Insmed Stock Plummets 19%. This Is What Sparked the Selloff.

Insmed stock was plunging on Thursday. (Dreamstime)

Key Points

• Insmed’s stock plummeted 19% after discontinuing development of brensocatib for chronic rhinosinusitis.
• The drug brensocatib failed to meet its main goals in a mid-stage trial for chronic rhinosinusitis without nasal polyps.
• Insmed announced the acquisition of antibody INS1148 for Phase 2 development in interstitial lung disease and asthma.

Insmed stock was tumbling Thursday after the biopharmaceutical company said it was discontinuing development of a drug to treat a chronic sinus condition.

Shares plummeted 19% to $159.78 ahead of the opening bell. Futures tracking the S&P 500 were 0.4% higher.

The selloff came after Insmed said Wednesday that a mid-stage trial for its drug brensocatib had failed to meet its main goals. The company was testing to see if Insmed improved symptoms in patients with the inflammatory condition chronic rhinosinusitis without nasal polyps.

Investors had priced in $500 million to $1 billion in peak sales of the drug, Cantor analyst Olivia Brayer said. She rates the stock Overweight, with a price target of $230.

“Not everyone expected brenso to work…but expectations had been creeping up into year-end and this afternoon’s negative phase 2 readout is undoubtedly a near-term setback for the story,” Brayer wrote in a research note. “The timing doesn’t help either with only a few trading sessions left in the year.”

Insmed also said on Wednesday that it was acquiring the antibody INS1148, and launching a Phase 2 development to study if that can treat interstitial lung disease and moderate-to-severe asthma.

As of Wednesday’s close, Insmed stock was up 187% for the year. The S&P 500 has risen 14% in 2025.

Write to George Glover at george.glover@dowjones.com