AstraZeneca and Ionis' ATTR-CM Treatment, Eplontersen, Fails to Achieve Primary Endpoint in Phase 3 Trial
Analysis of the CARDIO-TTRansform Clinical Trial Failure
Eplontersen (Wainua), a ligand-binding antisense oligonucleotide (ASO) therapy co-developed by AstraZeneca and Ionis Pharmaceuticals, failed to achieve its primary endpoint in the CARDIO-TTRansform Phase 3 trial for patients with transthyretin-mediated amyloid cardiomyopathy (ATTR-CM). The trial, which involved 1,432 patients, showed that eplontersen did not reduce cardiovascular mortality or cardiovascular-related recurrent clinical events compared to placebo. This is attributed to the fact that approximately 57% of the patients in the trial were already receiving tafamidis, the standard treatment for ATTR-CM, making it difficult to demonstrate additional clinical benefits compared to the existing treatment. However, in the subgroup of patients who were not receiving tafamidis as a monotherapy, eplontersen showed statistically significant and meaningful effects, suggesting that the drug does have some efficacy.
Shift in the ATTR-CM Treatment Market Landscape
This clinical trial failure is expected to have a significant impact on the rapidly growing global ATTR-CM market. ATTR-CM is a life-threatening rare disease caused by the abnormal accumulation of TTR protein in the heart, and the global market size is estimated at $6 billion to $9.5 billion in 2025, with the potential to exceed $20 billion in the 2030s. Eplontersen has already been approved and is being marketed as a treatment for hereditary transthyretin-mediated amyloid polyneuropathy (ATTRv-PN), but its expansion into the much larger cardiomyopathy market has been halted, making adjustments to future revenue forecasts inevitable. The developers plan to review detailed pharmacokinetic data and assess the possibility of additional approval applications as the data becomes available.
Competitors Benefit from a Strengthened Oligopoly
The poor performance of eplontersen is expected to provide significant indirect benefits to competitors that have already successfully commercialized products in the ATTR-CM space. Pfizer's tafamidis franchise (Vyndamax), which currently dominates the market, recorded global sales of $6.38 billion in 2025, further strengthening its market position. In addition, Alnylam Pharmaceuticals' RNA interference (RNAi) therapy, Amvuttra (vutrisiran), which received FDA approval in March 2025, and BridgeBio Pharma's attruby (acoramidis), which was approved in November 2024, have entered the market, creating a duopoly or triopoly. With eplontersen losing its potential to be a strong competitor, the market share of these competing drugs is expected to expand at an even faster rate.
Impact on Partnership Financial Structure and Portfolio
Under the terms of the co-development agreement between the two companies, Ionis received a $200 million upfront payment from AstraZeneca, as well as milestone payments of up to $485 million for development and regulatory milestones, and up to $2.9 billion in sales milestones upon commercial success. This clinical trial failure in the cardiomyopathy area significantly limits the future opportunities for substantial commercial milestone payments and high-double-digit royalty revenue. AstraZeneca is also facing the challenge of having to rethink its cardiovascular portfolio, as its core asset has been shaken, and it needs to explore alternative pipelines or make major revisions to its existing clinical design. This situation serves as a prime example of how a failed late-stage clinical trial can have a significant impact on the corporate value and financial structure of both companies in a large-scale partnership deal.
This CARDIO-TTRansform Phase 3 failure is a pivotal event that will solidify the ATTR-CM market, which is expected to exceed $6 billion annually by 2025, into an oligopoly dominated by Pfizer, Alnylam, and BridgeBio. In the short term, it ensures the continued dominance of Pfizer's Vyndamax, while also providing Alnylam's Amvuttra and BridgeBio's Attruby, which recently received FDA approval, with the opportunity to rapidly gain market share. In the long term, it will serve as a benchmark for researchers developing follow-on pipelines, forcing them to make major revisions to their clinical trial design strategies, as it demonstrates how difficult it is to prove add-on benefits when a significant portion of patients (57%) are already receiving standard treatment (tafamidis). Furthermore, Ionis will have to re-evaluate the future cash flow value of its platform, as it will lose a significant portion of the potential $2.9 billion in sales milestones and high royalties from AstraZeneca.