwhile. Lp(a) is an important risk factor for CVD, and high levels of Lp(a) usually do not present with any symptoms,” Nissen said. He emphasized that Lp(a) levels, along with blood pressure, cholesterol, and blood sugar, inform prevention and treatment strategies. The American Heart Association provides resources on what lipoprotein (a) is and how it impacts heart health, and the association’s Scientific Sessions 2026 continue to serve as a platform for such pivotal research. Additional details are available in the abstract and the Scientific Sessions 2026 Online Program Planner.
The trial also had limitations: it was conducted partly during the COVID-19 pandemic, and 78% of participants self-identified as white, underrepresenting groups such as people of African ancestry, who have higher average Lp(a) levels. Future trials will need broader representation. Despite the neutral outcome, the Lp(a) HORIZON trial represents a critical step in understanding Lp(a) biology and the challenges of targeting it therapeutically. As Nissen noted, “Lp(a) is still an important piece of the overall cardiovascular disease puzzle, an important cause of morbidity and mortality worldwide.” The findings underscore the need for continued research and vigilant cardiovascular risk assessment, including Lp(a) measurement, to help prevent major cardiovascular events.
