Novartis and Ionis suffer pelacarsen setback as 8,000-patient heart trial misses endpoint

Ionis Pharmaceuticals, Inc. (Nasdaq: IONS) and Novartis AG (SIX/NYSE: NOVN/NVS) have suffered a major late-stage clinical setback after experimental cardiovascular drug pelacarsen failed the primary endpoint of the Phase III Lp(a)HORIZON trial despite successfully reducing levels of lipoprotein(a), the inherited cardiovascular risk factor it was specifically designed to target. The study enrolled more than 8,000 patients with established cardiovascular disease and elevated Lp(a), making the result considerably more consequential than the failure of a small experimental programme.

The central problem is scientifically uncomfortable. Pelacarsen substantially lowered Lp(a), demonstrating that the antisense drug produced its intended biological effect, but patients receiving it did not experience a statistically significant reduction in the trial’s composite measure of cardiovascular death, non-fatal heart attack, non-fatal stroke and urgent coronary revascularisation requiring hospitalisation compared with placebo. Novartis said patients were already receiving guideline-directed treatments including lipid-lowering and antihypertensive therapies.

Ionis shares closed regular trading on September 4 at $58.09, almost unchanged for the session, before falling to about $52.29 in after-hours trading, a decline of nearly 10%. That put the stock close to the bottom of its 52-week range of $50.01 to $86.74 and demonstrated how heavily investors had been weighting the cardiovascular programme despite Ionis increasingly building its own commercial portfolio.

The setback is also important beyond the two companies involved. Elevated Lp(a) affects approximately one in five people worldwide, yet there is currently no approved treatment specifically targeting the risk factor. The HORIZON trial was therefore being watched not merely as a test of pelacarsen but as one of the most important experiments yet conducted into whether aggressively lowering Lp(a) translates into fewer heart attacks, strokes and other serious cardiovascular events.

Why did pelacarsen fail Phase III even though the drug successfully lowered lipoprotein(a)?

Pelacarsen is an antisense oligonucleotide originally developed by Ionis Pharmaceuticals and subsequently licensed to Novartis. The therapy is designed to interfere with production of apolipoprotein(a), thereby reducing circulating Lp(a) concentrations at their biological source. That mechanism worked in HORIZON in the narrow sense that patients receiving pelacarsen achieved substantially lower Lp(a) levels. What did not follow was the expected reduction in serious cardiovascular outcomes.

This distinction between changing a biomarker and improving clinical outcomes is the defining issue emerging from the study. Elevated Lp(a) has been strongly associated with cardiovascular risk, but an association does not automatically establish that reducing the biomarker pharmacologically will reverse that risk sufficiently to improve outcomes in patients already receiving contemporary cardiovascular care.

HORIZON was designed precisely to answer that question. Its patients had established cardiovascular disease and were receiving guideline-directed therapies addressing other major risk factors. Pelacarsen therefore had to demonstrate incremental benefit on top of existing treatments rather than simply lower Lp(a) in isolation. Novartis said the trial failed to demonstrate that the observed Lp(a) reduction translated into lower cardiovascular risk across the overall study population.

Full data will now become crucial. Topline failure establishes that the primary endpoint was missed but does not yet reveal whether particular patient subgroups benefited, how deeply Lp(a) was reduced, whether the magnitude of reduction correlated with outcomes or whether differences emerged across heart attacks, strokes, cardiovascular deaths and revascularisation procedures.

Those details could determine whether HORIZON undermines the entire Lp(a)-lowering therapeutic hypothesis or instead suggests that future drugs need deeper suppression, different patient selection or different treatment duration.

Why was the 8,000-patient Lp(a)HORIZON study such an important cardiovascular experiment?

Lp(a) is largely determined genetically and is difficult to modify through conventional lifestyle interventions. Unlike low-density lipoprotein cholesterol, where statins and several newer medicines have established that lowering the biomarker reduces cardiovascular events, medicine still lacks comparable outcome evidence supporting targeted Lp(a) reduction.

That created an unusually large commercial opportunity. An inherited risk factor affecting roughly 20% of the global population potentially represents tens of millions of patients, although only a subset would meet treatment criteria for any eventual drug. Successful outcome data could therefore have opened an entirely new cardiovascular therapeutic category.

HORIZON enrolled patients who already had cardiovascular disease rather than attempting to prevent a first cardiovascular event in otherwise healthy individuals. That population is generally at higher baseline risk, theoretically providing greater opportunity to demonstrate whether an intervention reduces additional heart attacks, strokes or cardiovascular deaths.

However, those patients were also receiving modern guideline-directed treatment. That raises the bar for a new medicine because many modifiable cardiovascular risks are already being managed using established therapies. Pelacarsen therefore needed to demonstrate that specifically targeting Lp(a) added meaningful protection beyond the benefits patients were already receiving.

The failure does not necessarily establish that Lp(a) is irrelevant to cardiovascular disease. Instead, it demonstrates that lowering it with this particular drug, using this treatment strategy and in this particular population, did not produce a statistically significant improvement in the prespecified primary outcome.

What does the pelacarsen setback mean for other companies developing Lp(a)-lowering drugs?

The consequences extend well beyond Ionis Pharmaceuticals and Novartis because several major pharmaceutical companies have invested heavily in Lp(a)-targeted drug development. Amgen is developing olpasiran, while Eli Lilly and Company is pursuing its own programmes aimed at reducing the cardiovascular risk associated with elevated Lp(a).

Investors will now scrutinise differences between those programmes and pelacarsen rather than assuming that all Lp(a)-lowering drugs have been invalidated simultaneously. Different technologies can produce different degrees and durations of target suppression, and competing trials may use different inclusion criteria, baseline Lp(a) thresholds, endpoints and treatment periods.

The crucial question is whether HORIZON failed because reducing Lp(a) simply does not provide sufficient cardiovascular protection or because pelacarsen did not reduce it deeply enough, early enough or in the most responsive patients.

That distinction could be worth billions of dollars across the pharmaceutical industry. If subsequent outcome trials involving other molecules also fail despite dramatic Lp(a) reductions, confidence in the target would weaken substantially. If competitors succeed, by contrast, attention will turn to what their drugs or trial designs achieved that pelacarsen did not.

For now, HORIZON introduces significant scientific uncertainty without definitively resolving the wider Lp(a) debate.

How important was pelacarsen to Novartis as it searches for its next major cardiovascular growth driver?

Pelacarsen was considered one of Novartis’s important late-stage pipeline opportunities as the Swiss pharmaceutical company works to maintain growth while navigating patent expirations across established products. The company already has a major cardiovascular franchise through products including Leqvio, and success in Lp(a) could have added another large genetically defined patient population to that business.

Novartis generated $14.41 billion in second-quarter 2026 net sales, up 3% in reported U.S. dollar terms and 1% at constant currencies. Core operating income was essentially flat at $5.94 billion, while net income fell 19% to $3.26 billion. Management nevertheless reaffirmed its full-year outlook for low-single-digit sales growth at constant currencies.

Several growth brands continue to perform strongly, with Kisqali sales up 43% at constant currencies, Kesimpta up 32%, Scemblix up 89%, Pluvicto up 43% and Leqvio up 59% during the second quarter. That diversification means the pelacarsen failure is a significant pipeline disappointment rather than an existential problem for Novartis.

The timing nevertheless matters. Novartis needs a continuing sequence of new products and indication expansions to compensate for eventual erosion of older franchises. A successful Lp(a) medicine could have addressed an enormous untreated population and strengthened the company’s position in cardiovascular medicine.

Novartis shares consequently fell following the announcement as investors reassessed the expected value attached to pelacarsen. The reaction demonstrates that even for a pharmaceutical group with more than $14 billion in quarterly sales, an unsuccessful pivotal trial can remove meaningful future revenue expectations from valuation models.

How damaging is the failed pelacarsen trial to Ionis Pharmaceuticals after its commercial transformation?

For Ionis, the setback is proportionately more visible because partnered medicines remain an important component of its pipeline economics. However, the company has been deliberately moving away from a business model dominated by licensing and milestone payments toward independently commercialising more of its own medicines.

Ionis reported second-quarter revenue of $268 million and first-half revenue of $514 million. Commercial revenue reached $119 million during the quarter, up 15% year over year, while first-half commercial revenue increased 27% to $226 million. The company ended June with approximately $2.1 billion in cash, cash equivalents and short-term investments.

The financial picture is not yet conventionally profitable. Ionis recorded a second-quarter operating loss of $102 million compared with operating income of $140 million a year earlier, when the comparable period benefited from a large one-time licensing payment. First-half operating losses reached $220 million as the company increased spending behind research and development and its expanding commercial infrastructure.

Management has nevertheless maintained its objective of reaching cash-flow breakeven in 2028, supported increasingly by products it controls directly. DAWNZERA generated $26 million in second-quarter U.S. net product sales, up 63% sequentially, while TRYNGOLZA is being expanded into the considerably larger severe hypertriglyceridemia market.

This diversification reduces Ionis’s dependence on any single partnered programme, but pelacarsen was still an important potential source of future milestones and royalties. More importantly, successful HORIZON results would have added another major validation of Ionis’s antisense technology in a very large cardiovascular population.

The nearly 10% after-hours stock decline therefore reflects lost pipeline optionality rather than immediate deterioration in Ionis’s cash position or current product sales.

Why is Ionis investor sentiment complicated by a second major cardiovascular disappointment?

Pelacarsen is not Ionis’s first painful cardiovascular readout of 2026. The company had already been hit when eplontersen, developed with AstraZeneca for transthyretin cardiomyopathy, failed to deliver the hoped-for Phase III cardiovascular outcome earlier in the year, triggering a much larger selloff in Ionis shares at the time.

Two major cardiovascular disappointments within a relatively short period naturally increase investor sensitivity to partnered pipeline risk. The scientific mechanisms and diseases are different, so the failures should not be treated as evidence of a single underlying problem with every Ionis programme. Nevertheless, each unsuccessful late-stage asset removes future milestone, royalty or commercial opportunities that had been incorporated into longer-term expectations.

The counterargument is that Ionis is simultaneously becoming less dependent on precisely those binary partnered readouts. Revenue from independently commercialised medicines is increasing, the company retains more than $2 billion in cash and short-term investments, and management continues to guide toward cash-flow breakeven in 2028.

Investor sentiment therefore sits between two narratives. The bearish interpretation focuses on repeated late-stage cardiovascular setbacks and the loss of potentially large partnered revenue streams. The more constructive interpretation is that Ionis’s underlying commercial transformation continues even as individual pipeline programmes inevitably succeed or fail.

The stock reaction shows that investors are not dismissing the setback, but the company’s future valuation is becoming increasingly tied to its wholly owned launches rather than pelacarsen alone.

Could the full HORIZON data rescue part of the pelacarsen investment thesis?

The topline announcement leaves several clinically important questions unanswered. Novartis has not yet disclosed the precise magnitude of Lp(a) lowering achieved in HORIZON, results across individual components of the primary endpoint or whether benefit appeared stronger among patients with particular baseline Lp(a) levels.

The company intends to present detailed findings at an upcoming medical congress. Those data may help researchers understand whether the trial showed no meaningful cardiovascular trend whatsoever or whether the overall miss concealed potentially informative subgroup or dose-response relationships.

Such findings would not retroactively turn a failed primary endpoint into a successful Phase III trial. They could, however, influence whether Novartis continues investigating pelacarsen, whether additional analysis or studies are justified and how rival companies design their own Lp(a) programmes.

The broader scientific community may ultimately gain as much from the failed study as investors lose from it. More than 8,000 patients were followed in a major cardiovascular outcomes trial designed around a genetic risk factor for which no targeted therapy is currently approved. That dataset could materially change understanding of the relationship between Lp(a), treatment intensity and residual cardiovascular risk.

Commercially, however, a missed pivotal endpoint is still a missed pivotal endpoint. Pelacarsen’s regulatory path is now substantially less certain, and any previous assumptions about near-term approval or large-scale commercialisation need to be reconsidered.

What should Ionis and Novartis investors watch after the pelacarsen Phase III failure?

The first priority will be the complete HORIZON dataset. Investors should watch the achieved magnitude of Lp(a) reduction, event rates in each trial arm, individual cardiovascular endpoints, subgroup responses and any evidence suggesting that patients with particularly high baseline Lp(a) experienced different outcomes.

Novartis’s decision on the future of the programme will follow from those analyses. Continuing development would suggest the company believes an identifiable path remains, while discontinuation would effectively remove pelacarsen from near-term pipeline expectations.

For Ionis, attention should increasingly return to independently controlled commercial products and upcoming neurological programmes. The company’s ability to grow DAWNZERA and TRYNGOLZA while maintaining its 2028 cash-flow breakeven target will determine whether investors eventually view setbacks such as pelacarsen as painful but manageable failures inside a diversified RNA-medicine business.

The deeper issue, however, belongs to the entire cardiovascular drug industry. Pelacarsen succeeded at lowering the biomarker it was engineered to attack and still failed to reduce the cardiovascular events that matter to patients. That is precisely why HORIZON was needed.

The next question is no longer whether pharmaceutical companies can lower Lp(a). They clearly can. The multibillion-dollar question is whether anyone can prove that lowering it actually prevents enough heart attacks, strokes and deaths to justify creating a new global treatment category.