Novartis\' $12B del-desiran flops in crucial phase 3 trial

Overview

Updated Sep 8

Novartis' experimental muscle-disease drug del-desiran failed its phase 3 Harbor trial, missing the primary endpoint and sending shares down. The drug was the centerpiece of the company's $12 billion acquisition of Avidity Biosciences, which closed last year.

The miss asts doubt on Novartis' pipeline strategy just when its older blockbusters face patent expiries. It also deals a blow to the broader class of RNA-based therapies;del-desiran was meant to prove the platform's worth.

Why it matters

The failure puts Novartis' $12 billion bet in question, threatening its plan to replace revenue from older drugs losing patent protection.

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Key Indicators

$12B

Acquisition price for Avidity Biosciences

Novartis paid this to acquire the RNA therapy platform in 2024.

Missed

Phase 3 Harbor trial primary endpoint

del-desiran did not beat placebo on the composite measure of disease progression.

1 win, 2 failures

Novartis' late-stage pipeline record since August 2026

Remibrutinib succeeded in MS; pelacarsen and del-desiran both flunked phase 3.

Voices

Curated perspectives — historical figures and your fellow readers.

Ever wondered what historical figures would say about today's headlines?

People Involved

Vas Narasimhan

Chief Executive Officer, Novartis

Leading company through back-to-back clinical setbacks

Sarah Boyce

Chief Executive Officer, Avidity Biosciences

Awaiting full Harbor data before commenting

Shreeram Aradhye

President, Development, and Chief Medical Officer, Novartis

Overseeing clinical development after multiple setbacks

Organizations Involved

Novartis Pharmaceuticals

Pharmaceutical company

Facing investor pressure after two phase 3 failures

Swiss drugmaker that spent $12 billion to acquire Avidity Biosciences.

Avidity Biosciences

Biotechnology company

Subsidiary of Novartis;flagship asset in limbo

Developer of antibody-oligonucleotide conjugates, a platform for delivering RNA therapeutics.

Timeline

August 2024 September 2026

3 events Latest: September 8th, 2026 · 2 months ago

September 2026
Harbor trial flops for del-desiran
Latest Clinical Trial

Del-desiran failed its phase 3 Harbor trial, missing the primary endpoint and dealing a major blow to Novartis' Avidity acquisition.
September 8th, 2026
July 2026
Pelacarsen fails phase 3 Lp(a) trial
Clinical Trial

Novartis' cholesterol drug pelacarsen missed its primary endpoint, a separate setback for the pipeline.
July 12th, 2026
August 2024
Novartis bets $12B on Avidity
Acquisition

Novartis agreed to buy Avidity Biosciences, whose RNA platform includes del-desiran, arare-muscle-disease therapy.
August 13th, 2024

Scenarios

Novartis discontinues del-desiran program

Likely Resolves by Mar 8, 2027

Discussed by: UBS analysts, Reuters

Full trial data confirms no benefit in any subgroup. Novartis halts development, takes a writedown on the Avidity asset, andredirectionals resources to remibrutinib and other pipeline candidates. Investors greet the move as decisive, but the writedown erases most of the acquisition value.

Novartis salvages platform with earlier-stage assets

Possible Resolves by Sep 8, 2027

Discussed by: Barclays analysts, Biopharma Dive

Novartis attributes the Harbor failure to trial design or patient selection, and continues testing del-desiran in biomarker-defined subsets or opens new trials for other Avidity candidates. The company argues the $12B platform still holds value, but subscribers remain skeptical until a success materializes.

Novartis takes writedown and divests Avidity assets

Unlikely Resolves by Mar 8, 2028

Discussed by: Citi analysts

Unable to justify keeping the unit, Novartis writes down the acquisition and seeks abuyerfor Avidity's preclinical assets. The company refocuses on profitable existing drugs and in-licenses safer bets, accepting a multibillion-dollar loss on its biggest M&A gambit.

Historical Context

2 moments from history that rhyme with this story — and how they unfolded.

December 2019 - March 2020

Astellas/Audentes Therapeutics (2019-2020)

Astellas paid $3 billion for Audentes, betting on its gene therapy for a rare muscle disease. In clinical hold issued in early 2020 after a patient died of liver toxicity, and the program never recovered.

Then

Astellas halted the trial, took awritedown, andabandoned the program.

Now

The failure chilled investor enthusiasm for high-priced rare-disease acquisitions.

Why this matters now

Like Astellas, Novartis paid a premium for arsingle-platform bet in rare muscle disease;the clinical failure now threatens to erase most of that value.

April 2018 - May 2019

Novartis/AveXis Zolgensma (2018-2019)

Novartis paid $8.7 billion for AveXis, whose gene therapy Zolgensma treated spinal muscular atrophy. The drug won FDA approval with strong efficacy data, becoming one of the most expensive drugs ever sold.

Then

Zolgensma generated billions in revenue and validated Novartis' rare-disease M&A strategy.

Now

It set a precedent that big bets on muscle-disease gene therapies could pay off,numazzicando later deals like Avidity.

Why this matters now

The AveXis success is why investors hoped del-desiran could repeat that magic;the Harbor failure now breaks that pattern, making the $12B Avidity purchase look far riskier.