Shares of Ionis Pharmaceuticals plunged 20.7% in pre-open trading after the company and partner AstraZeneca reported that the Phase 3 CARDIO-TTRansform study evaluating eplontersen in adults with transthyretin-mediated amyloid cardiomyopathy (ATTR-CM) did not achieve its primary endpoint. The trial’s primary outcome was a composite measure of cardiovascular mortality and recurrent cardiovascular events through Week 140 versus placebo.
CARDIO-TTRansform was the largest ATTR-CM study conducted to date, enrolling 1,432 patients across 130 sites in 20 countries. Management had positioned the readout as a pivotal component of Ionis’s 2026 growth narrative, suggesting that a positive result could meaningfully expand eplontersen’s commercial opportunity beyond its current WAINUA approval for hereditary transthyretin-mediated amyloid polyneuropathy.
Within a prespecified subgroup analysis, patients who received eplontersen as monotherapy demonstrated a nominally significant hazard ratio of 0.71 for reduced cardiovascular mortality and recurrent events compared to placebo. However, that subgroup finding did not alter the overall declaration that the trial missed its primary endpoint.
Chief Executive Officer Brett P. Monia commented on the outcome, acknowledging the company’s disappointment and attributing part of the result to changes in the treatment landscape. He said, "we believe these findings reflect the rapidly evolving treatment landscape, in which contemporary ATTR-CM patients are widely treated with stabilizers," and added that the company was "disappointed that the study did not meet the primary endpoint."
The negative readout is significant against a backdrop of competing therapies in ATTR-CM. Alnylam Pharmaceuticals already holds an approved ATTR-CM indication for Amvuttra (vutrisiran), a product that has been building commercial traction. The failure of the eplontersen trial reduces an immediate competitive threat in cardiomyopathy, a dynamic that could benefit Alnylam and other established firms in the space.
Investor sentiment turned sharply after the announcement. Ionis shares, which had reached a 52-week high of $86.74 in the prior session, were quoted at $66.98 following the update - a dramatic reversal that erases months of gains and forces a reassessment of eplontersen’s short-term commercial prospects.
The broader market provided little offset for Ionis’s decline. The S&P 500 edged slightly lower and the Dow Jones Industrial Average fell, while the Nasdaq posted a modest gain, indicating that the drop in Ionis stock was driven by company-specific news rather than a general market move.
Context and implications
- CARDIO-TTRansform’s size - 1,432 patients across 130 sites in 20 countries - made it the largest trial in ATTR-CM to date.
- Management viewed the trial as central to expanding eplontersen’s commercial reach beyond its WAINUA approval.
- Despite a nominally significant monotherapy subgroup result (hazard ratio 0.71), the overall trial outcome failed to meet the pre-specified primary endpoint.
The announcement has prompted analysts and investors to re-evaluate near-term expectations for Ionis. Prior to the result, Wall Street sentiment had been broadly positive, with an average analyst price target above the current trading level and firms such as H.C. Wainwright and Wells Fargo recently reiterating buy ratings.
For market participants, the outcome highlights how a single late-stage trial can reshape a company’s expected growth path and competitive position within a therapeutic area.