Full Breakdown
Novartis’ del-desiran Phase III Failure Raises Doubt Over $12 B Avidity Bet
9/10/2026, 12:47:07 AM
Core Event: HARBOR Trial Misses Primary Endpoint
Novartis announced that its Phase III HARBOR study of del-desiran in myotonic dystrophy type 1 (DM1) did not achieve a statistically significant improvement in video hand-opening time (vHOT) versus placebo. The trial enrolled roughly 150 patients who received del-desiran or placebo every eight weeks for 54 weeks. The primary efficacy measure failed to show a meaningful difference, prompting the company to halt further development pending regulatory discussion.
Background & Context
Del-desiran is an antibody-oligonucleotide conjugate (AOC) acquired when Novartis completed a $12 billion purchase of Avidity Biosciences on February 27. The acquisition was intended to add three late-stage neuromuscular programs and an AOC platform that delivers siRNA payloads into muscle cells via the transferrin-receptor 1 (TfR1). The drug was promoted as a “must-win” asset that could generate $5 billion-plus in peak annual sales and help offset a patent cliff affecting products such as Entresto and Cosentyx. The failure follows a week that also saw the cardiovascular candidate pelacarsen miss its primary endpoint and the suspension of eight rap-cel cell-therapy trials after three patient deaths on September 2.
Timeline
- February 27 – Novartis finalises $12 billion acquisition of Avidity Biosciences, adding del-desiran and two other AOC candidates.
- September 2 – Novartis pauses eight clinical studies of the CAR-T therapy rap-cel after three fatalities.
- September 8 – Results of the HARBOR trial are released; del-desiran fails its primary endpoint.
Data & Statistics
- Enrollment: ~150 patients across ~40 sites.
- Study duration: 54 weeks, dosing every eight weeks.
- Primary endpoint (vHOT) – no statistically significant improvement versus placebo.
- Secondary analyses showed “evidence of clinical activity,” but no numbers were disclosed.
- Analyst peak-sales forecasts ranged from $2 billion (UBS) to $5 billion-plus (CEO statement); success probabilities cited between 60 % and 80 %.
- Share price reaction: declines of 9 %–13 % on the announcement day.
Official Statements & Responses
President of development and chief medical officer Shreeram Aradhye said, “Developing therapies for a complex disease like DM1 remains challenging, and setbacks are part of scientific progress.” CEO Vas Narasimhan reiterated the firm’s expectation of 5 %–6 % average annual sales growth through 2030 despite the setback.
Conflicting Reports & Gaps
Peak-sales estimates differ: Vontobel projected up to $3 billion, UBS up to $2 billion, while the CEO cited a “$5 billion-plus” figure. Success-probability assessments also vary, with Jefferies at 60 % and others at up to 80 %. No detailed efficacy data for secondary endpoints have been released.
What’s Next
Novartis will present the full HARBOR dataset to regulators and decide whether to pursue additional studies, seek accelerated-approval pathways, or discontinue the program. The company continues to advance other Avidity assets—del-zota for Duchenne muscular dystrophy and del-brax for facioscapulohumeral dystrophy—and has reported positive Phase III data for the BTK inhibitor remibrutinib in relapsing multiple sclerosis. Analysts will watch forthcoming guidance on these programs and any potential M&A activity intended to sustain the 5 %–6 % growth outlook through 2030.
