Here is the number that frames what happened Friday: $900 million. That is the total in milestones and tiered royalties Ionis Pharmaceuticals stood to collect from Novartis if pelacarsen won approval and sold. On September 4, that figure moved from plausible to theoretical, possibly permanently. And because US markets are closed for Labor Day, investors have until Tuesday to decide what to do about it.
The facts are clean enough. Novartis announced on September 4 that pelacarsen failed the pivotal Phase 3 Lp(a)HORIZON trial, which studied whether the drug could reduce a composite of cardiovascular death, heart attack, stroke, and urgent artery-clearing procedures requiring hospitalization compared with placebo. Pelacarsen did the hard part, slashing Lp(a) as expected, but that drop did not translate into fewer heart attacks or strokes, leaving open the central question of whether lowering Lp(a) actually protects the heart. The trial enrolled 8,323 patients with elevated Lp(a) who had established cardiovascular disease.
The royalty math matters most for Ionis shareholders. Over the term of the collaboration, Ionis was eligible to receive up to $900 million, comprising an upfront payment, a license fee, development milestone payments, regulatory milestone payments, and tiered royalties in the mid-teens to low 20 percent range on net sales. None of the regulatory or commercial milestones will now arrive. As part of its January 2023 funding agreement with Ionis, Royalty Pharma ascribed $150 million of value to royalties acquired on pelacarsen. Based on the HORIZON results, Royalty Pharma does not anticipate making any milestone payments to Ionis. That $150 million capsizes quietly, alongside the larger commercial royalty stream that was supposed to follow.
This is the second major clinical setback for Ionis in roughly two months. On July 9, Ionis and partner AstraZeneca disclosed that the Phase 3 CARDIO-TTRansform study of eplontersen in transthyretin-mediated amyloid cardiomyopathy failed to meet its primary efficacy endpoint. Both programs had been flagged as key value drivers for 2026. Both are now gone.
The question investors face Tuesday is whether this is asset-specific or platform-wide damage. The bear argument writes itself: two partnered cardiovascular outcomes trials, two misses, two royalty streams deleted. Ionis discovers and develops antisense drugs internally, commercializes selected rare-disease medicines itself, and licenses other programs to larger companies. Some revenue is recurring and therapy-driven, such as royalties, while some is episodic and deal-driven, such as milestones and collaboration payments. The episodic side just took two direct hits.
The bull argument is narrower but worth taking seriously. Analysts at William Blair wrote Friday that it may be that pelacarsen did not reduce Lp(a) enough to produce an effect. Other RNA interference candidates from Amgen and Eli Lilly reduce Lp(a) by more than 90 percent, compared with roughly 72 percent for pelacarsen. If the dose-response hypothesis holds, pelacarsen’s failure becomes a mechanism problem specific to this molecule rather than evidence that Lp(a) lowering is therapeutically irrelevant. Citi analyst Geoff Meacham wrote that the first dedicated outcomes failure places greater pressure on later studies to demonstrate that deeper lowering of Lp(a) can produce a clinically meaningful reduction of major cardiovascular events.
Ionis still has live shots. The zilganersen PDUFA for Alexander disease had been set for September 22, 2026, but the FDA approved the drug on September 3, 2026. The bepirovirsen decision in chronic hepatitis B is still due on October 26. Revenue in the first half of 2026 increased 69 percent compared with the same period last year, excluding the one-time sapablursen upfront payment, driven by commercial success and R&D revenue from multiple partnerships. The company entered this weekend with real commercial momentum.
But the model has a hole in it that no quarterly sales figure fills. The street’s pre-failure average price target on IONS was around $89, implying meaningful upside that presumed at least a reasonable probability of pelacarsen approval. Shares of Ionis fell about 6 percent in after-hours trading when the news broke Friday, and that move was priced before a full weekend of analyst revisions. Tuesday’s open is the real verdict.
Watch whether management revises 2026 guidance at the next investor appearance, and watch what language they use about the RNA platform’s cardiovascular credibility. If they lean on the depth-of-reduction argument to distinguish pelacarsen from the siRNA drugs at Amgen and Lilly, that is the signal that they believe the science survives. If the language turns defensive, the discount on future partnered royalties will deepen accordingly.
